I made a screen like the image.

As you can see, the Set information items are in the red box.

I want to store these data in Room DB.

The red box is composed of Workout Class, and the blue box (WorkoutSetInfo class) is included in it.

I just want to get a list of set information from Room.

But I wrote a query to get a list of set information, I got the following error:

error: The columns returned by the query does not have the fields [id,set,weight,reps] in com.example.lightweight.data.db.entity.WorkoutSetInfo even though they are annotated as non-null or primitive. Columns returned by the query: [sets]
    public abstract androidx.lifecycle.LiveData<java.util.List<com.example.lightweight.data.db.entity.WorkoutSetInfo>> getWorkoutSetInfoList()

There have been several similar questions to mine, but I still haven't been able to solve them. How can I get only the list of set information?

---

WorkoutSetInfo

data class WorkoutSetInfo(
    val id: String = UUID.randomUUID().toString(), // For comparison in DiffUtil.
    val set: Int,
    val weight: String = "",
    val reps: String = ""
)

Workout

@Entity
data class Workout(
    @PrimaryKey(autoGenerate = true)
    val id: Int,
    val title: String = "",
    val unit: String = "kg",
    val memo: String = "",
    var sets: List<WorkoutSetInfo> = emptyList()
)

DAO

@Dao
interface WorkoutDao {
    @Query("SELECT sets FROM Workout")
    fun getWorkoutSetInfoList() : LiveData<List<WorkoutSetInfo>>

    @Insert
    fun insert(workout: Workout)
}

Repository

class WorkoutRepository(private val workoutDao : WorkoutDao, title: String) {
    val workout = Workout(0, title)
    var setInfoList : ArrayList<WorkoutSetInfo> = arrayListOf()
    
    val _items: LiveData<List<WorkoutSetInfo>> = workoutDao.getWorkoutSetInfoList()

    fun add(item: WorkoutSetInfo) {
        setInfoList.add(item)
        workout.sets = setInfoList

        workoutDao.insert(workout)
    }
}

ViewModel

class DetailViewModel(application: Application, title: String) : ViewModel() {
    private val repository: WorkoutRepository

    private lateinit var _items: LiveData<List<WorkoutSetInfo>>
    val items = _items
    private val list: List<WorkoutSetInfo>
        get() = _items.value ?: emptyList()

    init {
        val workoutDao = DetailDatabase.getDatabase(application)!!.workoutDao()
        repository = WorkoutRepository(workoutDao, title)
        _items = repository._items
    }

    fun addDetail() {

        viewModelScope.launch(Dispatchers.IO){
            val item = WorkoutSetInfo(set = list.size 1)
            repository.add(item)
        }
    }
}

CodePudding user response：

You are trying to save a list of complex object in a column. Room does not know how to save that.

var sets: List<WorkoutSetInfo> = emptyList() <-- this is complex

Remember room is just sqlite underneath and your entities represent tables. Sqlite recognizes basic types but storing a list of complex objects is not something it can do by default. You can explore TypeConverters as a solution if you want to save this object in the same table.

See below for a relational solution that utilizes separate tables:

What you are looking for here is a one-to-many relation. A single Workout can have one or more WorkoutSetInfo

In the world of relational databases, you can represent this by having a separate table for WorkoutSetInfo and use the id from id of the work out to create a relation.

data class WorkoutSetInfo(
    val id: String = UUID.randomUUID().toString(), // For comparison in DiffUtil.
    val set: Int,
    val weight: String = "",
    val reps: String = "",
    val workoutId: String // <-- this is the id of the workout that this set is associated with
)

Once you have that you can either write a join query or use a data object to query as defined here

You can have something like this:

data class WorkoutWithSets(
    @Embedded val workout: Workout,
    @Relation(
        parentColumn = "id",
        entityColumn = "workoutId"
    )
    val sets: List<WorkoutSetInfo>
)

And use something like this to query it

    @Transaction
    @Query("SELECT * FROM Workout WHERE id = :workoutId")
    fun getWorkoutWithSets(workoutId: String) : LiveData<WorkoutWithSets>

This will give the workout for the given id along with all the sets that match that workout id in the set table.

CodePudding user response：

currently your posted error is telling that set is not found in selection

data class WorkoutSetInfo(
    val id: String = UUID.randomUUID().toString(), // For comparison in DiffUtil.
    val set: Int,//Add Any value or make it nullable here for get temp rid of this error
    val weight: String = "",
    val reps: String = ""
)

but As Naveeds Answer, you have to use typeConvertor or solve this problem with relational database type without implementing this typeconvertor or relational structure room will give you error