title: Roomdate: 2021-07-08 23:43:27.536

updated: 2021-07-08 23:53:06.871
url: /?p=270
categories: Jetpack
tags: Jetpack

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);

@Insert

插入

     - [@Insert ](/Insert )

void insert(Student… students);

@Delete

删除

     - [@Delete ](/Delete )

void delete(Student student);

@Update

更新

     - [@Update ](/Update )

void update(Student student);

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 {

@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;

public String title;

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

}

创建嵌套对象

public class Address {

public String street;
public String state;
public String city;

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

}

@Entity

public class User {

@PrimaryKey

public int id;

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”);

}

};

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