How to delete a row in Android Room Database

In this android programming source code example, we are going to delete a row 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 delete a row 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/deleteBtn"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="@color/colorAccent"
        android:layout_below="@id/nameinput"
        android:textColor="#ffffff"
        android:text="Delete"/>



</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 RoomDatabaseActivity3 extends AppCompatActivity {
    private EditText name;
    private Button delete;
    private UserDatabase userDatabase;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_room_database3);
        name = (EditText) findViewById(R.id.name);
        delete = (Button) findViewById(R.id.deleteBtn);
        userDatabase = UserDatabase.getInstance(this);
        delete.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                String enteredname = name.getText().toString();
                deleteUser(enteredname);
            }
        });
    }

    private void deleteUser(final String ename){
        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(RoomDatabaseActivity3.this, "Data deleted successfully",Toast.LENGTH_LONG).show();
                    }

                    @Override
                    public void onError(Throwable e) {
                        Toast.makeText(RoomDatabaseActivity3.this, "Data not deleted",Toast.LENGTH_LONG).show();
                    }
                });
    }
}

UserDatabase.java

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

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

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'