I am looking for way how to add new objects to existing queryset, or how to implement what I want by other way.
contact = watson.filter(contacts, searchline)
This line returns queryset, which I later use to iterate.
Then I want to do this to add more objects, which watson couldn't find
contact_in_iteration = Contact.objects.get(id = fild.f_for)
contact.append(contact_in_iteration)
And sorry for my poor english
Did this
contacts = Contact.objects.filter(crm_id=request.session['crm_id'])
query = Q(contacts,searchline)
contact = watson.filter(query)
and get 'filter() missing 1 required positional argument: 'search_text'' error
You can use | and Q lookups. See the docs.
I'm not sure I've fully understood your initial query, but I think that in your case you would want to do:
query = Q(contacts='Foo', searchline='Bar')
contact = watson.filter(query)
Then later:
contact = watson.filter(query | Q(id=field.f_for))
Strictly speaking it won't append to the queryset, but will return a new queryset. But that's okay, because that's what .filter() does anyway.
You should look at a queryset as a sql query that will be executed later. When constructing a queryset and save the result in a variable, you can later filter it even more, but you can not expand it. If you need a query that has more particular rules (like, you need an OR operation) you should state that when you are constructing the query. One way of doing that is indeed using the Q object.
But it looks like you are confused about what querysets really are and how they are used. First of all:
Contact.objects.get(id = fild.f_for)
will never return a queryset, but an instance, because you use get and thus ask for a single particular record. You need to use filter() if you want to get a quersyet. So if you had an existing queryset say active_contacts and you wanted to filter it down so you only get the contacts that have a first_name of 'John' you would do:
active_contacts = Contact.objects.filter(active=True)
active_contacts_named_John = active_contacts.filter(first_name='John')
Of course you could do this in one line too, but I'm assuming you do the first queryset construction somewhere else in your code.
Second remark:
If in your example watson is a queryset, your user of filter() is unclear. This doesn't really make sense:
contact = watson.filter(contacts, searchline)
As stated earlier, filtering a queryset returns another queryset. So you should use a plurar as your variable name e.g. contacts. Then the correct use of filter would be:
contacts = watson.filter(first_name=searchline)
I'm assuming searchline here is a variable that contains a user inputted search term. So maybe here you should name your variable searchterm or similar. This will return all contacts that are filtered by whatever watson is filtering out already and whose first_name matches searchline exactly. You could also use a more liberate method and filter out results that 'contains' the searching term, like so:
contacts = watson.filter(first_name__contains=searchline)
Hope this helps you get on the right path.
Related
I have a collection with multiple Course documents. On it, i have an array of course_users like the following example:
Like this, I can have multiple courses in the same collection.
My purpose is to do something with any given User id, but first, I need to know if this user exists on any of the courses of the collection, for example, if User with an ID of 123 is on Course A OR Course B, I should return True. If user with an ID 456 is not on any Course I should return False.
Is there a way to make this query in as few steps as possible using mongoengine in flask?
My idea was to use the $ operator like the following:
def userIsInCourse(user_id):
course_students = Course.objects(students__S__in=[user_id])
print(course_students)
Thinking that Course.objects will retrieve every course filtered with students__S__in=user_id_ but I'm failing.
Sorry for the vague question.
I ended up modifying my query.
Instead of trying to use the $ operator, I modified my query to use a raw query:
def userIsInCourse(user_id):
course_students = Course.objects(__raw__={'students': {'$elemMatch': {'student_id': user_id}}})
if course_students:
return True
else:
return False
It retrieves the whole Courses array, and looks in each Course's students array of objects, then filters using the given user's id. If the user exists on the course, returns true.
With this approach it was simpler than i thought.
