I have seen this question several times on SO. however the solution doesn't seem to apply to my problem.
I have a Kotlin data-class that is used as an Entity in Room
@Entity(tableName = "training_session")
data class SessionEntity(
@PrimaryKey(autoGenerate = false) val id: Long,
@ColumnInfo(name = "current_state_marker") val currentState: Short,
@Embedded val states: List<Int>
)
It is producing
> Task :training-infrastructure:kaptDebugKotlin FAILED
error: Entities and POJOs must have a usable public constructor. You can have an empty constructor or a constructor whose parameters match the fields (by name and type). - java.util.List
error: Entities and POJOs must have a usable public constructor. You can have an empty constructor or a constructor whose parameters match the fields (by name and type). - java.util.List
In the same project I have a very similar entity which also has a list and that doesn't produce any errors.
Tried out the answer provided by MikeT, for me it required a small change in the way the converters were defined
data class SessionStateList (val stateList : List<Int>)
class SessionStateListConverter {
@TypeConverter
fun fromArraySessionStateList(sh: List<Int>?): String? {
return Gson().toJson(sh)
}
@TypeConverter
fun toArraySessionStateList(sh: String?): List<Int>? {
val listType: Type = object : TypeToken<ArrayList<Int?>?>() {}.type
return Gson().fromJson(sh,listType)
}
}
A quick follow-up. I had mentioned that I have another Entity that has an Embedded val something: List<Int> and I had not noticed any compiler errors.
The reason, I had not noticed any compiler errors was because the entity was not included in the @Database annotation.
You cannot have a List/Array etc as a column type. So your issue is centred on @Embedded val states: List<Int>
You could have a POJO e.g. StatesHolder :-
data class StatesHolder(
val stateList: List<Int>
)
and then have
@Entity(tableName = "training_session")
data class SessionEntity(
@PrimaryKey(autoGenerate = false) val id: Long,
@ColumnInfo(name = "current_state_marker") val currentState: Short,
val states: StatesHolder
)
You will then need TypeConverters to convert to and from a StatesHolder object to a type that can be stored. Probably a String and Probably a JSON respresentation of the StatesHold object e.g.
class Converters {
@TypeConverter
fun fromStatesHolder(sh: StatesHolder): String {
return Gson().toJson(sh)
}
@TypeConverter
fun toStatesHolder(sh: String): StatesHolder {
return Gson().fromJson(sh,StatesHolder::class.java)
}
}
You additionally need to use @TypeConverters annotation that defines the Converts::class. If coded at the @Database level the converters have full scope.
So after @Database(.....) you could have :-
@TypeConverters(Converters::class)