ngrx-entity-relationship/community

No problem.

There is an example how I collect all relationships to send a request to load them.
I think, you could adapt it for your needs to verify which data is missed in a selected entity and to send an additional request in order to load it.

export const selectorToRelations = (
    selector: {relationships: Array<HANDLER_RELATED_ENTITY<unknown, unknown>>},
    prefix: string = '',
): Array<string> => {
    const relationships: Array<string> = [];
    for (const relationship of selector.relationships) {
        if (typeof relationship.keyValue === 'symbol') {
            continue;
        }
        const key = `${prefix ? `${prefix}.` : ''}${relationship.keyValue}`;
        if (!relationships.includes(key)) {
            relationships.push(key);
        }
        relationships.push(...selectorToRelations(relationship, key));
    }

    return relationships;
};