Room DAO Order By ASC or DESC variable

Question

I'm trying to make a @Query function in my @Dao interface which has a boolean parameter, isAsc to determine the order:

@Query("SELECT * FROM Persons ORDER BY first_name (:isAsc ? ASC : DESC)")
List<Person> getPersonsAlphabetically(boolean isAsc);

Apparently this isn't allowed. Is there a work around here?

EDIT:

It seemed odd to use two queries (below) since the only difference is ASC and DESC:

@Query("SELECT * FROM Persons ORDER BY last_name ASC")
List<Person> getPersonsSortByAscLastName();

@Query("SELECT * FROM Persons ORDER BY last_name DESC")
List<Person> getPersonsSortByDescLastName();

Answer 1

Use CASE Expression for SQLite to achieve this in Room DAO,

@Query("SELECT * FROM Persons ORDER BY 
        CASE WHEN :isAsc = 1 THEN first_name END ASC, 
        CASE WHEN :isAsc = 0 THEN first_name END DESC")
List<Person> getPersonsAlphabetically(boolean isAsc);

Answer 2

Create two queries, one with ASC and one with DESC.

@Query("SELECT * FROM Persons ORDER BY last_name ASC")
List<Person> getPersonsSortByAscLastName();

@Query("SELECT * FROM Persons ORDER BY last_name DESC")
List<Person> getPersonsSortByDescLastName();