mirror of
https://github.com/django/django.git
synced 2024-11-18 15:34:16 +00:00
728effcfbd
Thanks, Ramiro Morales. git-svn-id: http://code.djangoproject.com/svn/django/trunk@13608 bcc190cf-cafb-0310-a4f2-bffc1f526a37
106 lines
4.4 KiB
Plaintext
106 lines
4.4 KiB
Plaintext
FAQ: Databases and models
|
|
=========================
|
|
|
|
.. _faq-see-raw-sql-queries:
|
|
|
|
How can I see the raw SQL queries Django is running?
|
|
----------------------------------------------------
|
|
|
|
Make sure your Django ``DEBUG`` setting is set to ``True``. Then, just do
|
|
this::
|
|
|
|
>>> from django.db import connection
|
|
>>> connection.queries
|
|
[{'sql': 'SELECT polls_polls.id,polls_polls.question,polls_polls.pub_date FROM polls_polls',
|
|
'time': '0.002'}]
|
|
|
|
``connection.queries`` is only available if ``DEBUG`` is ``True``. It's a list
|
|
of dictionaries in order of query execution. Each dictionary has the following::
|
|
|
|
``sql`` -- The raw SQL statement
|
|
``time`` -- How long the statement took to execute, in seconds.
|
|
|
|
``connection.queries`` includes all SQL statements -- INSERTs, UPDATES,
|
|
SELECTs, etc. Each time your app hits the database, the query will be recorded.
|
|
Note that the raw SQL logged in ``connection.queries`` may not include
|
|
parameter quoting. Parameter quoting is performed by the database-specific
|
|
backend, and not all backends provide a way to retrieve the SQL after quoting.
|
|
|
|
.. versionadded:: 1.2
|
|
|
|
If you are using :doc:`multiple databases</topics/db/multi-db>`, you can use the
|
|
same interface on each member of the ``connections`` dictionary::
|
|
|
|
>>> from django.db import connections
|
|
>>> connections['my_db_alias'].queries
|
|
|
|
Can I use Django with a pre-existing database?
|
|
----------------------------------------------
|
|
|
|
Yes. See :doc:`Integrating with a legacy database </howto/legacy-databases>`.
|
|
|
|
If I make changes to a model, how do I update the database?
|
|
-----------------------------------------------------------
|
|
|
|
If you don't mind clearing data, your project's ``manage.py`` utility has an
|
|
option to reset the SQL for a particular application::
|
|
|
|
manage.py reset appname
|
|
|
|
This drops any tables associated with ``appname`` and recreates them.
|
|
|
|
If you do care about deleting data, you'll have to execute the ``ALTER TABLE``
|
|
statements manually in your database. That's the way we've always done it,
|
|
because dealing with data is a very sensitive operation that we've wanted to
|
|
avoid automating. That said, there's some work being done to add partially
|
|
automated database-upgrade functionality.
|
|
|
|
Do Django models support multiple-column primary keys?
|
|
------------------------------------------------------
|
|
|
|
No. Only single-column primary keys are supported.
|
|
|
|
But this isn't an issue in practice, because there's nothing stopping you from
|
|
adding other constraints (using the ``unique_together`` model option or
|
|
creating the constraint directly in your database), and enforcing the
|
|
uniqueness at that level. Single-column primary keys are needed for things such
|
|
as the admin interface to work; e.g., you need a simple way of being able to
|
|
specify an object to edit or delete.
|
|
|
|
How do I add database-specific options to my CREATE TABLE statements, such as specifying MyISAM as the table type?
|
|
------------------------------------------------------------------------------------------------------------------
|
|
|
|
We try to avoid adding special cases in the Django code to accommodate all the
|
|
database-specific options such as table type, etc. If you'd like to use any of
|
|
these options, create an :ref:`SQL initial data file <initial-sql>` that
|
|
contains ``ALTER TABLE`` statements that do what you want to do. The initial
|
|
data files are executed in your database after the ``CREATE TABLE`` statements.
|
|
|
|
For example, if you're using MySQL and want your tables to use the MyISAM table
|
|
type, create an initial data file and put something like this in it::
|
|
|
|
ALTER TABLE myapp_mytable ENGINE=MyISAM;
|
|
|
|
As explained in the :ref:`SQL initial data file <initial-sql>` documentation,
|
|
this SQL file can contain arbitrary SQL, so you can make any sorts of changes
|
|
you need to make.
|
|
|
|
Why is Django leaking memory?
|
|
-----------------------------
|
|
|
|
Django isn't known to leak memory. If you find your Django processes are
|
|
allocating more and more memory, with no sign of releasing it, check to make
|
|
sure your ``DEBUG`` setting is set to ``False``. If ``DEBUG`` is ``True``, then
|
|
Django saves a copy of every SQL statement it has executed.
|
|
|
|
(The queries are saved in ``django.db.connection.queries``. See
|
|
`How can I see the raw SQL queries Django is running?`_.)
|
|
|
|
To fix the problem, set ``DEBUG`` to ``False``.
|
|
|
|
If you need to clear the query list manually at any point in your functions,
|
|
just call ``reset_queries()``, like this::
|
|
|
|
from django import db
|
|
db.reset_queries()
|