Welcome I have a problem. What field should be in model to substract times. I mean for example: 1st car made 500h 28 mins, 2nd car made 350h 15 min and i need a column substract where I'll have substraction from this two times. I made currently working model but only on integer field. When i tried time field and add something like 500:28 it gave me an error " incorrect time".
Current model:
class Aircraft (models.Model):
id = models.AutoField(primary_key=True)
registration = models.CharField(max_length=7)
#hours to maintenance
hours_to_maintenance = models.IntegerField(help_text = "test", null = True)
#current hours
ch = models.IntegerField(help_text = "test", null = True)
#rm = models.IntegerField(help_text = "test", null = True)
added_by = models.ForeignKey('auth.User', on_delete = models.CASCADE,)
def __str__(self):
return self.registration
Really thanks for help
Django has a field type designated for this type of data: DurationField. See the docs: Django DurationField
You’re definitely going to want to use a models.DateTimeField(...). This object is a python Date object. Here’s the documentation https://docs.python.org/2/library/datetime.html.
Make sure you click on the DateTime objects in the left nav panel
It’s really important you read the documentation because this will layout in more detail stack exchange can provide on this solution.
If you want to know how many minutes are between two DateTime values, you’ll have to calculate it using the min, hr, day etc attributes.
Related
Good day, everyone. Hope you're doing well. I'm a Django newbie, trying to learn the basics of RESTful development while helping in a small app project. Currently, there's a really difficult query that I must do to create a calculated field that updates my student's status accordingly to the time interval the classes are in. First, let me explain the models:
class StudentReport(models.Model):
student = models.ForeignKey(Student, on_delete=models.CASCADE,)
headroom_teacher = models.ForeignKey(Teacher, on_delete=models.CASCADE,)
upload = models.ForeignKey(Upload, on_delete=models.CASCADE, related_name='reports', blank=True, null=True,)
exams_date = models.DateTimeField(null=True, blank=True)
#Other fields that don't matter
class ExamCycle(models.Model):
student = models.ForeignKey(student, on_delete=models.CASCADE,)
headroom_teacher = models.ForeignKey(Teacher, on_delete=models.CASCADE,)
#Other fields that don't matter
class RecommendedClasses(models.Model):
report = models.ForeignKey(Report, on_delete=models.CASCADE,)
range_start = models.DateField(null=True)
range_end = models.DateField(null=True)
# Other fields that don't matter
class StudentStatus(models.TextChoices):
enrolled = 'enrolled' #started class
anxious_for_exams = 'anxious_for_exams'
sticked_with_it = 'sticked_with_it' #already passed one cycle
So this app will help the management of a Cram school. We first do an initial report of the student and its best/worst subjects in StudentReport. Then a RecommendedClasses object is created that tells him which clases he should enroll in. Finally, we have a cycle of exams (let's say 4 times a year). After he completes each exam, another report is created and he can be recommended a new class or to move on the next level of its previous class.
I'll use the choices in StudentStatus to calculate an annotated field that I will call status on my RecommendedClasses report model. I'm having issues with the sticked_with_it status because it's a query that it's done after one cycle is completed and two reports have been made (Two because this query must be done in StudentStatus, after 2nd Report is created). A 'sticked_with_it' student has a report created after exams_date where RecommendedClasses was created and the future exams_date time value falls within the 30 days before range_start and 60 days after the range_end values of the recommendation (Don't question this, it's just the way the higherups want the status)
I have already come up with two ways to do it, but one is with a RAW SQL query and the other is waaay to complicated and slow. Here it is:
SELECT rec.id AS rec_id FROM
school_recommendedclasses rec LEFT JOIN
school_report original_report
ON rec.report_id = original_report.id
AND rec.teacher_id = original_report.teacher_id
JOIN reports_report2 future_report
ON future_report.exams_date > original_report.exams_date
AND future_report.student_id = original_report.student_id
AND future_report.`exams_date` > (rec.`range_start` - INTERVAL 30 DAY)
AND future_report.`exams_date` <
(rec.`range_end` + INTERVAL 60 DAY)
AND original_report.student_id = future_report.student_id
How can I transfer this to a proper DJANGO ORM that is not so painfully unoptimized? I'll show you the other way in the comments.
