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

django/db/backends/__init__.py

@@ -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
@@ -394,7 +430,6 @@ class BaseDatabaseIntrospection(object):
 
         return sequence_list
 
-        
 class BaseDatabaseClient(object):
     """
     This class encapsualtes all backend-specific methods for opening a

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',
@@ -84,7 +87,7 @@ 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)

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
+

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):

django/db/transaction.py

@@ -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 #
 ##############

tests/modeltests/force_insert_update/models.py

@@ -2,7 +2,7 @@
 Tests for forcing insert and update queries (instead of Django's normal
 automatic behaviour).
 """
-from django.db import models
+from django.db import models, transaction
 
 class Counter(models.Model):
     name = models.CharField(max_length = 10)
@@ -40,15 +40,13 @@ ValueError: Cannot force an update in save() with no primary key.
 >>> c1.save(force_insert=True)
 
 # Won't work because we can't insert a pk of the same value.
+>>> sid = transaction.savepoint()
 >>> c.value = 5
 >>> c.save(force_insert=True)
 Traceback (most recent call last):
 ...
 IntegrityError: ...
-
-# Work around transaction failure cleaning up for PostgreSQL.
->>> from django.db import connection
->>> connection.close()
+>>> transaction.savepoint_rollback(sid)
 
 # Trying to update should still fail, even with manual primary keys, if the
 # data isn't in the database already.

tests/modeltests/one_to_one/models.py

@@ -6,7 +6,7 @@ To define a one-to-one relationship, use ``OneToOneField()``.
 In this example, a ``Place`` optionally can be a ``Restaurant``.
 """
 
-from django.db import models, connection
+from django.db import models, transaction
 
 class Place(models.Model):
     name = models.CharField(max_length=50)
@@ -178,13 +178,11 @@ DoesNotExist: Restaurant matching query does not exist.
 
 # This will fail because each one-to-one field must be unique (and link2=o1 was
 # used for x1, above).
+>>> sid = transaction.savepoint()
 >>> MultiModel(link1=p2, link2=o1, name="x1").save()
 Traceback (most recent call last):
     ...
 IntegrityError: ...
+>>> transaction.savepoint_rollback(sid)
 
-# Because the unittests all use a single connection, we need to force a
-# reconnect here to ensure the connection is clean (after the previous
-# IntegrityError).
->>> connection.close()
 """}