Hibernate One to Many Annotation Example

0.pom.xml

......
	<properties>
		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
		<hibernate-version>3.6.10.Final</hibernate-version>
		<javassist-version>3.12.1.GA</javassist-version>
		<slf4j-nop-version>1.6.6</slf4j-nop-version>
		<mysql-connector-version>5.1.21</mysql-connector-version>
	</properties>

	<dependencies>
		<dependency>
			<groupId>org.hibernate</groupId>
			<artifactId>hibernate-core</artifactId>
			<version>${hibernate-version}</version>
		</dependency>

		<dependency>
			<groupId>javassist</groupId>
			<artifactId>javassist</artifactId>
			<version>${javassist-version}</version>
		</dependency>

		<dependency>
			<groupId>org.slf4j</groupId>
			<artifactId>slf4j-nop</artifactId>
			<version>${slf4j-nop-version}</version>
		</dependency>

		<dependency>
			<groupId>mysql</groupId>
			<artifactId>mysql-connector-java</artifactId>
			<version>${mysql-connector-version}</version>
		</dependency>
	</dependencies>
......

 

1.schema.sql

create table idcard 
(
	iid integer not null, 
	num integer, 
	primary key (iid)
);

create table student 
(	id integer not null auto_increment, 
	name varchar(255), 
	team_id integer, 
	primary key (id)
);

create table team 
(
	id integer not null auto_increment, 
	name varchar(255), 
	primary key (id)
);

alter table student add index FK8FFE823BEC0561A1 (team_id), 
add constraint FK8FFE823BEC0561A1 foreign key (team_id) references team (id);

表结构如下图所示。 

student表和idcard表实现一对一主键关联，team和student实现一对多关联。

 

2.Hibernate Configuration File

......
	<mapping class="org.fool.model2.Student" />
	<mapping class="org.fool.model2.IdCard" />
	<mapping class="org.fool.model2.Team" />
......

 

3.Hibernate Model Class

IdCard.java

package org.fool.model2;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.OneToOne;
import javax.persistence.PrimaryKeyJoinColumn;
import javax.persistence.Table;

import org.hibernate.annotations.Fetch;
import org.hibernate.annotations.FetchMode;
import org.hibernate.annotations.GenericGenerator;
import org.hibernate.annotations.Parameter;

@Entity
@Table(name = "idcard")
public class IdCard {

	@Id
	@GenericGenerator(name = "generator", strategy = "foreign", 
		parameters = @Parameter(name = "property", value = "student"))
	@GeneratedValue(generator = "generator")
	@Column(name = "iid")
	private int id;

	@Column(name = "num")
	private int num;

	@OneToOne(cascade = CascadeType.ALL)
	@PrimaryKeyJoinColumn
	@Fetch(FetchMode.SELECT)
	private Student student;

	public int getId() {
		return id;
	}

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

	public int getNum() {
		return num;
	}

	public void setNum(int num) {
		this.num = num;
	}

	public Student getStudent() {
		return student;
	}

	public void setStudent(Student student) {
		this.student = student;
	}

} 

以上Annotation代码相当于以下的IdCard.hbm.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>

	<class name="org.fool.model2.IdCard" table="idcard">

		<id name="id" column="iid" type="integer">
			<generator class="foreign">
				<param name="property">student</param> 
			</generator>
		</id>

		<property name="num" column="num" type="integer" />

		<one-to-one name="student" class="org.fool.model2.Student"
			cascade="all" fetch="select"></one-to-one>

	</class>

</hibernate-mapping>

 

 

Student.java

package org.fool.model2;

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

import org.hibernate.annotations.Fetch;
import org.hibernate.annotations.FetchMode;

@Entity
@Table(name = "student")
public class Student {

	@Id
	@GeneratedValue(strategy = GenerationType.IDENTITY)
	@Column(name = "sid")
	private int id;

	@Column(name = "name")
	private String name;

	@OneToOne(cascade = CascadeType.ALL, mappedBy = "student")
	@Fetch(FetchMode.SELECT)
	private IdCard idCard;

	@ManyToOne(cascade = CascadeType.ALL)
	@JoinColumn(name = "team_id")
	@Fetch(FetchMode.SELECT)
	private Team team;

	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;
	}

	public IdCard getIdCard() {
		return idCard;
	}

	public void setIdCard(IdCard idCard) {
		this.idCard = idCard;
	}

	public Team getTeam() {
		return team;
	}

	public void setTeam(Team team) {
		this.team = team;
	}

}

 以上Annotation代码相当于以下的Student.hbm.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>

