hibernate一对多，多对一，一对多双向关联

hibernate之多对一。在多对一中，在多的一方设置many-to-one，而在一的一方不设置。
1、新建一个java项目hibernate，新建类Employee.java与Department.java

Employee.java

package cn.ehoo.hibernate.domain;
/**
 *@author whp
 *@Email [e-mail]
 *@Nov 11, 2010
 *
 */
public class Employee {
	private Long id;
	private String name;
	private Department depart;
	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 Department getDepart() {
		return depart;
	}
	public void setDepart(Department depart) {
		this.depart = depart;
	}
}

Employee.java的配置文件Employee.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 package="cn.ehoo.hibernate.domain" >
	<class name="Employee" table="employee" dynamic-update="true" >
		<id name="id" type="long">
			<generator class="native" />
		</id>
		<property name="name" />
		<many-to-one name="depart" column="depart_id" cascade="save-update"/>
	</class>
</hibernate-mapping>

Department.java

package cn.ehoo.hibernate.domain;


/**
 *@author whp
 *@Email [e-mail]
 *@Nov 11, 2010
 *
 */
public class Department {
	private Long id;
	private String name;
	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;
	}
}

Department.java的配置文件Department.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 package="cn.ehoo.hibernate.domain">
	<class name="Department" table="department" >
		<id name="id" type="long">
			<generator class="native" />
		</id>
		<property name="name" />
	</class>

</hibernate-mapping>

2、新建类Many2One.java

package cn.ehoo.hibernate;

import org.hibernate.Session;
import org.hibernate.Transaction;

import cn.ehoo.hibernate.domain.Department;
import cn.ehoo.hibernate.domain.Employee;

/**
 * @author whp
 * @Email [e-mail]
 * @Nov 11, 2010
 * 
 */
public class Many2One {
	public static void main(String[] args) {
		Session s = null;
		Transaction tr = null;
		s = HibernateUtil.getCurrentSession();
		tr = s.beginTransaction();
		tr.begin();
		/*Department dep = (Department) s.load(Department.class, 1L);
		dep.setName("department_1");
		Employee em = new Employee();
		em.setName("employee_2");
		em.setDepart(dep);
		s.save(em);*/
		Department dep = (Department) s.load(Department.class, 1L);
		Employee em = (Employee)s.load(Employee.class, 1L);
		em.setName("whp1");
		em.setDepart(dep);
		s.update(em);
		tr.commit();
	}

}

3、hibernate.cfg.xml文件的配置

<!DOCTYPE hibernate-configuration PUBLIC
	"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
	"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

<hibernate-configuration>
<session-factory>
	<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
	<property name="connection.url">jdbc:mysql:///test</property>
	<property name="connection.username">root</property>
	<property name="connection.password">123</property>
	<property name="dialect">org.hibernate.dialect.MySQLDialect</property>
	<property name="current_session_context_class">thread</property>
	<property name="hbm2ddl.auto">update</property>
	<property name="show_sql">true</property>
	<property name="format_sql">true</property>
	<property name="generate_statistics">true</property>
	<mapping resource="cn/ehoo/hibernate/domain/Department.hbm.xml" />
	<mapping resource="cn/ehoo/hibernate/domain/Employee.hbm.xml" />
</session-factory>
</hibernate-configuration>

hibernate之一对多。在一对多中，在多的一方不设置many-to-one，而在一的一方设置one-to-many。

1、新建一个java项目hibernate，新建类Employee.java与Department.java

Employee.java

package cn.ehoo.hibernate.domain;
/**
 *@author whp
 *@Email [e-mail]
 *@Nov 11, 2010
 *
 */
public class Employee {
	private Long id;
	private String name;
	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;
	}
}

Employee.java的配置文件Employee.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 package="cn.ehoo.hibernate.domain" >
	<class name="Employee" table="employee" dynamic-update="true" >
		<id name="id" type="long">
			<generator class="native" />
		</id>
		<property name="name" />
	</class>
</hibernate-mapping>

Department.java

package cn.ehoo.hibernate.domain;

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

/**
 *@author whp
 *@Email [e-mail]
 *@Nov 11, 2010
 *
 */
public class Department {
	private Long id;
	private String name;
	private Set<Employee> emps = new HashSet<Employee>();
	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 Set<Employee> getEmps() {
		return emps;
	}
	public void setEmps(Set<Employee> emps) {
		this.emps = emps;
	}
}

Department.java的配置文件Department.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 package="cn.ehoo.hibernate.domain">
	<class name="Department" table="department" >
		<id name="id" type="long">
			<generator class="native" />
		</id>
		<property name="name" />
		<set name="emps" cascade="save-update">
			<key column="depart_id" />
			<one-to-many class="Employee" />
		</set>
	</class>
</hibernate-mapping>

2、新建类One2Many.java

package cn.ehoo.hibernate;

import org.hibernate.Session;
import org.hibernate.Transaction;

import cn.ehoo.hibernate.domain.Department;
import cn.ehoo.hibernate.domain.Employee;

