Django/Python Chain and Sort Querysets

Question

I have an inventory count that has N locations, this locations needs to be counted N times, so I have one model for "the location header" and another for the item list of every header.

I need to chain,sort AND get unique results of the items in N querysets

I have this:

loc_id = request.POST['loc_id'] # the Id of my location pivot
inv_location = InventoryLocations.objects.get(pk=loc_id) # get the location count pivot
inv_locations = InventoryLocations.objects.filter(location=inv_location.location,
                inventory=inv_location.inventory) #get all related locations counts

# At this point i can have N inv_locations

count_items = [] # list of items in all inventory counts 
for l in inv_locations:
    items = InventoryDetails.objects.filter(inventory_location = l) # get items of every count 
    count_items.append(items)

# Now I have all the items counted in the counts_items array, I need to get from this a single
# list of items Ordered and not repeated    

all_items = chain(count_items) <<< IS THIS CORRECT??
sorted_items = sorted(all_items,key=lambda item: item.epc) << THIS GIVE ME ERROR
unique_items = ???

My models are:

class InventoryCount(models.Model):
    ...nothing important

class InventoryLocation(models.Model):
    inventory= models.ForeignKey(InventoryCount)
    location= models.ForeignKey(Location)
    ...

class InventoryDetails(models.Model):
    inventory_location= models.ForeignKey(InventoryLocations)
    epc = models.CharField(max_length=25, null=True, blank=True)
    item= models.ForeignKey(Item)
    ...

Basically, I need a list of all items counted in all inventoryDetails in the array sorted by epc and not repeated

I'm stuck in here, i dont know if the chain is doing it right and the sort function gives me an error saying that the item has no 'epc' attribute.

Help plz!

Can you add your models plz?

cdvv7788
– cdvv7788

2014-12-01 16:56:58 +00:00
Commented Dec 1, 2014 at 16:56 — cdvv7788
– cdvv7788, Commented Dec 1, 2014 at 16:56

Peter DeGlopper · Accepted Answer · 2014-12-01 17:04:04Z

1

To solve your immediate problem - assuming that's itertools.chain, chain takes multiple iterables. Use chain(*count_items) to expand your list of querysets.

But you can save yourself some trouble by using InventoryDetails.objects.filter(inventory_location__in=inv_locations).order_by('epc').distinct() - that'll do the sorting and uniquing in the database rather than you doing it in your view.

answered Dec 1, 2014 at 17:04

Peter DeGlopper

37.5k7 gold badges95 silver badges88 bronze badges

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

2 Comments

Alex Lord Mordor Over a year ago

with an empty parameter in distinct() will unique all fields? or should I put a field like .distinct('epc')?

Peter DeGlopper Over a year ago

See the docs for full details: docs.djangoproject.com/en/dev/ref/models/querysets/… Short version, it uniques all fields - each underlying DB row will be returned only once. You might not need it here, and if you want each epc only once you might need to do that part in Python. On PostgreSQL only, you can use .distinct('epc').

Collectives™ on Stack Overflow

Django/Python Chain and Sort Querysets

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related