Let\'s say I have a ForeignKey from Coconut to Swallow (ie, a swallow has carried many coconuts, but each coconut has been carried by only one swallow). Now let\'s say that
If i understood your altered question correctly you should be able to compare the coconut_carried_set of the swallow with the list of coconuts that have been carried.
see docs
I'm not entirely sure that this is what you want - I guess it depends on if you know which swallow you want to check beforehand or if you want to check it against all swallows - in that case there may be a better solution.
See the docs on queries spanning multi-valued relationships -- you should chain filter calls.
A simple way to go would be something like
queryset = Swallow.objects.all()
for coconut in coconuts:
queryset = queryset.filter(coconuts_carried=coconut)
A fancy way to do this in one line using reduce
would be
reduce(lambda q, c: q.filter(coconuts_carried=c), coconuts, Swallow.objects.all())
I can have swallow.objects.filter(coconuts_carried__husk_sements__in = husk_segment_list) to show that this swallow has gripped at least one husk segment in the list.
No, this is wrong, this gives you a list of swallows which have carried at least one husk segment from *husk_segment_list*.
If I've understood right, we are talking about checking for a specific swallow.
So, from your description I guess your models look something like this:
class Swallow(models.Model):
name = models.CharField(max_length=100)
class Coconut(models.Model):
swallow = models.ForeignKey(Swallow, related_name='coconuts_carried')
class HuskSegment(models.Model):
coconut = models.ForeignKey(Coconut, related_name='husk_segments')
If you already have the husk segment list you need to check againts the swallows segments, there's no reason you need to resolve it in a query. Get the swallows' segments and check if it's a superset of your husk segment list.
So we have:
#husk_segment_list = [<object: HuskSegment>, <object: HuskSegment>, <object: HuskSegment>...]
husk_segments_set = set((husk.pk for husk in husk_segment_list))
whitey = Swallow.object.get(name='Neochelidon tibialis')
wh_segments_set = set((value[0] for value in HuskSegment.objects.filter(coconut__in=whitey.coconuts_carried.all()).values_list('id')))
whitey_has_carried_all = wh_segments_set.issuperset(husk_segments_set)