In this model:
class Rank(models.Model):
User = models.ForeignKey(User)
Rank = models.ForeignKey(RankStructure)
date_promoted = models.DateField()
def __str__(self):
return self.Rank.Name.order_by('promotion__date_promoted').latest()
I'm getting the error:
Exception Value:
'str' object has no attribute 'order_by'
I want the latest Rank as default. How do I set this?
Thanks.
Update #1
Added Rank Structure
class RankStructure(models.Model):
RankID = models.CharField(max_length=4)
SName = models.CharField(max_length=5)
Name = models.CharField(max_length=125)
LongName = models.CharField(max_length=512)
GENRE_CHOICES = (
('TOS', 'The Original Series'),
('TMP', 'The Motion Picture'),
('TNG', 'The Next Generation'),
('DS9', 'Deep Space Nine'),
('VOY', 'VOYAGER'),
('FUT', 'FUTURE'),
('KTM', 'KELVIN TIMELINE')
)
Genre = models.CharField(max_length=3, choices=GENRE_CHOICES)
SPECIALTY_OPTIONS = (
('CMD', 'Command'),
('OPS', 'Operations'),
('SCI', 'Science'),
('MED', 'Medical'),
('ENG', 'Engineering'),
('MAR', 'Marine'),
('FLT', 'Flight Officer'),
)
Specialty = models.CharField(max_length=25, choices=SPECIALTY_OPTIONS)
image = models.FileField(upload_to=image_upload_handler, blank=True)
This is the Rank_structure referenced by Rank in Class Rank.
THe User Foreign key goes to the standard User table.
The reason that you’re getting an error is because self.Rank.Name is not a ModelManager on which you can call order_by. You’ll need an objects in there somewhere if you want to call order_by. We can’t help you with the django formatting for the query you want unless you also post the model definitions as requested by several commenters. That said, I suspect that what you want is something like:
def __str__(self):
return self.objects.filter(Rank_id=self.Rank_id).order_by('date_promoted').latest().User.Name
Related
can someone help me and teach me what happens?
For me not to make mistakes again?
I want to bind a foreign key (class category) to my course class. And I did something that doesn't allow me to get out of it.
Error: django.db.utils.IntegrityError: The row in table 'courses_course'
with primary key '3' has an invalid foreign key:
courses_course.category_id contains a value 'outros' that does not have a
corresponding value in courses_category.id.
CATEGORY = [('eng','ENGENHARIA'),('prog','PROGRAMAÇÃO'),('hum','HUMANAS'),('saude','SAÚDE'),
('outros','OUTROS')] // i'm from brazil
class Category(models.Model):
title_category = models.CharField('Nome da Categoria', max_length= 63 , choices = CATEGORY )
class Course(models.Model):
title = models.CharField('Nome', max_length= 100)
slug = models.SlugField('Atalho',max_length=50)
description = models.TextField('Descricao',blank = True)
follows = models.IntegerField(default = 0) //allows negative numbers, I know. I'll fix it ...
imagem = models.ImageField(upload_to = 'courses/images',verbose_name= 'Imagem',
null=True, blank = True)
category = models.ForeignKey('Category', on_delete = models.CASCADE)
created_at = models.DateTimeField('Criado em',auto_now_add = True )
updated_at= models.DateTimeField( 'Atualizado em', auto_now = True )
Does anyone imagine another structure or class that allows you to create educational courses / videos that have categories? Or am I on the right track for a beginner?
The only thing I can guess with the information you gave (you didn't say WHEN you get this error) is that you tried to do something such as :
my_course.category = 'outros'
my_course.save()
Which is incorrect since it isn't a Category object. A ForeignKey field must refer to an object of type to which you point to.
category = Category.objects.create(title_category='outros')
my_course.category = category
my_course.save()
This would work since you give a reference to a Category object in your Course object.
Do not hesitate to read the documentation about ForeignKey fields again.
I currently have the following 3 models
class modelToolName(models.Model):
tool_name = models.CharField(max_length=250,unique=True)
class modelBodyPart(models.Model):
part_name = models.CharField(max_length=128,unique=True)
class modelNormalBodyPartResult(models.Model):
body_part = models.ForeignKey(modelBodyPart, default=None)
tool_name = models.ManyToManyField(modelToolName, default=None, blank=True)
result = models.TextField(blank=True, null=True)
Now I am attempting to insert value into the modelNormalBodyPartResult in this way
result="xxxx"
bodpart = modelBodyPart.objects.get(part_name="xxx") #--->returns object fine
toolqset = modelToolName.objects.get(tool_name="xxx")#--->returns object fine
modelNormalBodyPartResult.objects.create(body_part=bodpart,tool_name = toolqset,result=result) --->error
and I get the error
<modelNormalBodyPartResult: modelNormalBodyPartResult object> needs to have a value for field "modelnormalbodypartresult" before this many-to-many relationship can be used.
