Re: Problem with CircularDependency Model
Thank you very much for the great answer!
You are correct, I didn't had a clear understanding of the RelatedObject
Principle. I think I added this when I was fiddling with the rest framework.
Of course, I also had thought about making MasterUser a boolean, but I need
to ensure that there is only one MasterUser. I thought about doing it in
the Code, but I thought it might be better to enforce it at Database Level.
However, I think your solution is much better.
I also thought having a separate Table for the MasterUser Relationship,
like you suggested. I tried to some find some suggestions on how to model a
relationship like that. I think, I will go for the boolean field but my
intuitive assumption would be to overwrite the pre_save method. post_save
kinda sounds like it is too late at that point.
Anyway, thanks a lot for you recommendations!
On Friday, May 19, 2017 at 5:50:42 PM UTC+2, Melvyn Sopacua wrote:
>
>
>
> Yep, let me see if I got it right:
>
> - The User model is defined as AUTH_USER_MODEL in settings.py
>
> - User points to institute
>
> - Institute points to User
>
>
>
> So it is in fact a circular dependency on the model level as well. And one
> you don't need.
>
>
>
> From the way you defined the related_name it is also clear you don't get
> the RelatedObject principle of Django.
>
>
>
> A ForeignKey creates a bridge between two models: you can travel in both
> directions. Using your models:
>
>
>
> class User(AbstractBaseUser, PermissionsMixin):
>
> username = ...
>
>
>
> class Institute(models.Model):
>
> master_user = models.ForeignKey(settings.AUTH_USER_MODEL,
> related_name='institute')
>
> members = models.ManyToManyField(settings.AUTH_USER_MODEL)
>
>
>
> Because of the ForeignKey on Institute, Django creates an attribute on
> User, called 'institute'. It uses institute, because I specified that as
> related_name. You could use a different name there, but it has to be a name
> that can be used on the model you point to.
>
>
>
> However, this isn't a good representation of realitity, given your own
> description.
>
> So this is a better way to do it:
>
>
>
> class User(AbstractBaseUser, PermissionsMixin):
>
> institute = models.ForeignKey('port.Institute', related_name='members')
>
> is_master_user = models.BooleanField(default=False)
>
>
>
> class Institute(models.Model)
>
> name = models.CharField(max_length=255)
>
> # members is now created by the foreign key
>
> @property
>
> def master_user(self):
>
> return self.members.get(is_master_user=True)
>
>
>
> This model is much simpler. All you need to do is to verify that when
> someone is made master user, that all other members of the institute are
> *not* master user.
>
>
>
> You can do this in a post_save signal or in the clean method of User ,
> both with its own caveats.
>
>
>
> Another way would be to define a MasterUser model, which is easier to
> maintain in the admin:
>
>
>
> class MasterUser(models.Model):
>
> # Assume one person can be master user of many institutes
>
> # if not, this also has to be a OneToOneFIeld
>
> user = models.ForeignKey(settings.AUTH_USER_MODEL)
>
> institute = models.OneToOneField(Institute, related_name='master_user')
>
> --
>
> Melvyn Sopacua
>
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Re: Problem with CircularDependency Model
On Friday 19 May 2017 00:19:04 Tobias Dacoir wrote:
> No, I am trying to deploy it locally. I have no sqlite DB and no
> migrations. For some strange reason I used to just run manage.py
> makemigrations and would create the initial migrations for all Apps.
> This doesn't work for some reason anymore. So I have to to
> makemigrations APPname for each app and when I run to migrate to
> create the intial database schema, it doesn't work. So I figured my
> Data Model is crap.
Yep, let me see if I got it right:
- The User model is defined as AUTH_USER_MODEL in settings.py
- User points to institute
- Institute points to User
So it is in fact a circular dependency on the model level as well. And one you
don't need.
>From the way you defined the related_name it is also clear you don't get the
>RelatedObject
principle of Django.
A ForeignKey creates a bridge between two models: you can travel in both
directions. Using
your models:
class User(AbstractBaseUser, PermissionsMixin):
username = ...
class Institute(models.Model):
master_user = models.ForeignKey(settings.AUTH_USER_MODEL,
related_name='institute')
members = models.ManyToManyField(settings.AUTH_USER_MODEL)
Because of the ForeignKey on Institute, Django creates an attribute on User,
called 'institute'. It
uses institute, because I specified that as related_name. You could use a
different name there,
but it has to be a name that can be used on the model you point to.
