Cannot save list of Integers in Room Database after adding type converter in Database and the entity-CodePudding

My Entity

@Entity(tableName = "doctor_table")
data class DoctorEntity(
    @PrimaryKey(autoGenerate = true)
    var id : Int = AppUtil.defId,
    var doc_id : Int = AppUtil.defId,
    var name : String = AppUtil.defString,
    @field:TypeConverters(IntTypeConverter::class)
    var days : List<Int> = AppUtil.emptyIntArray,
    @field:TypeConverters(LongTypeConverter::class)
    var numbers : List<Long> = AppUtil.emptyLongArray,
    @field:TypeConverters(IntTypeConverter::class)
    var clinic_ids : List<Int> = AppUtil.emptyIntArray
    )

The empty int array : val emptyIntArray = arrayListOf<Int>()

IntTypeConverter class:

class IntTypeConverter {
    @TypeConverter
    fun saveIntList(list: List<Int>): String? {
        return Gson().toJson(list)
    }

    @TypeConverter
    fun getIntList(list: List<Int>): List<Int> {
        return Gson().fromJson(
            list.toString(),
            object : TypeToken<List<Int?>?>() {}.type
        )
    }

DB class:

@Database(
    entities = [DoctorEntity::class, ClinicEntity::class,
        DocClinicEntity::class, DocTreatmentEntity::class,
               TreatmentEntity::class],
    version = 1,
    exportSchema = false
)
@TypeConverters(LongTypeConverter::class,IntTypeConverter::class)

abstract class Db : RoomDatabase() {
    abstract fun getDao(): DbDao
}

I am using hilt to inject the DB @Module @InstallIn(SingletonComponent::class) object AppModules {

@Provides
@Singleton
fun provideDatabase(
    @ApplicationContext app: Context
) = Room.databaseBuilder(
    app,
    Db::class.java,
    "medical_db.db"
).fallbackToDestructiveMigration()
    .build()

}

The error while trying to run the app.

\room\entities\DoctorEntity.java:15: error: Cannot figure out how to save this field into database. You can consider adding a type converter for it.
    private java.util.List<java.lang.Integer> days;

What am I missing ??

CodePudding user response：

In your second type convertor, you should input a String instead of a List because you are saving a String representation of you list (according to your first convertor).

Something like this:

@TypeConverter
fun getIntList(list: String): List<Int> {
    return Gson().fromJson(
        list,
        object : TypeToken<List<Int>>() {}.type
    )
}

Also, you need not worry about nullable types here because the list that you are saving in saveIntList is non-nullable and contains non-nullable Ints. So you can safely convert the stored string back to a list which is non-nullable.