title: airflow xcom.pull() access to a implicitly returned value of upstream task
body: <p>I am new to Python and new to Airflow.</p>
  
  <p>I am using the Snowflake database.</p>
  
  <p>I have created an operator <code>SnowflakeGetDataOperator</code> that returns the snowflake <code>hook.get_records</code> method (i am returning a small amount of kines - usually a single cell)</p>
  
  <p>so now I have this task in the dag:</p>
  
  <pre><code>check_last_run_date=SnowflakeGetDataOperator(
      task_id='check_last_run_date',
      sql="SELECT COALESCE (max(update_date), '2000-01-01') FROM poc.dwh.fact_collector",
      snowflake_conn_id='snowflake_default',
      dag=dag)
  </code></pre>
  
  <p>when this task runs I see in the Airfow backend the xcom object of this task (the returned value of the operator - i did not use <code>xcom.push()</code> )</p>
  
  <p>My question is how do I access this value from the next downstream task?</p>
  
  <p>I need to use it as a parameter for my next sql operator.</p>
  
  <p>I have tried the following line within the dag code</p>
  
  <pre><code>{{ task_instance.xcom_pull(task_ids='check_last_run_date') }}
  </code></pre>
  
  <p>but the code doesn't recognize the task_instance attribute.</p>
  
  <p><strong>EDIT</strong></p>
  
  <p>The next task should be something like </p>
  
  <pre><code>fill_agg_table = SnowflakeOperator( 
  task_id='fill_cust_agg_data', 
  sql= str.replace ("""INSERT INTO oc.TEMP_COMPUTING.collector_customer_aggregative_data 
    ( SELECT * FROM POC.STG."stg_atg_data" WHERE XXXXX &lt; current_date)""", 
      'XXXXX', 
      {{ task_instance.xcom_pull(task_ids='check_last_run_date') }}, 
  snowflake_conn_id='snowflake_default', 
  dag=dag )) 
  </code></pre>