Abstract Schema with no fields

[mackereldev]

I've discovered an error that occurs when synchronising a Schema with clients. This class is abstract, and does not contain any fields, and so never uses the "type" decorator to declare state fields. The class structure appears as follows:

import { Schema, type } from "@colyseus/schema";

export abstract class QuestRoom extends Schema {
	generate(): void;
}

export class BattleRoom extends QuestRoom {
	@type("string")
	foo: string = "bar"
}

I've tried making QuestRoom non-abstract and instantiating it directly, however this does not work. The exact error has something to do with decoding the schema on the client side:

Uncaught TypeError: decode2[type2] is not a function
    at decodePrimitiveType (index.js:2355:27)
    at Schema2.decode (index.js:2568:29)
    at SchemaSerializer2.patch (SchemaSerializer.ts:18:27)
    at Room2.patch (Room.ts:277:25)
    at Room2.onMessageCallback (Room.ts:245:18)

The problem appears to lie with QuestRoom not having any fields, and surely enough when adding any valid field (I added a boolean dummy field in my case) it resolves the error. Is this behaviour intended? Is it possible to have a Schema with no fields for the purpose of inheritance?

[endel]

Hi @mackereldev,

Inheritance with no fields on the base class is supported, just added a test scenario for this here and it's passing: colyseus/schema@5526c8e

Could you provide a test case like this one that fails? Cheers

[mackereldev]

I've just run a test on a minimal version of my game state. The state can decode the encoded state on the server side just fine as specified in my testState() function.

import { Schema, ArraySchema, type } from "@colyseus/schema";
import { Enemy, enemyRefs } from "../schema/quest/Enemy";

export abstract class QuestRoom extends Schema {
    abstract generate(): void;
}

export class BattleRoom extends QuestRoom {
    private enemyPrefabs: (() => Enemy)[];

    @type([ Enemy ])
    public enemies: ArraySchema<Enemy>;
    
    constructor(...enemyPrefabs: (keyof typeof enemyRefs)[]) {
        super();
        this.enemyPrefabs = enemyPrefabs.map((e) => enemyRefs[e]);
    }

    generate(): void {
        // Generation code here
        return;
    }
}

export class QuestState extends Schema {
    @type("boolean")
    public active: boolean = false;

    @type(QuestRoom)
    public room: QuestRoom;
}

export class GameState extends Schema {
    @type("number")
    serverStartTime: number = 0;

    @type(QuestState)
    questState: QuestState = new QuestState();

    @type("string")
    leader: string;

    constructor(serverStartTime: number) {
        super();
        this.serverStartTime = serverStartTime;
    }
}

export function testState() {
    const state = new GameState(Date.now());
    state.questState.room = new BattleRoom("skeleton", "bat");

    const decodedState = new GameState(Date.now());
    decodedState.decode(state.encode());
}

Once again however, the problem arises when I attempt to use this state in a Room instance, such as my Game class here:

import { Room } from "@colyseus/core";
import { BattleRoom, GameState } from "../test/Test";

export class Game extends Room<GameState> {
    async onCreate(options: any) {
        this.setState(new GameState(Date.now()));
        this.state.questState.room = new BattleRoom("skeleton", "bat");
    }
}

The error occurs on the client side upon joining a room (NOTE: the room is created before the page is loaded, and the following is SvelteKit code):

<script lang="ts">
    import { client } from "$lib/classes/Stores";
    import { onMount } from "svelte";
    import type { GameState } from "../../../../server/src/test/Test";
    import type { PageData } from "./$types";
    import { goto } from "$app/navigation";

    export let data: PageData;
    const { roomId } = data ?? {};

    onMount(() => {
        $client.joinById<GameState>(roomId, { clientId: "DEFAULT_CLIENTID" })
        .catch((err) => {
            goto(`/?error=${err.code}`);
        });
    });
</script>