FAQ: Databases and models¶

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 SQL recorded here may be incorrectly quoted under SQLite.

If you are using multiple databases, 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 Integrating with a legacy database.

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 a flush option to reset the database to the state it was in immediately after syncdb was executed.

If you do care about deleting data, you’ll have to execute the ALTER TABLE statements manually in your database.

There are external projects which handle schema updates, of which the current defacto standard is south.

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 SQL initial data file 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 SQL initial data file 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()