i do it the other way: generate diagrams from the models definition.
(django-extensions + graphviz).
code generators seem handy, but you have to tweak the code, and if you
later change the diagram regenerating the code usually stomps your
extra modifications.
Django models declaration style is terse enough to allow for quickly
testing lots of possibilities. with an autoupdating diagram on
another window you have a very clear picture of the design.
--
Javier