Django : count foreign key and display

Question

Suppose I have two table in my database,

1. booktable which have 3 attributes (id, book_name, writer_id(foreignkey))

2. writertable which have 2 attributes (id, writer_name)

I want to display writer name and how many books have that writer by calculate booktable

book table

---------------------------------------
|   id   |   book_name   |  writer_id |
|-------------------------------------|
|    1   |   abc         |      2     |
|    2   |   bcd         |      1     |
|    3   |   efg         |      1     |
|    4   |   htj         |      2     |
|    5   |   klm         |      1     |
|    6   |   nop         |      3     |
|-------------------------------------|

Writer table

----------------------------
|   id   |   writer_name   |
|---------------------------
|    1   |     xyz         |
|    2   |     bcb         |
|    3   |     eld         |
|    4   |     ccb         |
|---------------------------

so, 
  id 1 = 3 books
     2 = 3 books
     4 = 0 books

How can I display in html template. Here is my code,

models.py

class book(models.Model):
    book_name = models.CharField(max_length = 100)
    writer = models.ForeignKey(writer, on_delete = models.CASCADE)

class writer(models.Model):
    writer_name = models.CharField(max_length = 100)

    def __str__(self):
        return self.writer_name

view.py

def getwriters(request):
    wrt = writer.objects.all()
    return render(request, "writers.html", {"wrt":wrt})

writers.html

    {% for p in wrt %}  
        <tr>
            <td>{{ p.writer_name }}</td>
            <td>{{**Should display how many books have this writer**}}</td>
        </tr>
    {% endfor %}

Answer 1

You can annotate the queryset with:

def getwriters(request):
    wrt = writer.objects.annotate(
        numbooks=Count('book')
    )
    return render(request, "writers.html", {"wrt":wrt})

This will add to every writer object an extra attribute numbook that contains the number of related books (so in this case books written by that writer).

You can then render it as:

{% for p in wrt %}  
    <tr>
        <td>{{ p.writer_name }}</td>
        <td>{{ p.numbooks }}</td>
    </tr>
{% endfor %}

Answer 2

You can do something like this :

book.objects.filter(writer_pk=1).count()

This will return count of all books with writer whose pk is 1