title: AttributeError: 'CollectionReference' object has no attribute 'set'
body: <p>I am trying to retrieve data from my Firestore Database and then Make some changes and then set these data again in the database again.</p>
  
  <pre><code>import firebase_admin
  from PreProcessing import Pre_Processing
  import pandas as pd
  from FeatureExtraction import FeatureExtraction
  from Processing import Processing
  from firebase_admin import firestore , credentials
  def Classification(Data , ID ):
      Answers = []
      Message = Data['message']
      Answers.append(Data['message'])
      PreProcessing = Pre_Processing(Answers)
      Answers = PreProcessing.MainFunction()
      del Answers[0]
      Features = FeatureExtraction(Answers)
      Answers = Features.Test_TFIDF()
      print(Answers.shape)
      print("Finished TF-IDF Training")
      Data1 = pd.DataFrame(Answers)
      del Answers
      Data1 = Data1.fillna(0)
      SentimentList = Features.Sentiment()
      Data1[315477] = SentimentList       
      Processing_Object  = Processing(Data1)
      Results = Processing_Object.Testing()
      Classified = db.collection("Chat").document(Data['ChatID']).collection("chatting").set({
          "message" : Data['message'],
          "from" : Data['from'],
          "Classification" : Results,
          "time" : Data['time'],
      })
      print(Results)
  cred = credentials.Certificate("ssmproject-61dec-firebase-adminsdk-op5bp-d525c0a76e.json")
  firebase_admin.initialize_app(cred)
  
  db = firestore.client()
  
  NeedClassification = db.collection("NeedClassification")
  
  docs = NeedClassification.get()
  for doc in docs:
      if doc != None:
          data = doc.to_dict()
          Classification(data , doc.id)
  </code></pre>
  
  <p>That is the output</p>
  
  <pre><code>Test.py:39: DeprecationWarning: 'Collection.get' is deprecated:  please use 'Collection.stream' instead.
    docs = NeedClassification.get()
  (1, 315477)
  Finished TF-IDF Training
  Traceback (most recent call last):
    File "Test.py", line 43, in &lt;module&gt;
      Classification(data , doc.id , db)
    File "Test.py", line 25, in Classification
      Classified = db.collection("Chat").document(Data['ChatID']).collection("chatting").set({
  AttributeError: 'CollectionReference' object has no attribute 'set'
  </code></pre>
  
  <p>I just have problem in Setting the Data back to the Database
  Thanks in Advance</p>