whole_func_string: function (query, queryOptions, callback) {
      if (!queryOptions) {
        callback = query;
        query = {};
        queryOptions = {};
      } else if (!callback) {
        callback = queryOptions;
        queryOptions = {};
      }
  
      this.find(query, queryOptions, function (err, items) {
        if (err) {
          return callback(err);
        }
        callback(null, items[0]);
      });
    }
func_code_string: function (query, queryOptions, callback) {
      if (!queryOptions) {
        callback = query;
        query = {};
        queryOptions = {};
      } else if (!callback) {
        callback = queryOptions;
        queryOptions = {};
      }
  
      this.find(query, queryOptions, function (err, items) {
        if (err) {
          return callback(err);
        }
        callback(null, items[0]);
      });
    }
func_documentation_string: Use this function to find one viewmodel.
  @param  {String}   query    The query to find the viewmodel. (mongodb style) [optional]
  @param  {Function} callback The function, that will be called when the this action is completed.
  `function(err, vm){}` vm is of type Object.