I have a django form where in a choice field the users can not only select more values but also select more combinations of values , for example:
option1
option 2 and option 3
option 2 and option 4
here we have three combinations, the first one of one value (option1), the others of two values.
How can I do that?
Maybe I can use a M2M field with a through table where to associate at each option the combinations in which appear like this:
option1: combination 1
option2: combination 2 and combination 3
option3: combination 2
option4: combination 3
I'm not sure the through table can have an undetermined number of combinations. Maybe there's a better way.
Also any help on how to actually realize it will be appreciated because the widget allows only one combination.
Related
Is it possible to do an annotate count on technically 2 different tables, but same FK?
Example:
queryset = ModelName.objects
.annotate(mileage_emp_count=Count('mileageclaim__user',distinct=True))
.annotate(general_emp_count=Count('expenseclaim__user', distinct=True))
For instance using this, is User A has a mileage and an expense claim, they will appear in both queries. So I will have result of 2 if i add them together.
What i need to do, is get a total of 1 unique user instead.
Is it possible without a lot of extra checks?
Sheet_Table
id ref_id name data
1 10 A 9078
2 10 AAA 6789
3 12 C 345
Sheet Model have multiple Columns id,ref_id,name,data
Now i want to write this query in django
select data from Sheet_Table where ref_id=10
Here Model/Table name is Sheet_Table
It's pretty explicitly stated in the django doc on queries that filter(foo=bar) evaluates to a WHERE clause. In your specific case, try this to get a list of just the data elements (if your model is actually called Sheet_Table?):
Sheet_Table.objects.filter(ref_id=10).values_list('data', flat=True)
or you can leave off the values_list part if you want to iterate over the model objects (e.g., if you want to examine id as well as data).
I'm working on a student survey project. The model that stores the questions is something like:
ID Question Type
1 is good teacher? Choice
2 What do you like about Open-answer
the teacher?
Then in the choice type questions the student will choose an option (e.g.: fully agree) and this will store a numerical code (e.g. 5). But in the open-answer questions , the student will write text.
what kind of field should store these answers in the answers model? maybe TextField?
You ur choices as text if you want to use same column to open text... so instead of set 1,2,3,4 you can write a fixed text when user select the options, so this make your data more readeble
ANSWER = (
("Yes", "Yes"),
("No", "No"),
("Neutral", "Neutral"),
)
Or make 2 more columns... one to set type of question (select or text) and the other to store the options (that way you can setup as foreign key and instead of use static values this can be loaded from one model)
ID Question Type Answer-Text AnswerID
1 is good teacher? Choice null 1
2 What do you like about Open-answer "The way he swag" null
the teacher?
Or mix everything with String... but you will have some troubles getting this integer ids... will throw some erros when you try to get it as integer int("1") Will work but int("The way he swag") will raise a error
Using a TextField would probably be a bad idea since you're mixing int with string type objects which is definitely not recommended.
One thing you could do is consider this as two different fields. One Choicefield and one TextField. That way the user can choose an empty value (empty string '') when he wants to use the open-answer. You can then compute empty strings as being nothing later on.
I have a Result object that is tagged with "one" and "two". When I try to query for objects tagged "one" and "two", I get nothing back:
q = Result.objects.filter(Q(tags__name="one") & Q(tags__name="two"))
print len(q)
# prints zero, was expecting 1
Why does it not work with Q? How can I make it work?
The way django-taggit implements tagging is essentially through a ManytoMany relationship. In such cases there is a separate table in the database that holds these relations. It is usually called a "through" or intermediate model as it connects the two models. In the case of django-taggit this is called TaggedItem. So you have the Result model which is your model and you have two models Tag and TaggedItem provided by django-taggit.
When you make a query such as Result.objects.filter(Q(tags__name="one")) it translates to looking up rows in the Result table that have a corresponding row in the TaggedItem table that has a corresponding row in the Tag table that has the name="one".
Trying to match for two tag names would translate to looking up up rows in the Result table that have a corresponding row in the TaggedItem table that has a corresponding row in the Tag table that has both name="one" AND name="two". You obviously never have that as you only have one value in a row, it's either "one" or "two".
