new: GraphNotEmpty exception

Author: aMahanna

nx_arangodb/classes/graph.py

@@ -15,6 +15,7 @@
     DatabaseNotSet,
     EdgeTypeAmbiguity,
     GraphNameNotSet,
+    GraphNotEmpty,
     InvalidDefaultNodeType,
 )
 from nx_arangodb.logger import logger
@@ -439,6 +440,19 @@ def edge_type_func(u: str, v: str) -> str:
     def _load_nx_graph(
         self, nx_graph: nx.Graph, write_batch_size: int, write_async: bool
     ) -> None:
+        v_count = sum(
+            self.db.collection(v).count() for v in self.adb_graph.vertex_collections()
+        )
+
+        e_count = sum(
+            self.db.collection(e["edge_collection"]).count()
+            for e in self.adb_graph.edge_definitions()
+        )
+
+        if v_count > 0 or e_count > 0:
+            m = f"Graph '{self.adb_graph.name}' already has data. Use **overwrite_graph=True** to clear it."  # noqa: E501
+            raise GraphNotEmpty(m)
+
         controller = ADBNX_Controller
 
         if all([self.is_smart, self.smart_field]):

nx_arangodb/exceptions.py

@@ -14,6 +14,10 @@ class GraphNameNotSet(NetworkXArangoDBException):
     pass
 
 
+class GraphNotEmpty(NetworkXArangoDBException):
+    pass
+
+
 class InvalidTraversalDirection(NetworkXArangoDBException):
     pass