code: function getCollectionsCompact(forEntity, includeNew) {
    let associations = forEntity.getMeta().fetch('associations');
    let collections  = {};
  
    Object.getOwnPropertyNames(associations).forEach(index => {
      let association = associations[index];
  
      if (association.type !== 'collection') {
        return;
      }
  
      collections[index] = [];
      if (!Array.isArray(forEntity[index])) {
        return;
      }
  
      forEntity[index].forEach(entity => {
        if (typeof entity === 'number') {
          collections[index].push(entity);
  
          return;
        }
  
        if (!(entity instanceof Entity)) {
          return;
        }
  
        if (entity.getId()) {
          collections[index].push(entity.getId());
  
          return;
        }
  
        if (includeNew) {
          collections[index].push(entity);
  
          return;
        }
      });
    });
  
    return collections;
  }
docs: Get a compact object of collections (arrays of ids)
  
  @param {Entity}  forEntity
  @param {boolean} [includeNew]
  
  @return {{}}