If you have a dataset that is too large to fit in memory comfortably,
the ability to pass a generator to an httpresponse means you can break
it up into multiple smaller queries (outside the template system
anyway):
def queryset_to_csv(queryset,delimiter=',',steps=500):
""" generator for large querysets """
try: # raw query set
fieldmeta = queryset.model._meta.fields
except AttributeError: # it's been evaluated
fieldmeta = qs._meta.fields
fields = []
row= []
for f in fieldmeta:
fields.append(f.get_attname())
row.append('"'+f.name+'"')
yield "%s\r\n" % delimiter.join(row)
ids=[o["id"] for o in queryset.values("id")]
count=len(ids)
for n in range(steps,count+steps,steps):
lo,hi=n-steps,n
qs=queryset.model.objects.filter(pk__in=ids[lo:hi])
it=[]
for i in qs:
row = []
for f in fields:
val =
str(getattr(i,f)).replace('"',"'").replace(delimiter,' ')
row.append('"'+val+'"')
it.append(delimiter.join(row))
yield "\r\n".join(it)
...
return HttpResponse(queryset_to_csv(somequeryset,',',
250),mimetype='text/csv')
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