FWIW, I find this easier to read, but there's very little wrong with your query.
Transforming this to your ORM should be straightforward, and any further optimisations are down to indexes...
SELECT r.id rec_id
FROM reports_recommendation r
JOIN reports_report2 o
ON o.id = r.report_id
AND o.provider_id = r.provider_id
JOIN reports_report2 f
ON f.initial_exam_date > o.initial_exam_date
AND f.patient_id = o.patient_id
AND f.initial_exam_date > r.range_start - INTERVAL 30 DAY
AND f.initial_exam_date < r.range_end + INTERVAL 60 DAY
AND f.provider_id = o.provider_id
Please see EDIT1 below, as well.
Using Django 3.0.6 and python3.8, given following models
class Plants(models.Model):
plantid = models.TextField(primary_key=True, unique=True)
class Pollutions(models.Model):
pollutionsid = models.IntegerField(unique=True, primary_key=True)
year = models.IntegerField()
plantid = models.ForeignKey(Plants, models.DO_NOTHING, db_column='plantid')
pollutant = models.TextField()
releasesto = models.TextField(blank=True, null=True)
amount = models.FloatField(db_column="amount", blank=True, null=True)
class Meta:
managed = False
db_table = 'pollutions'
unique_together = (('plantid', 'releasesto', 'pollutant', 'year'))
class Monthp(models.Model):
monthpid = models.IntegerField(unique=True, primary_key=True)
year = models.IntegerField()
month = models.IntegerField()
plantid = models.ForeignKey(Plants, models.DO_NOTHING, db_column='plantid')
power = models.IntegerField(null=False)
class Meta:
managed = False
db_table = 'monthp'
unique_together = ('plantid', 'year', 'month')
I'd like to annotate - based on a foreign key relationship and a fiter a value, particulary - to each plant the amount of co2 and the Sum of its power for a given year. For sake of debugging having replaced Sum by Count using the following query:
annotated = tmp.all().annotate(
energy=Count('monthp__power', filter=Q(monthp__year=YEAR)),
co2=Count('pollutions__amount', filter=Q(pollutions__year=YEAR, pollutions__pollutant="CO2", pollutions__releasesto="Air")))
However this returns too many items (a wrong number using Sum, respectively)
annotated.first().co2 # 60, but it should be 1
annotated.first().energy # 252, but it should be 1
although my database guarantees - as denoted, that (plantid, year, month) and (plantid, releasesto, pollutant, year) are unique together, which can easily be demonstrated:
pl = annotated.first().plantid
testplant = Plants.objects.get(pk=pl) # plant object
pco2 = Pollutions.objects.filter(plantid=testplant, year=YEAR, pollutant="CO2", releasesto="Air")
len(pco2) # 1, as expected
Why does django return to many results and how can I tell django to limit the elements to annotate to the 'current primary key' in other words to only annotate the elements where the foreign key matches the primary key?
I can achieve what I intend to do by using distinct and Max:
energy=Sum('yearly__power', distinct=True, filter=Q(yearly__year=YEAR)),
co2=Max('pollutions__amount', ...
However the performance is inacceptable.
I have tested to use model_to_dict and appending the wanted values "by hand" to the dict, which works for the values itself, but not for sorting the resulted dict (e.g. by energy) and it is acutally faster than the workaround directly above.
It conceptually strikes to me that the manual approach is faster than letting the database do, what it is intended to do.
Is this a feature limitation of django's orm or am I missing something?
EDIT1:
The behaviour is known as bug since 11 years.
Even others "spent a whole day on this".
I am now trying it with subqueries. However the forein key I am using is not a primary key of its table. So the kind of "usual" approach to use "pk=''" does not work. More clearly, trying:
tmp = Plants.objects.filter(somefilter)
subq1 = Subquery(Yearly.objects.filter(pk=OuterRef('plantid'), year=YEAR)) tmp1 = tmp.all().annotate(
energy=Count(Subquery(subq1))
)
returns
OperationalError at /xyz
no such column: U0.yid
Which definitely makes sense because Plants has no clue what a yid is, it only knows plantids. How do I adjust the subquery to that?
my goal here seems to be simple: display the Sum (aggregation) of a foreign model particular field.
