Simplified DatabaseOperations.sql_flush() on Oracle and PostgreSQL.

Added early return to decrease an indentation level.

django/db/backends/oracle/operations.py

@@ -405,53 +405,52 @@ END;
         return lru_cache(maxsize=512)(self.__foreign_key_constraints)
 
     def sql_flush(self, style, tables, sequences, allow_cascade=False):
-        if tables:
+        if not tables:
-            truncated_tables = {table.upper() for table in tables}
-            constraints = set()
-            # Oracle's TRUNCATE CASCADE only works with ON DELETE CASCADE
-            # foreign keys which Django doesn't define. Emulate the
-            # PostgreSQL behavior which truncates all dependent tables by
-            # manually retrieving all foreign key constraints and resolving
-            # dependencies.
-            for table in tables:
-                for foreign_table, constraint in self._foreign_key_constraints(table, recursive=allow_cascade):
-                    if allow_cascade:
-                        truncated_tables.add(foreign_table)
-                    constraints.add((foreign_table, constraint))
-            sql = [
-                "%s %s %s %s %s %s %s %s;" % (
-                    style.SQL_KEYWORD('ALTER'),
-                    style.SQL_KEYWORD('TABLE'),
-                    style.SQL_FIELD(self.quote_name(table)),
-                    style.SQL_KEYWORD('DISABLE'),
-                    style.SQL_KEYWORD('CONSTRAINT'),
-                    style.SQL_FIELD(self.quote_name(constraint)),
-                    style.SQL_KEYWORD('KEEP'),
-                    style.SQL_KEYWORD('INDEX'),
-                ) for table, constraint in constraints
-            ] + [
-                "%s %s %s;" % (
-                    style.SQL_KEYWORD('TRUNCATE'),
-                    style.SQL_KEYWORD('TABLE'),
-                    style.SQL_FIELD(self.quote_name(table)),
-                ) for table in truncated_tables
-            ] + [
-                "%s %s %s %s %s %s;" % (
-                    style.SQL_KEYWORD('ALTER'),
-                    style.SQL_KEYWORD('TABLE'),
-                    style.SQL_FIELD(self.quote_name(table)),
-                    style.SQL_KEYWORD('ENABLE'),
-                    style.SQL_KEYWORD('CONSTRAINT'),
-                    style.SQL_FIELD(self.quote_name(constraint)),
-                ) for table, constraint in constraints
-            ]
-            # Since we've just deleted all the rows, running our sequence
-            # ALTER code will reset the sequence to 0.
-            sql.extend(self.sequence_reset_by_name_sql(style, sequences))
-            return sql
-        else:
             return []
 
+        truncated_tables = {table.upper() for table in tables}
+        constraints = set()
+        # Oracle's TRUNCATE CASCADE only works with ON DELETE CASCADE foreign
+        # keys which Django doesn't define. Emulate the PostgreSQL behavior
+        # which truncates all dependent tables by manually retrieving all
+        # foreign key constraints and resolving dependencies.
+        for table in tables:
+            for foreign_table, constraint in self._foreign_key_constraints(table, recursive=allow_cascade):
+                if allow_cascade:
+                    truncated_tables.add(foreign_table)
+                constraints.add((foreign_table, constraint))
+        sql = [
+            '%s %s %s %s %s %s %s %s;' % (
+                style.SQL_KEYWORD('ALTER'),
+                style.SQL_KEYWORD('TABLE'),
+                style.SQL_FIELD(self.quote_name(table)),
+                style.SQL_KEYWORD('DISABLE'),
+                style.SQL_KEYWORD('CONSTRAINT'),
+                style.SQL_FIELD(self.quote_name(constraint)),
+                style.SQL_KEYWORD('KEEP'),
+                style.SQL_KEYWORD('INDEX'),
+            ) for table, constraint in constraints
+        ] + [
+            '%s %s %s;' % (
+                style.SQL_KEYWORD('TRUNCATE'),
+                style.SQL_KEYWORD('TABLE'),
+                style.SQL_FIELD(self.quote_name(table)),
+            ) for table in truncated_tables
+        ] + [
+            '%s %s %s %s %s %s;' % (
+                style.SQL_KEYWORD('ALTER'),
+                style.SQL_KEYWORD('TABLE'),
+                style.SQL_FIELD(self.quote_name(table)),
+                style.SQL_KEYWORD('ENABLE'),
+                style.SQL_KEYWORD('CONSTRAINT'),
+                style.SQL_FIELD(self.quote_name(constraint)),
+            ) for table, constraint in constraints
+        ]
+        # Since we've just deleted all the rows, running our sequence ALTER
+        # code will reset the sequence to 0.
+        sql.extend(self.sequence_reset_by_name_sql(style, sequences))
+        return sql
+
     def sequence_reset_by_name_sql(self, style, sequences):
         sql = []
         for sequence_info in sequences:

django/db/backends/postgresql/operations.py

@@ -118,28 +118,28 @@ class DatabaseOperations(BaseDatabaseOperations):
         return "SET TIME ZONE %s"
 
     def sql_flush(self, style, tables, sequences, allow_cascade=False):
-        if tables:
+        if not tables:
-            # Perform a single SQL 'TRUNCATE x, y, z...;' statement.  It allows
-            # us to truncate tables referenced by a foreign key in any other
-            # table.
-            tables_sql = ', '.join(
-                style.SQL_FIELD(self.quote_name(table)) for table in tables)
-            if allow_cascade:
-                sql = ['%s %s %s;' % (
-                    style.SQL_KEYWORD('TRUNCATE'),
-                    tables_sql,
-                    style.SQL_KEYWORD('CASCADE'),
-                )]
-            else:
-                sql = ['%s %s;' % (
-                    style.SQL_KEYWORD('TRUNCATE'),
-                    tables_sql,
-                )]
-            sql.extend(self.sequence_reset_by_name_sql(style, sequences))
-            return sql
-        else:
             return []
 
+        # Perform a single SQL 'TRUNCATE x, y, z...;' statement. It allows us
+        # to truncate tables referenced by a foreign key in any other table.
+        tables_sql = ', '.join(
+            style.SQL_FIELD(self.quote_name(table)) for table in tables
+        )
+        if allow_cascade:
+            sql = ['%s %s %s;' % (
+                style.SQL_KEYWORD('TRUNCATE'),
+                tables_sql,
+                style.SQL_KEYWORD('CASCADE'),
+            )]
+        else:
+            sql = ['%s %s;' % (
+                style.SQL_KEYWORD('TRUNCATE'),
+                tables_sql,
+            )]
+        sql.extend(self.sequence_reset_by_name_sql(style, sequences))
+        return sql
+
     def sequence_reset_by_name_sql(self, style, sequences):
         # 'ALTER SEQUENCE sequence_name RESTART WITH 1;'... style SQL statements
         # to reset sequence indices