Question

I am having an issue with what appears Django using the string name and not getting the “object” associated with that name. I’m trying to use a ManyToMany relationship, but I can’t quite figure it out. The error I am getting is:

AttributeError at <URL>
'str' object has no attribute '_default_manager'

Here’s my model setup:

models/hood.py

class Hood(models.Model):
    name = models.CharField(unique=True)
    restaurants=models.ManyToManyField(Restaurant, through="restaurant_hood_map.RestaurantHoodMap")

    class Meta:
        db_table = "hoods"
        app_label="delivery"

models/restaurant.py

class Restaurant(models.model):
    name=models.ForeignKey(CompanyName)
    is_active=models.BooleanField(default=True)

    class Meta:
        db_table="restaurants"
        app_label="delivery"

models/restuarant_hood_map.py

<import restaurant and hood>
class RestaurantHoodMap(models.Model):
    restaurant = models.ForeignKey(Restaurant)
    hood = models.ForeignKey(Hood)

    class Meta:
        db_table="restaurant_hood_map"
        app_label="delivery"

Now, I know what the problem is…..when I attempt to get the related restaurants off of Hood, I am getting this error. That’s because it’s treating the “restaurant.Restaurant” as a string value. However, I thought it was accepted to use string values in order to avoid circular dependencies? At least thats what I thought from the docs:

https://docs.djangoproject.com/en/dev/ref/models/fields/#foreignkey

I also followed this example, which looked like exactly what I wanted:

How do I tell Django to not create a table for an M2M related field?

However, that doesn’t seem to work when you get a Hood object and do hood.restaurants….it barfs.

Any help would be AWESOME!

UPDATE: I made a slight change to the models to more accurately show what’s happening.

Answer 1

Alright, I got this figured out. It turns out that when you define the “through” parameter of the ManyToManyField it CANNOT point to a class in a different module.

So in my above example, the RestaurantHoodMap class has to be put into the “hood.py” module, and the through has to be changed so that it doesn’t have the module in the name:

restaurants=models.ManyToManyField(Restaurant, through="RestaurantHoodMap")

Now, I’m not sure if this is a bug in Django or not. I thought you could reference a different class with strong notation, but that doesn’t seem to be the case if the class is in a different module.