django: values() dictionnary with many to many relationship - django

Question

I'm trying (for training purposes) to make an application for a library catalogue. I took the decision to make a Person model for all people involved in creation of the book and join it with Book model through intermediary model (since one book may have several authors, redactors, translators etc), which would describe the role of this person.
The Book model is for an edition of a book. It stores information about book as a piece of literature. For each edition of a book there is a book instance.
The copy model is for a book as an object.
Now I'm trying to make search function. My goal is to display a list of all book which meets search criteria, but have all copies which share the authors and the title (regardless the fact, if it was the same publisher, translator, etc), as one row with the number indicating the number of copies. So, I understand, I should use annotate with Count on values() dictionnary. But I'm not able to get all information I need while using values().
If I make a query searching by the book title, I have all creators in the values() dictionnary. But if the search criteria is author, the values dictionnary keeps only the name which was used to filter, so if the book has two or three authors, I don't get their names.
Here are my models (for Book model only the relevant fields, to make shorter):
class Person(models.Model):
name = models.CharField(max_length=128, blank=True)
born = models.CharField(max_length=64, blank=True)
class Book(models.Model):
title = models.CharField(max_length=255, blank=True)
creators = models.ManyToManyField(Person, through='Creator')
class Copy(models.Model):
on_shelf = models.BooleanField()
location = models.CharField(max_length=32, blank=True)
remarques = models.CharField(max_length=255, blank=True)
signature_mark = models.CharField(max_length=32, blank=True)
approuved = models.BooleanField(default=False)
collection = models.ForeignKey(Collection, on_delete=models.CASCADE, blank=True, null=True)
book = models.ForeignKey(Book, on_delete=models.CASCADE, null=True)
class Creator(models.Model):
AUTHOR = 'A'
TRANSLATOR = 'T'
REDACTION = 'R'
INTRODUCTION = 'I'
ROLE_CHOICES = [
(AUTHOR, 'Autor'),
(TRANSLATOR, 'Tłumacz_ka'),
(REDACTION, 'Opracowanie, redakcja [Nazwisko Imię]'),
(INTRODUCTION, 'Wstęp, posłowie'),
]
person = models.ForeignKey(Person, on_delete=models.CASCADE)
book = models.ForeignKey(Book, on_delete=models.CASCADE, blank=True, null=True)
role = models.CharField(max_length=32, blank=True, choices=ROLE_CHOICES)
Here are my queries:
By title:
book = Copy.objects.filter(book__title='Rozwój cywilizacji amerykańskiej tom 1-2').values('book__creators__name', 'book__creator__role','book__title')
The output is:
{'book__creators__name': 'Garczyński Stefan', 'book__creator__role': 'T', 'book__title': 'Rozwój cywilizacji amerykańskiej tom 1-2'}
{'book__creators__name': 'Święcka Teresa', 'book__creator__role': 'T', 'book__title': 'Rozwój cywilizacji amerykańskiej tom 1-2'}
{'book__creators__name': 'Beard Charles', 'book__creator__role': 'A', 'book__title': 'Rozwój cywilizacji amerykańskiej tom 1-2'}
{'book__creators__name': 'Beard Mary', 'book__creator__role': 'A', 'book__title': 'Rozwój cywilizacji amerykańskiej tom 1-2'}
by author:
book = Copy.objects.filter(book__creators__name='Beard Mary', book__creator__role='A').values('book__creators__name', 'book__creator__role', 'book__title')
the output:
{'book__creators__name': 'Beard Mary', 'book__creator__role': 'A', 'book__title': 'Rozwój cywilizacji amerykańskiej tom 1-2'}
The view and template are just a draft, it doesn't work yet. I' trying first to find a solution in the shell.
the view:
class Searchg(View):
def get(self, request, *args, **kwargs):
form = SearchForm()
return render(request, 'working/search.html', {'form': form})
def post(self, request, *args, **kwargs):
form = SearchForm(request.POST)
if form.is_valid():
author = form.cleaned_data['author']
title = form.cleaned_data['title']
if author and title:
books = Book.objects.filter(creators__name__icontains=author,
creator__role='A', title__icontains=title).order_by('title')
print('a ' , len(books))
elif author:
books = Book.objects.filter(creators__name__icontains=author, creator__role='A').order_by('title')
print('b ' , len(books))
elif title:
books = Book.objects.filter(title__icontains=title).order_by('creators__name')
print('c ' , len(books))
else:
print("Please enter search criteria")
books = books.values('creators__name', 'title').annotate(title_count=Count('title'))
paginator = Paginator(books, 25)
page_number = request.GET.get('page')
page_obj = paginator.get_page(page_number)
cache.set('books', books)
return redirect(reverse('working:book_list'))
and template:
{% if page_obj %}
<table class="table table-bordered">
<thead>
<tr>
<th scope="col"></th>
<th scope="col"> Liczba egzemplarzy</th>
<th scope="col">Tytuł</th>
<th scope="col">Autor</th>
</tr>
</thead>
<tbody>
<tr>
{% for book in page_obj %}
<th scope="row">{{ forloop.counter0|add:page_obj.start_index}}</th>
<td>{{ book.title_count }}</td>
<td><em> {{ book.title }}</em></td>
<td> {{ book.creators__name }}</td>
</tr>
{% endfor %}
</tbody>
</table>
<div class="pagination">
<span class="step-links">
{% if page_obj.has_previous %}
<button class="btn btn-light">« first</button>
<button class="btn btn-light">previous </button>
{% endif %}
<span class="current">
Page {{ page_obj.number }} of {{ page_obj.paginator.num_pages }}.
</span>
{% if page_obj.has_next %}
<button class="btn btn-light">next</button>
<button class="btn btn-light">last »</button>
{% endif %}

Answer 1

This is one of the (many) reasons why using .values(…) [Django-doc] is often not a good idea. One typically uses this to group on a special field, etc. Not to obtain values.
Furtherdmore you probably want to query on the Book model, not on the Copy model, since that will make it harder to render each book with one record. You thus can filter with:
from django.db.models import Count
books = Book.objects.filter(
creator__name='Beard Mary',
creator__role='A'
).annotate(
ncopies=Count('copy')
).prefetch_related('creator_set')
and then in the template, you can render this for example with:
{% for book in books %}
{{ book.title }}: {{ book.ncopies }} copies
{% for creator in book.creator_set.all %}
{{ creator.person.name }}: {{ creator.role }}
{% endfor %}
{% endfor %}
Here the .creator_set will not take the filtering of the QuerySet into account, since this is handled in a separated query.
You can also query on the book.copy_set.all in the template, to retrieve all related Copy objects.