Django, get objects by multiple values - django

Question

There is a model
class Fabric(models.Model):
vendor_code = models.CharField(max_length=50)
color = models.CharField(max_length=50)
lot = models.CharField(max_length=50)
I've a list of objects
values = [
{'vendor_code': '123', 'color': 'aodfe', 'lot': 'some lot 1'},
{'vendor_code': '456', 'color': 'adfae', 'lot': 'some lot 2'},
{'vendor_code': '789', 'color': 'dvade', 'lot': 'some lot 3'},
]
There are no ids in dict objects. How can get objects checking for list of field values(for all 3 values per object at same time)?
I know that I can query one by one in loop as:
for item in values:
fabric = Fabric.objects.filter(vendor_code=item['vendor_code'], color=item['color'], lot=item['lot'])
but amount of objects in list can be large. Is there any proper way to get objects at once, if they exists? Or at least to get them with min amount of db hit.
Thanks in advance!

Answer 1

You can use the in (__in) filter like so:
fabrics = Fabric.objects.filter(
vendor_code__in=[value['vendor_code'] for value in values],
color__in=[value['color'] for value in values],
lot__in=[value['lot'] for value in values],
)
This will however iterate the values list 3 times, to only iterate it once use something like this:
vendor_codes = []
colors = []
lots = []
for value in values:
vendor_codes.append(value['vendor_code'])
colors.append(value['color'])
lots.append(value['lot'])
fabrics = Fabric.objects.filter(
vendor_code__in=vendor_codes,
color__in=colors,
lot__in=lots,
)
To filter according to all three values at the same time you will have to use Q objects like this:
q_objects = []
for value in values:
q_objects.append(Q(
vendor_code=value['vendor_code'],
color=value['color'],
lot=value['lot']
)
)
final_q_object = Q()
for q_object in q_objects:
final_q_object.add(q_object, Q.OR)
fabrics = Fabric.objects.filter(final_q_object)
The gist of it is to get this query:
Q(Q(a=i, b=j, c=k)) | Q(Q(a=l, b=m, c=n) | ...)
Final answer after a bit of optimization:
final_query = Q()
for item in values:
final_query.add(
Q(
vendor_code=value['vendor_code'],
color=value['color'],
lot=value['lot']
),
Q.OR
)
fabrics = Fabric.objects.filter(final_query)

Answer 2

You could use the field lookup "in".
# get all the vendor codes in a list
vendor_code_list = []
for v in values:
vendor_code_list.append(v['vendor_code'])
# query all the fabrics
fabrics = Fabric.objects.filter(vendor_code__in=vendor_code_list)

Answer 3

If you want to match exact values and you are sure that your item keys are valid field names you can just:
for item in values:
fabric = Fabric.objects.filter(**item)
otherwise if you want check if your items are contained inside existing items you can:
for item in values:
item_in = {'{}__in'.format(key):val for key, val in item.items()}
fabric = Fabric.objects.filter(**item_in)