Fix get_all_foreign_keys crash sorting implicit foreign key targets

datasette/utils/__init__.py

@@ -692,11 +692,21 @@ def get_all_foreign_keys(conn):
 
     # Sort foreign keys for deterministic ordering
     for table in table_to_foreign_keys:
+        # other_column is None when a foreign key targets a table's implicit
+        # primary key, so coerce to "" to keep the sort key totally ordered.
         table_to_foreign_keys[table]["incoming"].sort(
-            key=lambda fk: (fk["other_table"], fk["column"], fk["other_column"])
+            key=lambda fk: (
+                fk["other_table"] or "",
+                fk["column"] or "",
+                fk["other_column"] or "",
+            )
         )
         table_to_foreign_keys[table]["outgoing"].sort(
-            key=lambda fk: (fk["other_table"], fk["column"], fk["other_column"])
+            key=lambda fk: (
+                fk["other_table"] or "",
+                fk["column"] or "",
+                fk["other_column"] or "",
+            )
         )
 
     return table_to_foreign_keys

tests/test_utils.py

@@ -921,3 +921,28 @@ def test_deep_dict_update(dict1, dict2, expected):
     assert result == expected
     # Check that the original dict1 was modified
     assert dict1 == expected
+
+
+def test_get_all_foreign_keys_mixed_implicit_and_explicit_targets():
+    # Two foreign keys from the same table to the same parent, one targeting
+    # the implicit primary key (other_column is None) and one an explicit
+    # column. Sorting the collected keys must not crash comparing None to str.
+    conn = sqlite3.connect(":memory:")
+    conn.executescript("""
+        CREATE TABLE parent (id INTEGER PRIMARY KEY, alt TEXT UNIQUE);
+        CREATE TABLE child (
+            p_id1 INTEGER,
+            p_id2 INTEGER,
+            FOREIGN KEY(p_id1) REFERENCES parent,
+            FOREIGN KEY(p_id2) REFERENCES parent(alt)
+        );
+        """)
+    result = utils.get_all_foreign_keys(conn)
+    assert result["parent"]["incoming"] == [
+        {"other_table": "child", "column": None, "other_column": "p_id1"},
+        {"other_table": "child", "column": "alt", "other_column": "p_id2"},
+    ]
+    assert result["child"]["outgoing"] == [
+        {"other_table": "parent", "column": "p_id1", "other_column": None},
+        {"other_table": "parent", "column": "p_id2", "other_column": "alt"},
+    ]