2 也许在ROOM+RXJAVA中查询

Question

我在ANDROID应用程序中使用ROOM + RXJAVA作为SQLITE数据库。

我有一个问题。我需要插入一条新记录，但在此之前查询更多信息。

我使用 Maybe、Single 和 Completable。

我需要执行以下操作：

1 个查询。需要查出牛的ID：

@Query("SELECT " + COW_COLUMN_ID + " FROM " + TABLE_COW
        + " WHERE " + COW_COLUMN_RFID + " = :rfid ")
Maybe<Integer> getIdCowByRFID(String rfid);

2查询。我需要创建一个权重并将生成的牛 ID 添加到其中

@Insert
Maybe<Long> insert(WeightingDbEntity weighting);

如何正确做？将异步查询嵌套在另一个异步查询中并不完全正确。请告诉我。

如果你进行同步查询，那么就没有问题，因为1个查询的结果已经可用，如果需要的话，执行2个查询。在这种情况下，我是否需要向ROOM添加同步查询（allowMainThreadQueries）？或者我应该采取不同的做法？如何将 2 个 Maybe 查询合并为一个并以事务模式（@Transaction）执行？

我在这里读到：https://developer.android.com/reference/android/arch/persistence/room/Transaction

但是这个例子是关于同步查询的。以及如何使用 Maybe 正确地做到这一点？

Answer 1

使用带注释的

@Dao

而不是

abstract class

（因为后者不允许带有主体的方法）。如果您随后使用

interface

和

@Query("")

注释放在具有可以调用先前定义的方法的主体的方法之前。

带有空查询的

@Transaction
• 会愚弄（如果这是正确的词）Room 认为数据库正在被访问，从而将方法包装在事务中。
因此，如果

@Query

和

insert

位于同一个抽象类中（简化了问题），那么你可以得到类似的东西（注意我从未使用过 RXJava）：-getIdCowByRFID

以下是显示上述技术的屏幕截图，其中包含 

@Query("")
@Transaction
Maybe<Long> doBoth(String rfid, WeightingDbEntity w) {
    Maybe<Integer> id = getIdCowByRFID;
    .... do whatever needs to be done/checked
    return insert(w);
}

注解类，

@Dao

抽象类，其中包含检索

@Database

类的方法（以便编译将检查这些方法）。尽管底层

@Dao

带注释的类不同：-

Answer 2

这是我的 DAO：

@Entity

也许这样更好：

@Insert
public abstract Maybe<Long> insert(WeightingDbEntity weighting);

@Query("SELECT MAX(" + WEIGHTING_COLUMN_ID + ") FROM " + TABLE_WEIGHTING
        + " WHERE " + WEIGHTING_COLUMN_COW_ID + " = :id")
public abstract Maybe<Integer> getMaxIdFromWeightingByCowId(int id);

@Transaction
public Maybe<Long> addWeighting(int idCow, String date, float weight, float weightGain, String description){

    getMaxIdFromWeightingByCowId(idCow).subscribe(new MaybeObserver<>() {
        @Override
        public void onSubscribe(@NonNull Disposable d) {

        }

        @Override
        public void onSuccess(@NonNull Integer idCow) {
            WeightingDbEntity weightingDbEntity = new WeightingDbEntity(idCow, weight, weightGain, date, description);
            insert(weightingDbEntity);
        }

        @Override
        public void onError(@NonNull Throwable e) {

        }

        @Override
        public void onComplete() {

        }
    });
}

或者如果我想在另一个线程中得到结果

  @Insert
public abstract Long insertSync(WeightingDbEntity weighting);

@Query("SELECT MAX(" + WEIGHTING_COLUMN_ID + ") FROM " + TABLE_WEIGHTING
        + " WHERE " + WEIGHTING_COLUMN_COW_ID + " = :id")
public abstract int getMaxIdFromWeightingByCowId(int id);

@Transaction
public Long addWeighting(int idCow, String date, float weight, float weightGain, String description){

    long idCow = getMaxIdFromWeightingByCowId(idCow);

    // Here will be check for  idCow

    WeightingDbEntity weightingDbEntity = new WeightingDbEntity(idCow, weight, weightGain, date, description);
    insert(weightingDbEntity);
}

Answer 3

我有 2 个实体：

牛

   @Query("SELECT MAX(" + WEIGHTING_COLUMN_ID + ") FROM " + TABLE_WEIGHTING
        + " WHERE " + WEIGHTING_COLUMN_COW_ID + " = :id")
public abstract int getMaxIdFromWeightingByCowIdSync(int id);

