I have two models, subject and visit. I'm trying to select visits where the age in months was over a certain amount, but cannot simply filter on age_months, as it is not a field, but rather a calculated value associated with the visit model.
We are getting age_months from a form and then trying to convert it to a date (subject birthdate plus the age in months converted to a timedelta) then use F-filtering in our view to select visits where the visit_date is greater than this calculated subject age
Here is the code:
vform = VisSearchForm(request.POST,prefix='v')
if vform.is_valid():
e = vform.cleaned_data
vresults = Visit.objects.all()
if e['age_months']:
vresults.filter(visit_date__gt=F('subject__birthdate') + timedelta(days=30.44*e['age_months']))
the birthdate field is connected to the subject model, not the visit model and visit_date is connected to the visit model.
When I print the timedelta part I get a value, but when I print the F('subject__birthdate') + timedelta(days=30.44*e['age_months'])
I get
(+: (DEFAULT: ), 700 days, 2:52:48)
When what I want is the F('subject__birthdate') to return a date and not (+: (DEFAULT: )
It won't. The F object is a reference to a database field and holds absolutely no meaning outside the context of a database query.
Even when the query is built, it is still a reference to another database field, and doesn't hold an actual value.
Related
I show a model of sales that can be aggregated by different fields through a form. Products, clients, categories, etc.
view_by_choice = filter_opts.cleaned_data["view_by_choice"]
sales = sales.values(view_by_choice).annotate(........).order_by(......)
In the same form I have a string input where the user can filter the results. By "product code" for example.
input_code = filter_opts.cleaned_data["filter_code"]
sales = sales.filter(prod_code__icontains=input_code)
What I want to do is filter the queryset "sales" by the input_code, defining the field dynamically from the view_by_choice variable.
Something like:
sales = sales.filter(VARIABLE__icontains=input_code)
Is it possible to do this? Thanks in advance.
You can make use of dictionary unpacking [PEP-448] here:
sales = sales.filter(
**{'{}__icontains'.format(view_by_choice): input_code}
)
Given that view_by_choice for example contains 'foo', we thus first make a dictionary { 'foo__icontains': input_code }, and then we unpack that as named parameter with the two consecutive asterisks (**).
That being said, I strongly advice you to do some validation on the view_by_choice: ensure that the number of valid options is limited. Otherwise a user might inject malicious field names, lookups, etc. to exploit data from your database that should remain hidden.
For example if you model has a ForeignKey named owner to the User model, he/she could use owner__email, and thus start trying to find out what emails are in the database by generating a large number of queries and each time looking what values that query returned.
I have 3 tables:
Truck with the fields: id, name....
Menu with the fields: id, itemname, id_foodtype, id_truck...
Foodtype with the fields: id, type...
I want to get a summary like:
id name total
10 Alcoholic drink 0
5 Appetizer 11
My problem is to return the results with 0 elements.
I tried an SQL query like this:
SELECT
ft.id, ft.name, COUNT(me.id) total
FROM
foodtype ft LEFT JOIN menu me
ON ft.id = me.id_foodtype
LEFT JOIN truck tr
ON tr.id = me.id_truck AND tr.id = 3
GROUP BY ft.id, ft.name
ORDER BY ft.name
or a query in Django
Menu.objects.filter(id_truck=3).values("id_foodtype").annotate(cnt=Count("id_foodtype"))
But, neither is displaying the results with Zero elements.
At the moment to convert this query to Python code, any of my queries return the exact result that I expected.
How can I return results with the Left Join including the foodtypes with zero elements in the menu?
The direction of LEFT JOIN depends on the object, where you start the query. If it start on Menu you will never see a FoodType unused by selected Menu items. Then is important to filter (by Truck in your case) such way that also null value Menu.id is allowed in order to can get Count == 0.
from django.db.models import Q
qs = (
FoodType.objects
.filter(Q(menu_set__id_truck=3) | Q(menu_set__id__isnull=True))
.values() # not necessary, but useful if you want a dict, not a Model object
.annotate(cnt=models.Count("menu_set__id"))
)
Verify:
>>> print(str(qs.query))
SELECT foodtype.id, foodtype..., COUNT(menu.id) AS cnt
FROM foodtype
LEFT OUTER JOIN menu ON (foodtype.id = menu.id_foodtype)
WHERE _menu.id_truck = 3 OR menu.id IS NULL)
GROUP BY foodtype.id
It works with the current newest and oldest Django 2.0b1 and 1.8.
The query is the same with or without the line .values(). The results are dictionaries or FoodType objects with a cnt attribute.
Footnotes:
The name menu_set should be replaced by the real related_name of foreign key id_foodtype if you have defined the related_name.
class Menu(models.Model):
id_foodtype = models.ForeignKey('FoodType', on_delete=models.DO_NOTHING,
db_column='id_foodtype', related_name='menu_set'))
...
