I'm writing a simple scaffolding app in django, however I'm still not able to access a models fields and attributes(e.g. CharField, max_length=100, null=True, etc...). I know about the _meta class of models, but as far as I know it only retrieves basic info about the model not the fields. Is there a away to achieve this?
Update:
you can find the answer in this article:
http://www.b-list.org/weblog/2007/nov/04/working-models/
You should use the get_field method to get info for a particular field:
field = ModelName._meta.get_field('field_name')
Then you may check various attributes of field, like field.blank, field.null, field.name etc.
If on the other hand you want to get a list of all fields of a Model you should use fields:
fields = ModelName._meta.fields
For example to get the name of all your model fields you can do something like:
field_names = ', '.join(f.name for f in fields)
Hm... also I just noticed that your question is a duplicate of Get model's fields in Django !
Related
There's a lot of questions worded similarly, but every single one I've seen is somebody trying to get some kind of data through a ManyToMany relationship before saving it. I'm not trying to use the relationship at all before saving, I just want to see if the user put anything there or not.
My model has a ForeignKey field pointing to a parent model, and two ManyToMany fields pointing to other models, but I only want users to be able to use one M2M field or the other, not both. This model is being edited through the admin as an inline on its parent.
models.py
class ProductSpecial(models.Model):
# name, slug, image, etc
class ProductSpecialAmount(models.Model):
special = models.ForeignKey(ProductSpecial, related_name='amounts', on_delete=models.CASCADE)
amount = models.IntegerField()
brands = models.ManyToManyField(ProductBrand, related_name='specials', blank=True)
lines = models.ManyToManyField(ProductLine, related_name='specials', blank=True)
admin.py
class ProductSpecialAmountInline(admin.StackedInline):
model = ProductSpecialAmount
# fieldsets, etc
#admin.register(ProductSpecial)
class ProductSpecialAdmin(admin.ModelAdmin):
inlines = [ProductSpecialAmountInline]
# fieldsets, etc
I only want users to be able to choose from brands or lines, but not both, and I would like to validate this before save and throw a validation error if necessary. My initial attempt was to just do...
class ProductSpecialAmount(models.Model):
# ...
def clean(self):
if self.brands and self.lines:
raise ValidationError('Please choose either brands or lines, not both', code='invalid')
...but that throws ValueError: "<ProductSpecialAmount: ProductSpecialAmount object (None)>" needs to have a value for field "id" before this many-to-many relationship can be used.
I get that I can't actually query the related ProductBrand or ProductModel objects before this object is saved, but I don't actually want any data from those objects right now, I just want to know if the user left either of the fields blank or not, and am wondering if that's possible to see at the model level.
Whether you actually want to use the data from a field or just see if it is blank, the problem is caused by referencing the m2m field in any way before saving the object. I had a similar problem which I fixed using a custom form as per: https://stackoverflow.com/a/7986937/19837155
This might be more difficult when you're using inlines, but it may be the easiest way to solve your problem.
I'm struggling to display a manytomany field in the admin with the related model in a user-friendly manner. The project is already up and running so adding a through table is not preferred.
The set-up is something along these lines;
class User(AbstractUser):
is_member_of_organization = models.ManyToManyField(Organization, blank=True, verbose_name=_("is member of organization(s)"), related_name='orgmembers')
class Organization(models.Model):
name = models.CharField(max_length=60, verbose_name=_("organization name"))
the only reasonable way I manage to display the related users with organization admin is via a TabularInline
admin.py
class UserOrgAdminInLine(admin.TabularInline):
model = User.is_admin_for_organization.through
extra = 0
#admin.register(Organization)
class OrganizationAdmin(admin.ModelAdmin):
inlines = (UserOrgAdminInLine,)
However, looking up users is not convenient as soon as their number increases. I would like something similar to filer_horizontal but I am not sure how to include it directly in the OrganizationAdmin admin class. Furthermore, I am using fieldsets (which I believe should have no special rules or syntax to it compared to ordinary fields = .
One little subquestion - in the tabular inline, when I use only model = User django throws an error that there is no foreign key to it, but when I use the additional .is_admin_for_organization.through it works, but there is no through table and I though that this work just in that case. Why is that?
Any help would be much appreciated.
Try adding
class UserOrgAdminInLine
raw_id_fields = ("is_member_of_organization",)
I have model like this:
class Item(models.Model):
number = models.CharField()
menu = models.ForeignKey(Menu)
class Meta:
unique_together = ('number', 'menu')
what I would like to validate is, that 'number' is unique within certain menu, but ignoring case. E.g if ('a1', 1) then don't allow ('A1', 1).
1) I want do this validation on model level, not form.
2) I want store in database values for number EXACTLY as given on input
My first approach was to do it in model's clean method, but there always value of FK field menu is None, so I got RelatedObjectDoesNotExist. Is it issue with Django 1.8 or it was never possible to handle fk fields in models clean?
I noticed that in save method I can acces FK but I can not raise ValidationError which will be handled nice for user.
What is the best strategy to validate it?
See this ticket.
In a nutshell, you can just item.number = value.lower() before saving.
I am building a blog site and have models in respect of Category and Posts. Posts have a Many to Many relationship for Category.
class Post(models.Model):
categories = models.ManyToManyField(Category)
Everything is working fine aside from the fact that in the Category list in the template I only want to load categories that actually have posts.
If a category is empty I don't want to display it, I have tried to define a relationship in Category to Post to allow me to use something like {{ if category.posts }}. At the moment using another Many to Many field in Category is presently giving me an extra field in admin which I don't really want or feel that's needed.
