Hibernate：行太多了

Question

I have problem with getting rows from my database using Hibernate. When I would like to get only one row, I am receiving 20. When I would like to get all of rows from table with about 1.5k rows, I am receiving exactly 15.2k rows. Entity class of this table has composite primary key.

This is my code for getting all rows:

Criteria criteria = getSession().createCriteria(type);
criteria.setCacheable(true).setCacheRegion(BaseEntity.PACKAGE);
criteria.list();

And this is my Entity class:

@javax.persistence.Entity
@Table(name = "my_table")
public class My extends MyEntity<MyPK> {

    @EmbeddedId
    private MyPK id;

    @Column(name = "text", nullable = false)
    protected String text;

    @ManyToOne
    @JoinColumn(name = "property", nullable = false, insertable = false, updatable = false)
    protected Option option;

    @Override
    public MyPK getId() {
        return id;
    }

    @Override
    public void setId(MyPK id) {
        this.id = id;
    }

    //getters and setter
}

And this is MyPK class:

@Embeddable
public class MyPK implements Serializable {

   @Column(name = "qwerty")
   protected String qwerty;

   @Column(name = "property")
   protected String property;

   //constructors, getters and setters
}

MyEntity class is abstract class with @MappedSuperclass annotation. This is this class header:

@MappedSuperclass
public abstract class MyEntity<T extends Serializable>

What am I doing wrong? Is this problem with EmbeddedId ?

EDIT #1 As I have realized this is problem with this:

@ManyToOne
@JoinColumn(name = "property", nullable = false, insertable = false, updatable = false)
protected Option option;

This object contains foreign key to another table. And this another table has reference to another. And this last table has 10 rows for previous table. In the result I am getting rows amount * 10. The problem is probably with Hibernate annotation in my entities.

Answer 1

It looks like you're probably eagerly joining a many-to-one relationship somewhere. The default behavior is that you get one entity for each row returned by the database. If you don't want to change the eager fetching, but do want to remove duplicates in your result, you need to use this ResultTransformer :

criteria.setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY);

Answer 2

@Embeddable only means that MyPK 's columns will be columns in the My class. Your problem might be @ManyToOne @JoinColumn(name = "property") since it's the same with "property " in MyPK

Answer 3

您可以通过此方法在条件上设置此结果来设置最大结果数： setMaxResults（int maxResults）

Answer 4

Primary key classes need to define equals() and hashCode(), in terms of the aggregated values ( qwerty and property , here). Most likely when process the ResultSet, Hibernate is not seeing the entity keys across multiple rows as equal.

From Section 2.4 of the JPA 2.0 specification (in case it helps):

The primary key class must define equals and hashCode methods. The semantics of value equality for these methods must be consistent with the database equality for the database types to which the key is mapped