However, this isn't a good representation of realitity, given your own
description.
So this is a better way to do it:
class User(AbstractBaseUser, PermissionsMixin):
institute = models.ForeignKey('port.Institute', related_name='members')
is_master_user = models.BooleanField(default=False)
class Institute(models.Model)
name = models.CharField(max_length=255)
# members is now created by the foreign key
@property
def master_user(self):
return self.members.get(is_master_user=True)
This model is much simpler. All you need to do is to verify that when someone
is made master
user, that all other members of the institute are *not* master user.
You can do this in a post_save signal or in the clean method of User , both
with its own caveats.
Another way would be to define a MasterUser model, which is easier to maintain
in the admin:
class MasterUser(models.Model):
# Assume one person can be master user of many institutes
# if not, this also has to be a OneToOneFIeld
user = models.ForeignKey(settings.AUTH_USER_MODEL)
institute = models.OneToOneField(Institute, related_name='master_user')
> On Wednesday, May 17, 2017 at 5:41:41 PM UTC+2, Melvyn Sopacua wrote:
> > On Wednesday 17 May 2017 05:57:57 Tobias Dacoir wrote:
> > > Thanks Melvyn,
> > >
> > >
> > >
> > > I used promises before, when I use a foreign key for a class that
> > > is
> > >
> > > not yet defined, however it didn't change anything for my problem.
> > > I
> > >
> > > can make migrations, but not migrate. I am starting with a new
> > >
> > > database from scratch.
> > >
> > > self.ensure_not_cyclic(target, lambda x: (parent.key for parent in
> > >
> > > self. node_map[x].parents))
> > >
> > > File
> > >
> > > "/Users/no68tuh2/.virtualenvs/ihearu/lib/python2.7/site-packages/d
> > > jang
> > >
> > > o/db/migrations/graph.py" , line 370, in ensure_not_cyclic
> > >
> > > raise CircularDependencyError(", ".join("%s.%s" % n for n in
> > >
> > > cycle)) django.db.migrations.exceptions.CircularDependencyError:
> > >
> > > play.0001_initial, portal.0001_initial
> > >
> > >
> > >
> > > This CircularDependencyError is driving me crazy.
> >
> > Ah, now I see!
> >
> > This has nothing to do with *model* dependencies. Two *migrations*
> > depend on each other: play and port, both 0001_initial.
> >
> >
> >
> > Do you have any idea how you got into that jam? Did you fiddle with
> > django_migrations table? Maybe run --fake?
> >
> >
> > Melvyn Sopacua
--
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Re: Problem with CircularDependency Model
No, I am trying to deploy it locally. I have no sqlite DB and no
migrations. For some strange reason I used to just run manage.py
makemigrations and would create the initial migrations for all Apps. This
doesn't work for some reason anymore. So I have to to makemigrations
APPname for each app and when I run to migrate to create the intial
database schema, it doesn't work. So I figured my Data Model is crap.
On Wednesday, May 17, 2017 at 5:41:41 PM UTC+2, Melvyn Sopacua wrote:
>
> On Wednesday 17 May 2017 05:57:57 Tobias Dacoir wrote:
>
> > Thanks Melvyn,
>
> >
>
> > I used promises before, when I use a foreign key for a class that is
>
> > not yet defined, however it didn't change anything for my problem. I
>
> > can make migrations, but not migrate. I am starting with a new
>
> > database from scratch.
>
> > self.ensure_not_cyclic(target, lambda x: (parent.key for parent in
>
> > self. node_map[x].parents))
>
> > File
>
> > "/Users/no68tuh2/.virtualenvs/ihearu/lib/python2.7/site-packages/djang
>
> > o/db/migrations/graph.py" , line 370, in ensure_not_cyclic
>
> > raise CircularDependencyError(", ".join("%s.%s" % n for n in
>
> > cycle)) django.db.migrations.exceptions.CircularDependencyError:
>
> > play.0001_initial, portal.0001_initial
>
> >
>
> > This CircularDependencyError is driving me crazy.
