How to get specific value from room database by id?-CodePudding

I have a simple room database with LiveData, i want to get (cartPriceI: Double) values by id to use it within specific methods.

CartItemsDatabase.kt

@Parcelize
@Entity(tableName = "cart_table")
data class CartItemsDatabase(
    @PrimaryKey(autoGenerate = true) var cid: Int,
    @ColumnInfo(name = "titleD") var cartTitle: String?,
    @ColumnInfo(name = "imageD") var cartImage: Bitmap?,
    @ColumnInfo(name = "priceLD") var cartPriceL: Double?,
    @ColumnInfo(name = "priceID") var cartPriceI: Double?,
    @ColumnInfo(name = "itemNumD") var cartNum: Int?,
    @ColumnInfo(name = "descriptionD") var cartDes: String?): Parcelable

CartItemsDAO.kt

@Dao
interface CartItemsDAO {

    @Insert(onConflict = OnConflictStrategy.IGNORE)
    suspend fun addItem(cartItemsDatabase: CartItemsDatabase)

    @Update
    suspend fun updateCart(cartItemsDatabase: CartItemsDatabase)

    @Query("SELECT * FROM cart_table ORDER BY cid ASC")
    fun readAllData(): LiveData<List<CartItemsDatabase>>

    @Delete
    fun delete(cartItems: CartItemsDatabase)
}

CartRepository.kt

class CartRepository(private val cartItemsDAO: CartItemsDAO) {
    val readAllData: LiveData<List<CartItemsDatabase>> = cartItemsDAO.readAllData()
    suspend fun addItem(cartItemsDatabase: CartItemsDatabase){
        cartItemsDAO.addItem(cartItemsDatabase)
    }
    suspend fun updateCart(cartItemsDatabase: CartItemsDatabase){
        cartItemsDAO.updateCart(cartItemsDatabase)
    }
}

CartViewModel.kt

class CartViewModel(application: Application): AndroidViewModel(application) {
    val readAllData: LiveData<List<CartItemsDatabase>>
    private val repository: CartRepository

    init {
        val cartDao = AppDatabase.getDatabase(application).cartDao()
        repository = CartRepository(cartDao)
        readAllData = repository.readAllData
    }
    fun addItem(cartItemsDatabase: CartItemsDatabase){
        viewModelScope.launch(Dispatchers.IO){
            repository.addItem(cartItemsDatabase)
        }
    }
    fun updateCart(cartItemsDatabase: CartItemsDatabase){
        viewModelScope.launch(Dispatchers.IO) {
            repository.updateCart(cartItemsDatabase)
        }
    }
}

AppDatabase.kt

@Database(entities = [CartItemsDatabase::class], version = 1, exportSchema = false)
@TypeConverters(Converters::class)
abstract class AppDatabase : RoomDatabase() {
    abstract fun cartDao(): CartItemsDAO
    companion object {
        @Volatile
        private var INSTANCE: AppDatabase? = null

        fun getDatabase(context: Context): AppDatabase {
            // if the INSTANCE is not null, then return it,
            // if it is, then create the database
            val tempInstance = INSTANCE
            if (tempInstance != null){
                return tempInstance
            }
            synchronized(this){
                val instance = Room.databaseBuilder(
                    context.applicationContext,
                    AppDatabase::class.java,
                    "cart_database"
                ).build()
                INSTANCE = instance
                return instance
            }
        }

        private fun buildDatabase(context: Context): AppDatabase {
            return Room.databaseBuilder(
                context.applicationContext,
                AppDatabase::class.java,
                "cartItems_database"
            )
                .build()
        }
    }
}

I'm a beginner, i want to know if there is possible way to do that and retrieve specific values from database (ex. cartPriceI in Double) by id!

CodePudding user response：

You can query the database by the given id and return it asynchronously either with a suspend fun or LiveData/Flow

In the CartItemsDAO:

@Query("SELECT cartPriceI FROM cart_table WHERE cid = :id")
suspend fun getPrice(id: Int): Double


@Query("SELECT cartPriceI FROM cart_table WHERE cid = :id")
fun getPrice(id: Int): LiveData<Double>

CodePudding user response：

You can get a specific model by SELECT with WHERE statement

@Query("SELECT * FROM cart_table WHERE cid == : cid")
fun getCartItemsDatabase(cid: String): LiveData<CartItemsDatabase?>

Or you can Return a subset of a table's columns

@Query("SELECT priceID FROM cart_table WHERE cid == : cid")
fun getCartItemPrice(cid: String): LiveData<Double>