java - Just getting id column value not using join in hibernate object one to many relation

Question

I'm using hibernate 4+.

I have two sample tables.

Table A

public class A {
  @Id
  private int id;

  @OneToMany(fetch=LAZY)
  private List<B> list;

  // skip getter&setter
}

Table B

public class B {
  @Id
  private int id;

  @ManyToOne(fetch=LAZY)
  @JoinColumn(name="b_id")
  private A a;

  // skip getter&setter
}

Table A(1) - (n)Table B Relation

Can I just get A's id in object B not using join?

like int aid = b.getA().getId(); // b is instance of B;

Although I can use int value instead of A when I declare class B. But another service layer use A with join.

Can I just get id(fk) value?

please help.

Answer 1

Yes, because proxies contain the id anyway. To get the id of an A proxy without initializing it, first declare the id to be accessed via property:

@Entity
public class A {
  @Id
  @Access(AccessType.PROPERTY)
  private int id;

  @OneToMany(fetch=LAZY)
  private List<B> list;

  public int getId() {
    return id;
  }

  public void setId(int id) {
    this.id = id;
  }
}

Then, just read the id:

b.getA().getId();

Changing access type for the id is necessary because if you use field access, Hibernate does not distinguish getId() method from other ordinary methods (which trigger proxy initialization when invoked).