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Hibernate快速入门

Hibernate是一个开源，轻量级的ORM(对象关系映射)工具。Hibernate框架简化了java应用程序与数据库交互的开发。

ORM工具简化了数据创建，数据处理和数据访问。它是将对象映射到数据库中存储的数据(表)的编程技术。

注：为什么会有这篇教程文章？答：只是想写一篇最NB的Hibernate教程入门文章。NB代表人见人爱，花见花开，车见爆胎,飞鸟落地…，最后，需要注意的是：这篇文章包教不包会！除非你从头到尾认真看完并运行所有示例代码。

1. Hibernate快速入门简介

本教程文章基于以下工具(软件)：

Hibernate 5.2.2.Final
Eclipse 4.6 (MARS)

Hibernate.x ~ Hibernate.5 更新功能：

从Hibernate 5.0开始Hibernate Spatial是Hibernate项目的一部分，因此我们也可以处理GIS数据了。
域模型映射支持Java 8日期和时间类型。标准SQL日期/时间类型以及支持的Java 8 Date / Time类类型之间的映射，如下所示：
- DATE: java.time.LocalDate
- TIME: java.time.LocalTime, java.time.OffsetTime
- TIMESTAMP: java.time.Instant, java.time.LocalDateTime,java.time.OffsetDateTime 和 java.time.ZonedDateTime
字节码增强机制从头重新设计，Hibernate可支持Maven和Gradle插件。可以通过字节码仪器来增强三个主要方面：
- 懒初始化：字段可以声明为LAZY，只有在第一次被访问时，它们才被提取。
- 脏检查：实体被增强，使得它们可以跟踪在持久化上下文中加载之后变化的所有属性。
- 双向关联：即使开发人员仅更新单侧，但也可以自动同步双向关联的双方。
Hibernate的原生API(Session等)已更新为使用泛型类型化。无需在获取实体时转换。
Hibernate 5.0将其扩展到更广泛的类型(例如UUID)。
引用二级缓存，使实体引用能够直接存储到第二级缓存中(用于不可变实体)。

2. 准备数据库

Hibernate是一个库，为了处理所有类型的数据库，它不依赖于应用程序选择的任何类型的数据库，如果Java是“一次写入到处运行”的语言，Hibernate则是“写一次就可运行在所有类型的数据库“中的框架。

在这篇文章中，使用的是MySQL数据(你可使用其它的数据库，如：Oracle，MySQL或SQL Server)，并创建一个简单的数据库：mydb，完整的数据库创建语句如下所示：

创建数据：

CREATE DATABASE IF NOT EXISTS mydb default charset utf8 COLLATE utf8_general_ci;

需要创建以下几张表，它们的关系图如下所示 -

创建表语句：

create table DEPARTMENT (
   DEPT_ID integer not null,
   DEPT_NAME varchar(255) not null,
   DEPT_NO varchar(20) not null,
   LOCATION varchar(255),
   primary key (DEPT_ID),
   unique (DEPT_NO)
);

create table EMPLOYEE (
   EMP_ID bigint not null,
   EMP_NAME varchar(50) not null,
   EMP_NO varchar(20) not null,
   HIRE_DATE date not null,
   IMAGE longblob,
   JOB varchar(30) not null,
   SALARY float not null,
   DEPT_ID integer not null,
   MNG_ID bigint,
   primary key (EMP_ID),
   unique (EMP_NO)
);

create table SALARY_GRADE (
   GRADE integer not null,
   HIGH_SALARY float not null,
   LOW_SALARY float not null,
   primary key (GRADE)
);

create table TIMEKEEPER (
   Timekeeper_Id varchar(36) not null,
   Date_Time datetime not null,
   In_Out char(1) not null,
   EMP_ID bigint not null,
   primary key (Timekeeper_Id)
);

alter table EMPLOYEE
   add index FK75C8D6AE269A3C9 (DEPT_ID),
   add constraint FK75C8D6AE269A3C9
   foreign key (DEPT_ID)
   references DEPARTMENT (DEPT_ID);

alter table EMPLOYEE
   add index FK75C8D6AE6106A42 (EMP_ID),
   add constraint FK75C8D6AE6106A42
   foreign key (EMP_ID)
   references EMPLOYEE (EMP_ID);

alter table EMPLOYEE
   add index FK75C8D6AE13C12F64 (MNG_ID),
   add constraint FK75C8D6AE13C12F64
   foreign key (MNG_ID)
   references EMPLOYEE (EMP_ID);

alter table TIMEKEEPER
   add index FK744D9BFF6106A42 (EMP_ID),
   add constraint FK744D9BFF6106A42
   foreign key (EMP_ID)
   references EMPLOYEE (EMP_ID);

向上面创建的表中，分别插入一些测试数据，如下所示 -

insert into Department (DEPT_ID, DEPT_NAME, DEPT_NO, LOCATION)
values (10, 'ACCOUNTING', 'D10', 'NEW YORK');

insert into Department (DEPT_ID, DEPT_NAME, DEPT_NO, LOCATION)
values (20, 'RESEARCH', 'D20', 'DALLAS');

insert into Department (DEPT_ID, DEPT_NAME, DEPT_NO, LOCATION)
values (30, 'SALES', 'D30', 'CHICAGO');

insert into Department (DEPT_ID, DEPT_NAME, DEPT_NO, LOCATION)
values (40, 'OPERATIONS', 'D40', 'BOSTON');

-------------------------------------------------------------------------------------------------


insert into Employee (EMP_ID, EMP_NAME, EMP_NO, HIRE_DATE, JOB, SALARY, DEPT_ID, MNG_ID)
values (7839, 'KING', 'E7839', Str_To_Date('17-11-1981', '%d-%m-%Y'), 'PRESIDENT', 5000, 10, null);

insert into Employee (EMP_ID, EMP_NAME, EMP_NO, HIRE_DATE, JOB, SALARY, DEPT_ID, MNG_ID)
values (7566, 'JONES', 'E7566', Str_To_Date('02-04-1981', '%d-%m-%Y'), 'MANAGER', 2975, 20, 7839);

insert into Employee (EMP_ID, EMP_NAME, EMP_NO, HIRE_DATE, JOB, SALARY, DEPT_ID, MNG_ID)
values (7902, 'FORD', 'E7902', Str_To_Date('03-12-1981', '%d-%m-%Y'), 'ANALYST', 3000, 20, 7566);

insert into Employee (EMP_ID, EMP_NAME, EMP_NO, HIRE_DATE, JOB, SALARY, DEPT_ID, MNG_ID)
values (7369, 'SMITH', 'E7369', Str_To_Date('17-12-1980', '%d-%m-%Y'), 'CLERK', 800, 20, 7902);

insert into Employee (EMP_ID, EMP_NAME, EMP_NO, HIRE_DATE, JOB, SALARY, DEPT_ID, MNG_ID)
values (7698, 'BLAKE', 'E7698', Str_To_Date('01-05-1981', '%d-%m-%Y'), 'MANAGER', 2850, 30, 7839);

insert into Employee (EMP_ID, EMP_NAME, EMP_NO, HIRE_DATE, JOB, SALARY, DEPT_ID, MNG_ID)
values (7499, 'ALLEN', 'E7499', Str_To_Date('20-02-1981', '%d-%m-%Y'), 'SALESMAN', 1600, 30, 7698);

insert into Employee (EMP_ID, EMP_NAME, EMP_NO, HIRE_DATE, JOB, SALARY, DEPT_ID, MNG_ID)
values (7521, 'WARD', 'E7521', Str_To_Date('22-02-1981', '%d-%m-%Y'), 'SALESMAN', 1250, 30, 7698);

insert into Employee (EMP_ID, EMP_NAME, EMP_NO, HIRE_DATE, JOB, SALARY, DEPT_ID, MNG_ID)
values (7654, 'MARTIN', 'E7654', Str_To_Date('28-09-1981', '%d-%m-%Y'), 'SALESMAN', 1250, 30, 7698);

insert into Employee (EMP_ID, EMP_NAME, EMP_NO, HIRE_DATE, JOB, SALARY, DEPT_ID, MNG_ID)
values (7782, 'CLARK', 'E7782', Str_To_Date('09-06-1981', '%d-%m-%Y'), 'MANAGER', 2450, 30, 7839);

