Let us say I have a model for social network posts, users and likes:
class Post(models.Model):
submitter = models.ForeignKey(User, null=False, default=None)
content = models.CharField()
date = models.DateField()
with_likes = PostLikeCountManager()
objects = models.Manager()
class Like(models.Model):
user = models.ForeignKey(User)
post = models.ForeignKey(Post)
time = models.DateTimeField(auto_now_add=True)
It would be helpful to think of Post model as representing a Facebook post. Now, I would like to limit one like per post per user. How do I achieve that? One way would be to create a composite primary key on (user, post) attributes of Like class. I don't know how to achieve that in Django. The other would be to use unique=True on two attributes simultaneously. Is that possible?
Thanks.
Yes, use unique_together:
class Like(models.Model):
user = models.ForeignKey(User)
post = models.ForeignKey(Post)
time = models.DateTimeField(auto_now_add=True)
class Meta:
unique_together = ('user', 'post')
unique_together will be deprecated in the future version, instead you could apply UniqueConstraint. This and this link gives example code.
class Like(models.Model):
user = models.ForeignKey(User)
post = models.ForeignKey(Post)
time = models.DateTimeField(auto_now_add=True)
class Meta:
constraints = [
models.UniqueConstraint(fields=['user', 'post'], name='unique_user_post'),
]
Related
I have two django models as follows:
The first one is a user profile, which has a FK to User model:
class Profile(models.Model):
PRF_user = models.OneToOneField(User, related_name='related_PRF_user', on_delete=models.CASCADE)
PRF_Priority_Support = models.BooleanField(default=False)
and the second is ticket model which has a FK to User model:
class ticket(models.Model):
ticket_status_options = [
('open', 'open'),
('wait_customer_reply', 'wait_customer_reply'),
('replied_by_staff', 'replied_by_staff'),
('replied_by_customer', 'replied_by_customer'),
('solved', 'solved'),
]
TKT_USER = models.ForeignKey(User, related_name='TKT_USER', on_delete=models.CASCADE)
TKT_DEB = models.ForeignKey('Site_departments', related_name='related_ticket_department', on_delete=models.CASCADE)
TKT_SUB = models.CharField(max_length=50, db_index=True, verbose_name="ticket subject")
TKT_BOD = models.TextField(verbose_name="ticket body")
TKT_image_attachment = models.ImageField(upload_to='TKT_img_attachment', blank=True, null=True , default=None)
TKT_CREATED_DATE = models.DateTimeField(auto_now_add=True)
TKT_UPDATED_DATE = models.DateTimeField(auto_now=True)
I want to sort the tickets based on user profile Priority_Support:
If the user profile PRF_Priority_Support is True, I want to sort it first inside my views QuerySet, otherwise (if PRF_Priority_Support is False) I want to sort it normally.
How can I do this?
You should name your model starting with a capital letter.
And for ordering the tickets, you can use something like this:
' queryset_list = ticket.objects.order_by('-TKT_USER__related_PRF_user__PRF_Priority_Support')
In filtering, when you want to span relationships, you use double underscore __ .
More on this here:
https://docs.djangoproject.com/en/3.1/topics/db/queries/#lookups-that-span-relationships
Another way is adding ordering to your model's Meta class.
For Example:
MyModel(models.Model):
class Meta:
ordering = ('-my_boolean_field ',)
Hi you should filter as follow:
Model.objects.filter(field=True) or False depending on what you need
Regards
I am building an Instagram like app and trying to make a like model. Each user can like a post however, it should not be possible to like the same post twice.
class Like(models.Model):
user = models.ForeignKey(User, on_delete=models.CASCADE)
post = models.ForeignKey(Post, on_delete=models.CASCADE)
created = models.DateTimeField(auto_now_add=True)
This is my model however, I am able to create 2 identical objects. For example user 1 can have 2 like objects like to post 1.
Is there a way to do this?
Yes, you can mark the combination of the user and post field as unique with a UniqueConstraint [Django-doc]:
class Like(models.Model):
user = models.ForeignKey(User, on_delete=models.CASCADE)
post = models.ForeignKey(Post, on_delete=models.CASCADE)
created = models.DateTimeField(auto_now_add=True)
class Meta:
constraints = [
models.UniqueConstraint(fields=['user', 'post'], name='like_once')
]
Prior to django-2.2, you can make use of the unique_together option [Django-doc]:
class Like(models.Model):
user = models.ForeignKey(User, on_delete=models.CASCADE)
post = models.ForeignKey(Post, on_delete=models.CASCADE)
created = models.DateTimeField(auto_now_add=True)
class Meta:
unique_together = [['user', 'post']]
Note: It is normally better to make use of the settings.AUTH_USER_MODEL [Django-doc] to refer to the user model, than to use the User model [Django-doc] directly. For more information you can see the referencing the User model section of the documentation.
In the past, I think there was a model atrtibute named unique_for to define a foreignKey but I can't find it anymore.
Suppose a model named Recommendation. A User can recommend many websites but only one by domain. So, I wanted to set a unique_for('user', 'recommendation.domain') or something like like this.
What's the current way to do it ?