The difficulty consist in the current set-up, kindly take a look and let me know if this need to be changed or I can achieve the goal with current model:
class Route(models.Model):
name = models.CharField(max_length=50)
route_length = models.IntegerField()
class Race(models.Model):
race_cod = models.CharField(max_length=6, unique=True)
route_id = models.ForeignKey(Route, on_delete=models.CASCADE, related_name='b_route')
class Results(models.Model):
race_id = models.ForeignKey(Race, on_delete=models.CASCADE, related_name='r_race')
runner_id = models.ForeignKey(Runner, on_delete=models.CASCADE, related_name='r_runner')
Now, I am trying to have like a year summary:
Runner X have raced in 12 races with a total distance of 134 km.
While I was able to count the number of races like this (views.py)
runner = Runner.objects.get(pk=pk)
number_races = Results.objects.filter(runner_id=runner).count()
For computing the distance I have tried:
distance = Results.objects.filter(runner_id=runner).annotate(total_km=Sum(race_id.route_id.route_length))
This code error out stating that on views.py - distance line
Exception Type: NameError
Exception Value: name 'race_id' is not defined
I am sure I did not u/stood exactly how this works. Anybody kind enough to clarify this issue?
Thank you
My workaround is the following :
tmp_race_id = Results.objects.filter(runner_id=runner).values('race_id')
tmp_route_id = Race.objects.filter(pk__in=tmp_race_id).values('route_id')
distance = Route.objects.filter(pk__in=tmp_route_id).aggregate(Sum("route_length "))['route_length __sum'] or 0.00
Thank you Jorge Lopez for the hint.
you don´t need a Results Model, you can calculate using the data in the models, can you share your Runner Model? that model needs to have a foreign key to a Race. if that is so, you can go from Route's -> Race -> Runner in your query, and you can use the query for the count, so you will have a variable where you stored the count and a variable where you stored the distance. To do a Sum in your query do not use annotate, use aggregate, something like this:
.aggregate(total=Coalesce(Sum('route_lenght'), 0))['total']
do like this
from django.db.models import Sum, Count
u = Runner.objects.annotate(
tot_result=Count('r_runner'),
tot_km=Sum('r_runner__race_id__route_id__route_length')
)
for i in u:
print('Total_race {} -- Total_Km {}'.format(i.tot_result, i.tot_km))
I'm working on a Ticket/Issue-tracker in django where I need to log the status of each ticket. This is a simplification of my models.
class Ticket(models.Model):
assigned_to = ForeignKey(User)
comment = models.TextField(_('comment'), blank=True)
created = models.DateTimeField(_("created at"), auto_now_add=True)
class TicketStatus(models.Model):
STATUS_CHOICES = (
(10, _('Open'),),
(20, _('Other'),),
(30, _('Closed'),),
)
ticket = models.ForeignKey(Ticket, verbose_name=_('ticket'))
user = models.ForeignKey(User, verbose_name=_('user'))
status = models.IntegerField(_('status'), choices=STATUS_CHOICES)
date = models.DateTimeField(_("created at"), auto_now_add=True)
Now, getting the status of a ticket is easy sorting by date and retrieving the first column like this.
ticket = Ticket.objects.get(pk=1)
ticket.ticketstatus_set.order_by('-date')[0].get_status_display()
But then I also want to be able to filter on status in the Admin, and those have to get the status trough a Ticket-queryset, which makes it suddenly more complex. How would I get a queryset with all Tickets with a certain status?
I guess you are trying to avoid a cycle (asking for each ticket status) to filter manually the queryset. As far as I know you cannot avoid that cycle. Here are ideas:
# select_related avoids a lot of hits in the database when enter the cycle
t_status = TicketStatus.objects.select_related('Ticket').filter(status = ID_STATUS)
# this is an array with the result
ticket_array = [ts.ticket for ts in tickets_status]
Or, since you mention you were looking for a QuerySet, this might be what you are looking for
# select_related avoids a lot of hits in the database when enter the cycle
t_status = TicketStatus.objects.select_related('Ticket').filter(status = ID_STATUS)
# this is a QuerySet with the result
tickets = Tickets.objects.filter(pk__in = [ts.ticket.pk for ts in t_status])
However, the problem might be in the way you are modeling the data. What you called TickedStatus is more like TicketStatusLog because you want to keep track of the user and date who change the status.
