Question

I am trying to make “filter” search for all questions in my database. Now I get a exception telling me that I can’t compare enum values with string. Is it because I don’t use the fully qualified package name of wher the enum type is declared? If so, is it better ways than hard-coding the package name?

Exception Description: Error compiling the query [SELECT q FROM
Question q WHERE q.status = ‘APPROVED’], line 1, column 40: invalid
enum equal expression, cannot compare enum value of type
[app.utility.Status} with a non enum value of type
[java.lang.String].

public List<Question> all(Status status, ViewOption viewOption) {
    String jpql = "SELECT q FROM Question q ";
    boolean isWhereClauseAdded = false;

    if (status != Status.ALL) {
        if (!isWhereClauseAdded) {
            jpql += "WHERE ";
        }

        jpql += "q.status = '" + status + "'";
    }

    if (viewOption != ViewOption.ALL) {
        if (!isWhereClauseAdded) {
            jpql += "WHERE ";
        }

        // Check if 'AND' operator is needed.
        if (status != Status.ALL) {
            jpql += " AND ";
        }

        switch (viewOption) {
        case ONLY_IMAGES:
            jpql += "q.image != ''";
            break;
        case NO_IMAGES:
            jpql += "q.image = '' ";
            break;
        }
    }

    TypedQuery<Question> query = entityManager.createQuery(jpql,
            Question.class);

    return query.getResultList();
}

Answer 1

The right thing to do would be to use a query parameter:

String jpql = "select ... where q.status = :status";
Query query = em.createQuery(jpql).setParameter("status", status);

Rather than creating your query dynamically be concatenating query parts, you should also use the Criteria API, which has been designed with this goal in mind.