filter objects using other model's objects

Question

I have a Parent, Name, and Kid Models :

models.py

class Parent(models.Model):
    title = models.CharField(max_length=250)
    address = models.CharField(max_length=250)


class Name(models.Model):
    title = models.CharField(max_length=250)


class Kid(models.Model):
    family = models.ForeignKey(Parent)
    name = models.ForeignKey(Name)
    age = models.IntegerField()
    city = models.CharField(max_length=250)

and I have a view function to display Parent objects only if Kid objects related to the Parent are all in the dictionary:

views.py

def index(request):
    patterns = [
        {'name__title': 'samy', 'age__lt': 15, 'city': 'paris'},
        {'name__title': 'sally', 'age__gt': 20, 'city': 'london'}
    ]
    filter_q = reduce(operator.or_, map(lambda p: Q(**p), patterns))
    qs = Kid.objects.filter(filter_q).values_list('id', 'family_id')
    family_ids = set()
    child_ids = list()
    for child_id, family_id in qs:
        family_ids.add(family_id)
        child_ids.append(child_id)
    incomplete_family_ids = set(Kid.objects.exclude(id__in=child_ids).filter(family_id__in=family_ids).values_list('family_id', flat=True).distinct())
    complete_family_ids = family_ids - incomplete_family_ids
    parents = Parent.objects.filter(id__in=complete_family_ids)
    template = 'index.html'
    context = {'parents': parents}
    return render(request, template, context)

What if I want to replace the pattern dictionary with models objects, like:

class Pattern(models.Model):
    title = models.CharField(max_length=250)


class PatternItems(models.Model):
    name = models.ForeignKey(Name)
    age = models.integer()
    city = models.CharField(max_length=250)
    pattern = models.ForeignKey(Pattern)

so instead of the dictionary. I wonder if its possible to select a pattern from Pattern models to display Parent objects if all it's related Kid objects are in PatternItems using a Pattern object.

the whole idea is to make the filter dynamic and allow users to make their own filters .

Help?

Paolo Stefan · Accepted Answer · 2016-11-23 17:46:43Z

3

You can replace this piece of code:

patterns = [
    {'name__title': 'samy', 'age__lt': 15, 'city': 'paris'},
    {'name__title': 'sally', 'age__gt': 20, 'city': 'london'}
]
filter_q = reduce(operator.or_, map(lambda p: Q(**p), patterns))

with a loop in which you add as many filters as you like:

# init patterns as a list of PatternItems
patterns = [ PatternItem(name=Name(title='samy'), age=15, city='paris'),
             PatternItem(name=Name(title='sally'), age=20, city='london'),
           ]
# iterate through the list normally
filters = []
for pt_item in patterns:
    filters.append(Q(name__title=pt_item.name.title) & 
                    Q(age__lt=pt_item.age) & Q(city=pt_item.city))

filter_q = filters[0]
for f in filters[1:]:
    filter_q |= f

Another way of getting patterns could be evaluating a QuerySet, e.g. using filter():

# any_column__gte and value here are just examples
patterns = PatternItem.objects.filter(any_column__gte=value)
# iterate through the patterns using .all()
filters = []
for pt_item in patterns.all():
    ...

The only problem with this approach is that you have to use the same comparison (i.e. age__lt) for each PatternItem in the list.

Please note: I'm using loops instead of the reduce() function because it doesn't exist in Python 3.

edited Nov 23, 2016 at 17:46

answered Nov 23, 2016 at 15:49

Paolo Stefan

10.3k5 gold badges47 silver badges65 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

DjangoGuy Over a year ago

where do I specify the pattern name ?

Paolo Stefan Over a year ago

@DjangoGuy in the above code, you specify the name by setting PatternItem.name to an existing Name instance. Or -simpler- you can change your PatternItem.name field to a CharField and use Q(name__title=pt_item.name) instead.

DjangoGuy Over a year ago

Let's say I have a pattern called 'Adults' that has a X number of PatternItems related to it. where do I write 'Adults' in the code you wrote?

Paolo Stefan Over a year ago

@DjangoGuy assuming that, inside Adults, the PatternItems are in a queryset named PatternItems, change the 3rd line to for pr_item in Adults.PatternItems.all():

DjangoGuy Over a year ago

do I have to import something before using filter_q? cause my editior doesn't recognize it . I also get this error 'ModelBase' object is not iterable for pt_item in Pattern:

DjangoGuy · Accepted Answer · 2016-11-23 18:32:48Z

So Here is the answer for my question that probably was not clear. @Paolo Stefan code was so close to what I needed.

view.py

patterns = PatternItems.objects.filter(pattern__title='adults')
filters = []
for pt_item in patterns.all():
    filters.append(Q(name__title=pt_item.name.title) &
                   Q(age__lt=pt_item.age) & Q(city=pt_item.city))

filter_q = filters[0]
for f in filters[1:]:
    filter_q |= f
qs = Kid.objects.filter(filter_q).values_list('id', 'family_id')
family_ids = set()
child_ids = list()
for child_id, family_id in qs:
    family_ids.add(family_id)
    child_ids.append(child_id)
incomplete_family_ids = set(Kid.objects.exclude(id__in=child_ids).filter(family_id__in=family_ids).values_list('family_id', flat=True).distinct())
complete_family_ids = family_ids - incomplete_family_ids
parents = Parent.objects.filter(id__in=complete_family_ids)
template = 'index.html'
context = {'parents': parents}
return render(request, template, context)

The only difference is : patterns = PatternItems.objects.filter(pattern__title='adults')

which filters the patternitems with the pattern needed 'adults'.

Collectives™ on Stack Overflow

filter objects using other model's objects

2 Answers 2

5 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

5 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related