How to rollback transaction in Android Room Database

In this android programming source code example, we are going to rollback transaction in Android Room Database.

You can copy and adopt this source code example to your android project without reinventing the wheel.

Below is a step by step source code to rollback transaction in Android Room Database.

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_margin="15dp">

    <android.support.design.widget.TextInputLayout
        android:id="@+id/nameinput"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
        <EditText
            android:id="@+id/name"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:hint="@string/name"
            android:inputType="textNoSuggestions"
            android:maxLines="1"
            android:singleLine="true" />
    </android.support.design.widget.TextInputLayout>

    <Button
        android:id="@+id/transBtn"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="@color/colorAccent"
        android:layout_below="@id/nameinput"
        android:textColor="#ffffff"
        android:text="Transaction"/>

</RelativeLayout>

MainActivity.java

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
import io.reactivex.Completable;
import io.reactivex.CompletableObserver;
import io.reactivex.android.schedulers.AndroidSchedulers;
import io.reactivex.disposables.Disposable;
import io.reactivex.functions.Action;
import io.reactivex.schedulers.Schedulers;

public class RoomDatabaseActivity8 extends AppCompatActivity {
    private EditText name;
    private Button transBtn;
    private UserDatabase userDatabase;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_room_database8);
        name = (EditText) findViewById(R.id.name);
        transBtn = (Button) findViewById(R.id.transBtn);
        userDatabase = UserDatabase.getInstance(this);
        transBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                String enteredname = name.getText().toString();
                deleteUser(enteredname);
            }
        });
    }

    private void deleteUser(final String ename){
        runInTransaction(new Runnable() {
            @Override
            public void run() {
                Completable.fromAction(new Action() {
                    @Override
                    public void run() throws Exception {
                        User user = new User(1, ename);
                        userDatabase.userDAO().delete(user);
                    }
                }).observeOn(AndroidSchedulers.mainThread())
                        .subscribeOn(Schedulers.io())
                        .subscribe(new CompletableObserver() {
                            @Override
                            public void onSubscribe(Disposable d) {
                            }

                            @Override
                            public void onComplete() {
                                Toast.makeText(RoomDatabaseActivity8.this, "Data deleted successfully",Toast.LENGTH_LONG).show();
                            }

                            @Override
                            public void onError(Throwable e) {
                                Toast.makeText(RoomDatabaseActivity8.this, "Data not deleted",Toast.LENGTH_LONG).show();
                            }
                        });
                User user = new User(ename);
                userDatabase.userDAO().insert(user);
            }
        });
    }

    public void runInTransaction(Runnable body){
        userDatabase.beginTransaction();
        try{
            body.run();
            userDatabase.setTransactionSuccessful();
        }finally {
            userDatabase.endTransaction();
        }
    }
}

UserDatabase.java

package com.bluapp.androidview.RoomDatabase;

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.content.Context;
import android.support.annotation.NonNull;

import java.util.concurrent.Executors;

@Database(entities = { User.class }, version = 1, exportSchema = false)
public abstract class UserDatabase extends RoomDatabase {
    private static final String DB_NAME ="UserDb";
    private static UserDatabase instance;
    public abstract UserDAO userDAO();    

    public synchronized static UserDatabase getInstance(final Context context) {
        if (instance == null) {
            instance = Room.databaseBuilder(context, UserDatabase.class, DB_NAME)
                                        .allowMainThreadQueries().build();
        }
        return instance;
    }
}

User.java

package com.bluapp.androidview.RoomDatabase;

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

@Entity(tableName = "users")
public class User {
    @PrimaryKey(autoGenerate = true)
    private int id;
    @ColumnInfo(name = "name")
    private String name;
    public User(int id, String name){
        this.id = id;
        this.name = name;
    }
    @Ignore
    public User(String name){
        this.name = name;
    }
    public int getId() {
        return id;
    }
    public String getName() {
        return name;
    }
}

UserDAO.java

package com.bluapp.androidview.RoomDatabase;

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.ArrayList;
import java.util.List;

@Dao
public interface UserDAO {
    @Query("select * from users")
    List<User> getuserList();

    @Insert
    public void insert(User user);

    @Update
    public void update(User user);

    @Delete
    public void delete(User user);

}

build.gradle

implementation 'io.reactivex.rxjava2:rxjava:2.1.9'
implementation 'io.reactivex.rxjava2:rxandroid:2.0.1'
implementation 'android.arch.persistence.room:runtime:1.0.0' 
annotationProcessor 'android.arch.persistence.room:compiler:1.0.0'

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