JavaEE(13) - JPA属性映射

1. 映射实体的属性

　　#1. 使用@Transient修饰不想持久保存的Field

　　#2. 使用@Enumerated修饰枚举类型的Field

　　#3. 使用@Lob, @Basic修饰枚举类型的Field

　　#4. 使用@Temporal修饰枚举类型的Field

2. 将实体映射到多个数据表

3. 映射复合类型的属性

4. 映射实体的主键

　　#1. IdClass

　　#2. EmbeddedId

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1. 映射实体的属性

#1. 使用@Transient修饰不想持久保存的Field(Net Beans创建Java Project, 项目名称:Transient)

News.java

package org.crazyit.model;

import javax.persistence.*;

@Entity
@Table(name = "news_table")
public class News {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

    @Column(name = "news_title", length = 50)
    private String title;

    @Transient
    private String content;

    public News() {
    }

　　// getter
　　// setter

}

persistence.xml(参见12.2)

JpaQs.java(参见12.2)

#2. 使用@Enumerated修饰枚举类型的Field(Net Beans创建Java Project, 项目名称:Enumerated)

Season.java

package org.crazyit.model;

public enum Season {
    Spring,Summer,Autumn,Winter
}

News.java

package org.crazyit.model;

import javax.persistence.*;

@Entity
@Table(name = "news_table")
public class News {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

    @Column(name = "news_title", length = 50)
    private String title;

    private String content;

    @Enumerated(EnumType.ORDINAL)
    @Column(name = "happen_season")
    private Season happenSeason;

    public News() {
    }

    public News(int id, String title, String content, Season happenSeason) {
        this.id = id;
        this.title = title;
        this.content = content;
        this.happenSeason = happenSeason;
    }

    // getter
　　// setter
}

persistence.xml(参见12.2)

JpaQs.java(参见12.2)

#3. 使用@Lob, @Basic修饰枚举类型的Field(Net Beans创建Java Project, 项目名称:Lob)

Person.java

package org.crazyit.model;

import javax.persistence.*;

@Entity
@Table(name = "person_table")
public class Person {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

    @Column(name = "person_name", length = 50)
    private String name;

    @Lob
    @Basic(fetch = FetchType.LAZY)
    private byte[] pic;

    public Person() {
    }

    public Person(int id, String name, byte[] pic) {
        this.id = id;
        this.name = name;
        this.pic = pic;
    }

    // setter
    // getter
}

persistence.xml(参见12.2)

JpaQs.java

package lee;

import javax.persistence.*;

import org.crazyit.model.*;
import java.io.*;

public class JpaQs {

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

    public static void main(String[] args) throws IOException {
        final EntityManager em = emf.createEntityManager();

        File file = new File("img.png");
        byte[] content = new byte[(int) file.length()];
        new FileInputStream(file).read(content);

        Person person = new Person();
        person.setName("crazyit.org");
        person.setPic(content);

        try {
            em.getTransaction().begin();
            em.persist(person);
            em.getTransaction().commit();
        }
        finally {
            em.close();
        }
    }
}

#4. 使用@Temporal修饰枚举类型的Field(Net Beans创建Java Project, 项目名称:Temporal)

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 id;

    @Column(name = "person_name", length = 50)
    private String name;

    @Temporal(TemporalType.DATE)
    private Date birth;

    public Person() {
    }

    public Person(int id, String name, Date birth) {
        this.id = id;
        this.name = name;
        this.birth = birth;
    }

    // setter
    // getter
}

persistence.xml(参见12.2)

JpaQs.java(参见12.2)

2. 将实体映射到多个数据表(Net Beans创建Java Project, 项目名称:SecondaryTable)

Person.java

package org.crazyit.model;

import javax.persistence.*;

@Entity
@Table(name = "person_table")
@SecondaryTable(name = "person_detail", pkJoinColumns = @PrimaryKeyJoinColumn(name = "person_id"))
public class Person {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

    @Column(name = "person_name", length = 50)
    private String name;

    @Column(table = "person_detail", name = "email")
    private String email;

    @Column(table = "person_detail", name = "phone")
    private String phone;

    public Person() {
    }

    public Person(int id, String name, String email, String phone) {
        this.id = id;
        this.name = name;
        this.email = email;
        this.phone = phone;
    }

    // setter
    // getter
}

persistence.xml(参见12.2)

JpaQs.java(参见12.2)

3. 映射复合类型的属性(Net Beans创建Java Project, 项目名称:Embedded)

Person.java

package org.crazyit.model;

import javax.persistence.*;

@Entity
@Table(name = "person_table")
public class Person {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

    @Column(name = "person_name", length = 50)
    private String name;

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

    @Embedded
    @AttributeOverrides({
        @AttributeOverride(name = "name", column = @Column(name = "cat_name", length = 35)),
        @AttributeOverride(name = "color", column = @Column(name = "cat_color"))
    })
    private Cat cat;

    public Person() {
    }

    public Person(int id, String name, String email, Cat cat) {
        this.id = id;
        this.name = name;
        this.email = email;
        this.cat = cat;
    }

    // setter
    // getter
}

Cat.java

package org.crazyit.model;

import javax.persistence.*;

@Embeddable
public class Cat {

    private String name;
    private String color;

    public Cat() {
    }

    public Cat(String name, String color) {
        this.name = name;
        this.color = color;
    }

    // setter
    // getter
}

persistence.xml(参见12.2)

JpaQs.java(参见12.2)

4. 映射实体的主键

#1. IdClass (Net Beans创建Java Project, 项目名称:IdClass)

Person.java

package org.crazyit.model;

import javax.persistence.*;

@Entity
@Table(name = "person_table")
@IdClass(Name.class)
public class Person {

    //两个@Id定义了联合主键
    @Id
    private String first;
    @Id
    private String last;

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

    public Person() {
    }

    public Person(String first, String last, String email) {
        this.first = first;
        this.last = last;
        this.email = email;
    }

    // setter
    // getter
}

Name.java

package org.crazyit.model;

import javax.persistence.*;

public class Name implements java.io.Serializable {

    private String first;
    private String last;

    public Name() {
    }

    public Name(String first, String last) {
        this.first = first;
        this.last = last;
    }

    // setter
    // getter

    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj.getClass() == Name.class) {
            Name target = (Name) obj;
            if (target.getFirst().equals(first) && target.getLast().equals(last)) {
                return true;
            }
        }
        return false;
    }

    public int hashCode() {
        return first.hashCode() + last.hashCode() * 17;
    }
}

persistence.xml(参见12.2)

JpaQs.java(参见12.2)

#2. EmbeddedId (Net Beans创建Java Project, 项目名称:EmbeddedId)

Person.java

package org.crazyit.model;

import javax.persistence.*;

@Entity
@Table(name = "person_table")
public class Person {
    @EmbeddedId
    @AttributeOverrides({
        @AttributeOverride(name = "first", column = @Column(name = "person_first")),
        @AttributeOverride(name = "last", column = @Column(name = "person_last", length = 20))
    })
    private Name name;

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

    public Person() {
    }

    public Person(Name name, String email) {
        this.name = name;
        this.email = email;
    }

    // setter
    // getter
}

Name.java(参见#1)

persistence.xml(参见12.2)

JpaQs.java(参见12.2)