如何防止带有条​​件的左联接条件之后的Hibernate加载一对一字段？

Question

I have the following database tables:

Cats
ParentID | Name
-----------------
1        | Mittins
2        | Cuddles
3        | Spot

Kittens
ID | ParentID | Color
---------------------
1  | 1        | Red
2  | 1        | Yellow
3  | 1        | Blue
4  | 2        | Red
5  | 2        | Blue
6  | 3        | Red
7  | 3        | Yellow
8  | 3        | Blue

And the following Mapping classes:

class Cat
{
   @Id
   @Column(name="ParentID", nullable = false)
   public Integer parentID;

   @Column(name="Name", nullable = false)
   public String name;

   @OneToOne
   @JoinColumn(name="parentID")
   @NotFound(action=NotFoundAction.IGNORE)
   public Kitten kitten;
}

class Kitten
{
   @Id
   @Column(name="ID", nullable = false)
   public Integer id;

   @Column(name="ParentID", nullable = false)
   public Integer parentID;

   @Column(name="Color", nullable = false)
   public String color;
}

I want to join the cat with its kitten of a specified color. It is guaranteed that each cat has one-and-only-one kitten of the specified color. The mapping then will be one-to-one for this instance.

Criteria crit = sessionFactory.getCurrentSession().createCriteria(Cat.class, "cat");
crit.createCriteria("cat.kitten", "kitten", Criteria.LEFT_JOIN, Restrictions.eq("kitten.color", "Red"));

crit.list();

This will return 3 Cat objects each populated with their "Red" kitten objects. Hibernate gets this in one shot. The Kitten data is populated during this fetch and no subquery is performed to get the kitten data.

However, if for instance I search for "Yellow" kittens, I still want the 3 Cat objects which I do get. But I want null for the kitten field for the Cat that does not have a yellow kitten (cat #2).

Instead, what hibernate does is try to load all the kittens for cat 2 via another subquery on the parentID .

I do not want it to do this because the mapping does not know that my original left-join criteria was limited to "yellow" kittens. This of course results in the "More than one row with the given identifier was found" error.

When the original criteria is executed, hibernate should know that the "kitten" part of the query returned NULL. Is it possible to have Hibernate set that field null rather than a proxy that will later try a second incorrect query to load the kitten objects?

Answer 1

to start with, it is not oneToOne but OneToMany, as Cat can have many kittens. So you should map to OneToMany using Map in which the color is the key and the value is the correct kitten.

@OneToMany
@MapKey(name="color") 
@JoinColumn(name="parentID")
Map<String,Kitten> kittens;

Your java objects should represent the db model, not the possible query results. You can still query for cats having particual kittens.