Room db migration

.java

package net.ahammad.roomsample;

import android.arch.persistence.db.SupportSQLiteDatabase;
import android.arch.persistence.room.Database;
import android.arch.persistence.room.Room;
import android.arch.persistence.room.RoomDatabase;
import android.arch.persistence.room.migration.Migration;
import android.content.Context;
import android.support.annotation.NonNull;
import android.util.Log;

/**
 * Created by alahammad on 10/2/17.
 */

@Database(entities = {User.class}, version = 2)
public abstract class AppDatabase extends RoomDatabase {
    private static AppDatabase INSTANCE;
    private static final String DB_NAME = "database-name";

    static final Migration MIGRATION_1_2 = new Migration(1, 2) {
        @Override
        public void migrate(@NonNull SupportSQLiteDatabase database) {
            database.execSQL("ALTER TABLE users "
                    +"ADD COLUMN address TEXT");
        }
    };


    public static AppDatabase getDatabase(final Context context) {
        if (INSTANCE == null) {
            synchronized (AppDatabase.class) {
                if (INSTANCE == null) {
                    INSTANCE = Room.databaseBuilder(context.getApplicationContext(),
                            AppDatabase.class, DB_NAME)
                            .addMigrations(MIGRATION_1_2)
                            .build();
                }
            }
        }

        return INSTANCE;
    }

    public abstract UserDao userDao();
}

//// LocalCacheManager changes ////
    private LocalCacheManager(Context context) {
        db = AppDatabase.getDatabase(context);
    }

    public void findUserById(final DatabaseCallback databaseCallback, int id, final boolean delete) {
        db.userDao().findById(id).subscribeOn(Schedulers.newThread()).observeOn(AndroidSchedulers.mainThread()).subscribe(new Consumer<User>() {

            @Override
            public void accept(@io.reactivex.annotations.NonNull User user) throws Exception {
                if (user != null) {
                    if (!delete)
                        updateUser(databaseCallback, user);
                    else
                        deleteUser(databaseCallback, user);
                }
            }
        });
    }
    
    
    //// MainActivity changes /////
        private void getUser(int id, final boolean delete) {
        LocalCacheManager.getInstance(this).findUserById(this, id, delete);
    }


   //// User.java /////
package net.ahammad.roomsample;

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

/**
 * Created by alahammad on 10/2/17.
 */

@Entity(tableName = "users")
public class User {
    @PrimaryKey(autoGenerate = true)
    private int uid;

    @ColumnInfo(name = "first_name")
    private String firstName;

    @ColumnInfo(name = "last_name")
    private String lastName;

    @ColumnInfo(name = "address")
    private String address;

    public User(String firstName, String lastName, String address) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.address = address;
    }

    public int getUid() {
        return uid;
    }

    public void setUid(int uid) {
        this.uid = uid;
    }

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }
}