/**
 * @author whp
 * @Email [e-mail]
 * @Nov 11, 2010
 * 
 */
public class One2Many {
	public static void main(String[] args) {
		Session s = null;
		Transaction tr = null;
		s = HibernateUtil.getCurrentSession();
		tr = s.beginTransaction();
		tr.begin();
		 Department dep = new Department();
		dep.setName("department_1");
		Employee em = new Employee();
		em.setName("employee_2");
		dep.getEmps().add(em);
		s.save(dep); 
		tr.commit();
	}

}

3、hibernate.cfg.xml文件的配置

<!DOCTYPE hibernate-configuration PUBLIC
	"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
	"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

<hibernate-configuration>
<session-factory>
	<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
	<property name="connection.url">jdbc:mysql:///test</property>
	<property name="connection.username">root</property>
	<property name="connection.password">123</property>
	<property name="dialect">org.hibernate.dialect.MySQLDialect</property>
	<property name="current_session_context_class">thread</property>
	<property name="hbm2ddl.auto">update</property>
	<property name="show_sql">true</property>
	<property name="format_sql">true</property>
	<property name="generate_statistics">true</property>
	<mapping resource="cn/ehoo/hibernate/domain/Department.hbm.xml" />
	<mapping resource="cn/ehoo/hibernate/domain/Employee.hbm.xml" />
</session-factory>
</hibernate-configuration>

hibernate之一对多双向关联。在一的一方要配置one-to-many，在多的一方要配置many-to-one。在一对多双向关联时，一般要把一一方的集合中设置inverse=true，这样可以让一的一方来放弃关系的维护，从而节省资源。

1、新建一个java项目hibernate，新建类Employee.java与Department.java

Employee.java

package cn.ehoo.hibernate.domain;
/**
 *@author whp
 *@Email [e-mail]
 *@Nov 11, 2010
 *
 */
public class Employee {
	private Long id;
	private String name;
	private Department depart;
	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 Department getDepart() {
		return depart;
	}
	public void setDepart(Department depart) {
		this.depart = depart;
	}
}

Employee.java的配置文件Employee.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 package="cn.ehoo.hibernate.domain" >
	<class name="Employee" table="employee" dynamic-update="true" >
		<id name="id" type="long">
			<generator class="native" />
		</id>
		<property name="name" />
		<many-to-one name="depart" column="depart_id" cascade="save-update"/>
	</class>
</hibernate-mapping>

Department.java

package cn.ehoo.hibernate.domain;

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

/**
 *@author whp
 *@Email [e-mail]
 *@Nov 11, 2010
 *
 */
public class Department {
	private Long id;
	private String name;
	private Set<Employee> emps = new HashSet<Employee>();
	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 Set<Employee> getEmps() {
		return emps;
	}
	public void setEmps(Set<Employee> emps) {
		this.emps = emps;
	}
}

Department.java的配置文件Department.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 package="cn.ehoo.hibernate.domain">
	<class name="Department" table="department" >
		<id name="id" type="long">
			<generator class="native" />
		</id>
		<property name="name" />
		<set name="emps" cascade="save-update">
			<key column="depart_id" />
			<one-to-many class="Employee" />
		</set>
	</class>
</hibernate-mapping>

2、新建类One2Many.java

package cn.ehoo.hibernate;

import org.hibernate.Session;
import org.hibernate.Transaction;

import cn.ehoo.hibernate.domain.Department;
import cn.ehoo.hibernate.domain.Employee;

/**
 * @author whp
 * @Email [e-mail]
 * @Nov 11, 2010
 * 
 */
public class One2Many {
	public static void main(String[] args) {
		Session s = null;
		Transaction tr = null;
		s = HibernateUtil.getCurrentSession();
		tr = s.beginTransaction();
		tr.begin();
		 Department dep = new Department();
		dep.setName("department_1");
		Employee em = new Employee();
		em.setName("employee_2");
		dep.getEmps().add(em);
		s.save(dep); 
		tr.commit();
	}

}

3、hibernate.cfg.xml文件的配置

<!DOCTYPE hibernate-configuration PUBLIC
	"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
	"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

<hibernate-configuration>
<session-factory>
	<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
	<property name="connection.url">jdbc:mysql:///test</property>
	<property name="connection.username">root</property>
	<property name="connection.password">123</property>
	<property name="dialect">org.hibernate.dialect.MySQLDialect</property>
	<property name="current_session_context_class">thread</property>
	<property name="hbm2ddl.auto">update</property>
	<property name="show_sql">true</property>
	<property name="format_sql">true</property>
	<property name="generate_statistics">true</property>
	<mapping resource="cn/ehoo/hibernate/domain/Department.hbm.xml" />
	<mapping resource="cn/ehoo/hibernate/domain/Employee.hbm.xml" />
</session-factory>
</hibernate-configuration>

casecade为级联。inverse为关联。inverse设置为true是放弃关系的维护，一般在双向关联里使用。并且只有集合一端才有。而casecode在一的一端与多的一端里都会存在