Room使用

表的定义

@Entity

  • @PrimaryKey
    • 主键
    • autoGenerate=true  自增长
  • @ColumnInfo
    • 字段
    • name=”jett”  字段名
  • @Ignore
    • 表示一个属性不加入生成表的字段，只是临时使用

数据访问对象的定义

@Dao

  • 定义Dao层
    • @Dao
      public interface StudentDao {
      …..
      }
    • @Query
      • 查询
        • @Query(“select * from Student”)

List getAll();
- 可以把参数加入查询语句
- //查询一条记录
@Query(“select * from Student where name like:name”)
Student findByName(String name);
//查找部份ID号的记录
@Query(“select * from Student where uid in (:userIds)”)
List getAllId(int[] userIds);

数据库的定义

@Database

  • entities={Student.class}
    • 定义数据库中包含的表
  • version=1
    • 数据库版本号
  • @Database(entities = {Student.class},version = 1)
    public abstract class AppDatabase extends RoomDatabase {
    public abstract StudentDao userDao();
    }

返回例的子集

public class NameTuple {

1
2
3
4
5
@ColumnInfo(name="first_name")
public String firstName;

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

}

@Dao
public interface MyDao {
@Query(“SELECT first_name, last_name FROM user”)
public List loadFullName();
}

表与表之间的实体联系

@Entity(foreignKeys = @ForeignKey(entity = User.class,

1
2
parentColumns = "id",
childColumns = "user_id"))

public class Book {
@PrimaryKey
public int bookId;

1
2
3
4
public String title;

@ColumnInfo(name = "user_id")
public int userId;

}

创建嵌套对象

public class Address {

1
2
3
4
5
6
public String street;
public String state;
public String city;

@ColumnInfo(name = "post_code")
public int postCode;

}

@Entity
public class User {
@PrimaryKey
public int id;

1
2
3
4
public String firstName;

@Embedded
public Address address;

}

传递参数集合

@Dao

public interface MyDao {
@Query(“SELECT first_name, last_name FROM user WHERE region IN (:regions)”)
public List loadUsersFromRegions(List regions);
}

可观察的查询

@Dao

public interface MyDao {
@Query(“SELECT first_name, last_name FROM user WHERE region IN (:regions)”)
public LiveData loadUsersFromRegionsSync(List regions);
}

@Dao

public interface MyDao {
@Query(“SELECT user.name AS userName, pet.name AS petName “

  • “FROM user, pet “
  • “WHERE user.id = pet.user_id”)
    public LiveData loadUserAndPetNames();

// You can also define this class in a separate file, as long as you add the
// “public” access modifier.
static class UserPet {
public String userName;
public String petName;
}
}

支持Rxjava

@Dao

public interface MyDao {
@Query(“SELECT * from user where id = :id LIMIT 1”)
public Flowable loadUserById(int id);
}

返回Cursor

@Dao

public interface MyDao {
@Query(“SELECT * FROM user WHERE age > :minAge LIMIT 5”)
public Cursor loadRawUsersOlderThan(int minAge);
}

Room数据库迁移

Room.databaseBuilder(getApplicationContext(), MyDb.class, “database-name”)

1
.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”);
    }
    };

XMind - Trial Version