JavaEE(14) - JPA关联映射

时间：2023-11-21 12:53:44

1. 单向N-1关联映射

2. 单向1-1关联映射

3. 单向1-N关联映射

4. 单向N-N关联映射

5. 双向1-1关联映射

6. 双向1-N关联映射

7. 双向N-N关联映射

1. 单向N-1关联映射(Net Beans创建Java Project, 项目名称:UnidirectionalManyToOne)

Person.java

package org.crazyit.model;

import javax.persistence.*;

@Entity

@Table(name = "person_table")

public class Person {

    //标识属性

    @Id

    @GeneratedValue(strategy = GenerationType.IDENTITY)

    private int personid;

    private String name;

    private int age;

    // constructor

    // setter

    // getter

}

Address.java

package org.crazyit.model;

import javax.persistence.*;

@Entity

@Table(name = "address_table")

public class Address {

    @Id

    @GeneratedValue(strategy = GenerationType.IDENTITY)

    private int addressid;

    private String detail;

    @ManyToOne(optional = false, cascade = CascadeType.ALL, fetch = FetchType.LAZY, targetEntity = Person.class)

    @JoinColumn(name = "person_id", nullable = false, updatable = false)

    private Person person;

    public Address() {

    }

    public Address(String detail) {

        this.detail = detail;

    }

    // setter

    // getter

}

persistence.xml(参见12.2)

JpaQs.java(参见12.2)

2. 单向1-1关联映射(Net Beans创建Java Project, 项目名称:UnidirectionalOneToOne)

Person.java

package org.crazyit.model;

import javax.persistence.*;

@Entity

@Table(name = "person_table")

public class Person {

    @Id

    @GeneratedValue(strategy = GenerationType.IDENTITY)

    private int personid;

    private String name;

    private int age;

    // constructor

    // setter

    // getter

}

Address.java

package org.crazyit.model;

import javax.persistence.*;

@Entity

@Table(name = "address_table")

public class Address {

    //标识属性

    @Id

    @GeneratedValue(strategy = GenerationType.IDENTITY)

    private int addressid;

    private String detail;

    @OneToOne(optional = false, cascade = CascadeType.ALL, fetch = FetchType.LAZY, targetEntity = Person.class)

    @JoinColumn(name = "person_id", nullable = false, updatable = false)

    private Person person;

    // constructor

    // setter

    // getter

}

persistence.xml(参见12.2)

JpaQs.java(参见12.2)

3. 单向1-N关联映射(Net Beans创建Java Project, 项目名称:UnidirectionalOneToMany)

Person.java

package org.crazyit.model;

import javax.persistence.*;

import java.util.*;

@Entity

@Table(name = "person_table")

public class Person {

    @Id

    @GeneratedValue(strategy = GenerationType.IDENTITY)

    private int personid;

    private String name;

    private int age;

    //1－N关联关系，使用Set来保存关联实体

    @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY, targetEntity = Address.class)

    @JoinColumn(name = "person_id", nullable = false)

    private Set<Address> addresses = new HashSet<Address>();

    // constructor

    // setter

    // getter

}

Address.java

package org.crazyit.model;

import javax.persistence.*;

@Entity

@Table(name = "address_table")

public class Address {

    @Id

    @GeneratedValue(strategy = GenerationType.IDENTITY)

    private int addressid;

    private String detail;

    // constructor

    // setter

    // getter

}

persistence.xml(参见12.2)

JpaQs.java(参见12.2)

4. 单向N-N关联映射(Net Beans创建Java Project, 项目名称:UnidirectionalManyToMany)

Person.java

package org.crazyit.model;

import javax.persistence.*;

import java.util.*;

@Entity

@Table(name = "person_table")

public class Person {

    @Id

    @GeneratedValue(strategy = GenerationType.IDENTITY)

    private int personid;

    private String name;

    private int age;

    //N－N关联关系，使用Set来保存关联实体

    @ManyToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY, targetEntity = Address.class)

    @JoinTable(

            name = "person_address",

            joinColumns = @JoinColumn(name = "person_id"),

            inverseJoinColumns = @JoinColumn(name = "address_id")

    )

    private Set<Address> addresses = new HashSet<Address>();

    // constructor

    // setter

    // getter

}

Address.java

package org.crazyit.model;

import javax.persistence.*;

@Entity

@Table(name = "address_table")

public class Address {

    @Id

    @GeneratedValue(strategy = GenerationType.IDENTITY)

    private int addressid;

    private String detail;

    // constructor

    // setter

    // getter

}

persistence.xml(参见12.2)

JpaQs.java

package lee;

import java.util.List;

import javax.persistence.*;

import org.crazyit.model.*;

public class JpaQs {

    private static final EntityManagerFactory emf = Persistence.createEntityManagerFactory("qs");

    public static void main(String[] args) {

        EntityManager em = emf.createEntityManager();

        Person sun = new Person();

        sun.setName("sunwukong");

        sun.setAge(500);

        Person zhu = new Person();

        zhu.setName("zhubajie");

        zhu.setAge(380);