Therefore, the reasonable approach is to add a field 'current_status' to the Ticket model that is updated each time a new TicketStatus is created. In this way (1) you don't have to order a table each time you ask for a ticket and (2) you would simply do something like Ticket.objects.filter(current_status = ID_STATUS) for what I think you are asking.
I am trying to add an additional custom field to a django model. I have been having quite a hard time figuring out how to do the following, and I will be awarding a 150pt bounty for the first fully correct answer when it becomes available (after it is available -- see as a reference Improving Python/django view code).
I have the following model, with a custom def that returns a video count for each user --
class UserProfile(models.Model):
user = models.ForeignKey(User, unique=True)
positions = models.ManyToManyField('Position', through ='PositionTimestamp', blank=True)
def count(self):
from django.db import connection
cursor = connection.cursor()
cursor.execute(
"""SELECT (
SELECT COUNT(*)
FROM videos_video v
WHERE v.uploaded_by_id = p.id
OR EXISTS (
SELECT NULL
FROM videos_videocredit c
WHERE c.video_id = v.id
AND c.profile_id = p.id
)
) AS Total_credits
FROM userprofile_userprofile p
WHERE p.id = %d"""%(int(self.pk))
)
return int(cursor.fetchone()[0])
I want to be able to order by the count, i.e., UserProfile.objects.order_by('count'). Of course, I can't do that, which is why I'm asking this question.
Previously, I tried adding a custom model Manager, but the problem with that was I also need to be able to filter by various criteria of the UserProfile model: Specifically, I need to be able to do: UserProfile.objects.filter(positions=x).order_by('count'). In addition, I need to stay in the ORM (cannot have a raw sql output) and I do not want to put the filtering logic into the SQL, because there are various filters, and would require several statements.
How exactly would I do this? Thank you.
My reaction is that you're trying to take a bigger bite than you can chew. Break it into bite size pieces by giving yourself more primitives to work with.
You want to create these two pieces separately so you can call on them:
Does this user get credit for this video? return boolean
For how many videos does this user get credit? return int
Then use a combination of #property, model managers, querysets, and methods that make it easiest to express what you need.
For example you might attach the "credit" to the video model taking a user parameter, or the user model taking a video parameter, or a "credit" manager on users which adds a count of videos for which they have credit.
It's not trivial, but shouldn't be too tricky if you work for it.
"couldn't you use something like the "extra" queryset modifier?"
see the docs
I didn't put this in an answer at first because I wasn't sure it would actually work or if it was what you needed - it was more like a nudge in the (hopefully) right direction.
in the docs on that page there is an example
query
Blog.objects.extra(
select={
'entry_count': 'SELECT COUNT(*) FROM blog_entry WHERE blog_entry.blog_id = blog_blog.id'
},
)
resulting sql
SELECT blog_blog.*, (SELECT COUNT(*) FROM blog_entry WHERE blog_entry.blog_id = blog_blog.id) AS entry_count
FROM blog_blog;
Perhaps doing something like that and accessing the user id which you currently have as p.id as appname_userprofile.id
note:
Im just winging it so try to play around a bit.
perhaps use the shell to output the query as sql and see what you are getting.
models:
class Positions(models.Model):
x = models.IntegerField()
class Meta:
db_table = 'xtest_positions'
class UserProfile(models.Model):
user = models.ForeignKey(User, unique=True)
positions = models.ManyToManyField(Positions)
class Meta:
db_table = 'xtest_users'
class Video(models.Model):
usr = models.ForeignKey(UserProfile)
views = models.IntegerField()
class Meta:
db_table = 'xtest_video'
result:
test = UserProfile.objects.annotate(video_views=Sum('video__views')).order_by('video_views')
for t in test:
print t.video_views
doc: https://docs.djangoproject.com/en/dev/topics/db/aggregation/
This is either what you want, or I've completely misunderstood!.. Anywhoo... Hope it helps!