I have two entities:
class A {
#OneToMany(mappedBy = "a")
List<B> bs;
// getter/ setter
}
class B {
#ManyToOne
A a;
// getter/ setter
}
To delete one b, I first need to invalidate that relationship.
"Traditionally" I would do something like that:
A a = em.getReference(A.class, entityIdA)
B b = em.getReference(B.class, entityIdB);
a.getBs().remove(b);
b.setA(null);
em.remove(b);
This is not very performant, if the List of a's is getting large (a few hundreds in my case).
I know I can also use JPQL to create an update query.
something like this:
Query q = em.createQuery("UPDATE B b SET b.a = NULL");
q.executeUpdate();
Question: What would be the corresponding JPQL query to remove one b from a's list of bs?
In short:
How to translate
a.getBs().remove(b);
into a JPQL query?
EDIT: the mentioned update query translates to
UPDATE B SET A_ID = ? WHERE (ID = ?)
bind => [null, 2]
Tables look like this:
A
ID
B
ID A_ID
From the comments and from this question, changing the owning side of the relationship is sufficient.
Therefore, to do
a.getBs().remove(b);
as an jpql query, one can do
"UPDATE B b SET b.a = NULL"
This will release the bidirectional relationship between a and b.
Note that you might need to clear the L2 cache or close the EntitiyManagerFactory for this to take effect.
factory.getCache().evictAll();
Related
I've stumbled upon a problem with Hibernate. I've 2 entities - let's say A and B like so (Entity/Table annotations ommited):
class A {
#ManyToOne
#JoinColumn(name = "b_id")
private B b;
}
class B {
#Column(name = "name")
private String name;
}
Now, I'm trying to query all A entities and ordering them by name field of B's entity like so:
SELECT q FROM A AS q ORDER BY q.b.name asc nulls last
The problem is, there are rows in A's table having null foreign-key (b is null) - in result the aforementioned query returns only rows that don't contain null in b field, and I'd like to have them all.
I guess hibernate joins the table without using LEFT JOIN (OUTER JOIN?) resulting in null values being skipped.
Is there any way to change this behaviour? It would be great, if I could solve it by using annotations in entity classes, because the query-generating mechanism is pretty locked up.
You can use CriteriaBuilder and set alias on entityRoot
Root<A> entityRoot = criteriaQuery.from(A);
entityRoot.join("b", JoinType.LEFT).alias("b");
criteriaQuery.select(entityRoot)
.orderBy(criteriaBuilder.asc(entityRoot.get("b").get("name"))
;
you can use criteria query for this but you will have to create session while using that, it is simpler to access database using criteria:
Criteria criteria = session.createCriteria(A.class)
//create alias of your other class to provide ordering according to foriegn key
criteria.createAlias("foreignkey","keyin table A(eg..b)");
criteria.addOrder(Order.asc(b.name));
List list = criteria.getlist();
hope this helps
I cannot find a solution to a problem that seems to be easy. Say there are 2 entity classes:
class A {
Set<B> bs;
}
class B {
String text;
}
How to create a criteria query that returns all A's that contains at least one B entity which fulfills a given condition (like b.text = 'condition')?
I think this link can be useful:
http://mikedesjardins.net/2008/09/22/hibernate-criteria-subqueries-exists/
It contains the following example about how create n exists criteria:
"What you’re really trying to do is to obtain all Pizza Orders where an associated small pizza exists. In other words, the SQL query that you’re trying to emulate is
SELECT *
FROM PIZZA_ORDER
WHERE EXISTS (SELECT 1
FROM PIZZA
WHERE PIZZA.pizza_size_id = 1
AND PIZZA.pizza_order_id = PIZZA_ORDER.pizza_order_id)
The way that you do that is by using an “exists” Subquery, like this:
Criteria criteria = Criteria.forClass(PizzaOrder.class,"pizzaOrder");
DetachedCriteria sizeCriteria = DetachedCriteria.forClass(Pizza.class,"pizza");
sizeCriteria.add("pizza_size_id",1);
sizeCriteria.add(Property.forName("pizza.pizza_order_id").eqProperty("pizzaOrder.pizza_order_id"));
criteria.add(Subqueries.exists(sizeCriteria.setProjection(Projections.property("pizza.id"))));
List<pizzaOrder> ordersWithOneSmallPizza = criteria.list();
And voila, the result will contain two PizzaOrders!"
I have two entity objects (A and B) that have a One-To-Many relationship. I am using JPA (Hibernate) to join these tables and query them for a specific result set, but the criteria I specify for the child table (B) are not applied when fetching my results. This is how I have defined the query:
CriteriaBuilder builder = entityManager.getCriteriaBuilder();
CriteriaQuery<A> query = builder.createQuery(A.class);
Root<A> a = query.from(A.class);
Join<A, B> abJoined = a.join(A_.b);
query.distinct(true)
.where(builder.and(
builder.equal(a.get(A_.id), id),
builder.equal(a.get(A_.active), 1),
builder.equal(a.get(A_.location), 1011),
builder.equal(a.get(A_.status), "Pending"),
builder.equal(abJoined.get(B_.status), "Not Moved"),
builder.greaterThan(abJoined.get(B_.detailId), 0)
));
When I call entityManager.createQuery(query).getResultList(); I get one instance of entity 'A', but when I try to access 'B' through 'A' a.getB() the two criteria that I had specified for abJoined are not applied and I get all instances of 'B' that are joined to 'A'. Is there something more I need to do to get these criteria applied? If the criteria cannot be applied, is there a recommended method for removing the corresponding instances of 'B' from the result set?
I can provide more code or other details if necessary.
