Composite Model ID - Best Practices

[mashaalmemon]

I wanted to know what the best practices is for composite ids. In my app we use a combination of two fields in order to uniquely identify an entity. Here I have a toy User model. I've made it such that onInit() a string representing the composite id is set within this.$modelId. Is this an appropriate approach?:

/**
 * Build composite identifier from parts
 *
 * @param name
 * @param uuid
 */
export function buildCompositeIdUser(name:string, uuid: string):string {
    return name+"::"+uuid;
}

@model("User")
export class User extends Model({
    uuid: prop<string>(),
    name: prop<string>()
}) {

   /**
     * Set model id with composite id
     */
    protected onInit() {
        this.$modelId = buildCompositeIdUser(this.name, this.uuid);
    }

    /**
     * Get reference id using composite id
     */
    public getRefId(): string {
        return buildCompositeIdUser(this.name, this.uuid);
    }

    public static ref = customRef<User>("UserRef", {
        resolve(ref:Ref<User>) {
            const rootStore = findParent<RootStore>(ref, (n) => n instanceof RootStore);
            if (!rootStore) return undefined;
            return rootStore.users.get(ref.id)
        },

        onResolvedValueChange(ref:Ref<User>, newUser, oldUser) {
            if (oldUser && !newUser) {
                // if the user value we were referencing disappeared then remove the reference
                // from its parent
                detach(ref)
            }
        }
    })

}

Is this a reasonable approach? Is the onInit() method the right place to do this?