hibernate--一对多单向关联 (重点!!!)-白红宇

hibernate--一对多单向关联 (重点!!!)

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发布时间：2019-06-29

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多对一是在多的类上存在一的对象

一对多是在一的类上存在多的集合.

多的类

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;		@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;	}}

一的类Group.java, 需要多的集合:

package com.bjsxt.hibernate;import java.util.HashSet;import java.util.Set;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.Id;import javax.persistence.JoinColumn;import javax.persistence.OneToMany;import javax.persistence.Table;@Entity@Table(name="t_group")public class Group {	private int id;	private String name;	private Set
     
       users = new HashSet
      
       ();	@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;	}	@OneToMany	@JoinColumn(name="groupId")	public Set
       
         getUsers() {		return users;	}	public void setUsers(Set
        
          users) {		this.users = users;	}}

test文件:

package com.bjsxt.hibernate;import java.util.Date;import org.hibernate.Query;import org.hibernate.Session;import org.hibernate.SessionFactory;import org.hibernate.cfg.AnnotationConfiguration;import org.hibernate.tool.hbm2ddl.SchemaExport;import org.junit.AfterClass;import org.junit.BeforeClass;import org.junit.Test;public class HibernateORMappingTest {	private static SessionFactory sessionFactory;		//@BeforeClass	public static void beforeClass() {			sessionFactory = new AnnotationConfiguration().configure().buildSessionFactory();	}	//@AfterClass	public static void afterClass() {		sessionFactory.close();	}				@Test	public void testSchemaExport() {		new SchemaExport(new AnnotationConfiguration().configure()).create(false, true);	}		public static void main(String[] args) {		beforeClass();	}}

运行test的结果:

14:15:34,169 DEBUG org.hibernate.tool.hbm2ddl.SchemaExport:303 -     create table t_group (        id integer not null auto_increment,        name varchar(255),        primary key (id)    )14:15:34,304 DEBUG org.hibernate.tool.hbm2ddl.SchemaExport:303 -     create table t_user (        id integer not null auto_increment,        name varchar(255),        groupId integer,        primary key (id)    )14:15:34,409 DEBUG org.hibernate.tool.hbm2ddl.SchemaExport:303 -     alter table t_user         add index FKCB63CCB6C3D18669 (groupId),         add constraint FKCB63CCB6C3D18669         foreign key (groupId)         references t_group (id)14:15:34,674  INFO org.hibernate.tool.hbm2ddl.SchemaExport:196 - schema export complete

XML方式:

作为多的一方user正常写成: