hibernate对象关系的映射

hibernate对象之间存在关系，

 

=-=================================================================

 

 

 

一对一（主键关联，和单向的外键关联）

   ①单向（主键，外键）Husband和Wife表，a,主键关联 b，外键关联（wife为parent） ，c,主键关联 d，外键关联（husband为parent）

一对一单向外键关联：

annotation：@oneToOne  @JoinColumn(name="wifeId")

                    xml ：    <many-to-one  unique="true"/>

一对一单向主键关联：annotation：@PrimaryKeyJoinColumn(name="id",referencedColumnName="id")

                    xml: <one-to-one name="stu" constrained="true"/>

 

 ②双向（主键，外键）

一对一双向外键关联：

annotation：在husband类中：@oneToOne

              在wife类中：@OneToOne(mappedBy="wife")对方为主导，对于一对一双向外键关联必须写mappedBy

                    xml : <many-to-one name="stu" unique="true" column="stuid" not-null="true"/>

                        <one-to-one name="idCard

property-ref="stu"></one-to-one>

               <generator class="foreign">

                        <param name="property">stu</param>

</generator>

一对一双向主键关联：

annotation：

@OneToOne

    @PrimaryKeyJoinColumn(name="id",referencedColumnName="id")

 

    @OneToOne(mappedBy="wife")

    @PrimaryKeyJoinColumn(name="id",columnDefinition="id")

a ，Husband的id与wife的id相互关联  b，husband的外键wifeid和wife中husbandid

联合主键关联（不重要）：

Annotation：

    @OneToOne

    @JoinColumns(

        {

            @JoinColumn(name="wifid",referencedColumnName="id"),

            @JoinColumn(name="wifename",referencedColumnName="name")

        }     

    )

   ③中间表 建立一张中间表

一对一（主键关联，和单向的外键关联）

   ①单向（主键，外键）Husband和Wife表，a,主键关联 b，外键关联（wife为parent） ，c,主键关联 d，外键关联（husband为parent）

一对一单向外键关联：

annotation：@oneToOne  @JoinColumn(name="wifeId")

                    xml ：    <many-to-one  unique="true"/>

一对一单向主键关联：annotation：@PrimaryKeyJoinColumn(name="id",referencedColumnName="id")

                    xml: <one-to-one name="stu" constrained="true"/>

 

 ②双向（主键，外键）

一对一双向外键关联：

annotation：在husband类中：@oneToOne

              在wife类中：@OneToOne(mappedBy="wife")对方为主导，对于一对一双向外键关联必须写mappedBy

                    xml : <many-to-one name="stu" unique="true" column="stuid" not-null="true"/>

                        <one-to-one name="idCard

property-ref="stu"></one-to-one>

               <generator class="foreign">

                        <param name="property">stu</param>

</generator>

一对一双向主键关联：

annotation：

@OneToOne

    @PrimaryKeyJoinColumn(name="id",referencedColumnName="id")

 

    @OneToOne(mappedBy="wife")

    @PrimaryKeyJoinColumn(name="id",columnDefinition="id")

a ，Husband的id与wife的id相互关联  b，husband的外键wifeid和wife中husbandid

联合主键关联（不重要）：

Annotation：

    @OneToOne

    @JoinColumns(

        {

            @JoinColumn(name="wifid",referencedColumnName="id"),

            @JoinColumn(name="wifename",referencedColumnName="name")

        }     

    )

   ③中间表 建立一张中间表

  一对多

   ①单向:

annotation：在一的一方加集合（Set），这种处理方式，hibernate把它当做了多对多关系处理，在数据库中建立了一张关系表。

    @OneToMany

    @JoinColumn(name="groupid")

    public Set<User> getUsers() {

       return users;

    }

    public void setUsers(Set<User> users) {

       this.users = users;

    } 

Xml：

        <set name="users">

            <key column="groupid"></key>

            <one-to-many class="User"/>

        </set>

   ②双向（多对一的双向关联，一对多的双向关联是一样的）

多对一：

  ①单向（manytoone的单向关联）：在多的一方加外键。1NF，要有主键，列不可分；2NF联合主键不能存在部分依赖3NF不能存在传递依赖。设计原则：不能产生冗余。

 

     annotation：@ManyToOne 

     xml:<many-to-one name="g" column="groupid"></many-to-one>

 