>
>
>
> Ah, now I see!
>
> This has nothing to do with *model* dependencies. Two *migrations* depend
> on each other: play and port, both 0001_initial.
>
>
>
> Do you have any idea how you got into that jam? Did you fiddle with
> django_migrations table? Maybe run --fake?
>
> --
>
> Melvyn Sopacua
>
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Re: Problem with CircularDependency Model
On Wednesday 17 May 2017 05:57:57 Tobias Dacoir wrote:
> Thanks Melvyn,
>
> I used promises before, when I use a foreign key for a class that is
> not yet defined, however it didn't change anything for my problem. I
> can make migrations, but not migrate. I am starting with a new
> database from scratch.
>self.ensure_not_cyclic(target, lambda x: (parent.key for parent in
> self. node_map[x].parents))
> File
> "/Users/no68tuh2/.virtualenvs/ihearu/lib/python2.7/site-packages/djang
> o/db/migrations/graph.py" , line 370, in ensure_not_cyclic
> raise CircularDependencyError(", ".join("%s.%s" % n for n in
> cycle)) django.db.migrations.exceptions.CircularDependencyError:
> play.0001_initial, portal.0001_initial
>
> This CircularDependencyError is driving me crazy.
Ah, now I see!
This has nothing to do with *model* dependencies. Two *migrations* depend on
each other:
play and port, both 0001_initial.
Do you have any idea how you got into that jam? Did you fiddle with
django_migrations table?
Maybe run --fake?
--
Melvyn Sopacua
--
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Re: Problem with CircularDependency Model
I am not sure if this is solution but instead of running makemigrations first, I ran migrate --run-syncdb. That got me past this error. -- You received this message because you are subscribed to the Google Groups "Django users" group. To unsubscribe from this group and stop receiving emails from it, send an email to django-users+unsubscr...@googlegroups.com. To post to this group, send email to django-users@googlegroups.com. Visit this group at https://groups.google.com/group/django-users. To view this discussion on the web visit https://groups.google.com/d/msgid/django-users/8bb9c8f8-fd97-4331-bdbd-be01473fa67d%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: Problem with CircularDependency Model
Thanks Melvyn,
I used promises before, when I use a foreign key for a class that is not
yet defined, however it didn't change anything for my problem. I can make
migrations, but not migrate. I am starting with a new database from
scratch.
self.ensure_not_cyclic(target, lambda x: (parent.key for parent in self.
node_map[x].parents))
File
"/Users/no68tuh2/.virtualenvs/ihearu/lib/python2.7/site-packages/django/db/migrations/graph.py"
, line 370, in ensure_not_cyclic
raise CircularDependencyError(", ".join("%s.%s" % n for n in cycle))
django.db.migrations.exceptions.CircularDependencyError: play.0001_initial,
portal.0001_initial
This CircularDependencyError is driving me crazy.
--
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Re: Problem with CircularDependency Model
On Friday 05 May 2017 05:41:52 Tobias Dacoir wrote:
> I am trying to build a model (in two separate apps) which has the
> following constraints:
>
> - There can be many institutes
> - there can many users
> - each user is a member of exactly one institute
> - each institute has exactly one master user
>
> However I am running into CircularDependency errors when trying to
> create this model and database. Of course this model is a bit
> problematic because you can't have an institute without master user,
> but also you can't create a user without some default institute. How
> do I fix this? Should I be more lean on the model side and allow for
> a lot of blanks and null values and make all the exception handling
> somewhere else?
>
> Please tell me how to improve my model.
>
> >> class User(AbstractBaseUser, PermissionsMixin):
> > # account-related information
> > institute = models.ForeignKey(Institute, blank=True, null=True,
institute = models.ForeignKey('mycoolapp.Institute', )
This uses a promise and resolves the model at init stage (rather then class
declaration). Make
sure you remove the import of Institute or it won't help.
If you're interested in the topic of resolving models at runtime, take a loot
at django.apps.Apps,
specifically get_model. But all the work for foreign keys is already done for
you.