I looked at this post but still could not figure out the issue any suggestions in this regard would be appreciated.
You have to create an object first, then add the ManyToMany related objects to it,
result="xxxx"
bodpart = modelBodyPart.objects.get(part_name="xxx")
toolqset = modelToolName.objects.get(tool_name="xxx")
item = modelNormalBodyPartResult.objects.create(body_part=bodpart,result=result)
item.tool_name.add(toolqset)
item.save()
I have a History model like below
class History(models.Model):
class Meta:
app_label = 'subscription'
ordering = ['-start_datetime']
subscription = models.ForeignKey(Subscription, related_name='history')
FREE = 'free'
Premium = 'premium'
SUBSCRIPTION_TYPE_CHOICES = ((FREE, 'Free'), (Premium, 'Premium'),)
name = models.CharField(max_length=32, choices=SUBSCRIPTION_TYPE_CHOICES, default=FREE)
start_datetime = models.DateTimeField(db_index=True)
end_datetime = models.DateTimeField(db_index=True, blank=True, null=True)
cancelled_datetime = models.DateTimeField(blank=True, null=True)
Now i have a queryset filtering like below
users = get_user_model().objects.all()
queryset = users.exclude(subscription__history__end_datetime__lt=timezone.now())
The issue is that in the exclude above it is checking end_datetime for all the rows for a particular history object. But i only want to compare it with first row of history object.
Below is how a particular history object looks like. So i want to write a queryset filter which can do datetime comparison on first row only.
You could use a Model Manager method for this. The documentation isn't all that descriptive, but you could do something along the lines of:
class SubscriptionManager(models.Manager):
def my_filter(self):
# You'd want to make this a smaller query most likely
subscriptions = Subscription.objects.all()
results = []
for subscription in subscriptions:
sub_history = subscription.history_set.first()
if sub_history.end_datetime > timezone.now:
results.append(subscription)
return results
class History(models.Model):
subscription = models.ForeignKey(Subscription)
end_datetime = models.DateTimeField(db_index=True, blank=True, null=True)
objects = SubscriptionManager()
Then: queryset = Subscription.objects().my_filter()
Not a copy-pastable answer, but shows the use of Managers. Given the specificity of what you're looking for, I don't think there's a way to get it just via the plain filter() and exclude().
Without knowing what your end goal here is, it's hard to say whether this is feasible, but have you considered adding a property to the subscription model that indicates whatever you're looking for? For example, if you're trying to get everyone who has a subscription that's ending:
class Subscription(models.Model):
#property
def ending(self):
if self.end_datetime > timezone.now:
return True
else:
return False
Then in your code: queryset = users.filter(subscription_ending=True)
I have tried django's all king of expressions(aggregate, query, conditional) but was unable to solve the problem so i went with RawSQL and it solved the problem.
I have used the below SQL to select the first row and then compare the end_datetime
SELECT (end_datetime > %s OR end_datetime IS NULL) AS result
FROM subscription_history
ORDER BY start_datetime DESC
LIMIT 1;
I will select my answer as accepted if not found a solution with queryset filter chaining in next 2 days.
So I'm trying to populate a model in django using a postgres (postgis) database. The problem I'm having is inputting the datetimefield. I have written a population script but every time I run it I get the error django.db.utils.IntegrityError: null value in column "pub_date" violates not-null constraint. The code below shows my model and the part of the population script that applies to the table.
The model:
class Article(models.Model):
authors = models.ManyToManyField(Author)
location = models.ForeignKey(Location)
article_title = models.CharField(max_length=200, unique_for_date="pub_date")
pub_date = models.DateTimeField('date published')
article_keywords = ArrayField(ArrayField(models.CharField(max_length=20, blank=True), size=8), size=8,)
title_id = models.CharField(max_length=200)
section_id = models.CharField(max_length=200)
And the population script:
def populate():
add_article(
id = "1",
article_title = "Obama scrambles to get sceptics in Congress to support Iran nuclear deal",
pub_date = "2015-04-06T20:38:59Z",
article_keywords = "{obama, iran, debate, congress, america, un, republican, democrat, nuclear, isreal}",
title_id = "white-house-scrambles-sceptics-congress-iran-nuclear-deal",
section_id = "us-news",
location_id = "1"
)
def add_article(id, article_title, pub_date, article_keywords, title_id, section_id, location_id):
article = Article.objects.get_or_create(article_title=article_title)[0]
article.id
article.article_title
article.pub_date
article.article_keywords
article.title_id
article.section_id
article.location_id
article.save()
return article
if __name__ == '__main__':
print "Starting Newsmap population script..."
populate()
I've searched around for ages but there seems to be no solution to this specific problem. Any help much appreciated!!
