How to query a many to many relationship in Django

Question

I have a list of organizations that full under different organization types. I have a table that holds the name, phone, etc... and then another table that has an id fixed to an organization type. Then a table that holds the many to many relationship because an organization can have many different organization types.

What I'm wanting to do is list all the clubs alphabetically that fall under every organizational type.

I'm not sure if this needs to be done in views.py or if it should be done in my template file.

Here are my models:

class ClubType(models.Model):
    name = models.CharField(max_length = 250)

    def __unicode__(self):
        return self.name

class Club(models.Model):

    name = models.CharField(max_length = 250,
            verbose_name = "Club or Organization Name",
            )
    created_date = models.DateTimeField(
            auto_now_add = True,
            )
    updated_date = models.DateTimeField(
            auto_now = True,
            auto_now_add = True,
            )
    club_type = models.ManyToManyField(ClubType)
    username = models.CharField(max_length = 100,
            blank = True, null = True
            )
    contact_name = models.CharField(max_length = 250,
            blank = True, null = True,
            )
    phone_number = models.CharField(max_length = 250,
            blank = True, null = True,
            )

    def __unicode__(self):
        return self.name

    class Meta:
        ordering = ('name', )

I'm a noob to python and Django so any help would be greatly appreciated.

Thanks

Can you update the question with some code ? At least the models. Did you use ManyToManyField for the relation ? — mkriheli, Sep 08 '11 at 23:46
I second that motion, some code would be good, it is hard to answer this question otherwise. — James Hurford, Sep 09 '11 at 04:11
code from the models.py for those tables you have mentioned. — Pannu, Sep 09 '11 at 05:17

score 5 · Accepted Answer · edited May 23 '17 at 10:28

5

Basically you need to do the following steps:

Get the distinct club types
For each club type, select the clubs that include that type (also see this)
Sort the selection from #2 alphabetically

There are many ways to achieve this, and I would not recommend putting this logic into the template for the simple fact that expressing the logic behind it is probably easier in the view (or in a custom Manager if you get adventurous later in your Django life)

An example (warning: untested code):

# step 1
club_types = ClubTypes.objects.distinct()

# step 2 & #3
club_sets = []
for current_club_type in club_types:
    cset = Clubs.objects.filter(club_type__id=current_club_type.pk).order_by('name')
    club_sets.append((current_club_type, cset))

What you are left with in the end is a list of club type lists, each sorted by name that is of the form:

[ (clubtype1, [ club1, club2, ...]), (clubtype2, [ club2, club8, ...]), ... ]

edited May 23 '17 at 10:28

Community

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answered Sep 09 '11 at 17:40

awesomo

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what would the logic in my template file look like? Would I have to do a forloop there? This looks like it's creating one big array am I right? – bigmike7801 Sep 09 '11 at 17:51
Assuming you want to display the information as a list of clubtypes, each with a sublist of clubs, then you would just need a 2 nested for loops to walk over the ``club_sets`` result. updated answer with an example of what the data in ``club_sets`` will look like. – awesomo Sep 09 '11 at 17:55
This works mostly except I'd like to be able to display the club type name as well above each list of all club types – bigmike7801 Sep 09 '11 at 18:10
1

ok, it's simple to remember the clubtype as well. the example has been updated. now you get a list of tuples of the form (clubtype, clubs). – awesomo Sep 09 '11 at 19:04

How to query a many to many relationship in Django

1 Answers1