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pythondjangomany-to-many
Brian
Brian

Reputation: 1743

Django ManyToManyField ordering using through

Here is a snippet of how my models are setup:

class Profile(models.Model):     
    name = models.CharField(max_length=32)

    accout = models.ManyToManyField(
        'project.Account',
        through='project.ProfileAccount'
    )

    def __unicode__(self)
        return self.name

class Accounts(models.Model):
    name = models.CharField(max_length=32)
    type = models.CharField(max_length=32)

    class Meta:
        ordering = ('name',)

    def __unicode__(self)
        return self.name

class ProfileAccounts(models.Model):
    profile = models.ForeignKey('project.Profile')
    account = models.ForeignKey('project.Accounts')

    number = models.PositiveIntegerField()

    class Meta:
        ordering = ('number',)

Then when I access the Accounts, how can I sort by 'number' in the intermediary ProfileAccounts model, rather than the default 'name' in the Accounts Model?:

for acct_number in self.profile.accounts.all():
    pass

This does not work, but is the gist of how I want it to access this data:

for scanline_field in self.scanline_profile.fields.all().order_by('number'):
    pass

Upvotes: 29

Views: 28433

Answers (7)

zalun
zalun

Reputation: 4891

I just came through this.

class Profile(models.Model):     
    accounts = models.ManyToManyField('project.Account',
                                      through='project.ProfileAccount')

    def get_accounts(self):
        return self.accounts.order_by('link_to_profile')


class Account(models.Model):
    name = models.CharField(max_length=32)


class ProfileAccount(models.Model):
    profile = models.ForeignKey('project.Profile')
    account = models.ForeignKey('project.Account', related_name='link_to_profile')
    number = models.PositiveIntegerField()

    class Meta:
        ordering = ('number',)

I removed the fields which were off-topic except of Account.name. That's the shortest solution I've found, no idea if it was possible to use in 2010, but it certainly is now.

Upvotes: 32

racitup
racitup

Reputation: 464

I have this on a number of my models, but in my opinion (and unlike all the other answers) you shouldn't need to specify the order_by again because, well, it's already specified in the through model. Specifying it again breaks the DRY (don't repeat yourself) principle.

I would use:

qs = profile.profileaccounts_set.all()

This gives the set of ProfileAccounts associated with a profile using your configured ordering. Then:

for pa in qs:
    print(pa.account.name)

For bonus points, you can also speed up the overall process by using select_related in the query.

Upvotes: 0

Mikus
Mikus

Reputation: 322

The easiest solution for this particular problem seems to be

for acct in self.profile.accounts.order_by('profileaccounts'):
    pass

Upvotes: 0

Murat Çorlu
Murat Çorlu

Reputation: 8545

That worked for me:

Profile.objects.account.order_by('profileaccounts')

Upvotes: 6

Mp0int
Mp0int

Reputation: 18727

a ManyToManyField manager allows you to select/filter data from the related model directly, without using any model connection of the through model on your django level...

Likewise,

if you try:

pr = Profile.objects.get(pk=1)
pr.account.all()

returns you all account related to that profile. As you see, there exists no direct relation to the through model ProfileAccount, so you can not use the M2M relation at this point... You must use a reverse relation to the through model and filter the results...

pr = Profile.objects.get(pk=1)
pr.profileaccount_set.order_by('number')

will give you an ordered queryset, but, in this case, what you have in queryset is profileaccount objects, not account objects... So you have to use another django level relation to go to each related account with:

pr = Profile.objects.get(pk=1)
for pacc in pr.profileaccount_set.order_by('number'):
    pacc.account

Upvotes: 5

shabss
shabss

Reputation: 59

Add the related name to ProfileAccounts and then change the ordering in Accounts with that 'related_name__number'. Note two underscores between related_name and number. See below:

class Accounts(models.Model):
    .
    .
    .
    class Meta:
        ordering = ('profile_accounts__number',)


class ProfileAccounts(models.Model):
    .
    .
    .
    account = models.ForeignKey('project.Accounts', related_name='profile_accounts')

    number = models.PositiveIntegerField()

    class Meta:
        ordering = ('number',)

Upvotes: 5

Andrew Gorcester
Andrew Gorcester

Reputation: 19973

There's a typo in the Profile (it's "accout" when I think you mean "account"), but more importantly you have your singular/plural forms mixed up in the model.

In Django the practice is generally to name your classes singular, and your ManyToManyField names plural. So:

class Profile(models.Model):     
    name = models.CharField(max_length=32)

    accounts = models.ManyToManyField(
        'Account',
        through='ProfileAccount'
    )

    def __unicode__(self)
        return self.name

class Account(models.Model):
    name = models.CharField(max_length=32)
    type = models.CharField(max_length=32)

    class Meta:
        ordering = ('name',)

    def __unicode__(self)
        return self.name

class ProfileAccount(models.Model):
    profile = models.ForeignKey(Profile)
    account = models.ForeignKey(Account)

    number = models.PositiveIntegerField()

    class Meta:
        ordering = ('number',)

I'm a little confused at what you're trying to do with this model, but if you make those changes, then for acct_number in self.profile.accounts.all().order_by('number'): should work. Assuming no other issues.

Upvotes: 2

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