Add document for export_file (#633)

* Add document for export_file
astronomer · Aug 12, 2022 · 905f214 · 905f214
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diff --git a/docs/astro/sql/operators/export.rst b/docs/astro/sql/operators/export.rst
@@ -0,0 +1,30 @@
+.. _export_file:
+
+====================
+export_file operator
+====================
+
+.. _export_file_operator:
+
+When to use the ``export_file`` operator
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The ``export_file`` function writes SQL table to csv/parquet on local/S3/GCS. The ``export_file`` function imports data from :ref:`supported_databases` or pandas dataframe.
+
+There are two use cases of the ``export_file`` operator.
+
+
+Case 1: Export file from table.
+    The following example saves your :ref:`table` of data to file storage using the ``export_file``, which returns a pointer to File object.
+
+    .. literalinclude:: ../../../../example_dags/example_google_bigquery_gcs_load_and_save.py
+       :language: python
+       :start-after: [START export_example_1]
+       :end-before: [END export_example_1]
+
+Case 2: Export file from dataframe.
+    The following example saves your pandas dataframe of data to file storage using the ``aql.export_file``, which returns a pointer to File object.
+
+    .. literalinclude:: ../../../../example_dags/example_google_bigquery_gcs_load_and_save.py
+       :language: python
+       :start-after: [START export_example_2]
+       :end-before: [END export_example_2]
diff --git a/example_dags/example_google_bigquery_gcs_load_and_save.py b/example_dags/example_google_bigquery_gcs_load_and_save.py
@@ -53,13 +53,28 @@ def extract_top_5_movies(input_df: pd.DataFrame):
 
     t2 = extract_top_5_movies(input_df=t1)
 
+    # [START export_example_1]
     aql.export_file(
-        task_id="save_to_gcs",
+        task_id="save_file_to_gcs",
+        input_data=t1,
+        output_file=File(
+            path=f"{gcs_bucket}/{{ task_instance_key_str }}/all_movies.csv",
+            conn_id="gcp_conn",
+        ),
+        if_exists="replace",
+    )
+    # [END export_example_1]
+
+    # [START export_example_2]
+    aql.export_file(
+        task_id="save_dataframe_to_gcs",
         input_data=t2,
         output_file=File(
             path=f"{gcs_bucket}/{{ task_instance_key_str }}/top_5_movies.csv",
             conn_id="gcp_conn",
         ),
         if_exists="replace",
     )
+    # [END export_example_2]
+
     aql.cleanup()