Skip database calls in core.tx.load() if data list is empty (#1433)

### Summary
> Describe your changes.

If the list passed to load() is empty, we now return early to save time
from checking indexes, generating a query string, and talking to the
database.

Also fixes this for AWS' resourcegroupstaggingapi sync.

Since many cartography users likely have nothing in many regions, we
might as well save ourselves some network and database calls.


### Checklist

Provide proof that this works (this makes reviews move faster). Please
perform one or more of the following:
- [x] Update/add unit or integration tests.
- [ ] Include a screenshot showing what the graph looked like before and
after your changes.
- [ ] Include console log trace showing what happened before and after
your changes.

If you are changing a node or relationship:
- [ ] Update the
[schema](https://github.com/lyft/cartography/tree/master/docs/root/modules)
and
[readme](https://github.com/lyft/cartography/blob/master/docs/schema/README.md).

If you are implementing a new intel module:
- [ ] Use the NodeSchema [data
model](https://cartography-cncf.github.io/cartography/dev/writing-intel-modules.html#defining-a-node).

---------

Signed-off-by: Alex Chantavy <[email protected]>

cartography/client/core/tx.py

@@ -249,6 +249,9 @@ def load(
     :param kwargs: Allows additional keyword args to be supplied to the Neo4j query.
     :return: None
     """
+    if len(dict_list) == 0:
+        # If there is no data to load, save some time.
+        return
     ensure_indexes(neo4j_session, node_schema)
     ingestion_query = build_ingestion_query(node_schema)
     load_graph_data(neo4j_session, ingestion_query, dict_list, **kwargs)

cartography/intel/aws/resourcegroupstaggingapi.py

@@ -188,6 +188,9 @@ def load_tags(
     current_aws_account_id: str,
     aws_update_tag: int,
 ) -> None:
+    if len(tag_data) == 0:
+        # If there is no data to load, save some time.
+        return
     for tag_data_batch in batch(tag_data, size=100):
         neo4j_session.write_transaction(
             _load_tags_tx,

tests/unit/cartography/client/test_core.py

@@ -0,0 +1,19 @@
+from unittest.mock import MagicMock
+
+from cartography.client.core.tx import load
+from cartography.models.core.nodes import CartographyNodeSchema
+
+
+def test_load_empty_dict_list():
+    # Setup
+    mock_session = MagicMock()
+    mock_schema = MagicMock(spec=CartographyNodeSchema)
+    empty_dict_list = []
+
+    # Execute
+    load(mock_session, mock_schema, empty_dict_list)
+
+    # Assert
+    mock_session.run.assert_not_called()  # Ensure no database calls were made
+    # Verify that ensure_indexes was not called since we short-circuit on empty list
+    mock_session.write_transaction.assert_not_called()

tests/unit/cartography/intel/aws/test_resourcegroupstaggingapi.py

@@ -1,4 +1,5 @@
 import copy
+from unittest.mock import MagicMock
 
 import cartography.intel.aws.resourcegroupstaggingapi as rgta
 import tests.data.aws.resourcegroupstaggingapi as test_data
@@ -44,3 +45,28 @@ def test_transform_tags():
     assert 'resource_id' not in get_resources_response[0]
     rgta.transform_tags(get_resources_response, 'ec2:instance')
     assert 'resource_id' in get_resources_response[0]
+
+
+def test_load_tags_empty_data():
+    """
+    Ensure that the load_tags function returns early if the tag_data is empty
+    """
+    # Arrange
+    mock_neo4j_session = MagicMock()
+    resource_type = 'ec2:instance'
+    region = 'us-east-1'
+    account_id = '123456789012'
+    update_tag = 123456789
+
+    # Act
+    rgta.load_tags(
+        neo4j_session=mock_neo4j_session,
+        tag_data={},
+        resource_type=resource_type,
+        region=region,
+        current_aws_account_id=account_id,
+        aws_update_tag=update_tag,
+    )
+
+    # Assert
+    mock_neo4j_session.write_transaction.assert_not_called()