code: function(key, value, isUnique) {
        if(isUnique) {
          return this._op(key, value, 'pushUnique');
        } else {
          return this._op(key, value, 'push');
        }
      }
docs: Push the given value into the array field identified by the key.
  Pass true to isUnique to only push the value if the value does not
  already exist in the array.