Android Room Persistence Library

manish choudhary

2 January 2018

The Room persistence library provides an abstraction layer over SQLite to allow fluent database access while harnessing the full power of SQLite.

Add the Google Maven repository:

allprojects {
    repositories {
        jcenter()
        google()
    }
}

allprojects {

repositories {

jcenter()

google()

}

Add this dependencies in module build.gradle:

compile 'android.arch.persistence.room:runtime:' + rootProject.archRoomVersion;
annotationProcessor 'android.arch.persistence.room:compiler:' + rootProject.archRoomVersion;

1 2	compile 'android.arch.persistence.room:runtime:' + rootProject.archRoomVersion; annotationProcessor 'android.arch.persistence.room:compiler:' + rootProject.archRoomVersion;

Now let’s begin with Room persistence library create a class User. User Class is annotated with @Entity and name of the table. To make field primary key, you need to annotate a field with @PrimaryKey and property autoGenerate which assign automatic IDs.

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

    @PrimaryKey(autoGenerate = true)
    private int id;

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

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

    @ColumnInfo(name = "age")
    private int age;

    public int getId() {
        return uid;
    }

    public void setId(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 int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

}

@Entity(tableName = "user")

public class User {

@PrimaryKey(autoGenerate = true)

private int id;

@ColumnInfo(name = "first_name")

private String firstName;

@ColumnInfo(name = "last_name")

private String lastName;

@ColumnInfo(name = "age")

private int age;

public int getId() {

return uid;

}

public void setId(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 int getAge() {

return age;

}

public void setAge(int age) {

this.age = age;

}

Create a data access object using an interface. This class is annotated with @Dao annotation. Room will generate an implementation of defined methods. There are four annotations @Query, @Insert.

@Dao
public interface UserDao {

    @Query("SELECT * FROM user")
    List<User> getAll();

    @Insert
    void insertAll(User... users);

}

@Dao

public interface UserDao {

@Query("SELECT * FROM user")

List<User> getAll();

@Insert

void insertAll(User... users);

}

Create a database holder called AppDatabase extends RoomDatabase, we will define list of entities and database version. Class is annotated with @Database annotation. It is good practice to use singleton approach for the database, so you need to create an static method which will return instance of AppDatabase.

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

    private static AppDatabase mINSTANCE;

    public abstract UserDao userDao();

    public static AppDatabase getAppDatabase(Context context) {
        if (mINSTANCE == null) {
            mINSTANCE =
                    Room.databaseBuilder(context.getApplicationContext(), AppDatabase.class, "demo-database")
                            .allowMainThreadQueries()
                            .build();
        }
        return mINSTANCE;
    }

    public static void destroyInstance() {
        mINSTANCE = null;
    }
}

@Database(entities = {User.class}, version = 1)

public abstract class AppDatabase extends RoomDatabase {

private static AppDatabase mINSTANCE;

public abstract UserDao userDao();

public static AppDatabase getAppDatabase(Context context) {

if (mINSTANCE == null) {

mINSTANCE =

Room.databaseBuilder(context.getApplicationContext(), AppDatabase.class, "demo-database")

.allowMainThreadQueries()

.build();

}

return mINSTANCE;

}

public static void destroyInstance() {

mINSTANCE = null;

}

For insert data in database and get User list from the data:

    User user = new User();
    user.setFirstName("Ajay");
    user.setLastName("Saini");
    user.setAge(25);
// Get instance of AppDatabase
AppDatabase db=AppDatabase.getAppDatabase()
// Insert data into Database
db.userDao().insertAll(user);
// Get the list of User from the Database
List<User> user=db.userDao().getAll();

User user = new User();

user.setFirstName("Ajay");

user.setLastName("Saini");

user.setAge(25);

// Get instance of AppDatabase

AppDatabase db=AppDatabase.getAppDatabase()

// Insert data into Database

db.userDao().insertAll(user);

// Get the list of User from the Database

List<User> user=db.userDao().getAll();