Add remove_node method to SQLBackend

grand/backends/_sqlbackend.py

@@ -1,11 +1,10 @@
-from typing import Hashable, Generator, Optional, Iterable
+from typing import Hashable, Generator
 import time
 
 import pandas as pd
 import sqlalchemy
-from sqlalchemy.pool import NullPool
-from sqlalchemy.sql import select
-from sqlalchemy import and_, or_, func, Index
+from sqlalchemy.sql import delete, select
+from sqlalchemy import or_, func, Index
 
 from .backend import Backend
 
@@ -192,6 +191,29 @@ def _upsert_node(self, node_name: Hashable, metadata: dict) -> Hashable:
                 parameters={self._primary_key: node_name, "_metadata": metadata},
             )
 
+    def remove_node(self, name: Hashable) -> None:
+        """
+        Removes nodes and related edges for name.
+
+        Args:
+            node_name (Hashable): id of the node
+        """
+
+        # Remove nodes
+        statement = delete(self._node_table).where(
+            self._node_table.c[self._primary_key] == str(name)
+        )
+        self._connection.execute(statement)
+
+        # Remove edges for node
+        statement = delete(self._edge_table).where(
+            or_(
+                self._edge_table.c[self._edge_source_key] == str(name),
+                self._edge_table.c[self._edge_target_key] == str(name)
+            )
+        )
+        self._connection.execute(statement)
+
     def all_nodes_as_iterable(self, include_metadata: bool = False) -> Generator:
         """
         Get a generator of all of the nodes in this graph.

grand/backends/test_backends.py

@@ -151,6 +151,17 @@ def test_sqlite_persistence(self):
         nodes = list(backend.all_nodes_as_iterable())
         # assert
         assert node0 in nodes
+
+        # test remove_node
+        backend = SQLBackend(db_url=url, directed=True)
+        node1, node2 = backend.add_node("A", {}), backend.add_node("B", {})
+        backend.add_edge(node1, node2, {})
+        assert backend.has_node(node1)
+        assert backend.has_edge(node1, node2)
+        backend.remove_node(node1)
+        assert not backend.has_node(node1)
+        assert not backend.has_edge(node1, node2)
+
         # cleanup
         os.remove(dbpath)