I'm kinda new with delegates.. I'd like to create ...

# exposed

[Emil Kantis]

I'm kinda new with delegates.. I'd like to create one to help me store json in a varchar column.. My gut feeling tells me I'm overcomplicating things here.. Any feedback on better approaches? 🙏

// Entity
class Client(id: EntityID<Int>) : IntEntity(id) {
   companion object : IntEntityClass<Client>(Clients)
   // Some code omitted
   var tags2: List<String> by jsonStore(Clients.tags)
}

// Delegate provider
inline fun <reified S, T : Comparable<T>> Entity<T>.jsonStore(column: Column<String>) = JsonStore<T, S>(
   serializer(),
   column,
   { column.lookup() },
   { thisRef, property, value -> column.setValue(thisRef, property, value) }
)

// Delegate
class JsonStore<T : Comparable<T>, S>(
   val serializer: KSerializer<S>,
   val column: Column<String>,
   val lookup: (Column<String>) -> String,
   val write: (Entity<T>, KProperty<*>, String) -> Unit
) {
   
   operator fun getValue(thisRef: Any?, property: KProperty<*>): S = 
      json.decodeFromString(serializer, lookup(column))
   
   operator fun setValue(thisRef: Entity<T>, property: KProperty<*>, value: S) = 
      write(thisRef, property, json.encodeToString(serializer, value))
}

[rnett]

Seems pretty good, you can move both of the lambdas into JsonStore I think, you should have everything you need (you'll need to make `getValue`'s thisRef Entity, but that's going to be the case anyways).

[rnett]

Also wouldn't hurt to make JsonStore's constructor internal

[rnett]

You might be able to use Exposed's caching to avoid repeating serialization/deserialization, but I'm not sure how you would do that. Depends on how performant you need it to be, it shouldn't be that bad.

Also if this isn't just something for internal use considering making the Json instance a TextFormat parameter.

[Emil Kantis]

Thanks! Using Exposed's caching would be interesting 🙂

I don't believe I can move the lambdas from jsonStore to JsonStore since the column.lookup() function is defined in Entity , not accessible outside.. likewise with setValue

[rnett]

Yeah, but you get the Entity as thisRef in the get/setValue functions. You have it now in setValue, you would just have to change `getValue`'s thisRef type (which isn't an issue since you can only create the delegate inside of an Entity anyways).

[Emil Kantis]

good point.. updated version:

class JsonStore<T : Comparable<T>, S>(
   private val json: Json,
   private val serializer: KSerializer<S>,
   private val column: Column<String>,
) {

   operator fun getValue(thisRef: Entity<T>, property: KProperty<*>): S =
      json.decodeFromString(serializer, with(thisRef) { column.lookup() })

   operator fun setValue(thisRef: Entity<T>, property: KProperty<*>, value: S) =
      with(thisRef) { column.setValue(this, property, json.encodeToString(serializer, value)) }
}


inline fun <T : Comparable<T>, reified S> jsonStore(column: Column<String>, json: Json = Json.Default) = JsonStore<T, S>(
   json,
   serializer(),
   column,
)

[Emil Kantis]

much simpler, thanks!