整合SpringData JPA

一、Spring Data简介

项目的目的是为了简化构建基于 Spring 框架应用的数据访问技术，包括非关系数据库、
Map-Reduce 框架、云数据服务等等；另外也包含对关系数据库的访问支持。

SpringData为我们提供使用统一的API来对数据访问层进行操作：

Repository<T, ID extends Serializable>：统一接口
RevisionRepository<T, ID extends Serializable, N extends Number & Comparable<N>>：基于乐观
锁机制
CrudRepository<T, ID extends Serializable>：基本CRUD操作
PagingAndSortingRepository<T, ID extends Serializable>：基本CRUD及分页

二、JPA整合示例

　　工程目录

 引入依赖： spring-boot-starter-data-jpa

<dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>

1）编写一个实体类（bean）和数据表进行映射，并且配置好映射关系

Entity

Employee类

package com.example.demo.entity;

import java.util.Date;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.OneToMany;
import javax.persistence.Table;



//使用JPA注解配置映射关系
@Entity //告诉JPA这是一个实体类（和数据表映射的类）
@Table(name = "t_employee") //@Table来指定和哪个数据表对应;如果省略默认表名就是user；
public class Employee {

    @Id //这是一个主键
    @GeneratedValue(strategy = GenerationType.IDENTITY)//自增主键
    private Integer id;
    
    @Column(name = "last_name",length = 30) //这是和数据表对应的一个列
    private String lastName;

    @Column(name = "email")
    private String email;
    
    //1 male, 0 female
    @Column(name = "gender")
    private Integer gender;
    
    @ManyToOne(targetEntity=Department.class,cascade=CascadeType.ALL,optional=true)
    @JoinColumn(name="department_id",nullable=true)
    private Department department;
    
    @Column(name = "birth")
    private Date birth;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public Integer getGender() {
        return gender;
    }

    public void setGender(Integer gender) {
        this.gender = gender;
    }

    public Department getDepartment() {
        return department;
    }

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

    public Date getBirth() {
        return birth;
    }

    public void setBirth(Date birth) {
        this.birth = birth;
    }

    public Employee(Integer id, String lastName, String email, Integer gender,
            Department department, Date birth) {
        super();
        this.id = id;
        this.lastName = lastName;
        this.email = email;
        this.gender = gender;
        this.department = department;
        this.birth = birth;
    }
    
    public Employee() {
        super();
        // TODO Auto-generated constructor stub
    }

    @Override
    public String toString() {
        return "Employee [id=" + id + ", lastName=" + lastName + ", email="
                + email + ", gender=" + gender + ", department=" + department
                + ", birth=" + birth + "]";
  }
}

Department类

package com.example.demo.entity;

import java.util.Set;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;

@Entity //告诉JPA这是一个实体类（和数据表映射的类）
@Table(name = "t_department")
public class Department {
    
    @Id //这是一个主键
    @GeneratedValue(strategy = GenerationType.IDENTITY)//自增主键
    private Integer id;
    
    @Column(name = "department_name",length = 50) //这是和数据表对应的一个列
    private String departmentName;
    
    @OneToMany(mappedBy="department",cascade=CascadeType.ALL)
    private Set<Employee> emps ;
    
    
    public Department() {
    }
    
    public Department(int i, String string) {
        this.id = i;
        this.departmentName = string;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getDepartmentName() {
        return departmentName;
    }

    public void setDepartmentName(String departmentName) {
        this.departmentName = departmentName;
    }
    

    public Set<Employee> getEmps() {
        return emps;
    }

    public void setEmps(Set<Employee> emps) {
        this.emps = emps;
    }

    @Override
    public String toString() {
        return "Department [id=" + id + ", departmentName=" + departmentName + "]";
    }
    
}

多表联查的重点是：@ManyToOne@JoinColumn@OneToMany注解的使用

2）编写一个Dao接口来操作实体类对应的数据表（Repository）

repository层

EmployeeRepository

package com.example.demo.repository;

import org.springframework.data.domain.Example;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.Pageable;
import org.springframework.data.jpa.repository.JpaRepository;
import com.example.demo.entity.Employee;

public interface EmployeeRepository extends JpaRepository<Employee,Integer>{
    
    @Override
    public <S extends Employee> Page<S> findAll(Example<S> example,
            Pageable pageable);
    
}

3）基本的配置JpaProperties

spring.jpa.show-sql=true

Service 层

package com.example.demo.service;

import org.springframework.data.domain.Page;
import com.example.demo.entity.Employee;

public interface EmployeeService {
    public Page<Employee> findAll(String lastName , Integer gender , Integer deptId,Integer pageNumber,Integer pageSize);
}

ServiceImpl 层　　

package com.example.demo.service.impl;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.domain.Example;
import org.springframework.data.domain.ExampleMatcher;
import org.springframework.data.domain.ExampleMatcher.GenericPropertyMatchers;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.PageRequest;
import org.springframework.data.domain.Pageable;
import org.springframework.data.domain.Sort;
import org.springframework.stereotype.Service;
import org.springframework.util.StringUtils;

import com.example.demo.entity.Department;
import com.example.demo.entity.Employee;
import com.example.demo.repository.EmployeeRepository;
import com.example.demo.service.EmployeeService;

@Service
public class EmployeeServiceImpl implements EmployeeService {
    
    @Autowired
    private EmployeeRepository employeeRepository;

    @Override
    public Page<Employee> findAll(String lastName , Integer gender , Integer deptId ,Integer pageNumber,Integer pageSize) {
        
        Employee emp =new Employee();
        if (!StringUtils.isEmpty(lastName)) {
            emp.setLastName(lastName);
        }
        
        if (gender != null){
            emp.setGender(gender);
        }
        
        if (deptId != null){
            emp.setDepartment(new Department(deptId,null));
        }
        
        
        ExampleMatcher matcher = ExampleMatcher.matching();
        
        if (!StringUtils.isEmpty(lastName)) {
            matcher.withMatcher("lastName", GenericPropertyMatchers.contains());
        }
        
        if (gender != null){
            matcher.withMatcher("gender", GenericPropertyMatchers.exact());
        }
        
        if (deptId != null){
            matcher.withMatcher("department.id", GenericPropertyMatchers.exact());
        }
        
        Example<Employee> ex = Example.of(emp, matcher); 
        Pageable pageable = new PageRequest(pageNumber,pageSize,Sort.Direction.ASC,"id");                        
　　　　 return employeeRepository.findAll(ex, pageable);
    }
    
}

由于对Spring Data JPA 应用进行深入研究，此处就只是简单实现了JPA 的分页功能。

测试

package com.example.demo;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.data.domain.Page;
import org.springframework.test.context.junit4.SpringRunner;

import com.example.demo.entity.Employee;
import com.example.demo.repository.EmployeeRepository;
import com.example.demo.service.EmployeeService;

@RunWith(SpringRunner.class)
@SpringBootTest
public class SpringBoot02ApplicationTests {
    
    @Autowired
    EmployeeRepository empRepository;
    
    @Autowired
    EmployeeService employeeService;

    @Test
    public void contextLoads() {
        Page<Employee> page = employeeService.findAll(null, null, 2, 0, 2);
        System.out.println(page.getContent());
        System.out.println(page.getSize());
        System.out.println(page.getTotalPages());
    }
}

参考：https://blog.csdn.net/qq_34083066/article/details/80733512

　　　http://www.luckyzz.com/java/spring-data-jpa/