Hibernate Criteria - how to limit join results to a single entity type?

问题

Ok, so the following query:

SELECT O.*, P.* FROM ORDERS O, PRODUCT P WHERE
    O.ORDER_ID=P.ORDER_ID AND P.ID=’1234’;

can be done with Criteria as follows:

List ordersAndProducts = session.createCriteria(Order.class)
    .setFetchMode(“products”,FetchMode.JOIN)
    .add(Restrictions.eq(“id”,”1234”))
    .list();

but here Criteria.list() returns a List<Object[]> where Object[0] is an Order and Object[1] is a Product for each element in the List.

But how can I do the following SQL with Criteria:

SELECT O.* FROM ORDERS O, PRODUCT P WHERE 
    O.ORDER_ID=P.ORDER_ID AND P.ID=’1234’;

In other words, I want Criteria.list() to give me a List<Order>, I don't care about the Products. I've tried using createAlias() instead of setFetchMode() but the results are the same, and Projections don't let you specify an entity, only a property.

回答1:

You can use .setResultTransformer(CriteriaSpecification.DISTINCT_ROOT_ENTITY) on the criteria.

List ordersAndProducts = session.createCriteria(Order.class)
    .setResultTransformer(CriteriaSpecification.DISTINCT_ROOT_ENTITY)
    .setFetchMode(“products”,FetchMode.JOIN)
    .add(Restrictions.eq(“id”,”1234”))
    .list();

Now you retrieve all orders with eagerly loaded products.

回答2:

Use the createCriteria method on the Criteria class for the relationship.

List ordersAndProducts = session.createCriteria(Order.class)
    .createCriteria(“products”)
        .add(Restrictions.eq(“id”,”1234”))
    .list();

You can read the (slightly confusing) documentation about it here.

来源：https://stackoverflow.com/questions/4377249/hibernate-criteria-how-to-limit-join-results-to-a-single-entity-type

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hibernate

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