如何在Hibernate/javax.persistance中映射一个具有多个表的类？

Question

我想用一个类来映射三个表.我知道javax.persistance提供了@SecondaryTable将两个表映射到一个类的注释.

下面是我用过的代码@SecondaryTable.它允许我只定义一个辅助表.但是我需要同一个类使用3个表.

@Entity
@Table(name = "table1")
@SecondaryTable(name="table2")
public class TableConfig
    implements Serializable {

    /**
     * 
     */
    private static final long serialVersionUID = 1L;

    @Id
    @Column(name = "mac", table= "table1")
    private String uniqueIdentifier;

Answer 1

我想使用一个类来映射三个表,据我所知,javax.persistance提供了@SecondaryTable注释来将两个表映射到一个类

使用@SecondaryTables映射多个表.

您可以使用@SecondaryTables类级别注释将单个实体bean映射到多个表.要表示列在特定表中,请使用@Column或的表参数@JoinColumn.

例如,有3个实体即:Name,Address&Student:

Name 实体将如下所示:

@Entity
@Table(name="name")
public class Name implements Serializable {

    @Id
    @Column(name="id")
    private int id;
    @Column(name="name")
    private String name;

    public Name(){}

    public Name(int id,String name){
        this.id=id;
        this.name=name;
    }
        //getters and setters
}

Address 实体将如下所示:

@Entity
@Table(name="address")
public class Address implements Serializable {

    @Id
    @Column(name="id")
    private int id;
    @Column(name="address")
    private String address;

    public Address(){}

    public Address(int id, String address) {
        super();
        this.id = id;
        this.address = address;
    }
        //getters and setters
}

Student 实体将如下所示:

@Entity
@Table(name="student")
@SecondaryTables({
    @SecondaryTable(name="name", pkJoinColumns={
        @PrimaryKeyJoinColumn(name="id", referencedColumnName="student_id") }),
    @SecondaryTable(name="address", pkJoinColumns={
        @PrimaryKeyJoinColumn(name="id", referencedColumnName="student_id") })
})
public class Student implements Serializable {

    @Id
    @Column(name="student_id")
    private int studentId;

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

    @Column(table="address")
    private String address;

    public Student(){}

    public Student(int studentId){
        this.studentId=studentId;
    }
        //getters and setters
}

存储如:

    Student s= new Student(1);
    session.save(s);

    Name n=new Name(s.getStudentId(),"Bilal Hasan");
    session.save(n);    

    Address address = new Address(s.getStudentId(), "India");
    session.save(address);

    Student ob = (Student)session.get(Student.class, s.getStudentId());

    System.out.println(ob.getStudentId());
    System.out.println(ob.getName());
    System.out.println(ob.getAddress());

输出继电器:

1
Bilal Hasan
India

Answer 2

你可以定义一个类,如下所示:

@Entity
@Table(name="table1")
@SecondaryTables({
      @SecondaryTable(name="table2", pkColumnJoins={@PrimaryKeyJoinColumn(name = "id")}),
      @SecondaryTable(name="table3", pkColumnJoins={@PrimaryKeyJoinColumn(name = "id")})
  })
public class TestEntity {
      @Id
      @GeneratedValue
      private int id;

      private String field1;

      @Column(name="column2", table="table2")
      private String field2;

      @Column(name="column3", table="table3")
      private String field3;

      getter and setter...
}

在你的数据库中,应该有三个表,并且它们都应该具有相同的主键"id".

然后,使用可以像这样测试:

TestEntity test = new TestEntity();
test.setField1("field1");
test.setField2("field2");
test.setField3("field3");

em.merge(test);

在测试之后,在您的数据库中,您将在每个表中找到一条记录:

表格1:

 1, field1

表2:

 1, field2

表3:

 1, field3

所有这些都将共享主键值.希望这会帮助你.

Answer 3

在 Hibernate 映射文件中，您可以指定带有虚拟名称的实体名称映射，并且polymorphism="explicit"类名称将是物理类名称。像这样你可以做多个映射。加载对象时使用实体名称（虚拟名称）。