目录
- 1. 创建实体类User
- 2. 创建DAO
- 3. 数据库
- 4. 使用
Room的三个主要组件：
- 数据库类，用于保存数据库并作为应用持久性数据底层连接的主要访问点。
- 数据实体，@Entity，表示数据库中的表。
- 数据访问对象 (DAO)，@Dao，提供查询、更新、插入和删除数据的方法。
build.gradle添加
dependencies {
def room_version = "2.4.3"
implementation "android.arch.persistence.room:runtime:$room_version"
annotationProcessor "android.arch.persistence.room:compiler:$room_version"
implementation "android.arch.persistence.room:rxjava2:$room_version"
testImplementation "android.arch.persistence.room:testing:$room_version"
}
1. 创建实体类User
@Entity(tableName = "users")
public class User {
@PrimaryKey
public int uid;
@ColumnInfo(name = "first_name")
public String firstName;
@ColumnInfo(name = "last_name")
public String lastName;
}
@Entity实体类，users表的名称，不加默认user
@ColumnInfo列名
@PrimaryKey主键
2. 创建DAO
@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(onConflict = OnConflictStrategy.REPLACE)
void insertAll(User... users);
@Delete
void delete(User user);
}
增，删，改：将实例与表的主键进行匹配
查询结果将自动映射到对应类型的字段，若未映射将报警告
3. 数据库
抽象类AppDatabase 定义数据库配置，并作为应用对持久性数据的主要访问点，扩展了RommDataBase
@Database(entities = {User.class}, version = 1, exportSchema = false)
public abstract class AppDataBase extends RoomDatabase {
public abstract UserDao userDao();
}
4. 使用
AppDataBase db = Room.databaseBuilder(getApplicationContext(),
AppDataBase.class, "database-name").build();
for (int i = 0; i < 10; i++) {
User user = new User();
user.uid = i;
user.firstName = "Shell" + i;
user.lastName = "Hub" + i;
db.userDao().insertAll( user);
List<User> userList = db.userDao().getAll();
for(User user1 : userList) {
Log.d("mip",""+user1.firstName);
}
}
为了节约获取数据库的时间和资源，采取单例模式
简单实现：
public class Utils {
private static AppDataBase db = null;
private static Context context = null;
public static AppDataBase getDb(){
if( db == null) {
db = Room.databaseBuilder(context,
AppDataBase.class, "database-name").build();
}
return db;
}
public static void setContext(Context context){
Utils.context = context;
}
}
调用
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Utils.setContext(getApplicationContext());
new Thread(new Runnable() {
@Override
public void run() {
AppDataBase db = Utils.getDb();
for (int i = 0; i < 10; i++) {
User user = new User();
user.uid = i;
user.firstName = "Shell" + i;
user.lastName = "Hub" + i;
db.userDao().insertAll( user);
List<User> userList = db.userDao().getAll();
for(User user1 : userList) {
Log.d("mip",""+user1.firstName);
}
}
}
}).start();
}
}
路过的大佬们有更好的单例实现请告诉我一下，
提供CDN加速