如何根据Django中的模型对sql输入进行分类

Question

I want to learn django and I should categorize my sql inputs according to my models.

For example I have some models like this:

class Author(models.Model):
    authorName = models.CharField(max_length=30)

    def __str__(self):
        return self.authorName


class Book(models.Model):
    author = models.ForeignKey(Authors, on_delete=models.CASCADE)
    bookName = models.CharField(max_length=60)
    downloadLink = models.FileField()
    downloadCount = models.IntegerField(default=0)

    def __str__(self):
        return self.bookName

and I want to an output in my .html file like this;

---

Sherlock Holmes

• A Study in Scarlet
• The Sign of the Four
• The Hound of the Baskervilles

Suzanne Collins

• The Hunger Games
• Catching Fire
• Mockingjay

---

I tried this code in my html file but it doesn't work

<ul>
  {% for author in all_authors %}

      <h2>{{ author.authorName }}</h2>

      {% for book in all_books %}
          {% if book.author == author.authorName %}

              <li><a href="{{ book.downloadLink.url }}" download="{{ book.downloadLink.url }}">{{ book.bookName }}</a></li>

          {% endif %}
      {% endfor %}

  {% endfor %}
</ul>

My output is;

---

Sherlock Holmes

Suzanne Collins

---

Here is my view.py file;

def books(request):
    return render(request,'../templates/library/library-template.html', {
        'all_authors': Author.objects.all(),
        'all_books': Book.objects.all(),
    })

How can I fix it? Or are there any different solution for fix this?

Thank you.. :)

Answer 1

Your if statement will never be true, you are comparing an object and a string

      {% if book.author == author.authorName %}

So you could change this to

      {% if book.author == author %}

But this is still wasteful, you can just use the reverse lookup so you won't need the if statement at all

<ul>
  {% for author in all_authors %}

      <h2>{{ author.authorName }}</h2>

      {% for book in author.book_set.all %}

              <li><a href="{{ book.downloadLink.url }}" download="{{ book.downloadLink.url }}">{{ book.bookName }}</a></li>
      {% endfor %}

  {% endfor %}
</ul>