Part 3 – DAO & RoomDatabase

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In part 3 of the Architecture Components tutorial, we will create our DAO and RoomDatabase.
The DAO is an interface that defines all the database operations we want to do on our entity. For this we declare methods without a method body and annotate them with @Insert, @Update, @Delete or the generic @Query, where we can pass an SQLite query.
Instead of a Cursor, we can let these queries return instances of our own Java objects, which we can also wrap into LiveData, so our activity or fragment gets notified as soon as a row in the queried database table changes.
The RoomDatabase is an abstract class that ties all the pieces together and connects the entities to their corresponding DAO. Just as in an SQLiteOpenHelper, we have to define a version number and a migration strategy. With fallbackToDestructiveMigration we can let Room recreate our database if we increase the version number.
We create our database in form of a static singleton with the databaseBuilder, where we have to pass our database class and a file name.

DAO documentation:
developer.android.com/training/data-storage/room/accessing-data

Room documentation:
developer.android.com/training/data-storage/room

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Links & DependenciesNoteDao.javaNoteDatabase.javaNote.java

“Adding Components” page with dependencies & instructions:

developer.android.com/topic/libraries/architecture/adding-components

CardView & Design Support Library:

developer.android.com/topic/libraries/support-library/packages#v7-cardview

developer.android.com/topic/libraries/support-library/packages#design

package com.codinginflow.architectureexample;

import android.arch.lifecycle.LiveData;
import android.arch.persistence.room.Dao;
import android.arch.persistence.room.Delete;
import android.arch.persistence.room.Insert;
import android.arch.persistence.room.Query;
import android.arch.persistence.room.Update;

import java.util.List;

@Dao
public interface NoteDao {

    @Insert
    void insert(Note note);

    @Update
    void update(Note note);

    @Delete
    void delete(Note note);

    @Query("DELETE FROM note_table")
    void deleteAllNotes();

    @Query("SELECT * FROM note_table ORDER BY priority DESC")
    LiveData<List<Note>> getAllNotes();
}

package com.codinginflow.architectureexample;

import android.arch.persistence.room.Database;
import android.arch.persistence.room.Room;
import android.arch.persistence.room.RoomDatabase;
import android.content.Context;

@Database(entities = {Note.class}, version = 1)
public abstract class NoteDatabase extends RoomDatabase {

    private static NoteDatabase instance;

    public abstract NoteDao noteDao();

    public static synchronized NoteDatabase getInstance(Context context) {
        if (instance == null) {
            instance = Room.databaseBuilder(context.getApplicationContext(),
                    NoteDatabase.class, "note_database")
                    .fallbackToDestructiveMigration()
                    .build();
        }
        return instance;
    }
}

package com.codinginflow.architectureexample;

import android.arch.persistence.room.Entity;
import android.arch.persistence.room.PrimaryKey;

@Entity(tableName = "note_table")
public class Note {

    @PrimaryKey(autoGenerate = true)
    private int id;

    private String title;

    private String description;

    private int priority;

    public Note(String title, String description, int priority) {
        this.title = title;
        this.description = description;
        this.priority = priority;
    }

    public void setId(int id) {
        this.id = id;
    }

    public int getId() {
        return id;
    }

    public String getTitle() {
        return title;
    }

    public String getDescription() {
        return description;
    }

    public int getPriority() {
        return priority;
    }
}