insert into Employee (EMP_ID, EMP_NAME, EMP_NO, HIRE_DATE, JOB, SALARY, DEPT_ID, MNG_ID)
values (7788, 'SCOTT', 'E7788', Str_To_Date('19-04-1987', '%d-%m-%Y'), 'ANALYST', 3000, 20, 7566);

insert into Employee (EMP_ID, EMP_NAME, EMP_NO, HIRE_DATE, JOB, SALARY, DEPT_ID, MNG_ID)
values (7844, 'TURNER', 'E7844', Str_To_Date('08-09-1981', '%d-%m-%Y'), 'SALESMAN', 1500, 30, 7698);

insert into Employee (EMP_ID, EMP_NAME, EMP_NO, HIRE_DATE, JOB, SALARY, DEPT_ID, MNG_ID)
values (7876, 'ADAMS', 'E7876', Str_To_Date('23-05-1987', '%d-%m-%Y'), 'CLERK', 1100, 20, 7698);

insert into Employee (EMP_ID, EMP_NAME, EMP_NO, HIRE_DATE, JOB, SALARY, DEPT_ID, MNG_ID)
values (7900, 'ADAMS', 'E7900', Str_To_Date('03-12-1981', '%d-%m-%Y'), 'CLERK', 950, 30, 7698);

insert into Employee (EMP_ID, EMP_NAME, EMP_NO, HIRE_DATE, JOB, SALARY, DEPT_ID, MNG_ID)
values (7934, 'MILLER', 'E7934', Str_To_Date('23-01-1982', '%d-%m-%Y'), 'CLERK', 1300, 10, 7698);

-------------------------------------------------------------------------------------------------

insert into Salary_Grade (GRADE, HIGH_SALARY, LOW_SALARY)
values (1, 9999, 3001);

3. 创建Maven项目和声明库

在这里，创建一个Maven项目并在pom.xml中声明使用的Hibernate库。打开 Eclipse，选择菜单 File-> New -> Other…，在弹出框中选择 Maven，如下所示 -

下一步选择工作目录，如下图所示 -

下一步，选择模板类型，如下图所示 -

下一步，写入工程名称：HibernateQuickStart，以及输入包信息：com.yiibai 等信息。

项目(HibernateQuickStart)创建完成后，如下图所示 -

在pom.xml中，需要声明使用Hibernate 5库，以及用于各种数据库类型(如Oracle，MySQL和SQL Server)的JDBC库，这里使用 MySQL JDBC。

完整的 pom.xml 配置/声明如下所示 -

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.yiibai</groupId>
    <artifactId>HibernateQuickStart</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>HibernateQuickStart</name>
    <url>http://maven.apache.org</url>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>

    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>3.8.1</version>
            <scope>test</scope>
        </dependency>

        <!-- Hibernate Core -->
        <!-- http://mvnrepository.com/artifact/org.hibernate/hibernate-core -->
        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-core</artifactId>
            <version>5.2.2.Final</version>
        </dependency>


        <!-- MySQL JDBC driver -->
        <!-- http://mvnrepository.com/artifact/mysql/mysql-connector-java -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.34</version>
        </dependency>

        <!-- SQLServer JDBC driver (JTDS) -->
        <!-- http://mvnrepository.com/artifact/net.sourceforge.jtds/jtds -->
        <dependency>
            <groupId>net.sourceforge.jtds</groupId>
            <artifactId>jtds</artifactId>
            <version>1.3.1</version>
        </dependency>
    </dependencies>
</project>

4. 实体类

在这一步中，我们来创建实体类。每个实体描述一个数据库中的表。这里先不说明每个类是做什么用的。一共要创建如下几个实体类(对应上面创建的四张表)，如下 -

Department.java
Employee.java
SalaryGrade.java
Timekeeper.java

所有创建的类如下图所示 -

这几个类的代码，分别如下所示 -

Department.java 类代码 -

package com.yiibai.entities;

import java.util.HashSet;
import java.util.Set;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;
import javax.persistence.UniqueConstraint;

@Entity
@Table(name = "DEPARTMENT", uniqueConstraints = { @UniqueConstraint(columnNames = { "DEPT_NO" }) })
public class Department {

    private Integer deptId;
    private String deptNo;

    private String deptName;
    private String location;
    private Set<Employee> employees = new HashSet<Employee>(0);

    public Department() {
    }

    public Department(Integer deptId, String deptName, String location) {
        this.deptId = deptId;
        this.deptNo = "D" + this.deptId;
        this.deptName = deptName;
        this.location = location;
    }

    @Id
    @Column(name = "DEPT_ID")
    public Integer getDeptId() {
        return deptId;
    }

    public void setDeptId(Integer deptId) {
        this.deptId = deptId;
    }

    @Column(name = "DEPT_NO", length = 20, nullable = false)
    public String getDeptNo() {
        return deptNo;
    }

    public void setDeptNo(String deptNo) {
        this.deptNo = deptNo;
    }

    @Column(name = "DEPT_NAME", nullable = false)
    public String getDeptName() {
        return deptName;
    }

    public void setDeptName(String deptName) {
        this.deptName = deptName;
    }

    @Column(name = "LOCATION")
    public String getLocation() {
        return location;
    }

    public void setLocation(String location) {
        this.location = location;
    }

    @OneToMany(fetch = FetchType.LAZY, mappedBy = "department")
    public Set<Employee> getEmployees() {
        return employees;
    }

    public void setEmployees(Set<Employee> employees) {
        this.employees = employees;
    }
}

Employee.java 类代码 -

package com.yiibai.entities;

import java.util.Date;
import java.util.HashSet;
import java.util.Set;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.Lob;
import javax.persistence.ManyToOne;
import javax.persistence.OneToMany;
import javax.persistence.Table;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;
import javax.persistence.UniqueConstraint;

@Entity
@Table(name = "EMPLOYEE", uniqueConstraints = { @UniqueConstraint(columnNames = { "EMP_NO" }) })
public class Employee {
    private Long empId;
    private String empNo;

    private String empName;
    private String job;
    private Employee manager;
    private Date hideDate;
    private Float salary;
    private byte[] image;

    private Department department;
    private Set<Employee> employees = new HashSet<Employee>(0);

    public Employee() {
    }

    public Employee(Long empId, String empName, String job, Employee manager, Date hideDate, Float salary, Float comm,
            Department department) {
        this.empId = empId;
        this.empNo = "E" + this.empId;
        this.empName = empName;
        this.job = job;
        this.manager = manager;
        this.hideDate = hideDate;
        this.salary = salary;
        this.department = department;
    }

    @Id
    @Column(name = "EMP_ID")
    public Long getEmpId() {
        return empId;
    }

    public void setEmpId(Long empId) {
        this.empId = empId;
    }

    @Column(name = "EMP_NO", length = 20, nullable = false)
    public String getEmpNo() {
        return empNo;
    }

    public void setEmpNo(String empNo) {
        this.empNo = empNo;
    }

    @Column(name = "EMP_NAME", length = 50, nullable = false)
    public String getEmpName() {
        return empName;
    }

    public void setEmpName(String empName) {
        this.empName = empName;
    }

    @Column(name = "JOB", length = 30, nullable = false)
    public String getJob() {
        return job;
    }

    public void setJob(String job) {
        this.job = job;
    }

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "MNG_ID")
    public Employee getManager() {
        return manager;
    }

    public void setManager(Employee manager) {
        this.manager = manager;
    }

    @Column(name = "HIRE_DATE", nullable = false)
    @Temporal(TemporalType.DATE)
    public Date getHideDate() {
        return hideDate;
    }

    public void setHideDate(Date hideDate) {
        this.hideDate = hideDate;
    }

    @Column(name = "SALARY", nullable = false)
    public Float getSalary() {
        return salary;
    }

    public void setSalary(Float salary) {
        this.salary = salary;
    }

    @Column(name = "IMAGE", length = 1111111, nullable = true)
    @Lob
    public byte[] getImage() {
        return image;
    }

    public void setImage(byte[] image) {
        this.image = image;
    }

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "DEPT_ID", nullable = false)
    public Department getDepartment() {
        return department;
    }

    public void setDepartment(Department department) {
        this.department = department;
    }

    @OneToMany(fetch = FetchType.LAZY, mappedBy = "empId")
    public Set<Employee> getEmployees() {
        return employees;
    }

    public void setEmployees(Set<Employee> employees) {
        this.employees = employees;
    }

