added support for adding columns to other columns in update queries

Applies to all operator types - multiplation, division etc too.

Author: dantownsend

piccolo/columns/column_types.py

@@ -88,12 +88,31 @@ def _get_querystring(self, operator: str, value: int, reverse=False):
 
         await Band.update({Band.popularity: Band.popularity + 100}).run()
         """
-        if not isinstance(value, (int, float)):
-            raise ValueError("Only integers and floats can be added.")
-        if reverse:
-            return QueryString(f"{{}} {operator} {self._meta.name} ", value)
+        if isinstance(value, Integer):
+            column: Integer = value
+            if len(column._meta.call_chain) > 0:
+                raise ValueError(
+                    "Adding values across joins isn't currently supported."
+                )
+            column_name = column._meta.name
+            if reverse:
+                return QueryString(
+                    f"{column_name} {operator} {self._meta.name}"
+                )
+            else:
+                return QueryString(
+                    f"{self._meta.name} {operator} {column_name}"
+                )
+        elif isinstance(value, (int, float)):
+            if reverse:
+                return QueryString(f"{{}} {operator} {self._meta.name}", value)
+            else:
+                return QueryString(f"{self._meta.name} {operator} {{}}", value)
         else:
-            return QueryString(f"{self._meta.name} {operator} {{}}", value)
+            raise ValueError(
+                "Only integers, floats, and other Integer columns can be "
+                "added."
+            )
 
     def __add__(self, value: int):
         return self._get_querystring("+", value)

tests/table/test_update.py

@@ -46,6 +46,17 @@ def test_add(self):
 
         self.assertEqual(response["popularity"], 1010)
 
+    def test_add_column(self):
+        self.insert_row()
+
+        Band.update(
+            {Band.popularity: Band.popularity + Band.popularity}
+        ).run_sync()
+
+        response = Band.select(Band.popularity).first().run_sync()
+
+        self.assertEqual(response["popularity"], 2000)
+
     def test_radd(self):
         self.insert_row()