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98 lines
3.5 KiB
Plaintext
98 lines
3.5 KiB
Plaintext
=========================
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FAQ: Databases and models
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=========================
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.. _faq-see-raw-sql-queries:
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How can I see the raw SQL queries Django is running?
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====================================================
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Make sure your Django :setting:`DEBUG` setting is set to ``True``.
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Then do this:
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.. code-block:: pycon
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>>> from django.db import connection
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>>> connection.queries
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[{'sql': 'SELECT polls_polls.id, polls_polls.question, polls_polls.pub_date FROM polls_polls',
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'time': '0.002'}]
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``connection.queries`` is only available if :setting:`DEBUG` is ``True``.
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It's a list of dictionaries in order of query execution. Each dictionary has
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the following:
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* ``sql`` - The raw SQL statement
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* ``time`` - How long the statement took to execute, in seconds.
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``connection.queries`` includes all SQL statements -- INSERTs, UPDATES,
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SELECTs, etc. Each time your app hits the database, the query will be recorded.
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If you are using :doc:`multiple databases</topics/db/multi-db>`, you can use the
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same interface on each member of the ``connections`` dictionary:
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.. code-block:: pycon
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>>> from django.db import connections
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>>> connections["my_db_alias"].queries
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If you need to clear the query list manually at any point in your functions,
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call ``reset_queries()``, like this::
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from django.db import reset_queries
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reset_queries()
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Can I use Django with a preexisting database?
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=============================================
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Yes. See :doc:`Integrating with a legacy database </howto/legacy-databases>`.
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If I make changes to a model, how do I update the database?
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===========================================================
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Take a look at Django's support for :mod:`schema migrations
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<django.db.migrations>`.
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If you don't mind clearing data, your project's ``manage.py`` utility has a
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:djadmin:`flush` option to reset the database to the state it was in
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immediately after :djadmin:`migrate` was executed.
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Do Django models support multiple-column primary keys?
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======================================================
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No. Only single-column primary keys are supported.
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But this isn't an issue in practice, because there's nothing stopping you from
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adding other constraints (using the ``unique_together`` model option or
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creating the constraint directly in your database), and enforcing the
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uniqueness at that level. Single-column primary keys are needed for things such
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as the admin interface to work; e.g., you need a single value to specify
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an object to edit or delete.
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Does Django support NoSQL databases?
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====================================
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NoSQL databases are not officially supported by Django itself. There are,
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however, a number of side projects and forks which allow NoSQL functionality in
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Django.
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You can take a look on `the wiki page`_ which discusses some projects.
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.. _the wiki page: https://code.djangoproject.com/wiki/NoSqlSupport
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How do I add database-specific options to my CREATE TABLE statements, such as specifying MyISAM as the table type?
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==================================================================================================================
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We try to avoid adding special cases in the Django code to accommodate all the
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database-specific options such as table type, etc. If you'd like to use any of
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these options, create a migration with a
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:class:`~django.db.migrations.operations.RunSQL` operation that contains
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``ALTER TABLE`` statements that do what you want to do.
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For example, if you're using MySQL and want your tables to use the MyISAM table
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type, use the following SQL:
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.. code-block:: sql
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ALTER TABLE myapp_mytable ENGINE=MyISAM;
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