[Answered ]-In upgrading to Django 1.8, why do I get the AttributeError 'ManyToManyRel' object has no attribute 'rel'?

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2đź‘Ť

Was responding to Alasdair’s comment and got to playing with our admin code, and I was able to narrow it down to the method call that was causing the error.

We have a Lead model that relates to our Company model via a ManyToManyField (i.e. one lead can be for one or more companies). The field that relates Lead to Company has a related_name of “leads”.

class Company(models.Model):
    ...

class Lead(models.Model):
    companies = models.ManyToManyField(Company, blank=True, related_name='leads')
    ...

The CompanyAdmin, looks like the following:

class CompanyAdmin(admin.ModelAdmin):
    ...
    readonly_fields = 'leads',
    ...
    def leads(self, obj):
        ...

So what appears to have been happening was, when we were trying to access the leads method from CompanyAdmin, Django was instead trying to access the company’s Lead objects via the related name — the ManyToManyField that was throwing the error. I resolved the conflict by changing the method name in the admin to “my_leads”.

Looks like something was changed somewhere between 1.8 and the final version of 1.6 that has opened the door to potential conflict between related names and admin methods. The solution, make sure there is no overlap in naming, and things should work fine.

👤meesterguyperson

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