Hibernate 再接触 多对一与一对多

多对一单向关联

数据库设计：

错误做法：在多方加外键

在多这一方加外键 

第一种 annotation

Group.java

package com.bjsxt.hibernate;

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

@Entity
@Table(name="t_group")
public class Group {
    private int id;
    private String name;
    @Id
    @GeneratedValue
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
}

User.java

package com.bjsxt.hibernate;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.ManyToOne;
import javax.persistence.Table;

@Entity
@Table(name="t_user")
public class User {
    private int id;
    private String name;
    private Group group;
    @ManyToOne   //多对一，在多一方加外键 ，若想改名字就用joincolumn
    
    public Group getGroup() {
        return group;
    }
    public void setGroup(Group group) {
        this.group = group;
    }
    @Id
    @GeneratedValue
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
}

XML

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>
    <class name="com.bjsxt.hibernate.Group" table="t_group">
        <id name="id">
            <generator class="native"></generator>
        </id>
        
        <property name="name"></property>
        
    </class>
    
</hibernate-mapping>

user.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>
    <class name="com.bjsxt.hibernate.User" table="t_user">
        <id name="id">
            <generator class="native"></generator>
        </id>
        
        <property name="name"></property>
        <many-to-one name="group" column="groupId" />
    </class>
    
</hibernate-mapping>

test

@Test
    public void testSchemaExport() {
        new SchemaExport(new AnnotationConfiguration().configure()).create(false, true);
    }