}

SalaryGrade.java 类代码 -

package com.yiibai.entities;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table(name = "SALARY_GRADE")
public class SalaryGrade {
    private Integer grade;
    private Float lowSalary;
    private Float highSalary;

    public SalaryGrade() {
    }

    public SalaryGrade(Integer grade, Float lowSalary, Float highSalary) {
        this.grade = grade;
        this.lowSalary = lowSalary;
        this.highSalary = highSalary;
    }

    @Id
    @Column(name = "GRADE")
    public Integer getGrade() {
        return grade;
    }

    public void setGrade(Integer grade) {
        this.grade = grade;
    }

    @Column(name = "LOW_SALARY", nullable = false)
    public Float getLowSalary() {
        return lowSalary;
    }

    public void setLowSalary(Float lowSalary) {
        this.lowSalary = lowSalary;
    }

    @Column(name = "HIGH_SALARY", nullable = false)
    public Float getHighSalary() {
        return highSalary;
    }

    public void setHighSalary(Float highSalary) {
        this.highSalary = highSalary;
    }
}

Timekeeper.java 类代码 -

package com.yiibai.entities;

import java.util.Date;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;

import org.hibernate.annotations.GenericGenerator;

@Entity
@Table(name = "TIMEKEEPER")
public class Timekeeper {
    public static final char IN = 'I';
    public static final char OUT = 'O';

    private String timekeeperId;

    private Date dateTime;

    private Employee employee;

    // 'I' or 'O'
    private char inOut;

    @Id
    @GeneratedValue(generator = "uuid")
    @GenericGenerator(name = "uuid", strategy = "uuid2")
    @Column(name = "Timekeeper_Id", length = 36)
    public String getTimekeeperId() {
        return timekeeperId;
    }

    public void setTimekeeperId(String timekeeperId) {
        this.timekeeperId = timekeeperId;
    }

    @Column(name = "Date_Time", nullable = false)
    @Temporal(TemporalType.TIMESTAMP)
    public Date getDateTime() {
        return dateTime;
    }

    public void setDateTime(Date dateTime) {
        this.dateTime = dateTime;
    }

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "EMP_ID", nullable = false)
    public Employee getEmployee() {
        return employee;
    }

    public void setEmployee(Employee employee) {
        this.employee = employee;
    }

    @Column(name = "In_Out", nullable = false, length = 1)
    public char getInOut() {
        return inOut;
    }

    public void setInOut(char inOut) {
        this.inOut = inOut;
    }

}

5. 配置hibernate

配置hibernate目的是让Hibernate可以连接数据库并与数据库交互，并声明在前面的步骤中创建的实体列表。

在src/main/java中创建一个名称为：hibernate.cfg.xml 的配置文件，当前项目结构如下图所示 -

hibernate.cfg.xml 配置文件的内容如下所示 -

<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">

<hibernate-configuration>

  <session-factory>
      <!-- Database connection settings -->
      <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
      <property name="connection.url">jdbc:mysql://localhost:3306/mydb?serverTimezone=UTC</property>
      <property name="connection.username">root</property>
      <property name="connection.password">123456</property>

      <!-- JDBC connection pool (use the built-in) -->
      <property name="connection.pool_size">1</property>

      <!-- SQL dialect -->
      <property name="dialect">org.hibernate.dialect.MySQLDialect</property>

      <!-- Enable Hibernate's automatic session context management -->
      <property name="current_session_context_class">thread</property>

      <!-- Disable the second-level cache -->
      <property name="cache.provider_class">org.hibernate.cache.internal.NoCacheProvider</property>

      <!-- Echo all executed SQL to stdout -->
      <property name="show_sql">true</property>

      <mapping class="com.yiibai.entities.Department" />
      <mapping class="com.yiibai.entities.Employee" />
      <mapping class="com.yiibai.entities.SalaryGrade" />
      <mapping class="com.yiibai.entities.Timekeeper" />

  </session-factory>

</hibernate-configuration>

每种数据库都有一个单独的方言，例如：

Oracle方言：

org.hibernate.dialect.Oracle10gDialect(Dùngcho 10g＆11g)
org.hibernate.dialect.Oracle12cDialect

SQL Server方言：

org.hibernate.dialect.SQLServerDialect并
org.hibernate.dialect.SQLServer2012Dialect
org.hibernate.dialect.SQLServer2008Dialect

MySQL方言

org.hibernate.dialect.MySQLDialect
org.hibernate.dialect.MySQL5Dialect

什么是方言？

Dialect是一个使用Hibernate的方式将数据库的数据类型转换为Java的数据类型，反之亦然。此外，它用于定义将HSQL(Hibernate SQL)的函数转换为数据中的函数的方式，如下列出的一部分 -

Java SQL类型	Oracle	MySQL	SQL Server
Types.BIT	number(1,0)	bit	bit
Types.BIGINT	number(19,0)	bigin	bigint
Types.DATE	date	date	date
…….	…	…	…
Types.CLOB	clob	longtext	varchar(MAX)
Types.BLOB	blob	longblob	varbinary(MAX)

6. SessionFactory

创建一个文件： HibernateUtils.java ，其代码如下 -

7. Hibernate查询语言(HQL)

Hibernate使用Hibernate查询语言(HQL)查询数据。 HQL与我们所了解的数据库SQL语句有点不同。

SQL：

在表中查询数据

HQL：

在实体类中查询对象数据

参考比较以下用法 -

-- SQL
-- This is a SQL query in table DEPARTMENT.
Select d.DEPT_NO, d.DEPT_NAME from DEPARTMENT d;

-- HQL
-- This is a HQL query in Entity Department.
Select d.deptNo, d.deptName from Department d;

-- Query Object
Select d from Department d;

Hibernate的操作规则：

应用程序编写的HQL在操作过程中，Hibernate本身就意识到它使用的数据库类型(如：MySQL)，它会自动将HQL转换为等价的数据库类型的SQL形式。事实上，各种类型的数据库之间的SQL语法有一些差异，比如：返回记录的行数的限制就不同(MySQL中使用 limit 子句)。

可以参考HQL语法： http://docs.jboss.org/hibernate/orm/3.6/reference/en-US/html/queryhql.html

8. 使用Hibernate查询数据

在Hibernate中有很多方法可以用来查询数据。在这部分中，将介绍一些查询数据的典型方法。

8.1 - 使用HQL的查询对象

查询对象示例-1
第一个例子，使用HQL查询对象(Entity)，创建一个Java类文件：QueryObjectDemo.java，其代码如下 -

package com.yiibai;

import java.util.List;

import org.hibernate.query.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import com.yiibai.HibernateUtils;
import com.yiibai.entities.Employee;

public class QueryObjectDemo {

   public static void main(String[] args) {
       SessionFactory factory = HibernateUtils.getSessionFactory();

       Session session = factory.getCurrentSession();

       try {

           // All the action with DB via Hibernate
           // must be located in one transaction.
           // Start Transaction.            
           session.getTransaction().begin();

           // Create an HQL statement, query the object.
           // Equivalent to the SQL statement:
           // Select e.* from EMPLOYEE e order by e.EMP_NAME, e.EMP_NO
           String sql = "Select e from " + Employee.class.getName() + " e "
                   + " order by e.empName, e.empNo ";


           // Create Query object.
           Query<Employee> query = session.createQuery(sql);


           // Execute query.
           List<Employee> employees = query.getResultList();

           for (Employee emp : employees) {
               System.out.println("Emp: " + emp.getEmpNo() + " : "
                       + emp.getEmpName());
           }

           // Commit data.
           session.getTransaction().commit();
       } catch (Exception e) {
           e.printStackTrace();
           // Rollback in case of an error occurred.
           session.getTransaction().rollback();
       }
   }

}

运行上面代码，得到以下结果 -

查询对象示例-2

创建一个Java类文件：QueryObjectDemo2.java，其代码如下 -

package com.yiibai;

import java.util.List;

import org.hibernate.query.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import com.yiibai.HibernateUtils;
import com.yiibai.entities.Employee;

public class QueryObjectDemo2 {

    public static void main(String[] args) {
        SessionFactory factory = HibernateUtils.getSessionFactory();

