Question

My Entity Model Class are

------- A -----------
private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @Column(name = "NameA")
    private String nameA;

    public B getBid() {
        return b;
    }

    public void setBid(B bid) {
        this.b = bid;
    }

    public String getNameA() {
        return nameA;
    }

    public void setNameA(String nameA) {
        this.nameA = nameA;
    }
    @JoinColumn(name = "BID", referencedColumnName = "ID")
    @ManyToOne(fetch= FetchType.LAZY)
    private B b;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }
--------------------------------------------
------------------ B -----------------------

private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @Column(name = "NameB")
    private String nameB;


    public String getNameB() {
        return nameB;
    }

    public void setNameB(String nameB) {
        this.nameB = nameB;
    }


    public Long getId() {
        return id;
    }

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

and
I want to
make this Query session.createQuery("select a.b from A a").list();

with Criteria API ????

Answer 1

Since you don’t have the inverse relationship, and since Criteria doesn’t allow selecting another entity than the root entity, you’ll have to use a subquery, but it’s ugly:

DetachedCriteria subquery = DetachedCriteria.forClass(A.class, "a");
subquery.createAlias("a.b", "b2");
subquery.setProjection(Projections.property("b2.id"));

Criteria c = session.createCriteria(B.class, "b1");
c.add(Subqueries.propertyIn("b1.id", subquery));

If you had the inverse OneToMany relationship from B to A, you would just have to do

Criteria c = session.createCriteria(B.class, "b1");
c.createAlias("b1.as", "a");

BTW, these non-dynamically constructed queries are better expressed with HQL than with the criteria API. If your real query is the one you asked, just use HQL: it’s more readable and more powerful.