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

5 files changed, 92 insertions, 12 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
diff --git a/django/db/backends/postgresql/base.py b/django/db/backends/postgresql/base.py
index 4a8d6ebef0..792026530f 100644
--- a/django/db/backends/postgresql/base.py
+++ b/django/db/backends/postgresql/base.py
@@ -63,6 +63,9 @@ class UnicodeCursorWrapper(object):
     def __iter__(self):
         return iter(self.cursor)
 
+class DatabaseFeatures(BaseDatabaseFeatures):
+    uses_savepoints = True
+
 class DatabaseWrapper(BaseDatabaseWrapper):
     operators = {
         'exact': '= %s',
@@ -83,8 +86,8 @@ class DatabaseWrapper(BaseDatabaseWrapper):
 
     def __init__(self, *args, **kwargs):
         super(DatabaseWrapper, self).__init__(*args, **kwargs)
-        
-        self.features = BaseDatabaseFeatures()
+
+        self.features = DatabaseFeatures()
         self.ops = DatabaseOperations()
         self.client = DatabaseClient()
         self.creation = DatabaseCreation(self)
diff --git a/django/db/backends/postgresql/operations.py b/django/db/backends/postgresql/operations.py
index de7b5a9520..4eb5ead47c 100644
--- a/django/db/backends/postgresql/operations.py
+++ b/django/db/backends/postgresql/operations.py
@@ -124,3 +124,13 @@ class DatabaseOperations(BaseDatabaseOperations):
                     style.SQL_KEYWORD('FROM'),
                     style.SQL_TABLE(qn(f.m2m_db_table()))))
         return output
+
+    def savepoint_create_sql(self, sid):
+        return "SAVEPOINT %s" % sid
+
+    def savepoint_commit_sql(self, sid):
+        return "RELEASE SAVEPOINT %s" % sid
+
+    def savepoint_rollback_sql(self, sid):
+        return "ROLLBACK TO SAVEPOINT %s" % sid
+
diff --git a/django/db/backends/postgresql_psycopg2/base.py b/django/db/backends/postgresql_psycopg2/base.py
index 139e36ba59..08014bd993 100644
--- a/django/db/backends/postgresql_psycopg2/base.py
+++ b/django/db/backends/postgresql_psycopg2/base.py
@@ -26,6 +26,7 @@ psycopg2.extensions.register_adapter(SafeUnicode, psycopg2.extensions.QuotedStri
 
 class DatabaseFeatures(BaseDatabaseFeatures):
     needs_datetime_string_cast = False
+    uses_savepoints = True
 
 class DatabaseOperations(PostgresqlDatabaseOperations):
     def last_executed_query(self, cursor, sql, params):
diff --git a/django/db/transaction.py b/django/db/transaction.py
index cd27cf6044..55fad9e457 100644
--- a/django/db/transaction.py
+++ b/django/db/transaction.py
@@ -19,7 +19,7 @@ except ImportError:
 try:
     from functools import wraps
 except ImportError:
-    from django.utils.functional import wraps  # Python 2.3, 2.4 fallback. 
+    from django.utils.functional import wraps  # Python 2.3, 2.4 fallback.
 from django.db import connection
 from django.conf import settings
 
@@ -30,9 +30,10 @@ class TransactionManagementError(Exception):
     """
     pass
 
-# The state is a dictionary of lists. The key to the dict is the current
+# The states are dictionaries of lists. The key to the dict is the current
 # thread and the list is handled as a stack of values.
 state = {}
+savepoint_state = {}
 
 # The dirty flag is set by *_unless_managed functions to denote that the
 # code under transaction management has changed things to require a
@@ -164,6 +165,36 @@ def rollback():
     connection._rollback()
     set_clean()
 
+def savepoint():
+    """
+    Creates a savepoint (if supported and required by the backend) inside the
+    current transaction. Returns an identifier for the savepoint that will be
+    used for the subsequent rollback or commit.
+    """
+    thread_ident = thread.get_ident()
+    if thread_ident in savepoint_state:
+        savepoint_state[thread_ident].append(None)
+    else:
+        savepoint_state[thread_ident] = [None]
+    tid = str(thread_ident).replace('-', '')
+    sid = "s%s_x%d" % (tid, len(savepoint_state[thread_ident]))
+    connection._savepoint(sid)
+    return sid
+
+def savepoint_rollback(sid):
+    """
+    Rolls back the most recent savepoint (if one exists). Does nothing if
+    savepoints are not supported.
+    """
+    connection._savepoint_rollback(sid)
+
+def savepoint_commit(sid):
+    """
+    Commits the most recent savepoint (if one exists). Does nothing if
+    savepoints are not supported.
+    """
+    connection._savepoint_commit(sid)
+
 ##############
 # DECORATORS #
 ##############