mirror of
https://github.com/django/django.git
synced 2024-12-26 19:16:11 +00:00
992ded1ad1
git-svn-id: http://code.djangoproject.com/svn/django/trunk@11022 bcc190cf-cafb-0310-a4f2-bffc1f526a37
90 lines
3.7 KiB
Plaintext
90 lines
3.7 KiB
Plaintext
.. _topics-db-sql:
|
|
|
|
Performing raw SQL queries
|
|
==========================
|
|
|
|
Feel free to write custom SQL statements in custom model methods and
|
|
module-level methods. The object ``django.db.connection`` represents the
|
|
current database connection, and ``django.db.transaction`` represents the
|
|
current database transaction. To use the database connection, call
|
|
``connection.cursor()`` to get a cursor object. Then, call
|
|
``cursor.execute(sql, [params])`` to execute the SQL and ``cursor.fetchone()``
|
|
or ``cursor.fetchall()`` to return the resulting rows. After performing a data
|
|
changing operation, you should then call
|
|
``transaction.commit_unless_managed()`` to ensure your changes are committed
|
|
to the database. If your query is purely a data retrieval operation, no commit
|
|
is required. For example::
|
|
|
|
def my_custom_sql(self):
|
|
from django.db import connection, transaction
|
|
cursor = connection.cursor()
|
|
|
|
# Data modifying operation - commit required
|
|
cursor.execute("UPDATE bar SET foo = 1 WHERE baz = %s", [self.baz])
|
|
transaction.commit_unless_managed()
|
|
|
|
# Data retrieval operation - no commit required
|
|
cursor.execute("SELECT foo FROM bar WHERE baz = %s", [self.baz])
|
|
row = cursor.fetchone()
|
|
|
|
return row
|
|
|
|
.. _transactions-and-raw-sql:
|
|
|
|
Transactions and raw SQL
|
|
------------------------
|
|
If you are using transaction decorators (such as ``commit_on_success``) to
|
|
wrap your views and provide transaction control, you don't have to make a
|
|
manual call to ``transaction.commit_unless_managed()`` -- you can manually
|
|
commit if you want to, but you aren't required to, since the decorator will
|
|
commit for you. However, if you don't manually commit your changes, you will
|
|
need to manually mark the transaction as dirty, using
|
|
``transaction.set_dirty()``::
|
|
|
|
@commit_on_success
|
|
def my_custom_sql_view(request, value):
|
|
from django.db import connection, transaction
|
|
cursor = connection.cursor()
|
|
|
|
# Data modifying operation
|
|
cursor.execute("UPDATE bar SET foo = 1 WHERE baz = %s", [value])
|
|
|
|
# Since we modified data, mark the transaction as dirty
|
|
transaction.set_dirty()
|
|
|
|
# Data retrieval operation. This doesn't dirty the transaction,
|
|
# so no call to set_dirty() is required.
|
|
cursor.execute("SELECT foo FROM bar WHERE baz = %s", [value])
|
|
row = cursor.fetchone()
|
|
|
|
return render_to_response('template.html', {'row': row})
|
|
|
|
The call to ``set_dirty()`` is made automatically when you use the Django ORM
|
|
to make data modifying database calls. However, when you use raw SQL, Django
|
|
has no way of knowing if your SQL modifies data or not. The manual call to
|
|
``set_dirty()`` ensures that Django knows that there are modifications that
|
|
must be committed.
|
|
|
|
Connections and cursors
|
|
-----------------------
|
|
|
|
``connection`` and ``cursor`` mostly implement the standard `Python DB-API`_
|
|
(except when it comes to :ref:`transaction handling <topics-db-transactions>`).
|
|
If you're not familiar with the Python DB-API, note that the SQL statement in
|
|
``cursor.execute()`` uses placeholders, ``"%s"``, rather than adding parameters
|
|
directly within the SQL. If you use this technique, the underlying database
|
|
library will automatically add quotes and escaping to your parameter(s) as
|
|
necessary. (Also note that Django expects the ``"%s"`` placeholder, *not* the
|
|
``"?"`` placeholder, which is used by the SQLite Python bindings. This is for
|
|
the sake of consistency and sanity.)
|
|
|
|
An easier option?
|
|
-----------------
|
|
|
|
A final note: If all you want to do is a custom ``WHERE`` clause, you can just
|
|
use the ``where``, ``tables`` and ``params`` arguments to the
|
|
:ref:`extra clause <extra>` in the standard queryset API.
|
|
|
|
.. _Python DB-API: http://www.python.org/peps/pep-0249.html
|
|
|