        Session session = factory.getCurrentSession();

        try {

            // All the action with DB via Hibernate
            // must be located in one transaction
            // Start Transaction.
            session.getTransaction().begin();

            // Create an HQL statement, query the object.
            // HQL with parameters.
            // Equivalent to the SQL statement:
            // Select e.* from EMPLOYEE e cross join DEPARTMENT d
            // where e.DEPT_ID = d.DEPT_ID and d.DEPT_NO = :deptNo;
            String sql = "Select e from " + Employee.class.getName() + " e " + " where e.department.deptNo=:deptNo ";

            // Create query object.
            Query<Employee> query = session.createQuery(sql);

            query.setParameter("deptNo", "D10");

            // Execute query.
            List<Employee> employees = query.getResultList();

            for (Employee emp : employees) {
                System.out.println("Emp: " + emp.getEmpNo() + " : " + emp.getEmpName());
            }

            // Commit data
            session.getTransaction().commit();
        } catch (Exception e) {
            e.printStackTrace();
            // Rollback in case of an error occurred.
            session.getTransaction().rollback();
        }
    }
}

运行上面代码，得到以下结果 -

......
org.hibernate.hql.internal.QueryTranslatorFactoryInitiator initiateService
INFO: HHH000397: Using ASTQueryTranslatorFactory
Hibernate: select employee0_.EMP_ID ..._NO=?
Emp: E7839 : KING
Emp: E7934 : MILLER
`

8.2 - 使用HQL查询读取多列数据

创建一个Java类文件：QuerySomeColumnDemo.java，其代码如下 -

package com.yiibai;

import java.util.List;

import org.hibernate.query.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import com.yiibai.HibernateUtils;
import com.yiibai.entities.Employee;

public class QuerySomeColumnDemo {

    public static void main(String[] args) {
        SessionFactory factory = HibernateUtils.getSessionFactory();

        Session session = factory.getCurrentSession();

        try {
            session.getTransaction().begin();

            // Query some columns.
            String sql = "Select e.empId, e.empNo, e.empName from "
                    + Employee.class.getName() + " e ";

            Query<Object[]> query = session.createQuery(sql);

            // Execute Query.
            // Get the array of Object
            List<Object[]> datas = query.getResultList();

            for (Object[] emp : datas) {
                System.out.println("Emp Id: " + emp[0]);
                System.out.println("    Emp No: " + emp[1]);
                System.out.println("    Emp Name: " + emp[2]);
            }

            // Commit data.
            session.getTransaction().commit();
        } catch (Exception e) {
            e.printStackTrace();
            // Rollback in case of an error occurred.
            session.getTransaction().rollback();
        }

    }
}

运行上面代码，得到以下结果 -

Hibernate: select employee0_.EMP_ID..._0_ from EMPLOYEE employee0_
Emp Id: 7369
    Emp No: E7369
    Emp Name: SMITH
Emp Id: 7499
    Emp No: E7499
    Emp Name: ALLEN
Emp Id: 7521
    Emp No: E7521
    Emp Name: WARD
Emp Id: 7566
    Emp No: E7566
    Emp Name: JONES
Emp Id: 7654
    Emp No: E7654
    Emp Name: MARTIN
Emp Id: 7698
    Emp No: E7698
    Emp Name: BLAKE
Emp Id: 7782
    Emp No: E7782
    Emp Name: CLARK
Emp Id: 7788
    Emp No: E7788
    Emp Name: SCOTT
Emp Id: 7839
    Emp No: E7839
    Emp Name: KING
Emp Id: 7844
    Emp No: E7844
    Emp Name: TURNER
Emp Id: 7876
    Emp No: E7876
    Emp Name: ADAMS
Emp Id: 7900
    Emp No: E7900
    Emp Name: ADAMS
Emp Id: 7902
    Emp No: E7902
    Emp Name: FORD
Emp Id: 7934
    Emp No: E7934
    Emp Name: MILLER
`

8.3 - 使用HQL和JavaBean查询多列数据

在这种情况下，如果需要在某些表中提取某些列的数据，最好的方法是使用Java bean。使用Java bean的构造函数来为不同的字段设置值。在此构造函数加入HQL查询。

创建一个Java类文件：ShortEmpInfo.java，其代码如下 -

package com.yiibai;

public class ShortEmpInfo {

    private Long empId;
    private String empNo;
    private String empName;

    //
    // Constructor have 3 parameters, will be used in the Hibernate Query.
    //
    public ShortEmpInfo(Long empId, String empNo, String empName) {
        this.empId = empId;
        this.empNo = empNo;
        this.empName = empName;
    }

    public Long getEmpId() {
        return empId;
    }

    public void setEmpId(Long empId) {
        this.empId = empId;
    }

    public String getEmpNo() {
        return empNo;
    }

    public void setEmpNo(String empNo) {
        this.empNo = empNo;
    }

    public String getEmpName() {
        return empName;
    }

    public void setEmpName(String empName) {
        this.empName = empName;
    }

}

创建一个Java类文件：ShortEmpInfoQueryDemo.java，其代码如下 -

package com.yiibai;

import java.util.List;

import org.hibernate.query.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import com.yiibai.HibernateUtils;
import com.yiibai.entities.Employee;

public class ShortEmpInfoQueryDemo {

    public static void main(String[] args) {
        SessionFactory factory = HibernateUtils.getSessionFactory();

        Session session = factory.getCurrentSession();

        try {
            session.getTransaction().begin();

            // Using constructor of ShortEmpInfo
            String sql = "Select new " + ShortEmpInfo.class.getName()
                    + "(e.empId, e.empNo, e.empName)" + " from "
                    + Employee.class.getName() + " e ";

            Query<ShortEmpInfo> query = session.createQuery(sql);


            // Execute query.
            // Get a List of ShortEmpInfo
            List<ShortEmpInfo> employees = query.getResultList();

            for (ShortEmpInfo emp : employees) {
                System.out.println("Emp: " + emp.getEmpNo() + " : "
                        + emp.getEmpName());
            }

            // Commit data.
            session.getTransaction().commit();
        } catch (Exception e) {
            e.printStackTrace();
            // Rollback in case of an error occurred.
            session.getTransaction().rollback();
        }
    }

}

运行上面代码，得到以下结果 -

8.4 - 查询检索唯一结果

创建一个Java类文件：UniqueResultDemo.java，其代码如下 -

package com.yiibai;

import java.util.Set;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.query.Query;

import com.yiibai.entities.Department;
import com.yiibai.entities.Employee;


public class UniqueResultDemo {

    public static Department getDepartment(Session session, String deptNo) {
        String sql = "Select d from " + Department.class.getName() + " d "//
                + " where d.deptNo= :deptNo ";
        Query<Department> query = session.createQuery(sql);
        query.setParameter("deptNo", deptNo);
        return (Department) query.getSingleResult();
    }

    public static Employee getEmployee(Session session, Long empId) {
        String sql = "Select e from " + Employee.class.getName() + " e "//
                + " where e.empId= :empId ";
        Query<Employee> query = session.createQuery(sql);
        query.setParameter("empId", empId);
        return (Employee) query.getSingleResult();
    }

    public static void main(String[] args) {
        SessionFactory factory = HibernateUtils.getSessionFactory();

        Session session = factory.getCurrentSession();

        try {
            session.getTransaction().begin();

            Department dept = getDepartment(session, "D10");
            Set<Employee> emps = dept.getEmployees();

            System.out.println("Dept Name: " + dept.getDeptName());
            for (Employee emp : emps) {
                System.out.println(" Emp name: " + emp.getEmpName());
            }

            Employee emp = getEmployee(session, 7839L);
            System.out.println("Emp Name: " + emp.getEmpName());

            session.getTransaction().commit();
        } catch (Exception e) {
            e.printStackTrace();
            session.getTransaction().rollback();
        }
    }

}

运行上面代码，得到以下结果 -

9. Hibernate瞬态，持久和分离

在这部分中，使用Session.persist(Object)将瞬态对象插入数据库的简单示例。本例中将介绍对象瞬态(Transitent)，持久(Persistent)和分离(Detached)的概念。

