Android/Kotlin Cheat Sheet

Room Local Database

Add dependencies to Manifest

def room_version = "1.1.1"
implementation "android.arch.persistence.room:runtime:$room_version"
kapt "android.arch.persistence.room:compiler:$room_version"

Room provides an abstraction layer over SQLite.

There are 3 major components:

  • Database
  • Entity
  • DAO

Entity

@Entity(tableName = "items")
data class Item(
        @PrimaryKey(autoGenerate = true)
        var id : Int,
        var content: String
) {
    constructor(): this(0, "test item")
}

DAO

@Dao
interface ItemDao {

    @Query("select * from items where id = :id limit 1")
    fun getItem(id: Int): Item

    @Query("select * from items")
    fun getAllItems(): List<Item>

    @Insert(onConflict = REPLACE)
    fun insertItem(item: Item)

    @Update
    fun updateItem(item: Item)
}

Database

@Database(entities = arrayOf(Item::class), version = 1, exportSchema = false)
abstract class Database : RoomDatabase() {
    abstract fun itemDao(): ItemDao
}

Initialization

val db = Room.databaseBuilder(this, Database::class.java,"list-master-db").build()

// add .fallbackToDestructiveMigration() to wipe DB on version change

Note: this should be a singleton!

companion object {
    var db: Database? = null
}

Usage

val items = db.itemDao().getAllItems()

// Access off the main thread
AsyncTask.execute({
    val items = db.itemDao().getAllItems()
})

Observing Changes

Add the dependencies to build.grade

def lifecycle_version = "1.1.1"
implementation "android.arch.lifecycle:livedata:$lifecycle_version"

Use LiveData in the ItemDao

import android.arch.lifecycle.LiveData

fun getAllItems(): LiveData<List<Items>>

Usage

items.observe(this, Observer<List<Item>> {
    // Update a recycler view
    itemList.adapter = ItemAdapter(items.value!!)
})

References

https://developer.android.com/training/data-storage/room/accessing-data#convenience-insert

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