Fixed #17027 -- Added support for the power operator in F expressions.

Thanks dan at dlo.me for the initial patch.

- Added __pow__ and __rpow__ to ExpressionNode
- Added oracle and mysql specific power expressions
- Added used-defined power function for sqlite

django/db/backends/mysql/base.py

@@ -386,6 +386,14 @@ class DatabaseOperations(BaseDatabaseOperations):
         items_sql = "(%s)" % ", ".join(["%s"] * len(fields))
         return "VALUES " + ", ".join([items_sql] * num_values)
 
+    def combine_expression(self, connector, sub_expressions):
+        """
+        MySQL requires special cases for ^ operators in query expressions
+        """
+        if connector == '^':
+            return 'POW(%s)' % ','.join(sub_expressions)
+        return super(DatabaseOperations, self).combine_expression(connector, sub_expressions)
+
 
 class DatabaseWrapper(BaseDatabaseWrapper):
     vendor = 'mysql'

django/db/backends/oracle/base.py

@@ -482,6 +482,8 @@ WHEN (new.%(col_name)s IS NULL)
             return 'BITAND(%s)' % ','.join(sub_expressions)
         elif connector == '|':
             raise NotImplementedError("Bit-wise or is not supported in Oracle.")
+        elif connector == '^':
+            return 'POWER(%s)' % ','.join(sub_expressions)
         return super(DatabaseOperations, self).combine_expression(connector, sub_expressions)
 
     def _get_sequence_name(self, table):

django/db/backends/sqlite3/base.py

@@ -304,6 +304,13 @@ class DatabaseOperations(BaseDatabaseOperations):
         res.extend(["UNION ALL SELECT %s" % ", ".join(["%s"] * len(fields))] * (num_values - 1))
         return " ".join(res)
 
+    def combine_expression(self, connector, sub_expressions):
+        # SQLite doesn't have a power function, so we fake it with a
+        # user-defined function django_power that's registered in connect().
+        if connector == '^':
+            return 'django_power(%s)' % ','.join(sub_expressions)
+        return super(DatabaseOperations, self).combine_expression(connector, sub_expressions)
+
 
 class DatabaseWrapper(BaseDatabaseWrapper):
     vendor = 'sqlite'
@@ -376,6 +383,7 @@ class DatabaseWrapper(BaseDatabaseWrapper):
         conn.create_function("django_datetime_trunc", 3, _sqlite_datetime_trunc)
         conn.create_function("regexp", 2, _sqlite_regexp)
         conn.create_function("django_format_dtdelta", 5, _sqlite_format_dtdelta)
+        conn.create_function("django_power", 2, _sqlite_power)
         return conn
 
     def init_connection_state(self):
@@ -567,3 +575,7 @@ def _sqlite_format_dtdelta(dt, conn, days, secs, usecs):
 
 def _sqlite_regexp(re_pattern, re_string):
     return bool(re.search(re_pattern, force_text(re_string))) if re_string is not None else False
+
+
+def _sqlite_power(x, y):
+    return x ** y

django/db/models/expressions.py

@@ -14,6 +14,7 @@ class ExpressionNode(tree.Node):
     SUB = '-'
     MUL = '*'
     DIV = '/'
+    POW = '^'
     MOD = '%%'  # This is a quoted % operator - it is quoted
                 # because it can be used in strings that also
                 # have parameter substitution.
@@ -85,6 +86,9 @@ class ExpressionNode(tree.Node):
     def __mod__(self, other):
         return self._combine(other, self.MOD, False)
 
+    def __pow__(self, other):
+        return self._combine(other, self.POW, False)
+
     def __and__(self, other):
         raise NotImplementedError(
             "Use .bitand() and .bitor() for bitwise logical operations."
@@ -119,6 +123,9 @@ class ExpressionNode(tree.Node):
     def __rmod__(self, other):
         return self._combine(other, self.MOD, True)
 
+    def __rpow__(self, other):
+        return self._combine(other, self.POW, True)
+
     def __rand__(self, other):
         raise NotImplementedError(
             "Use .bitand() and .bitor() for bitwise logical operations."