Django N:1 Realationship

🖋️ Byongho96

1. Many to One Relationship

One-to-Many relationship in DBMS is a relationship between instances of an entity with more than one instance of another entity. Many_to_one

1.1. Foreign Key

A foreign key is a column or columns of data in one table that refers to the unique data values (often the primary key data) in another table

2. Comment : Article (N:1)

  • models.py

    # articles/models.py
class Article(models.Model):
    title = models.CharField(max_length=10)
    content = models.TextField()
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)


class Comment(models.Model):
    article = models.ForeignKey(Article, on_delete=models.CASCADE, releated_name='comments')
    content = models.CharField(max_length=200)
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)
    • on_delete
      • Referential Integrity: what to do when the parent instance is deleted
      • CASCADE
        • The referencing instance is also deleted
      • PROTECT
        • Can't delete the parent instance
      • SET_NULL
      • SET_DEFAULT
    • related_name
      • The alias of the dereference manager
      • Default value is modelName_set

  • forms.py

    # articles/forms.py
class CommentForm(forms.ModelForm):

class Meta:
    model = Comment
    exclude = ('article',)

2.1. Create

  • urls.py 
    # articles/urls.py
urlpatterns = [
    ...,
    path('<int:pk>/comments/', views.comments_create, name='comments_create'),
]
  • views.py 
    # articles/views.py
def comments_create(request, pk):
    article = Article.objects.get(pk=pk)
    comment_form = CommentForm(request.POST)
    if comment_form.is_valid():
        comment = comment_form.save(commit=False)
        comment.accounts = article
        comment.save()
    return redirect('movies:detail', pk)
  • detail.html 
    <!-- articles/detail.html -->
<form
  action=" {% url 'articles:comments_create' article.pk %} "
  method="POST">
  {% csrf_token %} {{ comment_form }}
  <input type="submit" />
</form>

2.2. Read

  • views.py 
    # articles/views.py
def detail(request, pk):
    article = Article.objects.get(pk=pk)
    comment_form = CommentForm()
    # 역참조 manager 사용
    # related_name 미선언 시, comment_set
    comments = article.comments.all()
    context = {
        'movie': movie,,
        'comment_form': comment_form,
        'comments': comments
    }
    return render(request, 'articles/detail.html', context)
  • detail.html 
    <h4>댓글 목록</h4>
<ul>
  {% for comment in comments %}
  <li>{{ comment.content }}</li>
  {% endfor %}
</ul>

2.3. Delete

  • urls.py 
    # articles/urls.py
urlpatterns = [
    ...,
    path('<int:article_pk>/comments/<int:comment_pk>', views.comments_delete, name='comments_delete'),
]
  • views.py 
    # articles/views.py
def comments_delete(request, article_pk, comment_pk):
    comment = Comment.objects.get(pk=comment_pk)
    comment.delete()
    return redirect('articles:detail', article_pk)
  • detail.html 
    <h4>댓글 목록</h4>
<ul>
  {% for comment in comments %}
  <li>
    {{ comment.content }}
    <form
      action=" {% url 'articles:comments_delete' article.pk comment_pk %} "
      method="POST">
      {% csrf_token %}
      <input type="submit" value="DELETE" />
    </form>
  </li>
  {% endfor %}
</ul>

3. Article : User (N:1)

  • models.py

    # articles/models.py
from django.conf import settings

class Movie(models.Model):
user = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE)

  • forms.py

    # articles/forms.py
class ArticleForm(forms.ModelForm):

class Meta:
    model = Comment
    exclude = ('user',)

3.1. Create

  • views.py

    # articles/views.py

@login_required
@require_http_methods(['GET', 'POST'])
def create(request):
    if request.method == 'POST':
        form = ArticleForm(request.POST)
        if form.is_valid():
            article = form.save(commit=False)
            article.user = request.user
            article.save()
            return redirect('movies:detail', article.pk)
    else:
        form = ArticleForm()
    context = {
        'form': form,
    }
    return render(request, 'articles/create.html', context)

3.2. Update

  • views.py

    @login_required
@require_http_methods(['GET', 'POST'])
def update(request, pk):
    article = article.objects.get(pk=pk)
    if request.user == article.user:
        if request.method == 'POST':
            form = ArticleForm(request.POST, instance=article)
            if form.is_valid():
                form.save()
                return redirect('articles:detail', pk)
        else:
            form = ArticleForm(instance=article)
        context = {
            'article': article,
            'form': form
        }
        return render(request, 'articles/update.html', context)
    return HttpResponse(status=403)

  • detail.html

    {% if request.user == article.user %}
<a href="{% url 'articles:update' article.pk %}">UPDATE</a>
<form action="{% url 'articles:delete' article.pk %}" method="POST">
  {% csrf_token %}
  <input type="submit" value="DELETE" />
</form>
{% endif %}

3.3. Delete

  • views.py

    # articles/views.py

@require_POST
def delete(request, pk):
    article = Article.objects.get(pk=pk)
    if request.user.is_authenticated:
        if request.user == article.user:
            article.delete()
            return redirect('articles:index')
        return HttpResponse(status=403) # 권한없음
    return redirect('accounts:login')

  • detail.html

    {% if request.user == article.user %}
<a href="{% url 'articles:update' article.pk %}">UPDATE</a>
<form action="{% url 'articles:delete' article.pk %}" method="POST">
  {% csrf_token %}
  <input type="submit" value="DELETE" />
</form>
{% endif %}

4. Comment : User (N:1)

  • models.py

    # articles/models.py
class Comment(models.Model):
    article = models.ForeignKey(Article, on_delete=models.CASCADE, releated_name='comments'),
    user = mmodels.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE)

  • forms.py

    # articles/forms.py
class CommentForm(forms.ModelForm):

class Meta:
    model = Comment
    exclude = ('article', 'user',)

4.1. Create

  • views.py 
    # articles/views.py
def comments_create(request, pk):
    article = Article.objects.get(pk=pk)
    comment_form = CommentForm(request.POST)
    if comment_form.is_valid():
        comment = comment_form.save(commit=False)
        comment.accounts = article
        comment.user = request.user
        comment.save()
    return redirect('movies:detail', pk)

4.2. Read

  • detail.html 
    <h4>댓글 목록</h4>
<ul>
  {% for comment in comments %}
  <li>{{ comment.user }}: {{ comment.content }}</li>
  {% endfor %}
</ul>

4.3. Delete

  • views.py 
    # articles/views.py
def comments_delete(request, article_pk, comment_pk):
    comment = Comment.objects.get(pk=comment_pk)
    if request.user == comment.user:
        comment.delete()
    return redirect('articles:detail', article_pk)
  • detail.html 
    <h4>댓글 목록</h4>
<ul>
  {% for comment in comments %}
  <li>
    {{ comment.user }}: {{ comment.content }} {% if request.user ==
    comment.user %}
    <form
      action=" {% url 'articles:comments_delete' article.pk comment_pk %} "
      method="POST">
      {% csrf_token %}
      <input type="submit" value="DELETE" />
    </form>
    {% endif %}
  </li>
  {% endfor %}
</ul>