Recommendation Model:
class Recommendation(models.Model):
is_recommended = models.BooleanField(default=True)
what = models.ForeignKey('Website', on_delete=models.CASCADE)
who = models.OneToOneField(User, on_delete=models.CASCADE)
title = models.CharField(max_length=255)
why = models.CharField(max_length=255, null=True, blank=True)
when = models.DateTimeField(auto_now_add=True)
class Meta:
ordering = ["-when"]
User Model is the Django built in.
Thanks
I've found my answser.
The attribute is unique_together and not unique_for
I have the following three models structured around the premise of the Survey.
class Survey(models.Model):
...
id = models.UUIDField(_('Id'), primary_key=True, default=uuid.uuid4, editable=False,)
name = models.CharField(_('Name'), max_length=120, blank=True, unique=True)
slug = models.SlugField(_('Slug'), max_length=120, blank=True, unique=True)
description = models.TextField(_('Description'), blank=True)
...
Each Survey can have multiple questions SurveyQuestion:
class SurveyQuestion(models.Model):
...
survey = models.ForeignKey('surveys.Survey', on_delete=models.CASCADE, null=True, blank=True,)
And each SurveyQuestion can have multiple answers SurveyQuestionAnswer:
class SurveyQuestionAnswer(models.Model):
...
survey_question = models.ForeignKey('surveys.SurveyQuestion', on_delete=models.CASCADE, null=True, blank=True,)
For the sake of brevity, imagine my Survey serializers as being as simple as possible:
class SurveySerialializer(serializers.ModelSerializer):
class Meta:
model = Survey
fields = ('__all__')
Effectively, what I have is the following:
class Survey(APIView):
"""
Survey GET request endpoint: fetches Survey
"""
permission_classes = User
def get(self, request, survey_slug):
survey = Survey.objects.get(slug=survey_slug)
serializer = SurveySerializer(survey)
response = get_hug_response(message='Organisation Active Survey Fetched Successfully', data=serializer.data)
return Response(data=response, status=status.HTTP_200_OK)
But, as you could all probably tell, the corresponding surveys.get('slug') fetch only returns the fields in the Survey model. Ideally, I would like to have some sort of fetch for each SurveyQuestion, and within that nested the SurveyQuestionAnswers
Any pro-tips and pointers would be most appreciated.
I have tried a few things, that only throw errors. I'm struggling to know what this type of API relationship is called in DRF so I can't find appropriate example guides to base the same principles from...
Relevant versions:
Django==2.2.1
djangorestframework==3.9.3
Create two serializers, SurveyQuestionAnswerSerializer and SurveyQuestionSerializer
class SurveyQuestionAnswerSerializer(serializers.ModelSerializer):
class Meta:
model = SurveyQuestionAnswer
fields = '__all__'
class SurveyQuestionSerializer(serializers.ModelSerializer):
survey_questionanswers = SurveyQuestionAnswerSerializer(many=True, read_only=True, source="surveyquestionanswer_set")
class Meta:
model = SurveyQuestion
fields = '__all__'
class SurveySerializer(serializers.ModelSerializer):
survey_questions = SurveyQuestionSerializer(many=True, read_only=True, source="surveyquestion_set")
class Meta:
model = Survey
fields = '__all__'
For more info,
1. What is related_name used for in Django?
2. DRF Serializer's source argument
I'm new in Django and DRF, have questions with serialization.
I have models:
class Commodity(models.Model):
shop = models.ForeignKey(Company, on_delete=models.PROTECT)
price = models.DecimalField(max_digits=10, decimal_places=2)
active = models.BooleanField(default=False)
class Clother(models.Model):
commodity = models.ForeignKey(Commodity, related_name='commodity', on_delete=models.CASCADE)
color = models.ManyToManyField(Color, related_name='color')
material = models.ManyToManyField(Material, related_name='material')
gender = models.CharField(max_length=2, choices=GENDER_CHOICES, default=UNISEX)
class Outwear(models.Model):
clother = models.ForeignKey(Clother, on_delete=models.CASCADE)
name = models.CharField(max_length=30, blank=True)
outwear_type = models.ForeignKey(OutwearType, on_delete=models.CASCADE)
size = models.ManyToManyField(ClotherSize)
So I suppose to make a Serializer like that:
class OutwearSerializer(serializers.ModelSerializer):
commodity = CommoditySerializer(many=False, read_only=False)
clother = ClotherSerializer(many=False, read_only=False)
class Meta:
model = Outwear
fields = ('commodity', 'clother', 'name', 'outwear_type', 'size')
As I understand that read_only fields let me add or edit Outwear object further, but I supposed to have 2 types of permition:
All users can see only active Commodity objects.
Only Companies can create and edit their own objects.
Do I need to make 2 Serializer Models for read_only=True/False?
What is the best practice and where can I find good examples of something familiar?
I call User - unauthorized User. Company is authorized User.
Thanks!
For your first question:
class CommoditySerializer(ModelSerializer):
class Meta:
model = Commodity
fields = (shop, price)
Class CommodityActiveAPIView(generics.ListAPIView):
serializer_class = serializers.CommoditySerializer
queryset = Commodity.objects.filter(active=True)
second question is ambiguous. first define user role please