Question

Lets say we have the following models: (simplified)

class Collection(models.Model):
    slug = models.SlugField()

class Brochure(models.Model):
    collection = models.ForeignKey(Collection)

class Page(models.Model):
    brochures = models.ManyToMany(Brochure)

• There are 2 collections ‘x’ and ‘y’.
• A page has a selection of brochures, not all.

Is there a way to get a dictionary of brochures like this:

{'x': [brochure1, brochure2], 'y': [brochure3, brochure4]}

only by using the many-to-many manager:

page_instance.brochures.all()

EDIT

I want to work with the brochures related to Page. Not Brochures.objects.all() or collection_instance.brochure_set. That’s why I included Page.

I found defaultdict, which helps me do this:

collection_brochures = defaultdict(list)
for b in self.brochures.all():
    collection_brochures[b.collection.slug].append(b)

Actually this is the answer to my question.

I can work with this, but ideal would be a list with dicts like this:

[{'collection': 'x', 'brochures': [brochure1, brochure2]}, {'collection': 'y', 'brochures': [brochure3, brochure4]}]

Answer 1

I hope this code snippet will do the job.

collection_brochures = defaultdict(list)
for b in self.brochures.all():
    collection_brochures[b.collection.slug].append(b)
result = []
for collection, brochures in collection_brochures.iteritems():
    result.append({'collection': collection, 'brochures': brochures})

Also you can use model instances as keys, so if you wish to see Collection instances instead of their slugs, you may replace third line with this one:

collection_brochures[b.collection].append(b)

This will give you following data:

[{'collection': collection_x, 'brochures': [brochure1, brochure2]},
 {'collection': collection_y, 'brochures': [brochure3, brochure4]}]