Hibernate映射来自同一表的列值的集合

Question

Given the following table:

CREATE TABLE MY_SCHEMA.TABLE_A (
    id integer NOT NULL,
    value character varying(50) NOT NULL,
    linked_id integer
)

I want to know the hibernate annotations to complete my entity class:

public class TableA {
    @Id @Column(name="id", unique=true)
    private int id;
    @Column(name="value", nullable=false)
    private String value;
    // missing annotations
    private String linkedValue;
}

So that I get the linkedValue (which comes from a self join to TABLE_A on linked_id = id and select from the column value ) as String in my entity class TableA .

Similarly, in case it is not one-to-one:

CREATE TABLE MY_SCHEMA.TABLE_A (
    id integer NOT NULL,
    value character varying(50) NOT NULL
)

CREATE TABLE MY_SCHEMA.TABLE_B (
    table_a_id integer NOT NULL,
    linked_table_a_id integer NOT NULL
)

What are the hibernate annotations to complete my entity class:

public class TableA {
    @Id @Column(name="id", unique=true)
    private int id;
    @Column(name="value", nullable=false)
    private String value;
    // missing annotations
    private Set<String> linkedValues;
}

So that I get the set of linkedValues (which comes from joining TABLE_A to TABLE_B on id = table_a_id and joining TABLE_A again on linked_table_a_id = id to select from the column value ) in my entity class TableA .

Prefer answers without needing to introduce and extra entity class TableB . Thank you.

Answer 1

You can use JPA 2.0 's @ElementCollection :

public class TableA {

   @Id @Column(name="id", unique=true)
   private int id;

   @Column(name="value", nullable=false)
   private String value;

    @ElementCollection
    @CollectionTable(name = "TABLE_A",joinColumns = @JoinColumn(name = "linked_id"))
    @Column(name = "value")
    private Set<String> linkedValues = new HashSet<String>();
}