title: How can i use sensor in airflow to read from mongodb?
body: <p>i am looking to develop a workflow wherein my dag kick-starts a process on 
  remote server and monitor if the each task in process is succeeded or not, it should read the status from mongo-db and  if the task is succeeded then the next task is to be triggered. is there any way i can achieve it? 
  i think i should use a mongo_sensor but not sure how to use that.</p>
  
  <p>i have successfully read the mongodb using this code.</p>
  
  <pre><code>from airflow import DAG
  from airflow.operators.python_operator import PythonOperator
  from datetime import datetime, timedelta
  
  import pendulum
  
  local_tz = pendulum.timezone("Europe/Amsterdam")
  
  def function1():
      print("hello")
      import pymongo
      from pymongo import MongoClient
      client=MongoClient("mongodb://rpa_task:rpa_task123@ds141641.mlab.com:41641/rpa_task")
  
      mydb = client['rpa_task']
      collect2 = mydb['business_process_mgts']
      cursor=collect2.find({"process.id":"ross1335_testingpurchase_1915"})
      for i in cursor:
          print(i['sequenceFlow'])
  
  
  
  default_args = {
      'owner': 'airflow',
      'depends_on_past': False,
      'start_date': datetime(2019, 07, 8,  tzinfo=local_tz),
      'email': ['shubhamkalyankari01@gmail.com'],
      'email_on_failure': True,
      'email_on_retry': True,
      'retries': 3,
  
          'schedule_interval': '@hourly',
      'retry_delay': timedelta(seconds=5),
  }
  
  dag = DAG('mongo1.py', default_args=default_args)
  
  t1=PythonOperator(dag=dag,
       task_id='t1',
       provide_context=False,
       python_callable=function1,)
  
  
  it is reading the mongo documents successfully.
  </code></pre>