How to make a CriteriaBuilder join with a custom “on” condition?

问题

I want make a query where I join 2 tables, using the CriteriaBuilder. In MySQL the query I'm trying to make would look like this:

SELECT * FROM order
LEFT JOIN item
ON order.id = item.order_id
AND item.type_id = 1

I want to get all orders and if they have an item of type #1, I want to join with this item. However, if no item of type #1 is found, I still want to get the order. I can't figure out how to make this with the CriteriaBuilder. All I know how to make is:

CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<Order> cq = cb.createQuery(Order.class);
Root<Order> order = cq.from(Order.class);
Join<Order, Item> item = order.join(Order_.itemList, JoinType.LEFT);
Join<Item, Type> type = order.join(Item_.type, JoinType.LEFT);
cq.select(order);
cq.where(cb.equal(type.get(Type_.id), 1));

This query is broke, since it results in something like this in MySQL:

SELECT * FROM order
LEFT JOIN item
ON order.id = item.order_id
WHERE item.type_id = 1

The result will only contain orders with items of type #1. Orders without are excluded. How can I use the CriteriaBuilder to create a query like in the first example?

回答1:

It is possible using the on method Join<Z, X> on(Predicate... restrictions);

Here is how:

Root<Order> order = cq.from(Order.class);
Join<Order, Item> item = order.join(Order_.itemList, JoinType.LEFT);
item.on(cb.equal(item.get(Item_.type), 1));

回答2:

I think this is the same problem as posed in this question. It looks like it is not possible in CriteriaBuilder. It is possible in Hibernate Criteria API, but that probably won't help you.

JPA Criteria API: Multiple condition on LEFT JOIN

回答3:

I know this question was made a long time a go, but recently a had the same problem and i found this solution from an Oracle forum, i copied and pasted just in case the link is not longer available.

MiguelChillitupaArmijos 29-abr-2011 1:41 (en respuesta a 840578) Think you should use something like:

em.createQuery("SELECT DISTINCT e.Id" +
                    " from Email e " +
                    " left join e.idEmailIn e2 *with* e2.responseType = 'response'" +
                    "     where e.type = 'in' and e.responseMandatory = true").getSingleResult();

An this is the link.

JPA Criteria : LEFT JOIN with an AND condition

回答4:

There is a workaround if you are using Hibernate 3.6 with JPA 2.0 It is not the better solution, however it works perfect for me.

I´ve duplicate the entity with the @Where hibernate annotation.It means that everytime you use the join with this entity, hibernate will add the extra condition on the join statement at generated SQL.

For instance, initially we have the follow example:

@Entity
@Table(name = "PERSON")
public class Person {

    @Id
    @Column(name = "PERSON_ID")
    private Long id;

    @Id
    @Column(name = "PERSON_NAME")
    private String name;

   @OneToMany(mappedBy = "person", fetch = FetchType.LAZY)
   private Set<Address> addresses;

}

@Entity
@Table(name = "ADDRESS")
public class Address {

    @Id
    @Column(name = "ADDRESS_ID")
    private Long id;

    @Id
    @Column(name = "ADDRESS_STREET")
    private String street;

   @ManyToOne
   @JoinColumn(name = "PERSON_ID")
    private Person person;

}

In order to add extra conditions on criteria Join, we need duplicate the Address @Entity mapping , adding the @Where annotation @Where(clause = " ADDRESS_TYPE_ID = 2").

@Entity
@Table(name = "ADDRESS")
@Where(clause = " ADDRESS_TYPE_ID = 2")
public class ShippingAddress {

    @Id
    @Column(name = "ADDRESS_ID")
    private Long id;

    @Id
    @Column(name = "ADDRESS_STREET")
    private String street;

   @OneToOne
   @JoinColumn(name = "PERSON_ID")
    private Person person;

}

Also, we need to add the duplicate mapping association for the new entity.

@Entity
@Table(name = "PERSON")
public class Person {

    @Id
    @Column(name = "PERSON_ID")
    private Long id;

    @Id
    @Column(name = "PERSON_NAME")
    private String name;

   @OneToMany(mappedBy = "person", fetch = FetchType.LAZY)
   private Set<Address> addresses;

   @OneToOne(mappedBy = "person")
   private ShippingAddress shippingAddress;

}

Finally, you can use a join with this specific Entity in your criteria :

PersonRoot.join(Person_.shippingAddress, JoinType.LEFT);

The Hibernate Snippet SQL should seems like this :

 left outer join
        address shippingadd13_ 
            on person11_.person_id=shippingadd13_.person_id 
            and (
                shippingadd13_.ADDRESS_TYPE_ID = 2 
            )

回答5:

ON clause is supported in Hibernate 4.3 version, anyone is aware if there is a parameter indexing issue between the parameter index of the additional custom conditions with the index of the existing mapping filters when doing an outer join with ON clause?

Using the Person entity class below as an example, say I am adding this filter to limit the address types and the filter is enabled to populate the IN clause. The parameter index for the IN clause will cause the issue [2] when I add additional conditions (such as using 'street' column) part of the ON clause. Is is a known issue?

[1] @Filter(name = "addressTypes", condition = "ADDRESS_TYPE in (:supportedTypes)")

[2] Caused by: ERROR 22018: Invalid character string format for type BIGINT. private Set addresses;

来源：https://stackoverflow.com/questions/15990141/how-to-make-a-criteriabuilder-join-with-a-custom-on-condition

标签

jpa

jpa-2.0

criteria-api