Creates a $group object for Mongo aggregate that adds all the properties of a Model object and any other additions.

mongoGroupAggregateHelper.js

let Group = {
  /*
   * Description:
   * Creates a $group object for Mongo aggregate that adds all the properties
   * of a Model object and any other additions.
   *
   * Sample usage:
   * MyCoolModel.aggregate({$match:{..}, {$group:Group.withModel(MyCoolModel, {count: { $sum: 1 }})} })
   *
   * Parameters:
   *  - model: the mongoose model object
   *  - additions: additional custom properties
   */
  withModel(model, additions){
    var result = {};

    if(model) {
      model.schema.eachPath(function (path) {
        if (path === '_id') {
          result[path] = "$" + path;
        } else if (path && !path.startsWith('__'))
          result[path] = {"$first": "$" + path};
      });
    }

    if(additions) {
      Object.getOwnPropertyNames(additions).forEach(prop => {
        result[prop] = additions[prop];
      });
    }

    return result;
  }
}

export {Group};