Android架构组件Room指南

@Entity(tableName = "user" 
  indices = {@Index(value = {"first_name", "last_name"})})
public class User {
 @PrimaryKey
 private int uid;
 @ColumnInfo(name = "first_name")
 private String firstName;
 @ColumnInfo(name = "last_name")
 private String lastName;
 @Ignore
 public User(String firstName, String lastName) {
 this.uid = UUID.randomUUID().toString();
 this.firstName = firstName;
 this. lastName = lastName;
 }
 public User(String id, String firstName, String lastName) {
 this.uid = id;
 this.firstName = userName;
 this. lastName = userName;
 }
 // Getters and setters
}

@Entity(foreignKeys = @ForeignKey(entity = User.class,
     parentColumns = "id",
     childColumns = "user_id"))
class Book {
 @PrimaryKey
 public int bookId;
 public String title;
 @ColumnInfo(name = "user_id")
 public int userId;
}

class Address {
 public String street;
 public String state;
 public String city;
 @ColumnInfo(name = "post_code")
 public int postCode;
}
@Entity
class User {
 @PrimaryKey
 public int id;
 public String firstName;
 @Embedded
 public Address address;
}

@Dao
public interface UserDao {
 @Query("SELECT * FROM user")
 List<User> getAll();
 @Query("SELECT * FROM user WHERE uid IN (:userIds)")
 List<User> loadAllByIds(int[] userIds);
 @Query("SELECT * FROM user WHERE first_name LIKE :first AND "
  + "last_name LIKE :last LIMIT 1")
 User findByName(String first, String last);
 @Insert
 void insertAll(List<User> users);
 @Insert(onConflict = OnConflictStrategy.REPLACE)
 public void insertUsers(User... users);
 @Delete
 void delete(User user);
 @Update
 public void updateUsers(List<User> users);
}

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

@Query("SELECT * FROM user WHERE uid IN (:userIds)")
List<User> loadAllByIds(int[] userIds);
@Query("SELECT * FROM user WHERE first_name LIKE :first AND "
  + "last_name LIKE :last LIMIT 1")
User findByName(String first, String last);

public class NameTuple {
 @ColumnInfo(name="first_name")
 public String firstName;

 @ColumnInfo(name="last_name")
 public String lastName;
}

@Query("SELECT first_name, last_name FROM user")
public List<NameTuple> loadFullName();

@Query("SELECT first_name, last_name FROM user WHERE region IN (:regions)") 
public LiveData<List<User>> loadUsersFromRegionsSync(List<String> regions);
Flowablbe<T> Maybe<T> Single<T>:
Room 支持返回RxJava2 的Flowablbe, Maybe和Single对象，对于使用RxJava的项目可以很好的衔接， 但需要在gradle添加该依赖：android.arch.persistence.room:rxjava2。
@Query("SELECT * from user where id = :id LIMIT 1")
public Flowable<User> loadUserById(int id);

@Dao
public interface MyDao {
 @Query("SELECT * FROM book "
  + "INNER JOIN loan ON loan.book_id = book.id "
  + "INNER JOIN user ON user.id = loan.user_id "
  + "WHERE user.name LIKE :userName")
 public List<Book> findBooksBorrowedByNameSync(String userName);
}

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

AppDatabase db = Room.databaseBuilder(getApplicationContext(),
 AppDatabase.class, "database-name").build();

Room.databaseBuilder(getApplicationContext(), MyDb.class, "database-name")
 .addMigrations(MIGRATION_1_2, MIGRATION_2_3).build();
static final Migration MIGRATION_1_2 = new Migration(1, 2) {
 @Override
 public void migrate(SupportSQLiteDatabase database) {
 database.execSQL("CREATE TABLE `Fruit` (`id` INTEGER, "
  + "`name` TEXT, PRIMARY KEY(`id`))");
 }
};
static final Migration MIGRATION_2_3 = new Migration(2, 3) {
 @Override
 public void migrate(SupportSQLiteDatabase database) {
 database.execSQL("ALTER TABLE Book "
  + " ADD COLUMN pub_year INTEGER");
 }
};

@Database(entities = {User.class}, version = 2)
public abstract class UsersDatabase extends RoomDatabase {
…
static final Migration MIGRATION_1_2 = new Migration(1, 2) {
 @Override
 public void migrate(SupportSQLiteDatabase database) {
 // Since we didn't alter the table, there's nothing else to do here.
 }
};
…
database = Room.databaseBuilder(context.getApplicationContext(),
 UsersDatabase.class, "Sample.db")
 .addMigrations(MIGRATION_1_2)
 .build();

public class Converters {
 @TypeConverter
 public static Date fromTimestamp(Long value) {
 return value == null ? null : new Date(value);
 }
 @TypeConverter
 public static Long dateToTimestamp(Date date) {
 return date == null ? null : date.getTime();
 }
}

@Database(entities = {User.class}, version = 1)
@TypeConverters({Converters.class})
public abstract class AppDatabase extends RoomDatabase {
 public abstract UserDao userDao();
}
@Entity
public class User {
 ...
 private Date birthday;
}