How to implement a ManyToManyField with a View

[Bruce Whealton]

Hello all,

     I started a similar thread but couldn't find it.

I was creating a Personal Information Management Project, with Project name mypim.  My first app was a contacts app.

This has two Class based Models in the models.py in the contacts directory.  My first view works fine, where I display 

a list of contacts.  It seemed that the Django Admin got confused unless I put the Relationship model prior to the Resource model.

Ok, so, I call a Relationship model instead of Contact model for reasons unimportant to my question.  Here is what my models.py looks like

with some fields snipped to show only what is important.

class Relationship(models.Model):

    category = models.CharField(max_length=60)

    def __str__(self):

        return self.category

class Resource(models.Model):

    first_name = models.CharField(max_length=80)

    last_name = models.CharField(max_length=80)

    organization = models.CharField(max_length=100, null=True, blank=True)

    [snip]

    relationship = models.ManyToManyField(Relationship)

    class Meta:

        ordering = ['last_name',]

    def __str__(self):

        return self.first_name +  " " + self.last_name

And my views.py for the app:

def contact_list(request):

    contacts = Resource.objects.all()

    return render(request, 'contacts/contact_list.html', {'contacts': contacts })

def contact_detail(request, pk):

    contact = get_object_or_404(Resource, pk=pk)

    return render(request, 'contacts/contact_detail.html', {'contact': contact})

End of File.

Ok, so when I display the list of contacts/resources, things look fine and I can click on a contact and see

the details, aka full listing of the contact, minus the categories which come from the Resource.  I know things cannot be 

correct in that the view doesn't seem to query for the categories assigned to the Contact, aka Resource.  My contact_detail.html

template has this section for displaying the category in the Relationship model and I do have defined relationships.

    <section>

      {% for relationship in contact.relationship_set.all %}

        <h3>{{ relationship.category }}</h3>

      {% endfor %}

    </section>

Can someone guide me here, please?  I'd actually like to display the categories separated by commas on the same line.  However, I am not seeing

anything in this area.

Thanks in advance for any help,

Bruce

[Simon Charette]

Hi Bruce,

I think you want to call get_object_or_404 with the Contact model in your
contact_detail() view.

Cheers,
Simon

[Bruce Whealton]

I have that in the contacts/views.py
However, I don't know if it needs the context dictionary to have something which would
connect a contact to many categories.
Thanks,
Bruce

[Daniel Roseman]

The many-to-many field is defined on the Resource model itself, so you use that field itself, rather than any "reverse" relationship syntax.

     {% for relationship in contact.relationship.all %}

(Since that field refers to many objects, you may want to call it "relationships" instead.)

-- 

DR.

[Akhil Lawrence]

Hi Bruce,

You need to call `contact.relationship.all` instead of `contact.relationship_set.all`

We use `_set.all` when we want to retrieve the related items from the master/parent object (Relationship in your case). So if you want to retrieve all contacts under a relationship you can use `<Relationship-obj>.resource_set.all`