If you start a new project I recommend to rename the foreign key to a name without "id" and the db_column field is with "id". Then menu_item.foodtype is a Food object and menu_item.id_foodtype its id.
views.py:
q3=KEBReading.objects.filter(datetime_reading__month=a).filter(datetime_reading__year=selected_year).values("signed")
for item in q3:
item["signed"]="signed"
print item["signed"]
q3.save()
How do I save a field into the database? I'm trying to save the field called "signed" with a value. If I do q3.save() it gives a error as it is a queryset. I'm doing a query from the database and then, based on the result, want to set a value to a field and save it.
prevdate=KEBReading.objects.filter(datetime_reading__lt=date)
i am getting all the rows from the database less than the current date. but i want only the latest record. if im entering 2012-06-03. wen i query i want the date less than this date i.e the date just previous to this. can sumbody help?
q3 = KEBReading.objects.filter(datetime_reading__month=a,
datetime_reading__year=selected_year)
for item in q3:
item.signed = True
item.save()
q3=KEBReading.objects.filter(...)
will return you a list of objects. Any instance of a Django Model is an object and all fields of the instance are attributes of that object. That means, you must use them using dot (.) notation.
like:
item.signed = "signed"
If your object is a dictionary or a class derived from dictionary, then you can use named-index like:
item["signed"] = "signed"
and in your situation, that usage is invalid (because your object's type is not dictionary based)
You can either call update query:
KEBReading.objects.filter(...).update(selected="selected")
or set new value in a loop and then save it
for item in q3:
item.signed="signed"
q3.save()
but in your situation, update query is a better approach since it executes less database calls.
Try using update query:
If signed is a booleanfield:
q3 = KEBReading.objects.filter(datetime_reading__month = a).filter(datetime_reading__year = selected_year).update(signed = True)
If it is a charfield:
q3 = KEBReading.objects.filter(datetime_reading__month = a).filter(datetime_reading__year = selected_year).update(signed = "True")
Update for comments:
If you want to fetch records based datetime_reading month, you can do it by providing month as number. For example, 2 for February:
q3 = KEBReading.objects.filter(datetime_reading__month = 2).order_by('datetime_reading')
And if you to fetch records with signed = True, you can do it by:
q3 = KEBReading.objects.filter(signed = True)
If you want to fetch only records of previous date by giving a date, you can use:
prevdate = KEBReading.objects.filter(datetime_reading = (date - datetime.timedelta(days = 1)))
I need a solution for this problem:
I would like to have MultiField widget for a "value" field. This field should allow to input two values (two input widgets), and user should choose which of these values is to be saved (two checkbox widgets). However, one of these values must be recalculated with respect to other field's value.
I've taken this approach:
a MultiValueField with 4 fields:
class PriceDetailField(MultiValueField):
use_net = BooleanField(required=False)
net_value = DecimalField(required=False, decimal_places=2)
use_gross = BooleanField(required=False)
gross_value = DecimalField(required=False, decimal_places=2)
a MultiWidget:
class PriceDetailWidget(MultiWidget):
use_net = CheckboxInput()
net_value_widget = TextInput()
use_gross = CheckboxInput()
gross_value_widget = TextInput()
and a custom Form...
class PriceModelForm(ModelForm):
value = PriceDetailField()
...which overrides default model form for a model:
class Price(models.Model):
value = models.DecimalField(
max_digits=19,
decimal_places=2,
default=Decimal(0),
)
However, this solution seems to be messed up. In the form, I need to input all subfields (the MultiValueField subfields), otherwise "Please enter value" error appears (even though those fields are marked as required=False). Also,
I must recalculate the mentioned value upon a save, having returned a tuple from the field with information which checkbox was checked and the corresponding text value, then replace the tuple with the decimal value in clean_value method of form (also, saving the checkboxes state in temporary fields....). I think such a design is very weak.
The form should work both on its own and as inline (this means, the value of the field which is used to calculate the returned value can or cannot change during save).
Is such a thing even possible?
And the root of the problem: I want to store prices of items as net prices, but I would like to allow users to input them as net or gross prices, and then recalculate gross price to net price with respect to product's VAT tax level (since VAT is assigned to product or service, not to the price). A product can have many prices, so a price is backlinked to the product by a foreign key.
Cheers,
Tomek
The feature you're looking for on a MultiValueField (allowing the sub-fields to be required or not individually) is logged as a feature request on Django.
You could probably fix this for now by subclassing MultiValueField with a rewritten clean method based on the original and following suggestions from the bug report. You're not going to have a lot of the original MultiValueField left by that point though, and if you do, you should submit your patch to Django and put a note on the bug.
Ignoring for a moment the requiredness thing, have you written a compress method on your PriceDetailField? What does it look like? This is where you should be doing the work to turn your four sub-fields into a single field to save.
I have such model and query
class Employer(Models.model)
name = ...
class JobTitle(Models.model)
name = ...
employer = models.ForeignKey(Employer)
and query is
Employer.objects.select_related('jobtitle')
.filter(jtt__activatedate__range=[startdate,enddate])
.annotate(jtt_count=Count('jobtitle'))
.order_by('-jtt_count')[:5]
As you see it returns 5 employer list which has maximum number of jobtitles which are related to that employer and whose activation date is in some certain range.
However, I also want to get the total number of jobtitles of each employer in that query.
Of course I may loop over each employer and make such query JobTitle.objects.filter(employer = emp) and taking length of that query but it is bad solution.
How can I achive this in that query?
Although it may not be possible to get both total number and filtered number of job titles, I may get the jobttiles of each emplyoer such that len(emp.jobtitle) however it also didn't work.
Thanks
Try the extra lookup. So, in your case it may be like this:
.extra(
select={
'jobtitle_count': 'SELECT COUNT(*) FROM YOURAPP_jobtitle WHERE YOURAPP_jobtitle.employer_id = YOURAPP_employer.id'
},
)