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Fixed #5627: Added documentation and caveats about using the oracle


git-svn-id: bcc190cf-cafb-0310-a4f2-bffc1f526a37
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ikelly committed Sep 28, 2007
1 parent 4b4ecb6 commit e70ecc93ff3bc610ab976774786cfd22a15c80ef
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  1. +115 −0 docs/databases.txt
@@ -163,3 +163,118 @@ storage engine, you have a couple of options.
.. _AlterModelOnSyncDB:
+Oracle Notes
+Django supports `Oracle Database Server`_ versions 9i and higher. Oracle
+version 10g or later is required to use Django's ``regex`` and ``iregex`` query
+operators. You will also need the `cx_Oracle`_ driver, version 4.3.1 or newer.
+.. _`Oracle Database Server`:
+.. _`cx_Oracle`:
+To run ``python syncdb``, you'll need to create an Oracle database
+run Django's test suite, the user also needs CREATE and DROP DATABASE and
+Connecting to the Database
+Your Django file should look something like this for Oracle::
+ DATABASE_ENGINE = 'oracle'
+ DATABASE_USER = 'a_user'
+ DATABASE_PASSWORD = 'a_password'
+If you don't use a ``tnsnames.ora`` file or a similar naming method that
+recognizes the SID ("xe" in this example), then fill in both ``DATABASE_HOST``
+and ``DATABASE_PORT`` like so::
+ DATABASE_ENGINE = 'oracle'
+ DATABASE_USER = 'a_user'
+ DATABASE_PASSWORD = 'a_password'
+ DATABASE_PORT = '1540'
+You should supply both ``DATABASE_HOST`` and ``DATABASE_PORT``, or leave both
+as empty strings.
+Tablespace Options
+A common paradigm for optimizing performance in Oracle-based systems is the
+use of `tablespaces`_ to organize disk layout. The Oracle backend supports
+this use case by adding ``db_tablespace`` options to the ``Meta`` and
+``Field`` classes. (When using a backend that lacks support for tablespaces,
+these options are ignored.)
+.. _`tablespaces`:
+A tablespace can be specified for the table(s) generated by a model by
+supplying the ``db_tablespace`` option inside the model's ``Meta`` class.
+Additionally, the ``db_tablespace`` option can be passed to a ``Field``
+constructor to specify an alternate tablespace for the ``Field``'s column
+index. If no index would be created for the column, the ``db_tablespace``
+option is ignored.
+ class TablespaceExample(models.Model):
+ name = models.CharField(maxlength=30, db_index=True, db_tablespace="indexes")
+ data = models.CharField(maxlength=255, db_index=True)
+ edges = models.ManyToManyField(to="self", db_tablespace="indexes")
+ class Meta:
+ db_tablespace = "tables"
+In this example, the tables generated by the ``TablespaceExample`` model
+(i.e., the model table and the many-to-many table) would be stored in the
+``tables`` tablespace. The index for the name field and the indexes on the
+many-to-many table would be stored in the ``indexes`` tablespace. The ``data``
+field would also generate an index, but no tablespace for it is specified, so
+it would be stored in the model tablespace ``tables`` by default.
+Django does not create the tablespaces for you. Please refer to `Oracle's
+documentation`_ for details on creating and managing tablespaces.
+.. _`Oracle's documentation`:
+Naming Issues
+Oracle imposes a name length limit of 30 characters. To accommodate this, the
+backend truncates database identifiers to fit, replacing the final four
+characters of the truncated name with a repeatable MD5 hash value.
+NULL and Empty Strings
+Django generally prefers to use the empty string ('') rather than NULL, but
+Oracle treats both identically. To get around this, the Oracle backend
+coerces the ``null=True`` option on fields that permit the empty string as a
+value. When fetching from the database, it is assumed that a NULL value in
+one of these fields really means the empty string, and the data is silently
+converted to reflect this assumption.
+TextField Limitations
+The Oracle backend stores ``TextFields`` as ``NCLOB`` columns. Oracle imposes
+some limitations on the usage of such LOB columns in general:
+ * LOB columns may not be used as primary keys.
+ * LOB columns may not be used in indexes.
+ * LOB columns may not be used in a ``SELECT DISTINCT`` list. This means that
+ attempting to use the ``QuerySet.distinct`` method on a model that
+ includes ``TextField`` columns will result in an error when run against
+ Oracle. A workaround to this is to keep ``TextField`` columns out of any
+ models that you foresee performing ``.distinct`` queries on, and to
+ include the ``TextField`` in a related model instead.

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