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:

@Q         


        

Answer 1

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();

Answer 2

Why don't you try something like this? I have not tested it.

@Query("SELECT * FROM Persons ORDER BY first_name :order")
List<Person> getPersonsAlphabetically(String order);

And the logic you suggested should go before you make the query.

Answer 3

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);