code: function() {
      var self = this.chain()
  
      var args = this.definition.store.utils.args(arguments)
      var fields = []
      fields = fields.concat.apply(fields, args) // flatten
  
      self.addInternal('group', fields)
      self.asRaw()
  
      return self
    }
docs: Specify SQL group fields.
  @class Model
  @method group
  @param {array} fields - The field names
  
  
  @return {Model}