	<class name="org.fool.model2.Student" table="student">

		<id name="id" column="sid" type="integer">
			<generator class="identity">
			</generator>
		</id>

		<property name="name" column="name" type="string" />

		<one-to-one name="idCard" class="org.fool.model2.IdCard"
			cascade="all" fetch="select"></one-to-one>

		<many-to-one name="team" class="org.fool.model2.Team"
			column="team_id" cascade="all" fetch="select"></many-to-one>
	</class>

</hibernate-mapping>

 

 

Team.java

package org.fool.model2;

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
@Table(name = "team")
public class Team {
	@Id
	@GeneratedValue(strategy = GenerationType.IDENTITY)
	@Column(name = "tid")
	private int id;

	@Column(name = "name")
	private String name;

	@OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER, mappedBy = "team")
	private Set<Student> students;

	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;
	}

	public Set<Student> getStudents() {
		return students;
	}

	public void setStudents(Set<Student> students) {
		this.students = students;
	}

}

  以上Annotation代码相当于以下的Team.hbm.xml, 其中The mappedBy attribute of @OneToMany annotation behaves the same as inverse = “true” in the xml file.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>

	<class name="org.fool.model2.Team" table="team">

		<id name="id" column="tid" type="integer">
			<generator class="identity">
			</generator>
		</id>

		<property name="name" column="name" type="string" />

		<set name="students" lazy="false" cascade="all" inverse="true">
			<key column="team_id" />
			<one-to-many class="org.fool.model2.Student" />
		</set>
	</class>

</hibernate-mapping>

最佳实践：如果没有特殊情况，不要使用cascade；特别注意，可能使用cascade的地方一般都是一的一方进行删除时使用；特殊需求才会使用cascade的add，正常情况add方法都是应该有程序员完成添加，一定要先添加一的一方，之后再添加多的一方，不要使用一的一方来维护关系，在配置文件的set标签中可以通过inverse=true来明确不使用一的这一端维护关系。one-to-many在添加和维护关系时比较麻烦，所以在开发中不建议使用one-to-many的单向。

 

4.Test It

package org.fool.test;

import java.util.HashSet;

import org.fool.model2.IdCard;
import org.fool.model2.Student;
import org.fool.model2.Team;
import org.fool.util.HibernateUtil;
import org.hibernate.Session;
import org.hibernate.Transaction;

public class HibernateTest3 {
	public static void main(String[] args) {
		// insert();
		// select();
	}

	public static void insert() {
		Session session = HibernateUtil.openSession();
		Transaction tx = null;

		try {
			tx = session.beginTransaction();

			Student student1 = new Student();
			student1.setName("zhangsan");

			IdCard idCard1 = new IdCard();
			idCard1.setNum(99988);

			student1.setIdCard(idCard1);
			idCard1.setStudent(student1);

			Student student2 = new Student();
			student2.setName("lisi");

			IdCard idCard2 = new IdCard();
			idCard2.setNum(99977);

			student2.setIdCard(idCard2);
			idCard2.setStudent(student2);

			Team team = new Team();
			team.setName("team1");
			team.setStudents(new HashSet<Student>());
			team.getStudents().add(student1);
			team.getStudents().add(student2);

			student1.setTeam(team);
			student2.setTeam(team);

			session.save(team);

			tx.commit();
		} catch (Exception e) {
			e.printStackTrace();
			if (null != tx) {
				tx.rollback();
			}
		} finally {
			HibernateUtil.closeSession(session);
		}
	}

	public static void select() {
		Session session = HibernateUtil.openSession();
		Transaction tx = null;

		try {
			tx = session.beginTransaction();

			Team team = (Team) session.get(Team.class, 1);

			System.out.println(team.getName());

			Student student = (Student) session.get(Student.class, 2);
			System.out.println(student.getName());

			tx.commit();
		} catch (Exception ex) {
			ex.printStackTrace();
			if (null != tx) {
				tx.rollback();
			}
		} finally {
			HibernateUtil.closeSession(session);
		}
	}
}

 

5.result

 

 

6.Category一对多实现表自关联

shema.sql

 

alter table category drop foreign key FK302BCFEA51B0EBD;
drop table if exists category;
create table category (cid bigint not null auto_increment, name varchar(255), category_id bigint, primary key (cid));
alter table category add index FK302BCFEA51B0EBD (category_id), add constraint FK302BCFEA51B0EBD foreign key (category_id) references category (cid);

