mysql backend doesn't define a max_name_length()

[abeld@…]

MySql has a limit on the length of table, constaint, etc. names
(​http://dev.mysql.com/doc/refman/4.1/en/identifiers.html), however, a
max_name_length() is not defined in django/db/backends/mysql/base.py

This means that long model names can trigger #1820 (In my case, a name
of a constraint was too long, ending up triggering this bug, even
though comment no. 6 on that ticket (​http://code.djangoproject.com/ticket/1820#comment:6)
claims that is solved for constaints.)

Another comment might be comment no. 7 on #10358
(​http://code.djangoproject.com/ticket/10358#comment:7) which mentions
a lack of max_name_length() but somehow doesn't consider this a
problem.

In my case, adding the following:

   def max_name_length(self):
       return 64

to DatabaseOperations in django/db/backends/mysql/base.py appears to
solve the

_mysql_exceptions.OperationalError: (1059, "Identifier name 'somelongmodelname_id_refs_question_ptr_id_8c9b12fefd7d140' is too long")

problem

[Ramiro Morales]

Fixed in #13040.