Error with subtype association join using querydsl integration

[azizairo]

Hi, I am getting the error: Attribute not found while trying to join subtype associations. Here is my query:

blazeJPAQueryFactory.with(maxLessonContentVersionCTE, subquery1)
        .select(moduleUnit)
        .from(moduleUnit)
        .leftJoin(moduleUnit.as(QLesson.class).contents, lessonContent).fetchJoin()
        .fetchOne();

If i use querydsl without blazepersistance, this query will work

[jwgmeligmeyling]

I am not familiar with the .as(QClass) syntax, but contrary to HQL/JPQL, in JPQLNext I believe sub-type attributes are not present on the parent type. Instead the expression needs to be explicitly treated:

JPQLNextExpressions.treat(moduleUnit, QLesson.class)

Would be the syntax for that I guess

[azizairo]

As I understood from method treat, method does not give us possibility to treat parent classes as their subtypes

public static <T> Expression<T> treat(Class<T> result, Expression<?> expression) {
        if (Boolean.class.equals(result) || boolean.class.equals(result)) {
            return Expressions.simpleOperation(result, JPQLNextOps.TREAT_BOOLEAN, expression);
        } else if (Byte.class.equals(result) || byte.class.equals(result)) {
            return Expressions.simpleOperation(result, JPQLNextOps.TREAT_BYTE, expression);
        } else if (Short.class.equals(result) || short.class.equals(result)) {
            return Expressions.simpleOperation(result, JPQLNextOps.TREAT_SHORT, expression);
        } else if (Long.class.equals(result) || long.class.equals(result)) {
            return Expressions.simpleOperation(result, JPQLNextOps.TREAT_LONG, expression);
        } else if (Integer.class.equals(result) || int.class.equals(result)) {
            return Expressions.simpleOperation(result, JPQLNextOps.TREAT_INTEGER, expression);
        } else if (Float.class.equals(result) || float.class.equals(result)) {
            return Expressions.simpleOperation(result, JPQLNextOps.TREAT_FLOAT, expression);
        } else if (Double.class.equals(result) || double.class.equals(result)) {
            return Expressions.simpleOperation(result, JPQLNextOps.TREAT_DOUBLE, expression);
        } else if (Character.class.equals(result) || char.class.equals(result)) {
            return Expressions.simpleOperation(result, JPQLNextOps.TREAT_CHARACTER, expression);
        } else if (String.class.equals(result)) {
            return Expressions.simpleOperation(result, JPQLNextOps.TREAT_STRING, expression);
        } else if (BigInteger.class.equals(result)) {
            return Expressions.simpleOperation(result, JPQLNextOps.TREAT_BIGINTEGER, expression);
        } else if (BigDecimal.class.equals(result)) {
            return Expressions.simpleOperation(result, JPQLNextOps.TREAT_BIGDECIMAL, expression);
        } else if (Calendar.class.equals(result)) {
            return Expressions.simpleOperation(result, JPQLNextOps.TREAT_CALENDAR, expression);
        } else if (Timestamp.class.isAssignableFrom(result)) {
            return Expressions.simpleOperation(result, JPQLNextOps.TREAT_TIMESTAMP, expression);
        } else if (Time.class.isAssignableFrom(result)) {
            return Expressions.simpleOperation(result, JPQLNextOps.TREAT_TIME, expression);
        } else if (Date.class.isAssignableFrom(result)) {
            return Expressions.simpleOperation(result, JPQLNextOps.TREAT_DATE, expression);
        } else {
            throw new IllegalArgumentException("No cast operation for " + result.getName());
        }
    }

.as(QClass) casts the path to a subtype querytype, so with it i can join subtype association. But it does not work with BlazePersistance

[jwgmeligmeyling]

Treat should do precisely that, although I apparently mixed up the parameters:

JPQLNextExpressions.treat(QLesson.class, moduleUnit) should complile and return a QLesson instance (which has the contents) field.

[jwgmeligmeyling]

The issue with moduleUnit.as(QLesson.class) is that it doesn't actually render the cast in the query but rather just relies on subTypeField being present in the ParentEntity anyway. This behaviour is however Hibernate specific (or maybe JPA?) and Blaze-Persist decided to require explicit treat operations.

[azizairo]

JPQLNextExpressions.treat() method returns Expression type and it can not be cast to QLesson classes.

public static <T> Expression<T> treat(Class<T> result, Expression<?> expression) {...}

[azizairo]

I found the correct treat method that can cast parents to the specified subtype. Thank a lot! P.S.: The correct method was in JPAExpressions.class