Hibernate: Criteria with many-to-many join table

criteriahibernate

Consider following two relations:

@Entity class Foo {
    @Id id;

    @ManyToMany
    @JoinTable(name = "ATag", 
         joinColumns = @JoinColumn(name = "foo_id"),
         inverseJoinColumns = @JoinColumn(name = "tag_id"))
    Set<Tag> tags;
}

@Entity class Tag {
    @Id Long id;
    String name;
}

There is no corresponding entity class for the join table ATag. Now, I want to get all Foo instances with Tag named 'tag1', is it possible using only Criteria?

A sub-query maybe helpful, however, I can't create DetachedCriteria for class ATag.class which isn't existed.

Best Answer

Just dealt with this exact issue. You're thinking in tables, not objects. Just reference tags.name and let Hibernate take care of the rest:

Criteria crit = session.createCriteria(Foo.class);
crit.createAlias("tags", "tagsAlias");
crit.add(Restrictions.eq("tagsAlias.name", someValue);

If you watch the SQL Hibernate spits out, you'll see it uses the join table.

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e.g. validate | update | create | create-drop

So the list of possible options are,

validate: validate the schema, makes no changes to the database.
update: update the schema.
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Java – Constraint violation in Hibernate unidirectional OneToMany mapping with JoinTable and OrderColumn when removing elements

Your mapping is totally valid and works with EclipseLink as JPA 2.0 implementation (without the Fetch annotation of course), but indeed fails with Hibernate.

Here is the DDL with Hibernate:

create table foo_bar_map (foo_id bigint not null, bar_id bigint not null, order_index integer not null, primary key (foo_id, order_index), unique (bar_id))
alter table foo_bar_map add constraint FK14F1CB7FA042E82 foreign key (bar_id) references Bar4022509
alter table foo_bar_map add constraint FK14F1CB7B6DBCCDC foreign key (foo_id) references Foo4022509

So let's say Foo#1 holds a list with Bar#1, Bar#2, Bar#3, the join table contains:

foo_id | bar_id | order_index
     1 |      1 |           1
     1 |      2 |           2
     1 |      3 |           3

When removing, say the first item from the list, Hibernate first delete the last row (WTF?) from the join table:

foo_id | bar_id | order_index
     1 |      1 |           1
     1 |      2 |           2

And then tries to update the bar_id column in the join table instead of the order_index (WTF!?) to reflect the "new" ordering of the items in the list. First (schematically):

foo_id | bar_id | order_index
     1 |      2 |           1
     1 |      2 |           2

where the next step would result in:

foo_id | bar_id | order_index
     1 |      2 |           1
     1 |      3 |           2

Obviously, this approach doesn't sound right and doesn't work because of the unique constraint on bar_id. More generally, why the hell does Hibernate mess with the bar_id instead of updating the order_index column?

I consider this to be an Hibernate bug (reported as ~~HHH-5694~~, see HHH-1268 now).

Best Answer

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