房间多对多错误：查询返回的列没有字段

Question

我有一个包含两个实体的房间数据库，并且是多对多关系 但出现查询错误

我在使用 android room 时遇到错误

错误：查询返回的列在 com.example.sporttracker.room.relations.WorkoutWithExercises 中没有字段 [nameOfWorkout,dateOfWorkout,caloriesBurntInWorkout,workoutId]，即使它们被注释为非空或原始。查询返回的列：[amountExercise,caloriesBurntProExercise,exerciseName,exerciseId] 公共抽象 androidx.lifecycle.LiveData> fetchWorkoutWithExercises(long id);

我的实体：

@Entity(tableName = "exercise_table")
data class Exercise(
@NonNull
@ColumnInfo(name = "amountExercise")
var amountExercise: String,

@NonNull
@ColumnInfo(name = "caloriesBurntProExercise")
var caloriesBurntProExercise: String,

@NonNull
@ColumnInfo(name = "exerciseName")
var exerciseName: String,

@PrimaryKey(autoGenerate = true)
@NonNull
@ColumnInfo(name = "exerciseId")
var exerciseId: Long = 0L

---

@Entity(tableName = "workout_table")
data class Workout(
@NonNull
@ColumnInfo(name = "nameOfWorkout")
var nameOfWorkout: String,

@NonNull
@ColumnInfo(name = "dateOfWorkout")
var dateOfWorkout: String,

@NonNull
@ColumnInfo(name = "caloriesBurntInWorkout")
var caloriesBurntInWorkout: String,

@PrimaryKey(autoGenerate = true)
@NonNull
@ColumnInfo(name = "workoutId")
var workoutId: Long = 0L

我的道：

@Query("""
    SELECT *
    FROM exercise_table
    WHERE exerciseId = :id
    """)
fun fetchWorkoutWithExercises(id: Long): LiveData<List<WorkoutWithExercises>>

我的关系：

data class WorkoutWithExercises(
@Embedded val workout: Workout,
@Relation(
    parentColumn = "workoutId",
    entityColumn = "exerciseId",
    associateBy = Junction(ExerciseWorkoutCrossRef::class)
)
val exercises: List<Exercise>
)

---

// region: entity
@Entity(

primaryKeys = ["exerciseId", "workoutId"],
foreignKeys = [
    ForeignKey(
        entity = Exercise::class,
        parentColumns = ["exerciseId"],
        childColumns = ["exerciseId"]
    ),
    ForeignKey(
        entity = Workout::class,
        parentColumns = ["workoutId"],
        childColumns = ["workoutId"]
        )
      ]
  )
  //endregion

 // region: data class
 data class ExerciseWorkoutCrossRef(
   @ColumnInfo(name = "exerciseId")
   val exerciseId: Long,
    @ColumnInfo(name = "workoutId", index = true)
    val workoutId: Long
 )
 //endregion

Answer 1

我相信您可以通过修改 WorkoutWithExercises 来定义 exercise_table 和 ExerciseWorkoutCrossRef 表之间的关系来解决此问题。

• 外键只定义约束（规则）而不是关系（即使隐式存在）。

我相信将 WorkoutWithExercises 更改为如下代码会推动您前进：-

data class WorkoutWithExercises(
    @Embedded val workout: Workout,
    @Relation(
        entity = ExerciseWorkoutCrossRef::class,
        parentColumn = "workoutId",
        entityColumn = "workoutId"
    )
    val workoutwithexercises: List<WorkoutWithExercises>,
    @Relation(
        entity = Exercise::class,
        entityColumn = "exerciseId",
        parentColumn = "workoutid",
        associateBy = (Junction(ExerciseWorkoutCrossRef::class))
    )
    val exercises: List<Exercise>
)

即第一个 @Relation 描述了 Workout 和 ExerciseWorkoutCrossRef 表之间的关系 第二个@Relation 描述了ExerciseWorkoutCrossRef 和exercise_table 之间的关系。

（因此所有三个表都是相关的，而不是 2 个）

我相信正在发生的事情是您从 exercise_table 获取行但是无法链接（通过 ExerciseWorkoutCrossRef 表）以获取适当的 workout_table 行和列，因此是编译消息。