Resolving circular model imports caused by Haystack & Django
So, in converting our search to Haystack, I’ve found that some of my standalone maintainence scripts no longer work. They had an import error trying to import some of the models.
The issue is that I’ve updated my models.py with some Haystack code. The code at hand is in the save() method of the model object, and basically looks like this:
[... other misc django imports above ... ]
from haystack import site
class MyModel(models.Model):
[ ... fields of model, etc. ... ]
def save(self, force_insert=False, force_update=False):
super(MyModel, self).save(force_insert, force_update)
if self.is_child_node():
site.get_index(MyModel).update_object(self.parent)
The problem was that if I had a standalone script that said:
from mysite.models import MyModel
Then I would get a circular import, because the “from haystack import site” line ends up working it’s way over to search_sites.py that says “haystack.autodiscover()” which ends up looking for all search_indexes.py, and one of these says “from myapp.models import MyModel”. So, there’s your circular reference.
The solution to this problem is to put a haystack import at the top of my standalone script, before I import my model. Adding “from haystack import site” works, even though the code therein doesn’t actually use haystack.
I think the haystack code here:
/usr/lib/python2.5/site-packages/haystack/__init__.py in autodiscover()
88 # Step 3: import the app's search_index file. If this has errors we want them
89 # to bubble up.
---> 90 __import__("%s.search_indexes" % app)
91
92 # Make sure the site gets loaded.
Should have a try/except block around it, and then this extra import wouldn’t be necessary. The funny thing is that looking at the source, all the other imports there catch ImportError and don’t pass it back up, but this case does.
I was able to simply debug this in ipython my running “from myapp.models import MyModel” and debugging, per above. It was fairly clear that it’s a circular import. I’m surprised (in general) that Python doesn’t handle circular imports any more gracefully than saying “<type ‘exceptions.ImportError’>: cannot import name MyModel”
