Room Database Example

1/  Add room database dependency

implementation 'androidx.room:room-runtime:2.5.2'
annotationProcessor 'androidx.room:room-compiler:2.5.2'

2/  Design xml for room database implementation

*designed a list view to show room database data

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">
    
    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/list_item"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

    <com.google.android.material.floatingactionbutton.FloatingActionButton
        android:id="@+id/id_add_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentEnd="true"
        android:layout_alignParentBottom="true"
        android:layout_marginStart="18dp"
        android:layout_marginTop="18dp"
        android:layout_marginEnd="18dp"
        android:layout_marginBottom="18dp"
        android:src="@android:drawable/ic_input_add"
        app:tint="@color/white" />

</RelativeLayout>

3/  Create a model class for storing data

package com.example.myapplication;

import androidx.room.Entity;
import androidx.room.PrimaryKey;

@Entity(tableName = "user_table")
public class User {

    @PrimaryKey(autoGenerate = true)
    private int id;

    private String name;
    private String email;

    // Constructor
    public User(String name, String email) {
        this.name = name;
        this.email = email;
    }

    // Getters and Setters
    public int getId() { return id; }

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

    public String getName() { return name; }

    public void setName(String name) { this.name = name; }

    public String getEmail() { return email; }

    public void setEmail(String email) { this.email = email; }
}

4/  Create a Dao interface for room database.

package com.example.myapplication;

import androidx.room.Dao;
import androidx.room.Insert;
import androidx.room.Query;
import androidx.room.Delete;
import androidx.room.Update;

import java.util.List;

@Dao
public interface UserDao {

    @Insert
    void insert(User user);

    @Update
    void update(User user);

    @Delete
    void delete(User user);

    @Query("SELECT * FROM user_table WHERE id = :userId LIMIT 1")
    User getUserById(int userId);

    @Query("SELECT * FROM user_table ORDER BY name ASC")
    List<User> getAllUsers();
}

5/  Create room database class

package com.example.myapplication;

import androidx.room.Database;
import androidx.room.Room;
import androidx.room.RoomDatabase;
import android.content.Context;

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

    private static volatile UserDatabase INSTANCE;

    public abstract UserDao userDao();
    
    public static UserDatabase getInstance(Context context) {
        if (INSTANCE == null) {
            synchronized (UserDatabase.class) {
                if (INSTANCE == null) {
                    INSTANCE = Room.databaseBuilder(context.getApplicationContext(),
                                    UserDatabase.class, "user_database")
                            .allowMainThreadQueries()
                            .build();
                }
            }
        }
        return INSTANCE;
    }
}

6/ Post and get data from code

package com.example.myapplication;

import android.os.Bundle;

import androidx.activity.EdgeToEdge;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.graphics.Insets;
import androidx.core.view.ViewCompat;
import androidx.core.view.WindowInsetsCompat;

import java.util.List;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        UserDatabase db = UserDatabase.getInstance(this);
        UserDao userDao = db.userDao();

        User newUser = new User("John Doe", "john.doe@example.com");
        userDao.insert(newUser);


        List<User> userList =  userDao.getAllUsers();
        User user = userDao.getUserById(1);
        System.out.println(user.getName());

    }
}