创建一个Java类文件：DataUtils.java，其代码如下 -

package com.yiibai;

import org.hibernate.Session;
import org.hibernate.query.Query;
import com.yiibai.entities.Department;
import com.yiibai.entities.Employee;

public class DataUtils {

   public static Department findDepartment(Session session, String deptNo) {
       String sql = "Select d from " + Department.class.getName() + " d "//
               + " Where d.deptNo = :deptNo";
       Query<Department> query = session.createQuery(sql);
       query.setParameter("deptNo", deptNo);
       return query.getSingleResult();
   }

   public static Long getMaxEmpId(Session session) {
       String sql = "Select max(e.empId) from " + Employee.class.getName() + " e ";
       Query<Number> query = session.createQuery(sql);
       Number value = query.getSingleResult();
       if (value == null) {
           return 0L;
       }
       return value.longValue();
   }

   public static Employee findEmployee(Session session, String empNo) {
       String sql = "Select e from " + Employee.class.getName() + " e "//
               + " Where e.empNo = :empNo";
       Query<Employee> query = session.createQuery(sql);
       query.setParameter("empNo", empNo);
       return query.getSingleResult();
   }

}

创建一个Java类文件：PersistDemo.java，其代码如下 -

package com.yiibai;

import java.util.Date;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import com.yiibai.entities.Department;
import com.yiibai.entities.Employee;

public class PersistDemo {

   public static void main(String[] args) {

       SessionFactory factory = HibernateUtils.getSessionFactory();

       Session session = factory.getCurrentSession();
       Department department = null;
       Employee emp = null;
       try {
           session.getTransaction().begin();

           Long maxEmpId = DataUtils.getMaxEmpId(session);
           Long empId = maxEmpId + 1;

           // Get Persistent object.
           department = DataUtils.findDepartment(session, "D10");

           // Create transient object
           emp = new Employee();
           emp.setEmpId(empId);
           emp.setEmpNo("E" + empId);
           emp.setEmpName("Name " + empId);
           emp.setJob("Coder");
           emp.setSalary(1000f);
           emp.setManager(null);
           emp.setHideDate(new Date());
           emp.setDepartment(department);

           // Using persist(..)
           // Now 'emp' is managed by Hibernate.
           // it has Persistent status.
           // No action at this time with DB.
           session.persist(emp);


           // At this step the data is pushed to the DB.
           // Execute Insert statement.
           session.getTransaction().commit();
       } catch (Exception e) {
           e.printStackTrace();
           session.getTransaction().rollback();
       }

       // After the session is closed (commit, rollback, close)
       // Objects 'emp', 'dept' became the Detached objects.
       // It is no longer in the control of the session.        
       System.out.println("Emp No: " + emp.getEmpNo());

   }

}

运行上面代码，得到以下结果 -

10. Hibernate生命周期

Hibernate的Session类的有一些/几组的重要方法，如下图所示：

Hibernate中的一个对象存在于以下四个状态之中的一种：

短暂(Transient)
持久(Persistent)
Removed
Detached

以上几个状态在下面图中解释：

下面来看这几个状态的流转说明 -

当从一个实体创建一个新的Java对象时，该对象处于“短暂”状态。 Hibernate不知道它的存在，因为它独立于Hibernate的管理。
如果使用方法：get，load或find获取实体对象，则将获得一个等同于数据库中的1条记录的对象。此对象处于Persistent状态。它由Hibernate管理。
会话调用方法：save，saveOrUpdate和persist。合并将短暂(Transient)对象置于Hibernate的管理之下，此对象转为持久化(Persistent)状态。在使用的具体情况下，它向数据库插入或更新数据。
Session调用evict(..)或clear()，以便从处于Hibernate管理状态的对象处于关闭状态，并且这些对象处于分离(Detached)的状态。
使用update(..)，saveOrUpdate(..)，merge(..)将有助于重新连接分离对象。在具体情况下，它会向数据库中创建更新或插入数据。对象转回持久化(Persistent)状态。
Session调用方法：remove(..)，delete(..)删除除记录并持久化对象。

11. 用Hibernate插入，更新，删除

11.1 - 持久化(Persistent)

当一个对像使用 Session 的get(),load(),find()方法获取关联数据时，它处于持久化(Persistent)状态。

创建一个JAVA类文件：PersistentDemo.java，用于演示对象的持久化(Persistent)状态。

package com.yiibai;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import com.yiibai.entities.Department;
import com.yiibai.entities.Employee;

public class PersistentDemo {

   public static void main(String[] args) {

       SessionFactory factory = HibernateUtils.getSessionFactory();

       Session session = factory.getCurrentSession();
       Department department = null;

       try {
           session.getTransaction().begin();

           System.out.println("- Finding Department deptNo = D10...");

           // Persistent object.
           department = DataUtils.findDepartment(session, "D10");

           System.out.println("- First change Location");


           // Changing something on Persistent object.
           department.setLocation("Chicago " + System.currentTimeMillis());

           System.out.println("- Location = " + department.getLocation());

           System.out.println("- Calling flush...");

           // Use session.flush () to actively push the changes to the DB.
           // It works for all changed Persistent objects.
           session.flush();

           System.out.println("- Flush OK");

           System.out.println("- Second change Location");

           // Change something on Persistent object
           department.setLocation("Chicago " + System.currentTimeMillis());

           // Print out location
           System.out.println("- Location = " + department.getLocation());

           System.out.println("- Calling commit...");

           // Commit
           session.getTransaction().commit();

           System.out.println("- Commit OK");
       } catch (Exception e) {
           e.printStackTrace();
           session.getTransaction().rollback();
       }

       // Create the session after it had been closed earlier
       // (Cause by commit or update)
       session = factory.getCurrentSession();
       try {
           session.getTransaction().begin();

           System.out.println("- Finding Department deptNo = D10...");

           // Query lại Department D10.

           department = DataUtils.findDepartment(session, "D10");

           // Print out location
           System.out.println("- D10 Location = " + department.getLocation());

           session.getTransaction().commit();
       } catch (Exception e) {
           e.printStackTrace();
           session.getTransaction().rollback();
       }
   }

}

执行上面代码，得到以下结果 -

11.2 - 瞬态转为持久化状态

11.3 - 瞬态转为持久化状态：使用persist(Object)

创建一个JAVA类文件：PersistTransientDemo.java，用于演示对象的持久化(Persistent)状态。

package com.yiibai;

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import com.yiibai.DataUtils;
import com.yiibai.HibernateUtils;
import com.yiibai.entities.Employee;
import com.yiibai.entities.Timekeeper;

public class PersistTransientDemo {

   private static DateFormat df = new SimpleDateFormat("dd-MM-yyyy HH:mm:ss");

   private static Timekeeper persist_Transient(Session session, Employee emp) {

       // Note:
       // Configuring of timekeeperId
       // @GeneratedValue(generator = "uuid")
       // @GenericGenerator(name = "uuid", strategy = "uuid2")            
       Timekeeper tk1 = new Timekeeper();

       tk1.setEmployee(emp);
       tk1.setInOut(Timekeeper.IN);
       tk1.setDateTime(new Date());

       // Now, 'tk1' is transient object
       System.out.println("- tk1 Persistent? " + session.contains(tk1));

       System.out.println("====== CALL persist(tk).... ===========");


       // Hibernate assign value to Id of 'tk1'
       // No action to DB.
       session.persist(tk1);

       System.out
               .println("- tk1.getTimekeeperId() = " + tk1.getTimekeeperId());


       // Now 'tk1' is Persistent object.
       // But no action with DB.
       // ==> true
       System.out.println("- tk1 Persistent? " + session.contains(tk1));

       System.out.println("- Call flush..");


       // Flush data to DB.
       // Hibernate execute insert statement.
       session.flush();

       String timekeeperId = tk1.getTimekeeperId();
       System.out.println("- timekeeperId = " + timekeeperId);
       System.out.println("- inOut = " + tk1.getInOut());
       System.out.println("- dateTime = " + df.format(tk1.getDateTime()));
       System.out.println();
       return tk1;
   }

   public static void main(String[] args) {
       SessionFactory factory = HibernateUtils.getSessionFactory();

       Session session = factory.getCurrentSession();
       Employee emp = null;
       try {
           session.getTransaction().begin();

           emp = DataUtils.findEmployee(session, "E7499");

           persist_Transient(session, emp);

           session.getTransaction().commit();
       } catch (Exception e) {
           e.printStackTrace();
           session.getTransaction().rollback();
       }
   }

