Android Room Persistence Library

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();

manish choudhary 2 January 2018

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Android Room Persistence Library

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