These details are hidden away from you in the django-taggit implementation, but this is what happens whenever you have a ManytoMany relationship between objects.
To resolve this you can:
Option 1
Query tag after tag evaluating the results each time, as it is suggested in the answers from others. This might be okay for two tags, but will not be good when you need to look for objects that have 10 tags set on them. Here would be one way to do this that would result in two queries and get you the result:
# get the IDs of the Result objects tagged with "one"
query_1 = Result.objects.filter(tags__name="one").values('id')
# use this in a second query to filter the ID and look for the second tag.
results = Result.objects.filter(pk__in=query_1, tags__name="two")
You could achieve this with a single query so you only have one trip from the app to the database, which would look like this:
# create django subquery - this is not evaluated, but used to construct the final query
subquery = Result.objects.filter(pk=OuterRef('pk'), tags__name="one").values('id')
# perform a combined query using a subquery against the database
results = Result.objects.filter(Exists(subquery), tags__name="two")
This would only make one trip to the database. (Note: filtering on sub-queries requires django 3.0).
But you are still limited to two tags. If you need to check for 10 tags or more, the above is not really workable...
Option 2
Query the relationship table instead directly and aggregate the results in a way that give you the object IDs.
# django-taggit uses Content Types so we need to pick up the content type from cache
result_content_type = ContentType.objects.get_for_model(Result)
tag_names = ["one", "two"]
tagged_results = (
TaggedItem.objects.filter(tag__name__in=tag_names, content_type=result_content_type)
.values('object_id')
.annotate(occurence=Count('object_id'))
.filter(occurence=len(tag_names))
.values_list('object_id', flat=True)
)
TaggedItem is the hidden table in the django-taggit implementation that contains the relationships. The above will query that table and aggregate all the rows that refer either to the "one" or "two" tags, group the results by the ID of the objects and then pick those where the object ID had the number of tags you are looking for.
This is a single query and at the end gets you the IDs of all the objects that have been tagged with both tags. It is also the exact same query regardless if you need 2 tags or 200.
Please review this and let me know if anything needs clarification.
first of all, this three are same:
Result.objects.filter(tags__name="one", tags__name="two")
Result.objects.filter(Q(tags__name="one") & Q(tags__name="two"))
Result.objects.filter(tags__name_in=["one"]).filter(tags__name_in=["two"])
i think the name field is CharField and no record could be equal to "one" and "two" at same time.
in python code the query looks like this(always false, and why you are geting no result):
from random import choice
name = choice(["abtin", "shino"])
if name == "abtin" and name == "shino":
we use Q object for implement OR or complex queries
Into the example that works you do an end on two python objects (query sets). That gets applied to any record not necessarily to the same record that has one AND two as tag.
ps: Why do you use the in filter ?
q = Result.objects.filter(tags_name_in=["one"]).filter(tags_name_in=["two"])
add .distinct() to remove duplicates if expecting more than one unique object
I have a fairly simple query I'd like to make via the ORM, but can't figure that out..
I have three models:
Location (a place), Attribute (an attribute a place might have), and Rating (a M2M 'through' model that also contains a score field)
I want to pick some important attributes and be able to rank my locations by those attributes - i.e. higher total score over all selected attributes = better.
I can use the following SQL to get what I want:
select location_id, sum(score)
from locations_rating
where attribute_id in (1,2,3)
group by location_id order by sum desc;
which returns
location_id | sum
-------------+-----
21 | 12
3 | 11
The closest I can get with the ORM is:
Rating.objects.filter(
attribute__in=attributes).annotate(
acount=Count('location')).aggregate(Sum('score'))
Which returns
{'score__sum': 23}
i.e. the sum of all, not grouped by location.
Any way around this? I could execute the SQL manually, but would rather go via the ORM to keep things consistent.
Thanks
Try this:
Rating.objects.filter(attribute__in=attributes) \
.values('location') \
.annotate(score = Sum('score')) \
.order_by('-score')
Can you try this.
Rating.objects.values('location_id').filter(attribute__in=attributes).annotate(sum_score=Sum('score')).order_by('-score')