Hibernate初学者---一对多 /多对一 单向关联

Hibernate 版本： v5.2.10
Eclipse版本：v4.7.1
JDK版本: v1.8
MySQL版本：v5.7

一对多

POJO类一

package com.bak.bum.union;

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

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.OneToMany;
import javax.persistence.Table;

@Entity
@Table(name = "100_group")
public class Groups {
    int id;
    String name;
    Set user = new HashSet();

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    public int getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    @OneToMany
    @JoinColumn(name="Group_id")
    public Set getUser() {
        return user;
    }

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

    public void setName(String name) {
        this.name = name;
    }

    public void setUser(Set user) {
        this.user = user;
    }

}

POJO类二

package com.bak.bum.union;

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

@Entity
@Table(name = "100_user")
public class User {
    int id;

    String name;

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    public int getId() {
        return id;
    }

    public String getName() {
        return name;
    }

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

    public void setName(String name) {
        this.name = name;
    }

}

hibernate.cfg.xml

  



<hibernate-configuration>
    <session-factory>

        <property name="connection.driver_class">com.mysql.jdbc.Driverproperty>

        <property name="connection.url">jdbc:mysql://localhost/hibernateproperty>

        <property name="connection.username">rootproperty>

        <property name="connection.password">shwythnn00property>

        <property name="dialect">org.hibernate.dialect.MySQL5InnoDBDialectproperty>

        <property name="show_sql">trueproperty>

        <property name="hibernate.format_sql">trueproperty>

        <property name="hibernate.hbm2ddl.auto">createproperty>

        <mapping class="com.bak.bum.union.Groups" />
        <mapping class="com.bak.bum.union.User" />
    session-factory>
hibernate-configuration>  

Junit - Test类

package com.bak.fan.test;

import java.util.EnumSet;

import org.hibernate.boot.Metadata;
import org.hibernate.boot.MetadataSources;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.service.ServiceRegistry;
import org.hibernate.tool.hbm2ddl.SchemaExport;
import org.hibernate.tool.schema.TargetType;

public class Test {

    @org.junit.Test
    public void test() {
        ServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder().configure().build();
        Metadata metadata = new MetadataSources(serviceRegistry).buildMetadata();
        SchemaExport schemaExport = new SchemaExport();
        schemaExport.create(EnumSet.of(TargetType.DATABASE), metadata);


}
}

输出结果

SHOW数据库

JAR

---

多对一

• 与一对多基本一样，只是添加对方引用的位置不一样，换成了另一方，@One to Many换成@Many To one
• 多对一时，不用写JoinColumn，（ 一对多时，由于有的存在，所以Hibernate会把它当成多对多的情况处理，生成第三张中间表，所以需要写JoinColumn 去告诉hibernate 我是有外键的，有外键当然就不是多对多了，所以它就不会生成第三张表了。多对一它能正确识别，所以不用写JoinColumn）

---

POJO类一

package com.bak.bum.union;

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

@Entity
@Table(name = "200_user")
public class User {
    int id;

    String name;
    Groups groups;

    @ManyToOne
    public Groups getGroups() {
        return groups;
    }

    public void setGroups(Groups groups) {
        this.groups = groups;
    }

    @Id
    @GeneratedValue
    public int getId() {
        return id;
    }

    public String getName() {
        return name;
    }

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

    public void setName(String name) {
        this.name = name;
    }

}

POJO类二

package com.bak.bum.union;

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

@Entity
@Table(name = "200_group")
public class Groups {
    int id;
    String name;


    @Id
    @GeneratedValue
    public int getId() {
        return id;
    }

    public String getName() {
        return name;
    }



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

    public void setName(String name) {
        this.name = name;
    }



}

Junit - Test

package com.bak.fan.test;

import java.util.EnumSet;

import org.hibernate.boot.Metadata;
import org.hibernate.boot.MetadataSources;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.service.ServiceRegistry;
import org.hibernate.tool.hbm2ddl.SchemaExport;
import org.hibernate.tool.schema.TargetType;

public class Test {

    @org.junit.Test
    public void test() {
        ServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder().configure().build();
        Metadata metadata = new MetadataSources(serviceRegistry).buildMetadata();
        SchemaExport schemaExport = new SchemaExport();
        schemaExport.create(EnumSet.of(TargetType.DATABASE), metadata);


}
}

hibernate.cfg.xml

  



<hibernate-configuration>
    <session-factory>

        <property name="connection.driver_class">com.mysql.jdbc.Driverproperty>

        <property name="connection.url">jdbc:mysql://localhost/hibernateproperty>

        <property name="connection.username">rootproperty>

        <property name="connection.password">shwythnn00property>

        <property name="dialect">org.hibernate.dialect.MySQL5InnoDBDialectproperty>

        <property name="show_sql">trueproperty>

        <property name="hibernate.format_sql">trueproperty>

        <property name="hibernate.hbm2ddl.auto">createproperty>

        <property name="">property>


        <mapping class="com.bak.bum.union.Groups" />
        <mapping class="com.bak.bum.union.User" />
    session-factory>
hibernate-configuration>  

输出结果

SHOW数据库

JAR