Room Persistence @Relation working in Java but not

问题:

Base on my previous question (Android Persistence room: "Cannot figure out how to read this field from a cursor") which I got to work thanks the feedback, I implemented the same example in Kolin (see code below). I had to make some minor changes like the parameters that are now passed to a the query which have to be passed as "p0", "p1" etc. Now in Kotlin I get the following error related to the UserWithPets class:

error: Cannot figure out how to read this field from a cursor. e: private java.util.List pets;

@Dao
interface UserDAO {   

    @get:Query("SELECT * FROM user")
    val all: LiveData<List<User>>

    @Insert
    fun insertUser(user: User) //single one

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    fun insertUsers(vararg users: User)

    @Query("SELECT * FROM User")
    fun loadUsersWithPets(): LiveData<List<UserWithPets>>

}


@Entity
class Pet( var name: String?,  var ownerId: Int,@PrimaryKey(autoGenerate = true)var id:Int)



@Dao
interface PetDAO {
    @Query("SELECT * FROM pet")
    val all: List<Pet>

    @Query("SELECT * FROM pet WHERE id IN (:p0)")
    fun loadAllByIds(petIds: IntArray): List<Pet>


    @Insert
    fun insert(pet: Pet)

    @Insert
    fun insertAll(vararg pets: Pet)

    @Delete
    fun delete(user: Pet)
}


class UserWithPets {
    @Embedded
    var user: User? = null

    @Relation(parentColumn = "id", entityColumn = "ownerId", entity = Pet::class)
    var pets: List<Pet>? = null
}

It appears that if I write the UserWithPets class in Java it will work fine, but fails when it is written in Kotlin. Any ideas what is wrong? Is this an annotation processing issue?

回答1:

Try to update room to 1.0.0-alpha8 and add List<@JvmSuppressWildcards Pet>.

回答2:

try changing your query @Query("SELECT * FROM pet WHERE id IN (:p0)")

to @Query("SELECT * FROM pet WHERE id IN (:petIds)")

There was an issue between kotlin and Room lib, Kotlin wasn't preserving the actual parameter names of the arguments properly, so (:p0)/(:arg0) was work around that, its resolved now.

I hope this will resolve the issue