   ②双向：（多对一的双向关联，一对多的双向关联是一样的）

   Annotation：@ManyToOne 

 

   xml：

<set name="aliases" table="person_aliases" order-by="lower(name) asc">
    <key column="person"/>
    <element column="name" type="string"/>
</set>

 

 

 

 

多对多

   ①单向 

annotation： @ManyToMany

 

xml :

<class name="Person">

    <id name="id" column="personId">

        <generator class="native"/>

    </id>

    <set name="addresses" table="PersonAddress">

        <key column="personId"/>

        <many-to-many column="addressId"

            class="Address"/>

    </set>

</class>

 

<class name="Address">

    <id name="id" column="addressId">

        <generator class="native"/>

    </id>

</class>

 

   ②双向：

Annotation：

/**

 *ManyToMany指明多对多关系

 *JoinTable生成中间表，name指定中间表的名字，joinColumns

 *指定参考这张表的主键的中间表的属性名，inverseJoinColumns

 *指定参考相关表的主键的中间表的属性名。 

 *

 */

    @ManyToMany

    @JoinTable(name="t_t",joinColumns={

           @JoinColumn(name="t_id")

    },inverseJoinColumns={@JoinColumn(name="s_id")})

 

    @ManyToMany(mappedBy="students")

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="com.xie.hibernate.modal" >

 

    <class name="Teacher" table="t_teacher">

         <id name="id" column="id">

            <generator class="native"></generator>

         </id>

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

        <set name="students" table="t_s">

            <key column="t_id"></key>

            <many-to-many column="s_id" class="Student"/>

        </set>

    </class>

</hibernate-mapping>

 

<?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="com.xie.hibernate.modal" >

 

    <class name="Student" table="t_student">

         <id name="id" column="id">

            <generator class="native"></generator>

         </id>

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

         <set name="teachers" table="t_s" inverse="true">

            <key column="s_id"/>

            <many-to-many column="t_id" class="Teacher"/>

         </set>

        

    </class>

</hibernate-mapping>

  

=-=================================================================

该如何映射呢？有3中方式，反映在数据库表上：

Single table：Student和Teacher类的父类是Person类，用一张数据库表反应3个类的所有信息。这样设计的缺点是：表的信息反映了所有类的属性，造成大量的数据冗余。

Table per class:为每个类设计一张表，其缺点是：

Joined：用一张表存共有的字段，而其子类对应的表存其特有字段。优缺点：查询能提高效率，然而需要作表连接，当添加新的子类时，需要添加新的表。

=====================================继承关系的映射=====================================================

Annotation：

     ⑴sigle_table：

package com.xie.hibernate.modal;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.DiscriminatorColumn;
import javax.persistence.DiscriminatorType;
import javax.persistence.DiscriminatorValue;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Inheritance;
import javax.persistence.InheritanceType;
import javax.persistence.JoinColumn;
import javax.persistence.MapKey;
import javax.persistence.OneToMany;
import javax.persistence.Table;

import com.sun.xml.internal.bind.v2.runtime.Name;
@Entity
//指定继承映射的策略
@Inheritance(strategy=InheritanceType.SINGLE_TABLE)
//在数据库表中加上一个字段，用以区分是哪个子类,name表示表的字段名字，discriminatorType
//表示name字段的数据类型
@DiscriminatorColumn(name="dis",discriminatorType=DiscriminatorType.STRING)
//指定这个类存到数据库中用什么区分，value表明dis的值
@DiscriminatorValue(value="person")
public class Person {
      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;
 }    
}

package com.xie.hibernate.modal;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.DiscriminatorValue;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;

@Entity
@DiscriminatorValue("student")
public class Student extends Person {
 private int score;

 public int getScore() {
  return score;
 }

 public void setScore(int score) {
  this.score = score;
 } 
}

package com.xie.hibernate.modal;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.DiscriminatorValue;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.MapKey;
import javax.persistence.OneToMany;
import javax.persistence.Table;

@Entity
@DiscriminatorValue("teacher")
public class Teacher extends Person{
 private String title;

 public String getTitle() {
  return title;
 }

 public void setTitle(String title) {
  this.title = title;
 } 
}

 

 

