CODEWITHSUNDEEP
pythondjangosqlite
JimBob
JimBob

Reputation: 175

The model has two many-to-many relations through the intermediate model

I have a model that has 2 separate ManyToManyField relations back to itself

class Company(models.Model):
    parent          =     models.ManyToManyField("self", through='CompanyParent', through_fields=('company_child', 'company_parent'), related_name='+')
    child           =     models.ManyToManyField("self", through='CompanyParent', through_fields=('company_parent', 'company_child'), related_name='+')

The above works fine on my localhost Django v3.0.2/ SQLite 3.8.7.2

To actually publish it, I have had to use Django v2.1.15/ SQLite 3.7.17, but with the published version it is chucking out the following errors

companies.Company.child: (fields.E332) Many-to-many fields with intermediate tables must not be symmetrical.

companies.Company.parent: (fields.E332) Many-to-many fields with intermediate tables must not be symmetrical.

companies.Company: (models.E003) The model has two many-to-many relations through the intermediate model 'companies.CompanyParent'.

What's going on here? Solved the first 2 issues by adding symmetrical=False to each model, but no idea how to solve the final error?

Upvotes: 1

Views: 571

Answers (2)

JimBob
JimBob

Reputation: 175

In the event anyone happens across the same issue; the above is the answer but thought I would expand slightly after making the necessary changes to my own project

If you are looking to have numerous many-to-many within the same model and if you are on a version of Django after 2.2a1, then the best method is the one detailed in my question; two different models which you can easily call on views or templates; for example -

> data.manytomany1
> data.manytomany2

However, before 2.2a1 you will have issues. For me, this is because on cPanel, I have to use Django v2.1.15 due to the older SQLite 3.7.17 utilised. This means that you can only have one ManyToManyField (see above) and use a filter to get your 2nd manytomany > you will only be able to do this in the views.py

Hope that makes sense

Upvotes: 1

Jun Zhou
Jun Zhou

Reputation: 1117

You can check this answer to set up two many-to-many relations.

An example from the mentioned answer:

class Person(models.Model): 
    name = models.CharField(max_length=127, blank=False)
    to_users = models.ManyToManyField(
        'self', 
        symmetrical=False, 
        related_name='from_users',
        through='Event', 
        through_fields=('from_user', 'to_user'),
    )

class Event(models.Model):
    item = models.ForeignKey(Item, related_name='events')
    from_user = models.ForeignKey(Person, related_name='events_as_giver')
    to_user = models.ForeignKey(Person, related_name='events_as_receiver')

Upvotes: 3

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