code: function() {
      const Utils = this.definition.store.utils
      const self = this.chain()
  
      const includes = Utils.toIncludesList(Utils.args(arguments))
      const existingIncludes = self.getInternal('includes') || []
      const existingMap = {}
  
      existingIncludes.forEach(function(inc) {
        existingMap[inc.relation] = inc
      })
  
      includes.forEach(function(inc) {
        const relation = self.definition.relations[inc.relation]
        if (relation) {
          if (relation.through) inc.through = true
          if (existingMap[inc.relation]) return // ignore duplicated includes
  
          self.addInternal('includes', inc)
        } else {
          throw new Error(
            'Can\'t find relation "' +
              inc.relation +
              '" for ' +
              self.definition.modelName
          )
        }
      })
  
      return self
    }
docs: Include relations into the result
  @class Model
  @method include
  @param {array} includes - array of relation names to include
  @or
  @param {object} includes - for nested includes use objects
  
  @see Model.exec
  
  @return {Model}