code: function save(options) {
      const self = this
      options = options || {}
  
      if (self.options.polymorph) return this.callParent(options)
  
      return Promise.all(
        this.map(function(record) {
          // validate all records at once.
          return record.validate()
        })
      )
        .then(function() {
          // if validation succeeded, start the transaction
          return self.store.startTransaction(options, function() {
            return self
              ._runLazyOperation(options)
              .then(function() {
                // inside the transaction create all new records and afterwards save all the others
                return self._create(options)
              })
              .then(function() {
                // will save all existing records with changes...
                return self.callParent(options, save)
              })
          })
        })
        .then(function() {
          return self
        })
    }
docs: create multiple records at once