The issue is that you do not pass to Article.objects.get_or_create the data needed to create a new object in case none already exists.
What you need to do is (see the documentation for get_or_create):
article = Article.objects.get_or_create(
article_title=article_title,
pub_date=pub_date,
defaults={
'id': id,
'article_keywords': article_keywords,
# etc...
}
)[0]
The data passed using the defaults argument will only be used to create a new object. The data passed using other keyword arguments will be used to check if an existing object matches in the database.
I have this model in my code:
class Conversation(models.Model):
participants = models.ManyToManyField(User, related_name="message_participants")
and I need to filter this "Conversation" model objects by the "participants" many-to-many field.
meaning: I have for example 3 User objects, so I want to retrieve the only "Conversation" objects that has this 3 Users in it's "participants" field.
I tried doing this:
def get_exist_conv_or_none(sender,recipients):
conv = Conversation.objects.filter(participants=sender)
for rec in recipients:
conv = conv.filter(participants=rec)
where sender is a User object and "recipients" is a list of User objects.
it won't raise error but it gives me the wrong Object of Conversation.
Thanks.
edit:
A more recent try lead me to this:
def get_exist_conv_or_none(sender,recipients):
participants=recipients
participants.append(sender)
conv = Conversation.objects.filter(participants__in=participants)
return conv
which basically have the same problem. It yields Objects which has one or more of the "participants" on the list. but what Im looking for is exact match of the many-to-many object.
Meaning, an Object with the exact "Users" on it's many-to-many relation.
edit 2: My last attempt. still, won't work.
def get_exist_conv_or_none(sender,recipients):
recipients.append(sender)
recipients = list(set(recipients))
conv = Conversation.objects.annotate(count=Count('participants')).filter(participants=recipients[0])
for participant in recipients[1:]:
conv.filter(participants=participant)
conv.filter(count=len(recipients))
return conv
Ok so I found the answer:
In order to make an exact match I have to chain-filter the model and then make sure it has the exact number of arguments it needs to have, so that the many-to-many field will have in it all the objects needed and no more.
I will check for the objects number using annotation: ( https://docs.djangoproject.com/en/dev/topics/db/aggregation/ )
ended up with this code:
def get_exist_conv_or_none(recipients):
conv = Conversation.objects.annotate(count=Count('participants')).filter(participants=recipients[0])
for participant in recipients[1:]:
conv = conv.filter(participants=participant)
conv = conv.filter(count=len(recipients))
return conv
For fast search using database index, I use this code:
class YandexWordstatQueue(models.Model):
regions = models.ManyToManyField(YandexRegion)
regions_cached = models.CharField(max_length=10000, editable=False, db_index=True)
phrase = models.ForeignKey(SearchPhrase, db_index=True)
tstamp = models.DateTimeField(auto_now_add=True)
class YandexWordstatRecord(models.Model):
regions = models.ManyToManyField(YandexRegion)
regions_cached = models.CharField(max_length=10000, editable=False, db_index=True)
phrase = models.ForeignKey(SearchPhrase, db_index=True)
Shows = models.IntegerField()
date = models.DateField(auto_now_add=True)
#receiver(m2m_changed, sender=YandexWordstatRecord.regions.through)
#receiver(m2m_changed, sender=YandexWordstatQueue.regions.through)
def yandexwordstat_regions_changed(sender, **kwargs):
if kwargs.get('action') in ['post_add', 'post_remove']:
instance = kwargs.get('instance')
l = list(instance.regions.values_list('RegionID', flat=True))
l.sort()
instance.regions_cached = json.dumps(l)
instance.save()
This adds overhead when saving, but now I can perform fast filter with this snippet:
region_ids = [1, 2, 3] # or list(some_queryset.values_list(...))
region_ids.sort()
regions_cahed = json.dumps(region_ids)
YandexWordstatQueue.objects.filter(regions_cached=regions_cached)