I need to find a match between a serial number and a list of objects, each of them having a serial number :
models:
class Beacon(models.Model):
serial = models.CharField(max_length=32, default='0')
First I wrote:
for b in Beacon.objects.all():
if b.serial == tmp_serial:
# do something
break
Then I did one step ahead:
b_queryset = Beacon.objects.all().filter(serial=tmp_serial)
if b_queryset.exists():
#do something
Now, is there a second step for more optimization?
I don't think it would be faster to cast my QuerySet in a List and do a list.index('tmp_serial').
If your serial is unique, you can do:
# return a single instance from db
match = Beacon.objects.get(serial=tmp_serial)
If you have multiple objects to get with the same serial and plan do something on each of them, exist will add a useless query.
Instead, you should do:
matches = Beacon.objects.filter(serial=tmp_serial)
if len(matches) > 0:
for match in matches:
# do something
The trick here is that len(matches) will force the evaluation of the queryset (so your db will be queried). After that,
model instances are retrieved and you can use them without another query.
However, when you use queryset.exists(), the ORM run a really simple query to check if the queryset would have returned any element.
Then, if you iterate over your queryset, you run another query to grab your objects. See the related documentation for more details.
To sum it up: use exists only if you want to check that a queryset return a result a result or not. If you actually need the queryset data, use len().
I think you are at best but if you just want whether object exists or not then,
From django queryset exists()
https://docs.djangoproject.com/en/1.8/ref/models/querysets/#django.db.models.query.QuerySet.exists
if Beacon.objects.all().filter(serial=tmp_serial).exists():
# do something
Given a class:
from django.db import models
class Person(models.Model):
name = models.CharField(max_length=20)
Is it possible, and if so how, to have a QuerySet that filters based on dynamic arguments? For example:
# Instead of:
Person.objects.filter(name__startswith='B')
# ... and:
Person.objects.filter(name__endswith='B')
# ... is there some way, given:
filter_by = '{0}__{1}'.format('name', 'startswith')
filter_value = 'B'
# ... that you can run the equivalent of this?
Person.objects.filter(filter_by=filter_value)
# ... which will throw an exception, since `filter_by` is not
# an attribute of `Person`.
Python's argument expansion may be used to solve this problem:
kwargs = {
'{0}__{1}'.format('name', 'startswith'): 'A',
'{0}__{1}'.format('name', 'endswith'): 'Z'
}
Person.objects.filter(**kwargs)
This is a very common and useful Python idiom.
A simplified example:
In a Django survey app, I wanted an HTML select list showing registered users. But because we have 5000 registered users, I needed a way to filter that list based on query criteria (such as just people who completed a certain workshop). In order for the survey element to be re-usable, I needed for the person creating the survey question to be able to attach those criteria to that question (don't want to hard-code the query into the app).
The solution I came up with isn't 100% user friendly (requires help from a tech person to create the query) but it does solve the problem. When creating the question, the editor can enter a dictionary into a custom field, e.g.:
{'is_staff':True,'last_name__startswith':'A',}
That string is stored in the database. In the view code, it comes back in as self.question.custom_query . The value of that is a string that looks like a dictionary. We turn it back into a real dictionary with eval() and then stuff it into the queryset with **kwargs:
kwargs = eval(self.question.custom_query)
user_list = User.objects.filter(**kwargs).order_by("last_name")
Additionally to extend on previous answer that made some requests for further code elements I am adding some working code that I am using
in my code with Q. Let's say that I in my request it is possible to have or not filter on fields like:
publisher_id
date_from
date_until
Those fields can appear in query but they may also be missed.
This is how I am building filters based on those fields on an aggregated query that cannot be further filtered after the initial queryset execution:
# prepare filters to apply to queryset
filters = {}
if publisher_id:
filters['publisher_id'] = publisher_id
if date_from:
filters['metric_date__gte'] = date_from
if date_until:
filters['metric_date__lte'] = date_until
filter_q = Q(**filters)
queryset = Something.objects.filter(filter_q)...
Hope this helps since I've spent quite some time to dig this up.
