JPQL: "where" clause on "case" variable

Question

The following JPQL query runs without issues:

SELECT t, CASE WHEN (e.language.language = 'en' AND e.language.country = 'GB' AND e.language.variant = '') THEN e.text ELSE '' END sortProperty FROM Glossary g JOIN g.terms t JOIN t.expressions e ORDER BY sortProperty

whereas the following fails:

SELECT t, CASE WHEN (e.language.language = 'en' AND e.language.country = 'GB' AND e.language.variant = '') THEN e.text ELSE '' END sortProperty FROM Glossary g JOIN g.terms t JOIN t.expressions e WHERE sortProperty = 'asdf' ORDER BY sortProperty

With this exception:

Caused by: java.lang.IllegalArgumentException: Invalid unbound variable "sortproperty" in query.

Is this a limitation in the query syntax and can this somehow be circumvented (perhaps using the Criteria API)?

Thanks and best regards, Pascal

Answer 1

Problem does not have direct connection to CASE expression, in general result variables (sortProperty in this case) cannot be used in WHERE clause. That's why also following is invalid JPQL:

SELECT u.firstName AS someVar FROM User u WHERE someVar = 'blaa'

Criteria API does not help here. Similar limitation exists also in SQL:

SELECT u.first_name as someAlias 
FROM users u 
-- someAlias is not known here:
WHERE someAlias = 'blaa'

Whole condition should be pushed to WHERE clause.