Django / OnetoMany relation within the same class - django

Here is my models.py
class Scenes(models.Model):
name = models.SlugField('Scene name', max_length=60,unique=True)
record_date = models.DateTimeField('Scene date')
manager = models.ForeignKey(
settings.AUTH_USER_MODEL,
blank=True,
null=True,
on_delete=models.SET_NULL)
description = models.TextField(blank=True)
previous = models.OneToOneField(
'self',
blank=True,
null=True,
related_name='next',
on_delete=models.SET_NULL
)
I have started with one instance : Scene1
The problem is I want to have on to many choices and not one to one like explained below
Nevertheless, When I change to
previous = models.ManyToManyField(
Then I also get an error about on_delete :
TypeError: init() got an unexpected keyword argument 'on_delete'
What would be the best djangonic way ?

As I understand, your requirements are:
One scene can have only one previous scene
One scene can have many next scenes
You are almost there. Instead of OneToOneField, use ForeignKey with self reference:
previous = models.ForeignKey('self', related_name='next', ...)

Related

How to make django association reference to itself

I have:
class Direction(models.Model):
left = models.OneToOneField(
'self', on_delete=models.SET_NULL, null=True, related_name='right')
right = models.OneToOneField(
'self', on_delete=models.SET_NULL, null=True, related_name='left')
The error:
ant.Direction.left: (fields.E302) Reverse accessor for 'ant.Direction.left' clashes with field name 'ant.Direction.right'.
HINT: Rename field 'ant.Direction.right', or add/change a related_name argument to the definition for field 'ant.Direction.left'.
How does one make this relationship so that a.left = b and b.right = a?
You can not use as related_name the same as the fields that have been defined. You likely do not want to work with two OneToOneFields anyway, you can define a single OneToOneField, and set the related name to the opposite, so:
class Direction(models.Model):
left = models.OneToOneField(
'self',
on_delete=models.SET_NULL,
null=True,
related_name='right'
)
# no right
So now if a direction a has as .left a direction b, then b has as .right the object a.
If there is no .right, then accessing .right will raise a Direction.DoesNotExist exception, we can however fix this issue by making use of another for the related_name, and work with a property that will wrap it in a try-except:
class Direction(models.Model):
left = models.OneToOneField(
'self',
on_delete=models.SET_NULL,
null=True,
related_name='_right'
)
#property
def right(self):
try:
return self._right
except Direction.DoesNotExist:
return None
#right.setter
def _set_right(self, value):
self._right = value

django prefetch_related not working

I am trying to export all my database with a prefetch_related but I only get data from the main model.
My models:
class GvtCompoModel(models.Model):
gvtCompo= models.CharField(max_length=1000, blank=False, null=False)
...
class ActsIdsModel(models.Model):
year = models.IntegerField(max_length=4, blank=False, null=False)
...
class RespProposModel(models.Model):
respPropos=models.CharField(max_length=50, unique=True)
nationResp = models.ForeignKey('NationRespModel', blank=True, null=True, default=None)
nationalPartyResp = models.ForeignKey('NationalPartyRespModel', blank=True, null=True, default=None)
euGroupResp = models.ForeignKey('EUGroupRespModel', blank=True, null=True, default=None)
class ActsInfoModel(models.Model):
#id of the act
actId = models.OneToOneField(ActsIdsModel, primary_key=True)
respProposId1=models.ForeignKey('RespProposModel', related_name='respProposId1', blank=True, null=True, default=None)
respProposId2=models.ForeignKey('RespProposModel', related_name='respProposId2', blank=True, null=True, default=None)
respProposId3=models.ForeignKey('RespProposModel', related_name='respProposId3', blank=True, null=True, default=None)
gvtCompo= models.ManyToManyField(GvtCompoModel)
My view:
dumpDB=ActsInfoModel.objects.all().prefetch_related("actId", "respProposId1", "respProposId2", "respProposId3", "gvtCompo")
for act in dumpDB.values():
for field in act:
print "dumpDB field", field
When I display "field", I see the fields from ActsInfoModel ONLY, the starting model. Is it normal?
You haven't understood the arguments to prefetch_related. It's not a list of fields, but a list of models.
(Note that your field naming convention is also very misleading - respProposId1 and actId are not IDs, but actual instances of the models. Django has created an underlying field in each case by appending _id, so the db columns are respProposId1_id and actId_id. You should just call the fields resp_propos1 and resp_propos2 - also note that normal style is lower_case_with_underscore, not capWords.)
It is normal, that you are seeing fields from ActsInfoModel only. You can access related models via dot notation, like:
acts = ActsInfoModel.objects.all().prefetch_related("actId", "respProposId1", "respProposId2", "respProposId3", "gvtCompo")
for act in acts:
print act.respProposId1.respPropos
Related models are already prefetched, so it won't produce any additional queries. FYI, quote from docs:
Returns a QuerySet that will automatically retrieve, in a single
batch, related objects for each of the specified lookups.

