I'd like to use Hibernate's criteria api to formulate a particular query that joins two entities. Let's say I have two entities, Pet and Owner with a owner having many pets, but crucially that association is not mapped in the Java annotations or xml.
With hql, I could select owners that have a pet called 'fido' by specifying the join in the query (rather than adding a set of pets to the owner class).
Can the same be done using hibernate criteria? If so how?
Thanks, J
We can apply the Joins in Hibernate by using the HQL query or native SQL query. To make a join between the two tables, the two tables must be in a logical relationship. We can achieve the relationship between two tables by applying the parent table's primary key as a child table's foreign key.
Hibernate provides support for join statements where one can write single query to fetch data from multiple tables easily.
This is indeed possible with criteria:
DetachedCriteria ownerCriteria = DetachedCriteria.forClass(Owner.class); ownerCriteria.setProjection(Property.forName("id")); ownerCriteria.add(Restrictions.eq("ownername", "bob")); Criteria criteria = getSession().createCriteria(Pet.class); criteria.add(Property.forName("ownerId").in(ownerCriteria));
Update: This actually performs a sub-query instead of a join but it allows you to use Criteria on two entities that do not have a hibernate relationship defined.
My understanding is that if you do this using HQL, you are creating a Cartesian join with a filter, rather than an inner join. Criteria queries do not support doing this.
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