String list identity in where clause of JPA / JPQL Query

Question

Say I have an @Entity like

class C {
  List<String> sequence;
}

and I want to query for instances of C that exactly match a given list. (I am aware that this is order sensitive, and I'm ok with that.) I am using EclipseLink and query with JPQL.

I tried the obvious:

List<String> querySeq = ... // some list to be used in the where clause
em.createQuery("select c from C c where c.sequence = :qs", C.class)
            .setParameter("qs", querySeq);

This fails when I try to execute the query with getResultList() . The error is java.sql.SQLSyntaxErrorException: row column count mismatch .

I also tried with join :

select c from C c join c.sequence s where s in :qs

But this fails, too, saying The collection-valued path 'c.sequence' must resolve to an association field. My interpretation of this is that join does not work on a collection of primitives, but only on relations.

So my questions are:

What is the right way to do this?

Also, is there a way to do more complex operations on primitive collections, like querying for (set) intersections, unions or differences?

Answer 1

After research on the internet and the JPA specification, I see that we cannot compare two lists using the JPQL.

I suggest to select the entire list and then compare it with the second list using the Apache Commons CollectionUtils . It offers the functionality of intersection and subtraction .

Answer 2

I couldn't find any solution or article where JPQL could be used to directly compare lists. But there is a mechanism where you can test if a value is MEMBER OF the collection.

The process is not elegant but with a bit of tweaking we could build a query similar to this (Couldn't test the code, but I think it depicts the idea and logically should work):

String query = "SELECT c FROM C c";
String checkValue = "";

for(int i = 0; i<queryString.size();i++){

    checkValue = queryString.get(i);

    if(i==queryString.size()-1){
        query += " WHERE '" + checkValue + "'" + " MEMBER OF c.sequence";
    }else{
        query += " WHERE '" + checkValue + "'" + " MEMBER OF c.sequence AND";
    }
}