fixed bug with SchemaSnapshot when dropping columns, and added test

Author: dantownsend

piccolo/apps/migrations/auto/schema_snapshot.py

@@ -62,7 +62,9 @@ def get_snapshot(self) -> t.List[DiffableTable]:
                 )
                 for drop_column in drop_columns:
                     table.columns = [
-                        i for i in table.columns if i._meta.name != drop_column
+                        i
+                        for i in table.columns
+                        if i._meta.name != drop_column.column_name
                     ]
 
                 ###############################################################

tests/apps/migrations/auto/test_schema_snapshot.py

@@ -103,6 +103,29 @@ def test_rename_column(self):
         snapshot = schema_snapshot.get_snapshot()
         self.assertTrue(snapshot[0].columns[0]._meta.name == "label")
 
+    def test_drop_column(self):
+        """
+        Test dropping columns.
+        """
+        manager_1 = MigrationManager()
+        manager_1.add_table(class_name="Manager", tablename="manager")
+        manager_1.add_column(
+            table_class_name="Manager",
+            tablename="manager",
+            column_name="name",
+            column_class_name="Varchar",
+            params={"length": 100},
+        )
+
+        manager_2 = MigrationManager()
+        manager_2.drop_column(
+            table_class_name="Manager", tablename="manager", column_name="name"
+        )
+
+        schema_snapshot = SchemaSnapshot(managers=[manager_1, manager_2])
+        snapshot = schema_snapshot.get_snapshot()
+        self.assertEqual(len(snapshot[0].columns), 0)
+
     def test_alter_column(self):
         """
         Test altering columns.