The query is used to select which A entities must be returned by the query. But the A entities will never be partial entities containing only a subset of their Bs. They will always be complete instances of A, reflecting the state of what A is in the database, and which B this A is related to.
BTW, even if this was possible (it's not, and explicitely forbidden by the JPA spec), your query would at least have to load the Bs as well, using a fetch join. Otherwise only the state of A is returned by the query, and the linked Bs are loaded lazily.
But in JPA, for a #OneToMany relationship, Query is fired first on the master, with all the Criteria and fetches just master records.
Later Individually the query is fired, BUT BUT BUT......the B table criteria will not contain all the conditions, but only one condition i.e. just the primary key VALUE of master records fetched in i.e just with one condition "b.A_id=[primarykeyfetched from master]"
SOLUTION is simple
Make an Independent class, in which we require the fields of #OneToMany relationship
STEP 1
public class AB {
private A a;
private B b; //#OneToMany with A in the Entity class definitions
public AB(){}
public AB(A a, B b){ ///Very Important to have this constructor
this.a=a;
this.b=b;
}
getter setter....
}
STEP 2
CriteriaQuery<AB> q = criteriaBuilder.createQuery(AB.class);
Root<A> fromA = criteriaQuery.from(A.class);
List<Predicate> predicates = new ArrayList<Predicate>();
Join<A,B> fromB = fromA.join("b", JoinType.INNER);/*"b",fieldName of B in entity Class A*/
criteriaQuery.select(criteriaBuilder.construct(AB.class,A,B));//looks AB's 2 param constr.
predicates.add(criteriaBuilder.equal(fromA.get("name"), filter.getName()));
predicates.add(criteriaBuilder.equal(fromB.get("salary"), filter.getSalary()));
..........
List<AB> ABDataList = typedQuery.getResultList();
for(AB eachABData :ABDataList){
....put in ur objects
obj.setXXX(eachABData.getA().getXXX());
obj.setYYY(eachABData.getB().getYYY());
}
This will give all the results applying all the criteria to master table A, and comparing the primary key of Table B instead of foreign key.
Lets say that class 'X' is mapped to table 'X' class 'A' is mapped to Table 'A' and Class 'B is mapped to table 'B'.
Table X Structure:(X_ID, some other columns
Table A Structure:(A_Id,X_Id, some other columns)
Table B Structure:(A_Id, some other columns)...Table B also has A_Id
Class 'B' extends class 'A'. We have the mapping files for both of them as:
Class 'A' Parent Mapping file:
#Entity
#Table(name = 'A')
#Inheritance(stratergy=InheritanceType.Joined)
public abstract class A {
#Id #Clumns(name = "A_Id)
#GeneratedValue
protected Long aId;
-- some more A specific fields
}
Class 'B' Mapping file:
#Entity
#Table(name= 'B')
Public class B extends A{
---- B specific fields
}
Now, I have a SQL Query as below that I need to write using hibernate criteria API.
select * from X
INNER JOIN A
ON X.id = A.id
INNER JOIN B
ON A.id = B.id
where B.name = 'XYZ'
and B.Sex = 'M'
I have come up with:
Criteria c = session.createCriteria(x.class, "x");
.createAlias("x.a", "a")
.createAlias("a.b", "b")
.add(Restrictions.eq("b.sex", "M"))
.add(Restrictions.eq("b.name", "XYZ"));
But, if we check the mapping file, there is no direct reference of B in A. Hence hibernate throws out "B not related to A" entity.
Is there any way this inheritance can be mapped in query crteria
You shouldn't need to reference A at all in your criteria, or use any aliases.
Criteria c = session.createCriteria(B.class);
.add(Restrictions.eq("sex", "M"))
.add(Restrictions.eq("name", "XYZ"));
will give you the result you need.
Because of the InheritanceType.Joined, this will probably produce SQL that includes a join to the the A table (something close to the sql you show), but it isn't necessary to specify that join in the criteria.
The things that look like columns in the criteria are actually (reflective) references to fields in your Java objects. Hibernate figures out the columns to put in the sql from your annotations, and should the join to the A table if it's needed based on the inheritance annotation.
To be sure of this in your context, and to understand all this a bit better, I'd advise trying it and turning on logging of the generated sql as described in this answer to another SO hibernate question.
Try this way:
Criteria rootCrit = session.createCriteria(A.class);
rootCrit.createAlias("B", "B");
rootCrit.add(Restrictions.eq("B.sex", "M"));
rootCrit.add(Restrictions.eq("B.name", "XYZ"));
I want to annotate following structure:
I have this query:
SELECT A.*, BES.*, BES_2.*
INNER JOIN BES ON A.a = BES.a AND A.b = BES.b
INNER JOIN BES AS BES_2 ON A.a = BES_2.a AND A.b = BES_2.b
WHERE (BES.c = N'foo') AND (BES_2.c = N'bar')
I have the entities Job (representing A) and JobEndPoint (representing BES). The Job object should contain two JobEndPoint which map like a one-to-one relation. I need two JOIN the table two times checking for the same values only differed by the column "c" which I check in the WHERE statement.
#OneToOne
private JobEndPoint from;
#OneToOne
private JobEndPoint to;
My problem is now that the database columns and the object fields differ a lot and I don't know how to add the WHERE statement.
Create a JPA repository, and type a custom #Query.
I assume you already linked the parent and JobEndPoint classes over a and b fields. (To do that, define a multiple-column id on JobEndPoint and specify joinColumns in the parent class.)
#Query("SELECT u FROM parent
LEFT JOIN u.from bes
LEFT JOIN u.to bes2
WHERE bes.c = 'foo'
AND bes2.c = 'bar'")
Set<Parent> findMatchingParents()