docstr: We can't direct generate token for mldataset when we use
  ray client, so we use all mldataset's actor_id to generate
  token.
docstr_tok: ["We","ca","n't","direct","generate","token","for","mldataset","when","we","use","ray","client",",","so","we","use","all","mldataset","'s","actor_id","to","generate","token","."]
code: def _update_key(self):
      """We can't direct generate token for mldataset when we use
      ray client, so we use all mldataset's actor_id to generate
      token.
      """
      datas = []
      for value in self._values_:
          if isinstance(value, ray.util.data.MLDataset):
              actor_sets = [
                  (
                      [str(actor) for actor in actor_set.actors],
                      actor_set.transforms,
                  )
                  for actor_set in value.actor_sets
              ]
              datas.append(actor_sets)
              continue
          datas.append(value)
      self._obj_set("_key", tokenize(type(self).__name__, *datas))
      return self
  
imports: import functools
  import warnings
  import numpy
  import pandas
  from ...None import opcodes
  from ...core import OutputType
  from ...serialization.serializables import AnyField, BoolField, ListField, Int64Field, ReferenceField
  from ..utils import parse_index, lazy_import, tokenize
  from .core import IncrementalIndexDatasource, IncrementalIndexDataSourceMixin, HeadOptimizedDataSource
label_desc: Use image node_id 2 for calling the DataFrameReadMLDataset obj's underlying member method code with example usage: obj._update_key() and returns: self