}

执行上面代码，得到以下结果 -

11.4 - 瞬态转为持久化状态：使用save(Object)

创建一个JAVA类文件：SaveTransientDemo.java，用于演示对象的持久化(Persistent)状态。

package com.yiibai;

import java.io.Serializable;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import com.yiibai.DataUtils;
import com.yiibai.HibernateUtils;
import com.yiibai.entities.Employee;
import com.yiibai.entities.Timekeeper;

public class SaveTransientDemo {

   private static DateFormat df = new SimpleDateFormat("dd-MM-yyyy HH:mm:ss");

   private static Timekeeper persist_Transient(Session session, Employee emp) {

       // See configuration of timekeeperId:
       // @GeneratedValue(generator = "uuid")
       // @GenericGenerator(name = "uuid", strategy = "uuid2")
       // Create an Object, Transitent state.        
       Timekeeper tk2 = new Timekeeper();

       tk2.setEmployee(emp);
       tk2.setInOut(Timekeeper.IN);
       tk2.setDateTime(new Date());

       // Now 'tk3' are state Transient.        
       System.out.println("- tk2 Persistent? " + session.contains(tk2));

       System.out.println("====== CALL save(tk).... ===========");

       // save() very similar to persist()
       // save() return ID, persist() return void.
       // Hibernate assign ID value to 'tk2', no action with DB
       // And return ID of 'tk2'.        
       Serializable id = session.save(tk2);

       System.out.println("- id = " + id);

       //
       System.out
               .println("- tk2.getTimekeeperId() = " + tk2.getTimekeeperId());


       // Now, 'tk2' has Persistent state
       // It has been managed in Session.
       // ==> true
       System.out.println("- tk2 Persistent? " + session.contains(tk2));

       System.out.println("- Call flush..");

       // To push data into the DB, call flush().
       // If not call flush() data will be pushed to the DB when calling commit().
       // Will execute insert statement.
       session.flush();

       String timekeeperId = tk2.getTimekeeperId();
       System.out.println("- timekeeperId = " + timekeeperId);
       System.out.println("- inOut = " + tk2.getInOut());
       System.out.println("- dateTime = " + df.format(tk2.getDateTime()));
       System.out.println();
       return tk2;
   }

   public static void main(String[] args) {
       SessionFactory factory = HibernateUtils.getSessionFactory();

       Session session = factory.getCurrentSession();
       Employee emp = null;
       try {
           session.getTransaction().begin();

           emp = DataUtils.findEmployee(session, "E7499");

           persist_Transient(session, emp);

           session.getTransaction().commit();
       } catch (Exception e) {
           e.printStackTrace();
           session.getTransaction().rollback();
       }
   }
}

执行上面代码，得到以下结果 -

11.5 - 瞬态转为持久化状态：使用saveOrUpdate(Object)

创建一个JAVA类文件：SaveOrUpdateTransientDemo.java，用于演示对象的持久化(Persistent)状态。

package com.yiibai;

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import com.yiibai.DataUtils;
import com.yiibai.HibernateUtils;
import com.yiibai.entities.Employee;
import com.yiibai.entities.Timekeeper;

public class SaveOrUpdateTransientDemo {

   private static DateFormat df = new SimpleDateFormat("dd-MM-yyyy HH:mm:ss");

   private static Timekeeper saveOrUpdate_Transient(Session session,
           Employee emp) {

       // See configuration of timekeeperId:
       // @GeneratedValue(generator = "uuid")
       // @GenericGenerator(name = "uuid", strategy = "uuid2")
       // Create an Object, Transitent state.
       Timekeeper tk3 = new Timekeeper();

       tk3.setEmployee(emp);
       tk3.setInOut(Timekeeper.IN);
       tk3.setDateTime(new Date());

       // Now 'tk3' are state Transient.
       System.out.println("- tk3 Persistent? " + session.contains(tk3));

       System.out.println("====== CALL saveOrUpdate(tk).... ===========");

       // Here Hibernate checks, 'tk3' have ID or not (timekeeperId)
       // If no, it will be assigned automatically
       session.saveOrUpdate(tk3);

       System.out
               .println("- tk3.getTimekeeperId() = " + tk3.getTimekeeperId());

       // Now 'tk3' has Persistent state
       // It has been managed in Session.
       // But no action insert, or update to DB.
       // ==> true
       System.out.println("- tk3 Persistent? " + session.contains(tk3));

       System.out.println("- Call flush..");

       // To push data into the DB, call flush().
       // If not call flush() data will be pushed to the DB when calling commit().
       // Now possible to Insert or Update DB. (!!!)
       // Depending on the ID of 'tk3' exists in the DB or not
       session.flush();

       String timekeeperId = tk3.getTimekeeperId();
       System.out.println("- timekeeperId = " + timekeeperId);
       System.out.println("- inOut = " + tk3.getInOut());
       System.out.println("- dateTime = " + df.format(tk3.getDateTime()));
       System.out.println();
       return tk3;
   }

   public static void main(String[] args) {
       SessionFactory factory = HibernateUtils.getSessionFactory();

       Session session = factory.getCurrentSession();
       Employee emp = null;
       try {
           session.getTransaction().begin();

           emp = DataUtils.findEmployee(session, "E7499");

           saveOrUpdate_Transient(session, emp);

           session.getTransaction().commit();
       } catch (Exception e) {
           e.printStackTrace();
           session.getTransaction().rollback();
       }
   }
}

执行上面代码，得到以下结果 -

11.6 - 瞬态转为持久化状态：使用merge(Object)

创建一个JAVA类文件：MergeTransientDemo.java，用于演示对象的持久化(Persistent)状态。

package com.yiibai;

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import com.yiibai.DataUtils;
import com.yiibai.HibernateUtils;
import com.yiibai.entities.Employee;
import com.yiibai.entities.Timekeeper;

public class MergeTransientDemo {

   private static DateFormat df = new SimpleDateFormat("dd-MM-yyyy HH:mm:ss");

   private static Timekeeper saveOrUpdate_Transient(Session session,
           Employee emp) {

       // Note:
       // Configuring of timekeeperId
       // @GeneratedValue(generator = "uuid")
       // @GenericGenerator(name = "uuid", strategy = "uuid2")        
       Timekeeper tk4 = new Timekeeper();

       tk4.setEmployee(emp);
       tk4.setInOut(Timekeeper.IN);
       tk4.setDateTime(new Date());

       // Now 'tk4' Transient status.
       System.out.println("- tk4 Persistent? " + session.contains(tk4));

       System.out.println("====== CALL merge(tk).... ===========");


       // Hibernate2 has method saveOrUpdateCopy
       // Hibernate3 change saveOrUpdateCopy to merge
       // So there will be similarities between the two methods merge and copyOrUpdate
       // Here Hibernate check tk4 has ID or not
       // If not, Hibernate assign value to ID of tk4
       // Return copy of tk4.
       Timekeeper tk4Copy = (Timekeeper) session.merge(tk4);

       System.out
               .println("- tk4.getTimekeeperId() = " + tk4.getTimekeeperId());


       // Now 'tk4' still Transient state.
       // and 'tk4Copy' has Persistent status
       // No action with DB (insert or update).
       System.out.println("- tk4 Persistent? " + session.contains(tk4));

       // 'tk4Copy' has Persistent status
       // ==> true
       System.out
               .println("- tk4Copy Persistent? " + session.contains(tk4Copy));

       System.out.println("- Call flush..");


       // This time have Insert or Update to DB. (!!!)
       session.flush();

       // 'tk4' still Transitent, after flush().
       // merge(..) safer than saveOrUpdate().
       System.out.println("- tk4 Persistent? " + session.contains(tk4));

       //
       String timekeeperId = tk4.getTimekeeperId();
       System.out.println("- timekeeperId = " + timekeeperId);
       System.out.println("- inOut = " + tk4.getInOut());
       System.out.println("- dateTime = " + df.format(tk4.getDateTime()));
       System.out.println();
       return tk4;
   }

   public static void main(String[] args) {
       SessionFactory factory = HibernateUtils.getSessionFactory();

       Session session = factory.getCurrentSession();
       Employee emp = null;
       try {
           session.getTransaction().begin();

           emp = DataUtils.findEmployee(session, "E7499");

           saveOrUpdate_Transient(session, emp);

           session.getTransaction().commit();
       } catch (Exception e) {
           e.printStackTrace();
           session.getTransaction().rollback();
       }
   }
}