        Address road = new Address("The road to Indian.");

        try {

            em.getTransaction().begin();

            sun.getAddresses().add(new Address("The water hole to the mountain."));

            sun.getAddresses().add(road);

            zhu.getAddresses().add(new Address("Gao Laozhuang."));

            zhu.getAddresses().add(road);

            em.persist(sun);

            em.persist(zhu);

            em.getTransaction().commit();

        }

        finally {

            em.close();

        }

    }

}

5. 双向1-1关联映射(Net Beans创建Java Project, 项目名称:BidirectionalOneToOne)

Person.java

package org.crazyit.model;

import javax.persistence.*;

@Entity

@Table(name = "person_table")

public class Person {

    @Id

    @GeneratedValue(strategy = GenerationType.IDENTITY)

    private int personid;

    private String name;

    private int age;

    /* 设置了mappedBy属性表明Person实体不控制关联关系，*/

    @OneToOne(mappedBy = "person", cascade = CascadeType.ALL, fetch = FetchType.LAZY, targetEntity = Address.class)

    private Address address;

    // constructor

    // setter

    // getter

}

Address.java

package org.crazyit.model;

import javax.persistence.*;

@Entity

@Table(name = "address_table")

public class Address {

    @Id

    @GeneratedValue(strategy = GenerationType.IDENTITY)

    private int addressid;

    private String detail;

    @OneToOne(optional = false, cascade = CascadeType.ALL, fetch = FetchType.LAZY, targetEntity = Person.class)

    @JoinColumn(name = "person_id", nullable = false, updatable = false)

    private Person person;

    // constructor

    // setter

    // getter

}

persistence.xml(参见12.2)

JpaQs.java(参见12.2)

package lee;

import java.util.List;

import javax.persistence.*;

import org.crazyit.model.*;

public class JpaQs {

    private static final EntityManagerFactory emf = Persistence.createEntityManagerFactory("qs");

    public static void main(String[] args) {

        EntityManager em = emf.createEntityManager();

        Person person = new Person();

        person.setName("Sun");

        person.setAge(500);

        Address address = new Address();

        address.setDetail("Hua Guoshan");

        try {

            em.getTransaction().begin();

            //因为Person实体不控制关联关系，因此让Address实体控制关联关系

            address.setPerson(person); 

            em.persist(address);

            em.getTransaction().commit();

        }

        finally {

            em.close();

        }

    }

}

6. 双向1-N关联映射(Net Beans创建Java Project, 项目名称:BidirectionalOneToMany)

Person.java

package org.crazyit.model;

import javax.persistence.*;

import java.util.*;

@Entity

@Table(name = "person_table")

public class Person {

    @Id

    @GeneratedValue(strategy = GenerationType.IDENTITY)

    private int personid;

    private String name;

    private int age;

    /* 设置了mappedBy属性表明Person实体不控制关联关系，

     因此不能增加@JoinTable和@JoinColumn修饰*/

    @OneToMany(cascade = CascadeType.ALL, mappedBy = "person", targetEntity = Address.class)

    private Set<Address> addresses = new HashSet<Address>();

    // constructor

    // setter

    // getter

}

Address.java

package org.crazyit.model;

import javax.persistence.*;

@Entity

@Table(name = "address_table")

public class Address {

    @Id

    @GeneratedValue(strategy = GenerationType.IDENTITY)

    private int addressid;

    private String detail;

    @ManyToOne(fetch = FetchType.EAGER, targetEntity = Person.class, cascade = CascadeType.ALL)

    /* 使用@JoinColumn来配置外键列的信息 */

    @JoinColumn(name = "person_id", nullable = true)

    private Person person;

    // constructor

    // setter

    // getter

}

persistence.xml(参见12.2)

JpaQs.java(参见12.2)

7. 双向N-N关联映射(Net Beans创建Java Project, 项目名称:BidirectionalManyToMany)

Person.java

package org.crazyit.model;

import javax.persistence.*;

import java.util.*;

@Entity

@Table(name = "person_table")

public class Person {

    @Id

    @GeneratedValue(strategy = GenerationType.IDENTITY)

    private int personid;

    private String name;

    private int age;

    @ManyToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY, targetEntity = Address.class)

    @JoinTable(

            name = "person_address",

            joinColumns = @JoinColumn(name = "person_id"),

            inverseJoinColumns = @JoinColumn(name = "address_id")

    )

    private Set<Address> addresses = new HashSet<Address>();

    // constructor

    // setter

    // getter

}

Address.java

package org.crazyit.model;

import javax.persistence.*;

import java.util.*;

@Entity

@Table(name = "address_table")

public class Address {

    @Id

    @GeneratedValue(strategy = GenerationType.IDENTITY)

    private int addressid;

    private String detail;

    /* 设置了mappedBy属性表明Address实体不控制关联关系，

     因此不能增加@JoinTable和@JoinColumn修饰*/

    @ManyToMany(cascade = CascadeType.ALL, mappedBy = "addresses", fetch = FetchType.LAZY, targetEntity = Person.class)

    private Set<Person> persons = new HashSet<Person>();

    // constructor

    // setter

    // getter

}

persistence.xml(参见12.2)

JpaQs.java(参见12.2)

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