--
Melvyn Sopacua
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Re: Problem with CircularDependency Model
Thanks for the suggestion, but I the migration by itself is not the only problem. I still have the feeling I should fine-tune the model somehow. -- You received this message because you are subscribed to the Google Groups "Django users" group. To unsubscribe from this group and stop receiving emails from it, send an email to django-users+unsubscr...@googlegroups.com. To post to this group, send email to django-users@googlegroups.com. Visit this group at https://groups.google.com/group/django-users. To view this discussion on the web visit https://groups.google.com/d/msgid/django-users/884d4bc5-af88-484f-bc9b-e760796fc9f0%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: Problem with CircularDependency Model
Sorry, my earlier suggestion for Institute.members is incorrect. Here's the
correct code:
def members(self):
return self.user_set.all()
For example, if foo is an institute, then foo.user_set.all() would give all
users related to that institution.
Dartos
On Friday, May 5, 2017 at 11:00:46 AM UTC-4, Dartos wrote:
>
> Hi,
>
> Have you tried breaking up the migrations into multiple steps?
>
> First create User and Institute without reference to each other. Then try
> additional migrations.
>
> Also, you can simplify Institute.members using reverse relations as
> follows:
> def members(self):
> return Institute.user_set.all()
>
> Dartos
>
> On Friday, May 5, 2017 at 8:41:52 AM UTC-4, Tobias Dacoir wrote:
>>
>> I am trying to build a model (in two separate apps) which has the
>> following constraints:
>>
>> - There can be many institutes
>> - there can many users
>> - each user is a member of exactly one institute
>> - each institute has exactly one master user
>>
>> However I am running into CircularDependency errors when trying to create
>> this model and database. Of course this model is a bit problematic because
>> you can't have an institute without master user, but also you can't create
>> a user without some default institute. How do I fix this? Should I be more
>> lean on the model side and allow for a lot of blanks and null values and
>> make all the exception handling somewhere else?
>>
>> Please tell me how to improve my model.
>>
>>
>>>
class User(AbstractBaseUser, PermissionsMixin):
>>>
>>> # account-related information
>>> institute = models.ForeignKey(Institute, blank=True, null=True,
>>> on_delete=models.SET(get_default_institute))
>>> username = ...
>>>
>>>
>>> This is the model in another app for the institutes
>>>
>>> class Institute(models.Model):
>>> master_user = models.ForeignKey(settings.AUTH_USER_MODEL,
>>> related_name='master_user')
>>> name = models.CharField(max_length=255)
>>>
>>> def members(self):
>>> UserModel = apps.get_model('play', 'User') # need to avoid
>>> circular import
>>> return UserModel.objects.filter(institute=self)
>>>
>>>
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Re: Problem with CircularDependency Model
Hi,
Have you tried breaking up the migrations into multiple steps?
First create User and Institute without reference to each other. Then try
additional migrations.
Also, you can simplify Institute.members using reverse relations as follows:
def members(self):
return Institute.user_set.all()
Dartos
On Friday, May 5, 2017 at 8:41:52 AM UTC-4, Tobias Dacoir wrote:
>
> I am trying to build a model (in two separate apps) which has the
> following constraints:
>
> - There can be many institutes
> - there can many users
> - each user is a member of exactly one institute
> - each institute has exactly one master user
>
> However I am running into CircularDependency errors when trying to create
> this model and database. Of course this model is a bit problematic because
> you can't have an institute without master user, but also you can't create
> a user without some default institute. How do I fix this? Should I be more
> lean on the model side and allow for a lot of blanks and null values and
> make all the exception handling somewhere else?
>
> Please tell me how to improve my model.
>
>
>>
>>> class User(AbstractBaseUser, PermissionsMixin):
>>
>> # account-related information
>> institute = models.ForeignKey(Institute, blank=True, null=True,
>> on_delete=models.SET(get_default_institute))
>> username = ...
>>
>>
>> This is the model in another app for the institutes
>>
>> class Institute(models.Model):
>> master_user = models.ForeignKey(settings.AUTH_USER_MODEL,
>> related_name='master_user')
>> name = models.CharField(max_length=255)
>>
>> def members(self):
>> UserModel = apps.get_model('play', 'User') # need to avoid
>> circular import
>> return UserModel.objects.filter(institute=self)
>>
>>
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