Django model: manytomany with more than one object

I have an Event model. Events can have many 'presenters'. But each presenter can either 1 of 2 different types of profiles. Profile1 and Profile2. How do I allow both profiles to go into presenters?
This will be 100% backend produced. As to say, admin will be selecting "presenters".
(Don't know if that matters or not).
class Profile1(models.Model):
user = models.ForeignKey(User, null=True, unique=True)
first_name = models.CharField(max_length=20, null=True, blank=True)
last_name = models.CharField(max_length=20, null=True, blank=True)
created = models.DateTimeField(auto_now_add=True)
modified = models.DateTimeField(auto_now=True)
about = models.TextField(null=True, blank=True)
tags = models.ManyToManyField(Tag, null=True, blank=True)
country = CountryField()
avatar = models.ImageField(upload_to='avatars/users/', null=True, blank=True)
score = models.FloatField(default=0.0, null=False, blank=True)
organization = models.CharField(max_length=2, choices=organizations)
class Profile2(models.Model):
user = models.ForeignKey(User, null=True, unique=True)
first_name = models.CharField(max_length=20, null=True, blank=True)
last_name = models.CharField(max_length=20, null=True, blank=True)
created = models.DateTimeField(auto_now_add=True)
modified = models.DateTimeField(auto_now=True)
about = models.TextField(null=True, blank=True)
tags = models.ManyToManyField(Tag, null=True, blank=True)
country = CountryField()
avatar = models.ImageField(upload_to='avatars/users/', null=True, blank=True)
score = models.FloatField(default=0.0, null=False, blank=True)
...
class Event(models.Model):
title = models.CharField(max_length=200)
sub_heading = models.CharField(max_length=200)
presenters = ManyToManyField(Profile1, Profile2, blank=True, null=True) ?
...
# I've also tried:
profile1_presenters = models.ManyToManyField(Profile1, null=True, blank=True)
profile2_presenters = models.ManyToManyField(Profile2, null=True, blank=True)
# is there a better way to accomplish this?...
I think you have a desing problem here. In my opinion, you must think what is a Presenter and what's the different between a Presenter with "profile 1" and with "profile 2". What are you going to do with this models? Are you sure there are just two profiles? Is there any chance that, in some time from now, a different profile ("profile 3") appears? And profile 4? and profile N?
I recommend you to think again about your models and their relations. Do NOT make this decision thinking of how difficul/easy will be to handle these models from django admin. That's another problem and i'll bet that if you think your models a little bit, this won't be an issue later.
Nevertheless, i can give you some advice of how to acomplish what you want (or i hope so). Once you have think abount how to model these relations, start thinking on how are you going to write your models in django. Here are some questions you will have to answer to yourself:
Do you need one different table (if you are going to use SQL) per profile?
If you cannot answer that, try to answer these:
1) What's the difference between two different profiles?
2) Are there more than one profile?
3) Each presenter have just one profile? What are the chances that this property changes in near future?
I don't know a lot about what you need but i think the best option is to have a model "Profile" apart of your "Presenter" model. May be something like:
class Profile(models.Model):
first_profile_field = ...
second_profile_field = ...
# Each presenter have one profile. One profile can "represent"
# to none or more presenters
class Presenter(models.Model):
first_presenter_field = ....
second_presenter_field = ....
profile = models.ForeignKey(Profile)
class Event(models.Model):
presenters = models.ManyToManyField(Presenter)
....
This is just an idea of how i imagine you could design your model. Here are some links that may help you once you have design your models correctly and have answered the questions i made to you:
https://docs.djangoproject.com/en/dev/topics/db/models/#model-inheritance
https://docs.djangoproject.com/en/dev/misc/design-philosophies/#models
http://www.martinfowler.com/eaaCatalog/activeRecord.html
And to work with the admin once you decide how your design will be:
https://docs.djangoproject.com/en/dev/ref/contrib/admin/
EDIT:
If i'm not wrong, the only difference between profile 1 and 2 fields is the "organization" field. Am i right? So i recommend you to merge both models since they are almost the same. If they have different methods, or you want to add different managers or whatever, you can use the proxy option of django models. For example, you can do this:
class Profile(models.Model):
#All the fields you listed above, including the "organization" field
class GoldenProfile(models.Model):
#you can define its own managers
objects = GoldenProfileManager()
....
class Meta:
proxy = True
class SilverProfile(models.Model):
....
class Meta:
proxy = True
This way, you can define different methods or the same method with a different behaviour in each model. You can give them their own managers, etcetera.
And the event class should stay like this:
class Event(models.Model):
title = models.CharField(max_length=200)
sub_heading = models.CharField(max_length=200)
presenters = ManyToManyField(Profile, blank=True, null=True)
Hope it helps!