执行上面代码，得到以下结果 -

11.7 - 持久化转变为分离状态

由Hibernate管理的持久化(Persistent)条件中的一个对象可以通过以下两个Session的方法转换为Detached(独立于Hibernate的管理)状态：

evict (Object) - 从Hibernate管理中删除一个对象
clear() - 从Hibernate管理的对象中删除所有对象。

当然，当Session调用顺序为：commit()，close()或rollback()时，当前会话已经完成。此会话的所有Persistence对象将从新打开的会话中分离。

创建一个JAVA类文件：EvictDemo.java，用于演示对象持久化转变为分离状态。

package com.yiibai;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import com.yiibai.DataUtils;
import com.yiibai.HibernateUtils;
import com.yiibai.entities.Employee;

public class EvictDemo {

   public static void main(String[] args) {
       SessionFactory factory = HibernateUtils.getSessionFactory();

       Session session = factory.getCurrentSession();
       Employee emp = null;
       try {
           session.getTransaction().begin();

           // This is object has Persistent status
           emp = DataUtils.findEmployee(session, "E7499");

           // ==> true
           System.out.println("- emp Persistent? " + session.contains(emp));


           // using evict() to evicts a single object from the session
           session.evict(emp);

           // Now 'emp' has Detached status
           // ==> false
           System.out.println("- emp Persistent? " + session.contains(emp));


           // All change on the 'emp' will not update
           // if not reatach 'emp' to session
           emp.setEmpNo("NEW");

           session.getTransaction().commit();
       } catch (Exception e) {
           e.printStackTrace();
           session.getTransaction().rollback();
       }
   }
}

执行上面代码，得到以下结果 -

创建一个JAVA类文件：ClearDemo.java，用于演示将所有对象持久化转变为分离状态。

package com.yiibai;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import com.yiibai.DataUtils;
import com.yiibai.HibernateUtils;
import com.yiibai.entities.Department;
import com.yiibai.entities.Employee;

public class ClearDemo {


   public static void main(String[] args) {
       SessionFactory factory = HibernateUtils.getSessionFactory();

       Session session = factory.getCurrentSession();
       Employee emp = null;
       Department dept = null;
       try {
           session.getTransaction().begin();

           // It is an object has Persistent status.
           emp = DataUtils.findEmployee(session, "E7499");
           dept = DataUtils.findDepartment(session, "D10");


           // clear() evicts all the objects in the session.
           session.clear();


           // Now 'emp' & 'dept' has Detached status
           // ==> false
           System.out.println("- emp Persistent? " + session.contains(emp));
           System.out.println("- dept Persistent? " + session.contains(dept));

           // All change on the 'emp' will not update
           // if not reatach 'emp' to session
           emp.setEmpNo("NEW");

           dept = DataUtils.findDepartment(session, "D20");
           System.out.println("Dept Name = "+ dept.getDeptName());

           session.getTransaction().commit();
       } catch (Exception e) {
           e.printStackTrace();
           session.getTransaction().rollback();
       }
   }
}

执行上面代码，得到以下结果 -

11.8 - 分离状态转变为持久化状态

Hibernate管理分离的对象可以通过以下Session的一些方法重新附加：

update(Object)
saveOrUpdate(Object)
merge(Object)
refresh(Object)
lock(Object)

可以在以下示例中看到这些方法的区别：

11.9-分离转变为持久性状态：使用update(Object)

创建一个JAVA类文件：UpdateDetachedDemo.java，用于演示将对象分离转变为持久性状态。

package com.yiibai;

import org.hibernate.Session;
import org.hibernate.SessionFactory;

import com.yiibai.DataUtils;
import com.yiibai.HibernateUtils;
import com.yiibai.entities.Department;
import com.yiibai.entities.Employee;

public class UpdateDetachedDemo {

    public static void main(String[] args) {
        SessionFactory factory = HibernateUtils.getSessionFactory();

        Session session1 = factory.getCurrentSession();
        Employee emp = null;
        try {
            session1.getTransaction().begin();

            // This is a Persistent object.
            emp = DataUtils.findEmployee(session1, "E7499");

            // session1 was closed after a commit is called.
            session1.getTransaction().commit();
        } catch (Exception e) {
            e.printStackTrace();
            session1.getTransaction().rollback();
        }

        // Open other session
        Session session2 = factory.getCurrentSession();

        try {
            session2.getTransaction().begin();

            // Check state of 'emp'
            // ==> false
            System.out.println("- emp Persistent? " + session2.contains(emp));

            System.out.println("Emp salary: " + emp.getSalary());

            emp.setSalary(emp.getSalary() + 100);

            // update (..) is only used for Detached object.
            // (Not for Transient object).
            // Use the update (emp) to bring back emp Persistent state.
            session2.update(emp);

            // Call flush
            // Update statement will be called.
            session2.flush();

            System.out.println("Emp salary after update: " + emp.getSalary());

            // session2 was closed after a commit is called.
            session2.getTransaction().commit();
        } catch (Exception e) {
            e.printStackTrace();
            session2.getTransaction().rollback();
        }

    }
}

执行上面代码，得到以下结果 -

11.10 - 分离转变为持久性状态：使用saveOrUpdate(Object)

创建一个JAVA类文件：SaveOrUpdateDetachedDemo.java，用于演示将对象分离转变为持久性状态。

package com.yiibai;

import java.util.Random;

import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import com.yiibai.DataUtils;
import com.yiibai.HibernateUtils;
import com.yiibai.entities.Employee;

public class SaveOrUpdateDetachedDemo {

   public static void main(String[] args) {

       // An object Detached state.
       Employee emp = getEmployee_Detached();

       System.out.println(" - GET EMP " + emp.getEmpId());

       // Random delete or not delete Employee
       boolean delete = deleteOrNotDelete(emp.getEmpId());

       System.out.println(" - DELETE? " + delete);

       // Call saveOrUpdate for detached object.
       saveOrUpdate_test(emp);

       // After call saveOrUpdate()
       System.out.println(" - EMP ID " + emp.getEmpId());
   }


   // Return Employee object has Detached state
   private static Employee getEmployee_Detached() {
       SessionFactory factory = HibernateUtils.getSessionFactory();

       Session session1 = factory.getCurrentSession();
       Employee emp = null;
       try {
           session1.getTransaction().begin();

           Long maxEmpId = DataUtils.getMaxEmpId(session1);
           System.out.println(" - Max Emp ID " + maxEmpId);

           Employee emp2 = DataUtils.findEmployee(session1, "E7839");

           Long empId = maxEmpId + 1;
           emp = new Employee();
           emp.setEmpId(empId);
           emp.setEmpNo("E" + empId);

           emp.setDepartment(emp2.getDepartment());
           emp.setEmpName(emp2.getEmpName());

           emp.setHideDate(emp2.getHideDate());
           emp.setJob("Test");
           emp.setSalary(1000F);

           // emp has been managed by Hibernate
           session1.persist(emp);

           // session1 was closed after a commit is called.
           // An Employee record are insert into DB.            
           session1.getTransaction().commit();
       } catch (Exception e) {
           e.printStackTrace();
           session1.getTransaction().rollback();
       }
       // Session1 closed 'emp' switch to Detached state.
       return emp;
   }

   // Random: delete or not delete.
   private static boolean deleteOrNotDelete(Long empId) {
       // A random number 0-9
       int random = new Random().nextInt(10);
       if (random < 5) {
           return false;
       }
       SessionFactory factory = HibernateUtils.getSessionFactory();

       Session session2 = factory.getCurrentSession();
       try {
           session2.getTransaction().begin();
           String sql = "Delete " + Employee.class.getName() + " e "
                   + " where e.empId =:empId ";
           Query query = session2.createQuery(sql);
           query.setParameter("empId", empId);

           query.executeUpdate();

           session2.getTransaction().commit();
           return true;
       } catch (Exception e) {
           e.printStackTrace();
           session2.getTransaction().rollback();
           return false;
       }
   }

   private static void saveOrUpdate_test(Employee emp) {
       SessionFactory factory = HibernateUtils.getSessionFactory();

       // Open other session
       Session session3 = factory.getCurrentSession();

       try {
           session3.getTransaction().begin();

