TextField in unique_together breaks with MySQL BLOB index without index key length

[benjaoming]

I get this exception:

_mysql_exceptions.OperationalError: (1170, "BLOB/TEXT column 'text' used in key specification without a key length")

I'm not quite sure about what's the right thing to do. Apparently a text field can't be used in key combinations in MySQL and probably neither in other SQL flavors. So maybe Django should raise an exception and/or the documentation should include which kinds of fields that are valid for the unique_together meta attribute.

An example could be:

class Messages(models.model)
    subject = models.CharField(max_length=20)
    msg = models.TextField
    
    class Meta:
         unique_together = ("subject", "msg")

[benjaoming]

Sorry. That wasn't a runnable example. This one is:

class Message(models.Model):
    subject = models.CharField(max_length=20)
    msg = models.TextField()
    
    class Meta:
         unique_together = ("subject", "msg")

[Simon Greenhill]

Duplicate of the quite old bug #2495. The easy work-around is to leave unique=True off the model, and run ALTER TABLE manually to add the unique constraint.