querydsl joining ElementCollection

[Sebastian Dietrich]

Hi!

I can't figure out on how to correctly join an @ElementCollection annotated list in JPA.

Assuming that I have the following classes: A, B, C with:

public class A {

   @Id private Integer id;

   @ManyToOne private B b;

   ...

public class B {

   @Id private Integer id;

   @ElementCollection

   @CollectionTable(joinColumns = @JoinColumn(name=B_ID"))

   private List<C> cs;

   @Embeddable
   public static class C {
      private String name;

      private boolean whatever;

      ...

   ...

I'd like to get all As that reference Bs that have Cs with names matching a list of given names and whatever = true.

Joining A with B works fine, but joining B with C (or sub.selecting Bs with given Cs) gives me troubles.

Any suggestions would be appreciated...

Thanks,

Sebastian

[timowest]

Hi.

Could you be more explicit on what kind of trouble you get?

Br,

Timo

[Sebastian Dietrich]

Hi!

It's basically due to missing knowledge on my side. I just don't know how to join elementcollections in querydsl:

I've tried the following:

QB b = QB.b;

QB_C c = QB_C c;

return from(b).innerJoin(b.c, c).list(c);

but that gives me a SQLGrammarException: could not prepare statement: user lacks privilege or object not found: c.id

afaik this is due to the fact, that I list c and not b, but rephrasing it to

return from(b, c).innerJoin(b.c, c).list(c);

does not compile since c is no EntityPath but a BeanPath

So how can I query for specific elements in an element-collection?

[timowest]

Hi.

Joins to element collections are allowed, but in the projection you can only use entities and values. 

You can for example project the properties of C and construct a new C instance via Expressions.bean

from(b).innerJoin(b.cs, c).list(Expressions.bean(C.class, c.name. c.whatever));

Br,

Timo

[Sebastian Dietrich]

Thanks, that helped - though there is no Expressions.bean method I've found that it could be done via

from(b).innerJoin(b.cs, c).list(Expressions.list(C.class, c.name. c.whatever));

[Ruben Dijkstra]

Hello Sebastian,

Indeed there is no Expressions.bean, but it should be:

Projections.bean(C.class, c.name, c.whatever)

Hope that helps.

Br,

Ruben

[Timo Westkämper]

Hi.

Sorry. Projections.bean of course.

Timo

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