CODEWITHSUNDEEP
androidrx-javaandroid-room
Taha Sami
Taha Sami

Reputation: 1697

How can I create one connection using Transaction instead of two? Room with RxJava

Inside onCreateView method

MainActivity.localDatabase.categoriesDao().getCategories().subscribe(new SingleObserver<List<CategoriesModel>>() {
    @Override
    public void onSubscribe(@io.reactivex.rxjava3.annotations.NonNull Disposable d) {

    }

    @Override
    public void onSuccess(@io.reactivex.rxjava3.annotations.NonNull List<CategoriesModel> categoriesModels) {

    }

    @Override
    public void onError(@io.reactivex.rxjava3.annotations.NonNull Throwable e) {

    }
});

MainActivity.localDatabase.subcategoriesDao().getSubcategories(1).subscribe(new SingleObserver<List<SubcategoriesModel>>() {
    @Override
    public void onSubscribe(@io.reactivex.rxjava3.annotations.NonNull Disposable d) {

    }

    @Override
    public void onSuccess(@io.reactivex.rxjava3.annotations.NonNull List<SubcategoriesModel> subcategoriesModels) {

    }

    @Override
    public void onError(@io.reactivex.rxjava3.annotations.NonNull Throwable e) {

    }
});

CategoriesDao

@Dao
public interface CategoriesDao {

    @Query("SELECT * FROM CATEGORIES")
    Single<List<CategoriesModel>> getCategories();

    @Query("DELETE FROM CATEGORIES")
    void deleteCategories();

    @Insert
    void insertCategories(List<CategoriesModel> categoriesModelList);

}

SubcategoriesDao

@Dao
public interface SubcategoriesDao {

    @Query("SELECT * FROM SUBCATEGORIES WHERE category_id = :categoryId")
    Single<List<SubcategoriesModel>> getSubcategories(int categoryId);

    @Insert
    void insertSubcategories(List<SubcategoriesModel> subcategoriesModelList);

    @Query("DELETE FROM SUBCATEGORIES")
    void deleteSubcategories();

}

LocalDatabase

@Database(entities = {CategoriesModel.class, SubcategoriesModel.class}, version = 1)
public abstract class LocalDatabase extends RoomDatabase {

    public abstract CategoriesDao categoriesDao();

    public abstract SubcategoriesDao subcategoriesDao();

}

I want to get the categories and subcategories that are stored in the room database, I did it such as the code above, But how can I avoid creating multiple connections?

Is it possible to get the categories and subcategories in one connection only instead of two?

What about Transactions or is there another way?

Please leave an example with your answer.

Upvotes: 0

Views: 224

Answers (1)

Herry
Herry

Reputation: 7087

You need to apply JOIN between your CATEGORIES table and SUBCATEGORIES.

Below is an exam of doing the JOIN with android ROOM.

Make sure you have CategoryID as ForeignKey in SUBCATEGORIES table.

You can try the following.

class CatSubCate{
    @Embedded
    var mCat: CategoriesModel? = null
    //Declare Column you need from the SUBCATEGORIES table
    var mSubCatId: String? = null
    var mCatId: String? = null
}

In Side

@Dao
public interface CategoriesDao {

@Transaction
@Query("SELECT * FROM CATEGORIES LEFT  JOIN (SELECT S.SubCatId AS mSubCatId, S.ID as mCatId FROM SUBCATEGORIES S GROUP BY S.ID) AS SUBCATEGORIES ON CATEGORIES.ID=SUBCATEGORIES.ID WHERE CATEGORIES.ID != :catId ")
    abstract fun getAllCategory(catId: String): Flowable<List<CatSubCate>>

}

For more info see this android dev link

Upvotes: 1

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