Find select field

[hafarooki]

I have nations with settlements with members, I'm trying to get all of the members of the nation through the settlements.

        val members: List<SLPlayerId> = Settlement.COL
            .find(Settlement::nation eq id).projection(Settlement::members)
            .map { it.members }
            .flatten()

This gives me this error:

[08:01:22 ERROR]: [SLCore] [ACF] Caused by: com.fasterxml.jackson.module.kotlin.MissingKotlinParameterException: Instantiation of [simple type, class net.starlegacy.slcore.mongo.Settlement] value failed for JSON property territory due to missing (therefore NULL) value for creator parameter territory which is a non-nullable type
[08:01:22 ERROR]: [SLCore] [ACF]  at [Source: de.undercouch.bson4jackson.io.LittleEndianInputStream@24d5132b; pos: 148] (through reference chain: net.starlegacy.slcore.mongo.Settlement["territory"])

Is there a way to get the value without attempting to construct the whole object?

[zigzago]

You have two options:

1. project into Document (ie Map):

val members: List<SLPlayerId> = Settlement.COL
            .withDocumentClass<Document>()
            .find(Settlement::nation eq id)
            .projection(Settlement::members)
            .map { it.getString(Settlement::members.name) }
            .flatten()

This will not work if members is a complex object.

2. project into dedicated object

data class SettlementWithMembersOnly(val members: Array<Array<SLPlayerId>>)

val members: List<SLPlayerId> = Settlement.COL
            .withDocumentClass<SettlementWithMembersOnly>()
            .find(Settlement::nation eq id)
            .projection(Settlement::members)
            .map { it.members }
            .flatten()

Also I'm going to add a projection extension method, in order to project "out of the box" one, two or three fields.

HTH

[hafarooki]

Members is just a set of IDs so that'll work, thanks. Should I leave the issue open for the addition or close it?

[hafarooki]

Also, is there a slack or somewhere better to ask questions?

[hafarooki]

Okay... I made a generic utility for getting specific values, will this work?

fun <T> MongoCollection<T>.getValues(id: Any, vararg properties: KProperty<*>): Map<KProperty<*>, Any> {
    val map: MutableMap<KProperty<*>, Any> = mutableMapOf()

    val results: FindIterable<Document> = this.withDocumentClass<Document>()
        .find(Filters.eq("_id", id))
        .projection(*properties)

    for (document: Document in results) {
        for (property: KProperty<*> in properties) {
            val path: String = property.path()
            val value: Any = document[path] ?: error("Missing value for path $path")
            map[property] = value
        }
    }

    return map
}

@Suppress("UNCHECKED_CAST")
fun <T> Map<KProperty<*>, *>.getProperty(property: KProperty<T>): T = getValue(property) as T

Used like this:

    fun getName(settlementId: Id<Settlement>): String? {
        return Settlement.COL.getValues(settlementId, Settlement::name).getProperty(Settlement::name)
    }

[hafarooki]

Actually.. that wouldn't work with anything more complex than strings/numbers. Maybe this instead?:

inline fun <reified R> Map<KProperty<*>, *>.getProperty(property: KProperty<R>): R {
    val value: Any = get(property) ?: error("Property ${property.path()} not in collection")
    return value as R
}

inline fun <reified I, reified R> Map<KProperty<*>, *>.convertProperty(property: KProperty<R>, convert: (I) -> R): R {
    return convert.invoke(getProperty(property) as I)
}

Uses:

    fun getName(settlementId: Id<Settlement>): String? = Settlement.COL
        .getValues(settlementId, Settlement::name)
        .getProperty(Settlement::name)

    fun getLeader(settlementId: Id<Settlement>): Id<SLPlayer>? = Settlement.COL
        .getValues(settlementId, Settlement::leader)
        .convertProperty(Settlement::leader) { objectId: ObjectId -> objectId.toId() }

[hafarooki]

https://gist.github.com/c76df079bbc16fd318da551ef7e256f1 bit cleaner version, instead of using the confusing map class it extends LinkedHashMap to be ProjectedResults

EDIT: Updated it a lot, it's much improved over the original and very flexible

[zigzago]

to ask questions use gitter https://gitter.im/kmongoo/Lobby or google groups https://groups.google.com/forum/#!forum/kmongo

Your solution is interesting but will not work with complex objects. I'm going to provide a patch tomorrow (so keep open this ticket).

Thanks

[hafarooki]

Okay, hopefully you'll find what I came up with helpful :)