hql - org.hibernate.QueryException: illegal attempt to dereference collection

Question

I am trying following hql query to execute

SELECT count(*) 
  FROM BillDetails as bd
 WHERE bd.billProductSet.product.id = 1002
   AND bd.client.id                 = 1

But it is showing

org.hibernate.QueryException: illegal attempt to dereference collection 
[billdetail0_.bill_no.billProductSet] with element property reference [product] 
[select count(*) from iland.hbm.BillDetails as bd where bd.billProductSet.product.id=1001 and bd.client.id=1]
    at org.hibernate.hql.ast.tree.DotNode$1.buildIllegalCollectionDereferenceException(DotNode.java:68)
    at org.hibernate.hql.ast.tree.DotNode.checkLhsIsNotCollection(DotNode.java:558)

Answer 1

billProductSet is a Collection. As such, it does not have an attribute named product.

Product is an attribute of the elements of this Collection.

You can fix the issue by joining the collection instead of dereferencing it:

SELECT count(*) 
  FROM BillDetails        bd 
  JOIN bd.billProductSet  bps 
 WHERE bd.client.id       = 1
   AND bps.product.id     = 1002