How is best to navigate this relationship, or create one that's suitable?
Cheers
Kev
Django automatically creates a field on the related model of any ForeignKey or ManyToMany relationship. You can control the name of the field on the related model via the related_name option like that:
class Post(models.Model):
categories = models.ManyToManyField(Category,related_name='posts')
This way, your approach works without any additional fields. Btw, if you leave out the related_name argument, Django will create by default one with [field_name]_set.
You can use reverse relations on ManyToMany fields. In the reverse filter, you must use the related model name (if you did not use related_name attribute). So in your question you can use model name as the reverse name like:
{% if category.post %}
You can also use this in your filtering functions in views:
Category.objects.filter(post__isnull=False)
Reverse relation name must be lowercase.
Check the documentation here
This is how my models look:
class QuestionTagM2M(models.Model):
tag = models.ForeignKey('Tag')
question = models.ForeignKey('Question')
date_added = models.DateTimeField(auto_now_add=True)
class Tag(models.Model):
description = models.CharField(max_length=100, unique=True)
class Question(models.Model):
tags = models.ManyToManyField(Tag, through=QuestionTagM2M, related_name='questions')
All I really wanted to do was add a timestamp when a given manytomany relationship was created. It makes sense, but it also adds a bit of complexity. Apart from removing the .add() functionality [despite the fact that the only field I'm really adding is auto-created so it technically shouldn't interfere with this anymore]. But I can live with that, as I don't mind doing the extra QuestionTagM2M.objects.create(question=,tag=) instead if it means gaining the additional timestamp functionality.
My issue is I really would love to be able to preserve my filter_horizontal javascript widget in the admin. I know the docs say I can use an inline instead, but this is just too unwieldy because there are no additional fields that would actually be in the inline apart from the foreign key to the Tag anyway.
Also, in the larger scheme of my database schema, my Question objects are already displayed as an inline on my admin page, and since Django doesn't support nested inlines in the admin [yet], I have no way of selecting tags for a given question.
Is there any way to override formfield_for_manytomany(self, db_field, request=None, **kwargs) or something similar to allow for my usage of the nifty filter_horizontal widget and the auto creation of the date_added column to the database?
This seems like something that django should be able to do natively as long as you specify that all columns in the intermediate are automatically created (other than the foreign keys) perhaps with auto_created=True? or something of the like
There are ways to do this
As provided by #obsoleter in the comment below : set QuestionTagM2M._meta.auto_created = True and deal w/ syncdb matters.
Dynamically add date_added field to the M2M model of Question model in models.py
class Question(models.Model):
# use auto-created M2M model
tags = models.ManyToMany(Tag, related_name='questions')
# add date_added field to the M2M model
models.DateTimeField(auto_now_add=True).contribute_to_class(
Question.tags.through, 'date_added')
Then you could use it in admin as normal ManyToManyField.
In Python shell, use Question.tags.through to refer the M2M model.
Note, If you don't use South, then syncdb is enough; If you do, South does not like
this way and will not freeze date_added field, you need to manually write migration to add/remove the corresponding column.
Customize ModelAdmin:
Don't define fields inside customized ModelAdmin, only define filter_horizontal. This will bypass the field validation mentioned in Irfan's answer.
Customize formfield_for_dbfield() or formfield_for_manytomany() to make Django admin to use widgets.FilteredSelectMultiple for the tags field.
Customize save_related() method inside your ModelAdmin class, like
def save_related(self, request, form, *args, **kwargs):
tags = form.cleaned_data.pop('tags', ())
question = form.instance
for tag in tags:
QuestionTagM2M.objects.create(tag=tag, question=question)
super(QuestionAdmin, self).save_related(request, form, *args, **kwargs)
Also, you could patch __set__() of the ReverseManyRelatedObjectsDescriptor field descriptor of ManyToManyField for date_added to save M2M instance w/o raise exception.
From https://docs.djangoproject.com/en/dev/ref/contrib/admin/#working-with-many-to-many-intermediary-models
When you specify an intermediary model using the through argument to a ManyToManyField, the admin will not display a widget by default. This is because each instance of that intermediary model requires more information than could be displayed in a single widget, and the layout required for multiple widgets will vary depending on the intermediate model.
However, you can try including the tags field explicitly by using fields = ('tags',) in admin. This will cause this validation exception
'QuestionAdmin.fields' can't include the ManyToManyField field 'tags' because 'tags' manually specifies a 'through' model.
This validation is implemented in https://github.com/django/django/blob/master/django/contrib/admin/validation.py#L256
if isinstance(f, models.ManyToManyField) and not f.rel.through._meta.auto_created:
raise ImproperlyConfigured("'%s.%s' "
"can't include the ManyToManyField field '%s' because "
"'%s' manually specifies a 'through' model." % (
cls.__name__, label, field, field))
I don't think that you can bypass this validation unless you implement your own custom field to be used as ManyToManyField.
The docs may have changed since the previous answers were posted. I took a look at the django docs link that #Irfan mentioned and it seems to be a more straight forward then it used to be.
Add an inline class to your admin.py and set the model to your M2M model
class QuestionTagM2MInline(admin.TabularInline):
model = QuestionTagM2M
extra = 1
set inlines in your admin class to contain the Inline you just defined
class QuestionAdmin(admin.ModelAdmin):
#...other stuff here
inlines = (QuestionTagM2MInline,)
Don't forget to register this admin class
admin.site.register(Question, QuestionAdmin)
After doing the above when I click on a question I have the form to do all the normal edits on it and below that are a list of the elements in my m2m relationship where I can add entries or edit existing ones.