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    <ol> <li><p>Not having an actual constraint might lead to broken references, invalid parents and other sorts of data inconsistencies. I am not a Django expert but I would venture a guess that in most cases Django will still handle the relations fine unless you purposefully add some invalid records.</p></li> <li><p>Normally, if your RDBMS supports foreign key constraints, there is absolutely no reason not to use them, and it could potentially be considered a design flaw to ignore them.</p></li> <li><p>You should consider adding the key constraints. Not only do they give your DBMS a good idea of how to optimize the queries, they also ensure consistency in your data. I am pretty sure Django has a setting somewhere that will automatically generate the SQL to add the key constraints when you run <code>manage.py syncdb</code></p></li> </ol> <p>For more information about why you should prefer foreign keys, you should read the <a href="http://dev.mysql.com/doc/refman/5.5/en/innodb-foreign-key-constraints.html" rel="nofollow">MySQL Foreign Key Documentation</a></p> <p>Most interestingly:</p> <blockquote> <p>InnoDB requires indexes on foreign keys and referenced keys so that foreign key checks can be fast and not require a table scan. In the referencing table, there must be an index where the foreign key columns are listed as the first columns in the same order. Such an index is created on the referencing table automatically if it does not exist. (This is in contrast to some older versions, in which indexes had to be created explicitly or the creation of foreign key constraints would fail.) index_name, if given, is used as described previously.</p> </blockquote>
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    1. POUnderstanding / mySQL aka tricking ForeignKey relationships in Django
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    1. COThis is really good info - thanks so much for your detailed response - I certainly agree with you on the problems of not having it. That said do you see issues with simply assigning it as a FK without it imposing those constraints? It certainly makes my queries simpler...
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    2. COI'm not sure what you mean by not imposing the constraint. In InnoDB when you have `FOREIGN KEY REFERENCES`, it automatically creates and enforces existence constraints. You don't need a `CONSTRAINT` clause.
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    3. COPoorly worded. Do you see any issue with defining it as a ForeignKey in Django and not imposing that at the db level ; notice managed=False
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