           // Check state of emp
           // ==> false
           System.out.println(" - emp Persistent? " + session3.contains(emp));

           System.out.println(" - Emp salary before update: "
                   + emp.getSalary());

           // Set new salary for Detached emp object.
           emp.setSalary(emp.getSalary() + 100);


           // Using saveOrUpdate(emp) to switch emp to Persistent state
           // Note: If exists object same ID in session, this method raise Exception
           //
           // Now, no action with DB.            
           session3.saveOrUpdate(emp);

           // By pushing data into the DB.
           // It will call a Insert or update statement.
           // If the record is deleted before ==> insert
           // Else ==> update.    
           session3.flush();

           System.out
                   .println(" - Emp salary after update: " + emp.getSalary());

           // session3 was closed after a commit is called.
           session3.getTransaction().commit();
       } catch (Exception e) {
           e.printStackTrace();
           session3.getTransaction().rollback();
       }

   }

}

执行上面代码，多几次运行示例错码，可以看到两种情况，saveOrUpdate()方法调用在数据上插入或更新。得到以下结果 -

11.11-分离转变为持久性状态：使用merge(Object)

Hibernate 2版本有saveOrUpdateCopy(Object)方法。从Hibernate 3起，它被重命名为merge(Object)。因此与saveOrUpdate()相比，merge()方法有一些相似性和差异。

merge(Object)不会将对象置于Hibernate的管理下，而是创建一个对象的副本，而不是管理该对象。

如果调用saveOrUpdate(aObject)则aObject由Hibernate管理，并且与aObject具有相同的ID将会抛出异常，但是使用merge(aObject)时不会得到此异常。

创建一个JAVA类文件：MergeDetachedDemo.java，用于演示将对象分离转变为持久性状态。

package com.yiibai;

import java.util.Random;

import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import com.yiibai.DataUtils;
import com.yiibai.HibernateUtils;
import com.yiibai.entities.Employee;

public class MergeDetachedDemo {

   public static void main(String[] args) {

       // An object has Detached status
       Employee emp = getEmployee_Detached();

       System.out.println(" - GET EMP " + emp.getEmpId());

       // Random: delete or not delete the Employee by ID.
       boolean delete = deleteOrNotDelete(emp.getEmpId());

       System.out.println(" - DELETE? " + delete);

       // Call saveOrUpdate Detached object
       saveOrUpdate_test(emp);

       // After call saveOrUpdate
       // ...
       System.out.println(" - EMP ID " + emp.getEmpId());
   }


   // Method return Employee object
   // and has Detached status.
   private static Employee getEmployee_Detached() {
       SessionFactory factory = HibernateUtils.getSessionFactory();

       Session session1 = factory.getCurrentSession();
       Employee emp = null;
       try {
           session1.getTransaction().begin();

           Long maxEmpId = DataUtils.getMaxEmpId(session1);
           System.out.println(" - Max Emp ID " + maxEmpId);

           Employee emp2 = DataUtils.findEmployee(session1, "E7839");

           Long empId = maxEmpId + 1;
           emp = new Employee();
           emp.setEmpId(empId);
           emp.setEmpNo("E" + empId);

           emp.setDepartment(emp2.getDepartment());
           emp.setEmpName(emp2.getEmpName());

           emp.setHideDate(emp2.getHideDate());
           emp.setJob("Test");
           emp.setSalary(1000F);

           // 'emp' has Persistant state
           session1.persist(emp);


           // session1 was closed after a commit is called.
           // An Employee record are insert into DB.
           session1.getTransaction().commit();
       } catch (Exception e) {
           e.printStackTrace();
           session1.getTransaction().rollback();
       }
       // session1 closed, 'emp' switched Detached state.
       return emp;
   }


   // Delete Employee by ID
   // Random: delete or not delete
   private static boolean deleteOrNotDelete(Long empId) {
       // A random number 0-9
       int random = new Random().nextInt(10);
       if (random < 5) {
           return false;
       }
       SessionFactory factory = HibernateUtils.getSessionFactory();

       Session session2 = factory.getCurrentSession();
       try {
           session2.getTransaction().begin();
           String sql = "Delete " + Employee.class.getName() + " e "
                   + " where e.empId =:empId ";
           Query query = session2.createQuery(sql);
           query.setParameter("empId", empId);

           query.executeUpdate();

           session2.getTransaction().commit();
           return true;
       } catch (Exception e) {
           e.printStackTrace();
           session2.getTransaction().rollback();
           return false;
       }
   }

   private static void saveOrUpdate_test(Employee emp) {
       SessionFactory factory = HibernateUtils.getSessionFactory();

       // Open other session
       Session session3 = factory.getCurrentSession();

       try {
           session3.getTransaction().begin();


           // The fact, 'emp' has Detached state
           // It is not managed by Hibernate.
           // Check the status of emp:
           // ==> false
           System.out.println(" - emp Persistent? " + session3.contains(emp));

           System.out.println(" - Emp salary before update: "
                   + emp.getSalary());

           // Set new salary for Detached object 'emp'
           emp.setSalary(emp.getSalary() + 100);


           // merge(emp) return empMerge, a copy of 'emp',
           // empMerge managed by Hibernate
           // 'emp' still in Detached state
           //
           // At this time there is no action regarding DB.
           Employee empMerge = (Employee) session3.merge(emp);

           // ==> false
           System.out.println(" - emp Persistent? " + session3.contains(emp));
           // ==> true
           System.out.println(" - empMerge Persistent? "
                   + session3.contains(empMerge));


           // Push data into the DB.
           // Here it is possible to create the Insert or Update on DB.
           // If the corresponding record has been deleted by someone, it insert
           // else it update
           session3.flush();

           System.out
                   .println(" - Emp salary after update: " + emp.getSalary());

           // session3 closed after a commit is called.
           session3.getTransaction().commit();
       } catch (Exception e) {
           e.printStackTrace();
           session3.getTransaction().rollback();
       }

   }

}

执行上面代码，多几次运行示例错码，可以看到两种情况，得到以下结果 -

11.12 - 分离转变为持久性状态：使用refresh(Object)

创建一个JAVA类文件：RefreshDetachedDemo.java，用于演示将对象分离转变为持久性状态。

package com.yiibai;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import com.yiibai.DataUtils;
import com.yiibai.HibernateUtils;
import com.yiibai.entities.Employee;

public class RefreshDetachedDemo {

   public static void main(String[] args) {

       // an Object with Detached status
       Employee emp = getEmployee_Detached();

       System.out.println(" - GET EMP " + emp.getEmpId());

       // Refresh Object  
       refresh_test(emp);
   }


   // Return Employee object has Detached state
   private static Employee getEmployee_Detached() {
       SessionFactory factory = HibernateUtils.getSessionFactory();

       Session session1 = factory.getCurrentSession();
       Employee emp = null;
       try {
           session1.getTransaction().begin();

           emp = DataUtils.findEmployee(session1, "E7839");

           // session1 was closed after a commit is called.
           // An Employee record are insert into DB.
           session1.getTransaction().commit();
       } catch (Exception e) {
           e.printStackTrace();
           session1.getTransaction().rollback();
       }
       // Session1 closed 'emp' switch to Detached state.
       return emp;
   }

   private static void refresh_test(Employee emp) {
       SessionFactory factory = HibernateUtils.getSessionFactory();

       // Open other session
       Session session2 = factory.getCurrentSession();

       try {
           session2.getTransaction().begin();


           // Check the status of 'emp' (Detached)
           // ==> false
           System.out.println(" - emp Persistent? " + session2.contains(emp));

           System.out.println(" - Emp salary before update: "
                   + emp.getSalary());

            // Set new salary for 'emp'.
           emp.setSalary(emp.getSalary() + 100);


           // refresh: make a query statement
           // and switch 'emp' to Persistent state
           // The changes are ignored
           session2.refresh(emp);

           // ==> true
           System.out.println(" - emp Persistent? " + session2.contains(emp));

           System.out.println(" - Emp salary after refresh: "
                   + emp.getSalary());

           session2.getTransaction().commit();
       } catch (Exception e) {
           e.printStackTrace();
           session2.getTransaction().rollback();
       }

   }

}

执行上面代码，多几次运行示例错码，可以看到两种情况，得到以下结果 -

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原文地址：https://www.cnblogs.com/borter/p/9522226.html