      ⑵table_per_class：

 

package com.xie.hibernate.modal;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.DiscriminatorColumn;
import javax.persistence.DiscriminatorType;
import javax.persistence.DiscriminatorValue;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Inheritance;
import javax.persistence.InheritanceType;
import javax.persistence.JoinColumn;
import javax.persistence.MapKey;
import javax.persistence.OneToMany;
import javax.persistence.Table;
import javax.persistence.TableGenerator;

import com.sun.xml.internal.bind.v2.runtime.Name;
@Entity
//指定继承映射的策略
@Inheritance(strategy=InheritanceType.TABLE_PER_CLASS)
@TableGenerator(
  name="k_gen",
        table="key_table",
        pkColumnName="p_key",
        pkColumnValue="p_value",
        initialValue=1,
        allocationSize=1
)
public class Person {
      private int id;
      private String name;
     
      @Id
      @GeneratedValue(generator="k_gen",strategy=GenerationType.TABLE)
 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;
 }    
}

 

package com.xie.hibernate.modal;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.DiscriminatorValue;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.MapKey;
import javax.persistence.OneToMany;
import javax.persistence.Table;

@Entity
public class Teacher extends Person{
 private String title;

 public String getTitle() {
  return title;
 }

 public void setTitle(String title) {
  this.title = title;
 } 
}

 

 

      ⑶joined：

 

package com.xie.hibernate.modal;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.DiscriminatorColumn;
import javax.persistence.DiscriminatorType;
import javax.persistence.DiscriminatorValue;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Inheritance;
import javax.persistence.InheritanceType;
import javax.persistence.JoinColumn;
import javax.persistence.MapKey;
import javax.persistence.OneToMany;
import javax.persistence.Table;
import javax.persistence.TableGenerator;

import com.sun.xml.internal.bind.v2.runtime.Name;
@Entity
//指定继承映射的策略
@Inheritance(strategy=InheritanceType.JOINED)

public class Person {
      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;
 }    
}

 

package com.xie.hibernate.modal;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.DiscriminatorValue;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;

@Entity
public class Student extends Person {
 private int score;

 public int getScore() {
  return score;
 }

 public void setScore(int score) {
  this.score = score;
 } 
}

 

package com.xie.hibernate.modal;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.DiscriminatorValue;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.MapKey;
import javax.persistence.OneToMany;
import javax.persistence.Table;

@Entity
public class Teacher extends Person{
 private String title;

 public String getTitle() {
  return title;
 }

 public void setTitle(String title) {
  this.title = title;
 } 
}

 

===============================hibernate n+1==========================

 

 在多对一关系中，当我们需要查询多的一方对应的表的记录时，可以用一条sql语句就能完成操作。然而，在多的一方的实体类中的@ManyToOne标注的fetch的默认值是eager，这时，hibernate除了发出查询多的一方对应的表的记录的sql语句外，还会发出n（多方记录数）条sql语句，这就是1+n问题。如：bbs的板块（Category），主题（topic），回复（msg）。一个板块有多个主题，而一个主题属于一个板块，则Category和topic属于一对多的关系，在topic里设置@ManyToOne。当需要取出所有的主题时，只需要发出select * from topic一条语句就能做到。然而，hibernate会查询出每个topic所对应的Category，所以会发出1+n条sql语句。

 

解决的方法是：①设置@ManyToOne的fetch属性值为lasy，这种方式解决后，后面的n条sql语句按需而发。

②设置@BatchSize(size=5)，这样发出的sql语句减少。这个设置在一定程度上提高了效率。

③用join fetch，事实上Criteria用的就是这种方法。

 

 

 

    //join fetch

    @Test

    public void test1_N3(){

       Session session=sf.getCurrentSession();

       session.beginTransaction();

       //List<Topic> topics=(List<Topic>)session.createCriteria(Topic.class).list();

       List<Topic> topics=(List<Topic>)session.createQuery("from Topic t left join fetch t.category c").list();

       for (Topic t:topics) {

           System.out.println(t.getId()+"----"+t.getTitle());

           System.out.println(t.getCategory().getName());

       }

      

       session.getTransaction().commit();

      

  }

 

========================================================================

nativeSQL（本地sql，功能强大）>HQL>EJBQL（是hql的子集）>QBC(query by cretra,cretra接口查询)>QBE 

 

 

 

============================================================

 

===============================hibernate n+1  over=========================