Django ForeignKey TemplateSyntaxError and ProgrammingError

This is are my models i want to relate. i want for collection to appear in the form of occurrence.
class Collection(models.Model):
id = models.AutoField(primary_key=True, null=True)
code = models.CharField(max_length=100, null=True, blank=True)
address = models.CharField(max_length=100, null=True, blank=True)
collection_name = models.CharField(max_length=100)
def __unicode__(self):
return self.collection_name
class Meta:
db_table = u'collection'
ordering = ('collection_name',)
class Occurrence(models.Model):
id = models.AutoField(primary_key=True, null=True)
reference = models.IntegerField(null=True, blank=True, editable=False)
collection = models.ForeignKey(Collection, null=True, blank=True, unique=True),
modified = models.DateTimeField(null=True, blank=True, auto_now=True)
class Meta:
db_table = u'occurrence'
Every time i go to check the Occurrence object i get this error
TemplateSyntaxError at /admin/hotiapp/occurrence/
Caught an exception while rendering: column occurrence.collection_id does not exist
LINE 1: ...LECT "occurrence"."id", "occurrence"."reference", "occurrenc..
And every time i try to add a new occurrence object i get this error
ProgrammingError at /admin/hotiapp/occurrence/add/
column occurrence.collection_id does not exist
LINE 1: SELECT (1) AS "a" FROM "occurrence" WHERE "occurrence"."coll...
What am i doing wrong? or how does ForeignKey works?
The problem is that you have not updated your database table definition since adding the ForeignKey. syncdb doesn't do this for you, as the documentation clearly states. You need to update the SQL manually, or use a tool like South.
Are you sure you mean
collection = models.ForeignKey(Collection, null=True, blank=True, unique=True),
Nullable and Unique? This may not be possible in some databases.
Generally, the unique constraint doesn't seem to make much sense here.
Are you trying to force a 1-to-1 relationship? Use the OneToOneField. http://docs.djangoproject.com/en/1.1/ref/models/fields/#django.db.models.OneToOneField

Django models: Why the name clash?

Firstly, I know how to fix the problem, I'm just trying to understand why it's occuring. The error message:
users.profile: Reverse query name for field 'address' clashes with related field 'Address.profile'. Add a related_name a
rgument to the definition for 'address'.
And the code:
class Address(models.Model):
country = fields.CountryField(default='CA')
province = fields.CAProvinceField()
city = models.CharField(max_length=80)
postal_code = models.CharField(max_length=6)
street1 = models.CharField(max_length=80)
street2 = models.CharField(max_length=80, blank=True, null=True)
street3 = models.CharField(max_length=80, blank=True, null=True)
class Profile(Address):
user = models.ForeignKey(User, unique=True, related_name='profile')
primary_phone = models.CharField(max_length=20)
address = models.ForeignKey(Address, unique=True)
If I understand correctly, this line:
address = models.ForeignKey(Address, unique=True)
Will cause an attribute to be added to the Address class with the name profile. What's creating the other "profile" name?
What if I don't need a reverse name? Is there a way to disable it? Addresses are used for a dozen things, so most of the reverse relationships will be blank anyway.
Is there a way to copy the address fields into the model rather than having a separate table for addresses? Without Python inheritance (this doesn't make sense, and if an Model has 2 addresses, it doesn't work).
in the django docs it says:
If you'd prefer Django didn't create a backwards relation, set related_name to '+'. For example, this will ensure that the User model won't get a backwards relation to this model:
user = models.ForeignKey(User, related_name='+')
but I never tried it myself....
I'm not sure where the errant profile field is coming from… But one way to find out would be: temporary remove address = models.ForeignKey(…) from Profile, ./manage.py shell, from ... import Address then see what Address.profile will tell you.
I don't think there is any official way to inherit only the fields from some other Model without using inheritance… But you could fake it like this (where SourceModel is, eg, Address and TargetModel is, eg, Profile):
for field in SourceModel._meta.fields:
TargetModel.add_to_class(field.name, copy.deepcopy(field))
(this is coming from Django's ModelBase __new__ implementation)
I don't think it's possible to disable the reverse name.
I've just done a quick grep over the code and it doesn't look like there is any logic which will bypass setting up the related_name field on the related model.
For Example: Add just '+'
class GeneralConfiguration(models.Model):
created_at = models.DateTimeField(editable=False, default=settings.DEFAULT_DATE)
updated_at = models.DateTimeField(editable=False, default=settings.DEFAULT_DATE)
created_by = models.ForeignKey(settings.AUTH_USER_MODEL, blank=True, null=True, on_delete=models.PROTECT, related_name='+')
updated_by = models.ForeignKey(settings.AUTH_USER_MODEL, blank=True, null=True, on_delete=models.PROTECT, related_name='+')