(Data): Small extensions to core data interfaces.

Add `LEQ` condition type.
Ensure that batch updates don't fire with nothing to update.
Add `cast_row` to `update_many` for handling typed `NULL`s.

bot/data/conditions.py

@@ -45,6 +45,21 @@ class GEQ(Condition):
             values.append(item)
 
 
+class LEQ(Condition):
+    __slots__ = ('value',)
+
+    def __init__(self, value):
+        self.value = value
+
+    def apply(self, key, values, conditions):
+        item = self.value
+        if isinstance(item, (list, tuple)):
+            raise ValueError("Cannot apply LEQ condition to a list!")
+        else:
+            conditions.append("{} <= {}".format(key, _replace_char))
+            values.append(item)
+
+
 class Constant(Condition):
     __slots__ = ('value',)
 

bot/data/interfaces.py

@@ -113,7 +113,8 @@ class Row:
         try:
             yield self._pending
         finally:
-            self.update(**self._pending)
+            if self._pending:
+                self.update(**self._pending)
             self._pending = None
 
     def _refresh(self):

bot/data/queries.py

@@ -126,7 +126,7 @@ def upsert(table, constraint, cursor=None, **values):
     return cursor.fetchone()
 
 
-def update_many(table, *values, set_keys=None, where_keys=None, cursor=None):
+def update_many(table, *values, set_keys=None, where_keys=None, cast_row=None, cursor=None):
     cursor = cursor or conn.cursor()
 
     return execute_values(
@@ -134,13 +134,14 @@ def update_many(table, *values, set_keys=None, where_keys=None, cursor=None):
         """
         UPDATE {table}
         SET {set_clause}
-        FROM (VALUES %s)
+        FROM (VALUES {cast_row}%s)
         AS {temp_table}
         WHERE {where_clause}
         RETURNING *
         """.format(
             table=table,
             set_clause=', '.join("{0} = _t.{0}".format(key) for key in set_keys),
+            cast_row=cast_row + ',' if cast_row else '',
             where_clause=' AND '.join("{1}.{0} = _t.{0}".format(key, table) for key in where_keys),
             temp_table="_t ({})".format(', '.join(set_keys + where_keys))
         ),