表结构如下图所示

 Category.java

 

package org.fool.model;

import java.util.Set;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
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;

@Entity
@Table(name = "category")
public class Category {
	@Id
	@GeneratedValue(strategy = GenerationType.IDENTITY)
	@Column(name = "cid")
	private Long id;

	@Column(name = "name")
	private String name;

	@ManyToOne
	@JoinColumn(name = "category_id")
	private Category parentCategory;

	@OneToMany(cascade = CascadeType.ALL, mappedBy = "parentCategory")
	private Set<Category> childCategories;

	public Category() {
	}

	public Category(String name, Category parentCategory,
			Set<Category> childCategories) {
		super();
		this.name = name;
		this.parentCategory = parentCategory;
		this.childCategories = childCategories;
	}

	public Long getId() {
		return id;
	}

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

	public String getName() {
		return name;
	}

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

	public Category getParentCategory() {
		return parentCategory;
	}

	public void setParentCategory(Category parentCategory) {
		this.parentCategory = parentCategory;
	}

	public Set<Category> getChildCategories() {
		return childCategories;
	}

	public void setChildCategories(Set<Category> childCategories) {
		this.childCategories = childCategories;
	}

}

 以上Annotation代码相当于以下的Category.hbm.xml

 

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>

	<class name="org.fool.model.Category" table="category">

		<id name="id" column="cid" type="long">
			<generator class="identity">
			</generator>
		</id>

		<property name="name" column="name" type="string" />

		<set name="childCategories" cascade="all" inverse="true">
			<key column="category_id" />
			<one-to-many class="org.fool.model.Category" />
		</set>

		<many-to-one name="parentCategory" column="category_id"
			class="org.fool.model.Category">
		</many-to-one>

	</class>

</hibernate-mapping>

 测试一下

 

package org.fool.test;

import java.util.HashSet;

import org.fool.model.Category;
import org.fool.util.HibernateUtil;
import org.hibernate.Session;
import org.hibernate.Transaction;

public class HibernateTest2 {

	public static void main(String[] args) {
		// insert();
		// select();
		// delete();
	}

	/**
	 * 添加类别
	 */
	public static void insert() {
		Session session = HibernateUtil.openSession();
		Transaction tx = null;

		try {
			tx = session.beginTransaction();

			Category category1 = new Category("level1", null,
					new HashSet<Category>());
			Category category2 = new Category("level2", null,
					new HashSet<Category>());
			Category category3 = new Category("level2", null,
					new HashSet<Category>());
			Category category4 = new Category("level3", null,
					new HashSet<Category>());
			Category category5 = new Category("level3", null,
					new HashSet<Category>());
			Category category6 = new Category("level3", null,
					new HashSet<Category>());
			Category category7 = new Category("level3", null,
					new HashSet<Category>());

			category2.setParentCategory(category1);
			category3.setParentCategory(category1);

			category1.getChildCategories().add(category2);
			category1.getChildCategories().add(category3);

			category4.setParentCategory(category2);
			category5.setParentCategory(category2);

			category2.getChildCategories().add(category4);
			category2.getChildCategories().add(category5);

			category6.setParentCategory(category3);
			category7.setParentCategory(category3);

			category3.getChildCategories().add(category6);
			category3.getChildCategories().add(category7);

			session.save(category1);

			tx.commit();

		} catch (Exception ex) {
			ex.printStackTrace();
			if (null != tx) {
				tx.rollback();
			}
		} finally {
			HibernateUtil.closeSession(session);
		}
	}

	/**
	 * 查询类别
	 */
	public static void select() {
		Session session = HibernateUtil.openSession();
		Transaction tx = null;

		try {
			tx = session.beginTransaction();

			Category category = (Category) session.get(Category.class,
					new Long(1));

			System.out.println(category.getChildCategories().iterator().next()
					.getName());

			tx.commit();

		} catch (Exception ex) {
			ex.printStackTrace();
			if (null != tx) {
				tx.rollback();
			}
		} finally {
			HibernateUtil.closeSession(session);
		}
	}

	/**
	 * 删除类别
	 */
	public static void delete() {
		Session session = HibernateUtil.openSession();
		Transaction tx = null;

		try {
			tx = session.beginTransaction();

			Category category = (Category) session.get(Category.class,
					new Long(1));

			session.delete(category);

			tx.commit();

		} catch (Exception ex) {
			ex.printStackTrace();
			if (null != tx) {
				tx.rollback();
			}
		} finally {
			HibernateUtil.closeSession(session);
		}
	}

}