Question

Is there any way to use empty collection in IN operator?

List<Integer> idList = new ArrayList<Integer>();
Query query = em.createQuery("SELECT e FROM T e WHERE e.id IN ?1").setParameter(1, idList);
List results = query.getResultList();

produces:

Exception [EclipseLink-4002] (Eclipse Persistence Services - 2.3.2.v20111125-r10461): org.eclipse.persistence.exceptions.DatabaseException
Internal Exception: org.postgresql.util.PSQLException: ERROR: syntax error at or near ")"
  Position: 48
Error Code: 0
Call: SELECT id, other_id FROM t_table WHERE (id IN ())
Query: ReadAllQuery(referenceClass=T sql="SELECT id, other_id FROM t_table WHERE (id IN ?)")

This one:

List<Integer> idList = new ArrayList<Integer>();

CriteriaBuilder cb = EntityManagerProvider.getEmf().getCriteriaBuilder();
CriteriaQuery<T> c = cb.createQuery(T.class);
Root<T> t_class = c.from(T.class);
Expression<String> exp = t_class.get("id");
Predicate predicate = exp.in(idList);

c.select(t_class).where(predicate);

TypedQuery<T> q = em.createQuery(c);
List results = q.getResultList();   

produces:

Exception [EclipseLink-4002] (Eclipse Persistence Services - 2.3.2.v20111125-r10461): org.eclipse.persistence.exceptions.DatabaseException
Internal Exception: org.postgresql.util.PSQLException: ERROR: syntax error at or near ")"
  Position: 48
Error Code: 0
Call: SELECT id, other_id FROM t_table WHERE (id IN ())
Query: ReadAllQuery(referenceClass=T sql="SELECT id, other_id FROM t_table WHERE (id IN ())")       

Putting null explicity in IN:

Query query = em.createQuery("SELECT e FROM T e WHERE e.id IN (null)");

produces:

    java.lang.IllegalArgumentException: An exception occurred while creating a query in EntityManager: 
Exception Description: Syntax error parsing the query [SELECT e FROM T e WHERE e.id IN (null)], line 1, column 33: unexpected token [null].
Internal Exception: NoViableAltException(54@[709:9: (itemNode= scalarOrSubSelectExpression ( COMMA itemNode= scalarOrSubSelectExpression )* | subqueryNode= subquery )])

However, using native query works fine:

List<Integer> idList = new ArrayList<Integer>();
Query query = em.createNativeQuery("SELECT * FROM t_table WHERE t_table.id IN (null)");
List results = query.getResultList();   

Obviously, I don’t want to use native queries.
Of course I can do if-else checks before creating query and create different query for empty collection or in the most cases don’t create it at all, because in simple queries there won’t be any results.
But I have to change vendor from OpenJPA (which accepts empty collections) to EclipseLink in large project and sometimes queries contain few collections in different INs, so if-elsing this won’t be so easy.

Answer 1

The simply answer is: You can’t use an empty Array/List and set it as Parameter when using an IN query.
You might build your query using string concentation and if the list is empty / size() == 0 then you don’t add the IN part to the query string and don’t set the parameter.

There is no different in the resulting query if you have an empty collection in the IN parameter, you can just remove this condition then.
Except your goal is really to find no results. However logically you can catch this before you do the query, cause in your example:

“SELECT * FROM t_table WHERE t_table.id IN (null)”

=> that might need either:
a) ALL results are valid => then you can simply remove the where condition
b) NO results are valid => then you don’t need to perform the query and can just return an empty List of t_table in your method.

Sebastian