Edit:
As an additional benefit, you can use lists too. For previous example, if instead of publisher_id you have a list called publisher_ids, than you could use this piece of code:
if publisher_ids:
filters['publisher_id__in'] = publisher_ids
Django.db.models.Q is exactly what you want in a Django way.
This looks much more understandable to me:
kwargs = {
'name__startswith': 'A',
'name__endswith': 'Z',
***(Add more filters here)***
}
Person.objects.filter(**kwargs)
A really complex search forms usually indicates that a simpler model is trying to dig it's way out.
How, exactly, do you expect to get the values for the column name and operation?
Where do you get the values of 'name' an 'startswith'?
filter_by = '%s__%s' % ('name', 'startswith')
A "search" form? You're going to -- what? -- pick the name from a list of names? Pick the operation from a list of operations? While open-ended, most people find this confusing and hard-to-use.
How many columns have such filters? 6? 12? 18?
A few? A complex pick-list doesn't make sense. A few fields and a few if-statements make sense.
A large number? Your model doesn't sound right. It sounds like the "field" is actually a key to a row in another table, not a column.
Specific filter buttons. Wait... That's the way the Django admin works. Specific filters are turned into buttons. And the same analysis as above applies. A few filters make sense. A large number of filters usually means a kind of first normal form violation.
A lot of similar fields often means there should have been more rows and fewer fields.
Is it possible to add a field to a queryset in django which would do the following:
fitting_set_items_list = FittingSetItem.objects.exclude(fitting_pack = None).exclude(fitting_pack = '').order_by('usage_type')
fitting_pack_list = FittingPack.objects.filter(fittingsetitem__in=fitting_set_items_list).add_field({'fitting_set_item': fittingsetitem})
This way i could use:
for fitting_pack_item in fitting_pack_item_list:
fitting_set_item = fitting_pack_item.fitting_set_item
and it'd have the FittingSetItem that i came from in the first place.
The overall Idea is that Many FittingSetItems can point to a FittingPack, so i want to be able to know which FittingSetItem my FittingPack was sourced from, and the easiest way i saw was to have the reverse FK on the FittingPack. This would allow me to go backwards and forwards on possibly ambiguous FK relations
I assume this is what you seek, if FittingSetItem.fitting_pack is a ForeignKey
fitting_packs = FittingPack.objects.filter(fittingsetitem__fitting_pack__isnull=False)
It gets the fitting packs linked by a set item. You might add .distinct() or replace fittingsetitem with fitting_set_item.
is it possible to follow ForeignKey relationships backward for entire querySet?
i mean something like this:
x = table1.objects.select_related().filter(name='foo')
x.table2.all()
when table1 hase ForeignKey to table2.
in
https://docs.djangoproject.com/en/1.2/topics/db/queries/#following-relationships-backward
i can see that it works only with get() and not filter()
Thanks
You basically want to get QuerySet of different type from data you start with.
class Kid(models.Model):
mom = models.ForeignKey('Mom')
name = models.CharField…
class Mom(models.Model):
name = models.CharField…
Let's say you want to get all moms having any son named Johnny.
Mom.objects.filter(kid__name='Johnny')
Let's say you want to get all kids of any Lucy.
Kid.objects.filter(mom__name='Lucy')
You should be able to use something like:
for y in x:
y.table2.all()
But you could also use get() for a list of the unique values (which will be id, unless you have a different specified), after finding them using a query.
So,
x = table1.objects.select_related().filter(name='foo')
for y in x:
z=table1.objects.select_related().get(y.id)
z.table2.all()
Should also work.
You can also use values() to fetch specific values of a foreign key reference. With values the select query on the DB will be reduced to fetch only those values and the appropriate joins will be done.
To re-use the example from Krzysztof Szularz:
jonny_moms = Kid.objects.filter(name='Jonny').values('mom__id', 'mom__name').distinct()
This will return a dictionary of Mom attributes by using the Kid QueryManager.