Django unique together validation with request user - django

Question

In Django, I need to validate unique_together the author and title fields.
The problem is that the author is the request.user so what is the best approach to validate the admin form?
I have this admin:
#admin.register(Document)
class DocumentAdmin(admin.ModelAdmin):
exclude = ('author',)
def save_model(self, request, obj, form, change):
"""Save ``author`` as request user."""
if getattr(obj, 'author', None) is None:
obj.author = request.user
super().save_model(request, obj, form, change)
I can query inside the save_model() and filter both author and title but that doesn't really work well.
I also tried with a forms.ModelForm but I can't manage to get the request.user inside the clean() method.
This is my model:
class Document(models.Model):
title = models.CharField(max_length=32, blank=True)
author = models.ForeignKey(
settings.AUTH_USER_MODEL, on_delete=models.CASCADE
)
class Meta:
unique_together = (('title', 'author'),)
Thank you.

Answer 1

Put a unique_together constrain on your model
class Foo(models.Model):
field_1 = models.CharField(max_length=50)
field_2 = models.CharField(max_length=50)
class Meta:
unique_together = ('field_1', 'field_2')
Django will automatically do the validation for you, if it fails it will throw an IntegrityError (from django.db import IntegrityError)

Answer 2

The author field cannot be excluded from the admin. The solution is to hide the author using the get_form method. The save_model method is still useful if someone tries to change the hidden input value.
#admin.register(Document)
class DocumentAdmin(admin.ModelAdmin):
# exclude = ('author',)
def get_readonly_fields(self, request, obj=None):
"""Make ``author`` field readonly on update."""
return ['author'] if obj else []
def get_form(self, request, obj=None, **kwargs):
"""Hide ``author`` selection default to request user on create."""
form = super().get_form(request, obj, **kwargs)
if not obj:
form.base_fields['author'].initial = request.user
form.base_fields['author'].widget = forms.HiddenInput()
return form
def save_model(self, request, obj, form, change):
"""Save ``author`` field as request user on create."""
if getattr(obj, 'author') != request.user and not change:
obj.author = request.user
super().save_model(request, obj, form, change)