Android使用Room操作数据库流程详解

时间:2022-11-19 Flynn_MIMD 人气:0

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，

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