@Query("SELECT " + WEIGHTING_COLUMN_NUM + " FROM " + TABLE_WEIGHTING
        + " WHERE " + WEIGHTING_COLUMN_ID + " = :id")
public abstract int getNumWeightingByIdSync(int id);

@Insert
public abstract Maybe<Long> insert(WeightingDbEntity weighting);

@Transaction
public Maybe<Long> addWeighting(int idCow, String date, float weight, float weightGain){

    int maxIdWeighting = getMaxIdFromWeightingByCowIdSync(idCow);
    if (maxIdWeighting > 0) {
        int num = getNumWeightingByIdSync(maxIdWeighting);
        if (num > 0) {
            return insert(new WeightingDbEntity(num + 1, idCow, weight, weightGain, maxIdWeighting, date));
        }
    }

    return Maybe.empty();
}

公共类 CowDbEntity {

@Entity(tableName = TABLE_COW)

....

重量

@PrimaryKey(autoGenerate = true)
@ColumnInfo(name = COW_COLUMN_ID)
private int id;

@ColumnInfo(name = COW_COLUMN_RFID)
private String rfid;

@ColumnInfo(name = COW_COLUMN_EAR_TAG)
private String earTag;

@ColumnInfo(name = COW_COLUMN_GROUP)
private String group;

@ColumnInfo(name = COW_COLUMN_TYPE)
private String type;

@ColumnInfo(name = COW_COLUMN_NAME)
private String name;

@ColumnInfo(name = COW_COLUMN_IP_SERVER)
private String ipServer;

@ColumnInfo(name = COW_COLUMN_IS_DELETE)
private boolean isDelete;

...

我也使用DAO：

对于牛

public class WeightingDbEntity {

@PrimaryKey(autoGenerate = true)
@ColumnInfo(name = WEIGHTING_COLUMN_ID)
private int id;

@ColumnInfo(name = WEIGHTING_COLUMN_NUM, defaultValue = "0")
private int num;

@ColumnInfo(name = WEIGHTING_COLUMN_COW_ID)
private int cowId;

@ColumnInfo(name = WEIGHTING_COLUMN_FIXED_WEIGHT)
private float fixedWeight;

@ColumnInfo(name = WEIGHTING_COLUMN_WEIGHT_GAIN, defaultValue = "0")
private float weightGain;

@ColumnInfo(name = WEIGHTING_COLUMN_PREV_RECORD, defaultValue = "0")
private int prevRecord;

@ColumnInfo(name = WEIGHTING_COLUMN_DATE)
private String date;

@ColumnInfo(name = WEIGHTING_COLUMN_WEIGHT_SERVER_ID, defaultValue = "0")
private int idWeightServer;

公共接口 CowDao {

@Dao

...

和重量

@Query("SELECT * FROM " + TABLE_COW)
List<CowDbEntity> getAll();

@Transaction
@Query("SELECT * FROM " + TABLE_COW)
List<CowWithHistories> getAllCowWithHistories();

@Transaction
@Query("SELECT * FROM " + TABLE_COW)
List<CowWithWeightings> getAllCowWithWeightings();

@Insert
long insert(CowDbEntity cow);

@Update
int update(CowDbEntity cow);

@Delete
void delete(CowDbEntity cow);

@Query("SELECT EXISTS (SELECT " + COW_COLUMN_GROUP
        + " FROM " + TABLE_COW
        + " WHERE " + COW_COLUMN_GROUP + " = :group)")
boolean isGroupExist(String group);

@Query("SELECT DISTINCT " + COW_COLUMN_EAR_TAG + " FROM " + TABLE_COW)
List<String> readEarTags();

公共接口WeightingDao {

@Dao

...

我有一个问题。我需要做类似的事情：

@Query("SELECT * FROM " + TABLE_WEIGHTING)
List<WeightingDbEntity> getAll();

@Query("SELECT * FROM " + TABLE_WEIGHTING + " WHERE " + WEIGHTING_COLUMN_ID + " = :id")
WeightingDbEntity getById(long id);

@Transaction
@Query("SELECT * FROM " + TABLE_WEIGHTING)
List<WeightingWithComment> getAllWeightingWithComments();

@Insert
long insert(WeightingDbEntity weighting);

@Update
int update(WeightingDbEntity weighting);

@Delete
void delete(WeightingDbEntity weighting);

或

 @Transaction
insertWeightAndCow(CowDbEntity cow, WeightingDbEntity weighting) {
    insert(cow);
    insert(weighting);
}

但是查询属于不同的类别。我不知道如何做得更好。