Added savepoint support to the transaction code.

This is a no-op for most databases. Only necessary on PostgreSQL so that we can
do things which will possibly intentionally raise an IntegrityError and not
have to rollback the entire transaction. Not supported for PostgreSQL versions
prior to 8.0, so should be used sparingly in internal Django code.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@8314 bcc190cf-cafb-0310-a4f2-bffc1f526a37

1 files changed, 43 insertions, 8 deletions

diff --git a/django/db/backends/__init__.py b/django/db/backends/__init__.py
index f25a65bafb..074fa0ed70 100644
--- a/django/db/backends/__init__.py
+++ b/django/db/backends/__init__.py
@@ -9,7 +9,7 @@ try:
 except NameError:
     # Python 2.3 compat
     from sets import Set as set
-    
+
 from django.db.backends import util
 from django.utils import datetime_safe
 
@@ -31,6 +31,21 @@ class BaseDatabaseWrapper(local):
         if self.connection is not None:
             return self.connection.rollback()
 
+    def _savepoint(self, sid):
+        if not self.features.uses_savepoints:
+            return
+        self.connection.cursor().execute(self.ops.savepoint_create_sql(sid))
+
+    def _savepoint_rollback(self, sid):
+        if not self.features.uses_savepoints:
+            return
+        self.connection.cursor().execute(self.ops.savepoint_rollback_sql(sid))
+
+    def _savepoint_commit(self, sid):
+        if not self.features.uses_savepoints:
+            return
+        self.connection.cursor().execute(self.ops.savepoint_commit_sql(sid))
+
     def close(self):
         if self.connection is not None:
             self.connection.close()
@@ -55,6 +70,7 @@ class BaseDatabaseFeatures(object):
     update_can_self_select = True
     interprets_empty_strings_as_nulls = False
     can_use_chunked_reads = True
+    uses_savepoints = False
 
 class BaseDatabaseOperations(object):
     """
@@ -226,6 +242,26 @@ class BaseDatabaseOperations(object):
         """
         raise NotImplementedError
 
+    def savepoint_create_sql(self, sid):
+        """
+        Returns the SQL for starting a new savepoint. Only required if the
+        "uses_savepoints" feature is True. The "sid" parameter is a string
+        for the savepoint id.
+        """
+        raise NotImplementedError
+
+    def savepoint_commit_sql(self, sid):
+        """
+        Returns the SQL for committing the given savepoint.
+        """
+        raise NotImplementedError
+
+    def savepoint_rollback_sql(self, sid):
+        """
+        Returns the SQL for rolling back the given savepoint.
+        """
+        raise NotImplementedError
+
     def sql_flush(self, style, tables, sequences):
         """
         Returns a list of SQL statements required to remove all data from
@@ -259,7 +295,7 @@ class BaseDatabaseOperations(object):
         a tablespace. Returns '' if the backend doesn't use tablespaces.
         """
         return ''
-            
+
     def prep_for_like_query(self, x):
         """Prepares a value for use in a LIKE query."""
         from django.utils.encoding import smart_unicode
@@ -336,11 +372,11 @@ class BaseDatabaseIntrospection(object):
 
     def table_name_converter(self, name):
         """Apply a conversion to the name for the purposes of comparison.
-        
+
         The default table name converter is for case sensitive comparison.
         """
         return name
-        
+
     def table_names(self):
         "Returns a list of names of all tables that exist in the database."
         cursor = self.connection.cursor()
@@ -371,10 +407,10 @@ class BaseDatabaseIntrospection(object):
         for app in models.get_apps():
             for model in models.get_models(app):
                 all_models.append(model)
-        return set([m for m in all_models 
+        return set([m for m in all_models
             if self.table_name_converter(m._meta.db_table) in map(self.table_name_converter, tables)
         ])
-        
+
     def sequence_list(self):
         "Returns a list of information about all DB sequences for all models in all apps."
         from django.db import models
@@ -393,8 +429,7 @@ class BaseDatabaseIntrospection(object):
                     sequence_list.append({'table': f.m2m_db_table(), 'column': None})
 
         return sequence_list
-        
-        
+
 class BaseDatabaseClient(object):
     """
     This class encapsualtes all backend-specific methods for opening a