Return type for Android Room joins

Question

Let\'s say I want to do an INNER JOIN between two entities Foo and Bar:

@Query(\"SELECT * FROM Foo INNER JOIN Bar ON F         


        

Answer 1

This is my Food Table

@Entity(tableName = "_food_table")
data class Food(@PrimaryKey(autoGenerate = false)
            @ColumnInfo(name = "_food_id")
            var id: Int = 0,
            @ColumnInfo(name = "_name")
            var name: String? = "")

This is my Cart table and model class (Food Cart)

@Entity(tableName = "_client_cart_table")
data class CartItem(
                @PrimaryKey(autoGenerate = false)
                @ColumnInfo(name = "_food_id")
                var foodId: Int? = 0,
                @Embedded(prefix = "_food")
                var food: Food? = null,
                @ColumnInfo(name = "_branch_id")
                var branchId: Int = 0)

Note: Here we see _food_id column in two table. It will throw compile time error. From @Embedded doc, you have to use prefix to differentiate between them.

Inside dao

@Query("select * from _client_cart_table inner join _food_table on _client_cart_table._food_id = _food_table._food_id where _client_cart_table._branch_id = :branchId")
fun getCarts(branchId: Int) : LiveData>

This query will return data like this

CartItem(foodId=5, food=Food(id=5, name=Black Coffee), branchId=1)

I have done this in my project. So Give it a try. Happy coding