1. Intro
2. Like (Article-User)
3. Follow (User-User)
- 3.1. Profile Page
- 3.2. Follow

1. Intro

1.1. Terms

Source Model
- The model that has ManyToManyField
Target model
- The model that doesn't have ManyToManyField

1.2. The limits of N:1 Relationship

class Doctor(models.Model):
    name = models.TextField()

class Patient(models.Model):
    doctor = models.ForeignKey(Doctor, on_delete=modles.CASCADE)
    name = models.TextField()

If one patient make reservations with 2 diffrent doctors, you can't distingush whether the first Alex and the second Alex is the same person.

id	name	doctor_id
1	Alex	1
1	Alex	2

1.3. Intermediary Model

class Doctor(models.Model):
    name = models.TextField()

class Patient(models.Model):
    name = models.TextField()

class Reservation(models.Model):
    doctor = models.ForeignKey(Doctor, on_delete=modles.CASCADE)
    patient = models.ForeignKey(Patient, on_delete=modles.CASCADE)

Create
- Reservation.objects.create(doctor=doctor_instance, patient=patient_instance)
Read
- if doctor1 wants to read all the reservation
  - doctor1.reservaton_set.all()
- if patient1 wants to read all the reservation
  - patinet1.reservaton_set.all()

1.4. Many To Many Field

class Doctor(models.Model):
    name = models.TextField()

class Patient(models.Model):
    doctors = models.ManyToManyField(Doctor)
    name = models.TextField()

MantoToManyField(to, **options)
- to
  - the target model
- options
  - related_name
    - The alias of the dereference manager.
    - Default value is modelName_set
  - through
    - Desginate an intermediary table
  - symmetrical
    - Default: True
    - This argument is valid, only when to = 'self'
    - When it's True, the record for the opposite direction is automatically added.

Create
- patient1.doctors.add(doctor1)
- doctor1.patient_set.add(patient1)

Read
- if doctor1 wants to read all the reservation
  - doctor1.patient_set.all()
  - doctor1.patient_set.get(id=doctor_id)
- if patient1 wants to read all the reservation
  - patient1.doctors.all()
  - doctor1.patient_set.get(id=patient_id)
Delete
- if doctor1 wants to cancel the reservation with patient1
  - doctor1.patient_set.remove(patient1)
- if patient1 wants to cancel the reservation with doctor1
  - patient1.doctors.remove(doctor1)

1.5. Many To Many Table

Table Name
- Default: AppName_ModelName_FieldName
- db_table
  - the argument for changing the table name
Field name
- source model != target model
  
  id SourceModel_id TargetModel_id
- source model == target model (to = 'self')
  
  id form_ModelName_id to_ModelName_id

1.6. with Extra Fields

Make an intermediary model

class Doctor(models.Model):
    name = models.TextField()

class Patient(models.Model):
    doctors = models.ManyToManyField(Doctor, related_name='patients', through='Reservation')
    name = models.TextField()

class Reservation(models.Model):
    doctor = models.ForeignKey(Doctor, on_delete=modles.CASCADE)
    patient = models.ForeignKey(Patient, on_delete=modles.CASCADE)
    symptom = models.TextField()
    reserved_at = models.DateTimeField(auto_now_add=True)

Create
- through Reservation Model
  - Reservation.objects.create(doctor=doctor1, patient=patient1, symptom='stomachache')
- through ManyToMany Field
  - patient1.doctors.add(doctor1, through_defaults={'symptom': 'flu'})
  - through_defaults can be defined as a function

2. Like (Article-User)

models.py

class Article(models.Model):
    user = models.ForeignKey(setttings.AUTH_USER_MODEL, on_delete=models.CASCADE)
    like_users = models.ManyToManyField(settings.AUTH_USER_MODEL, related_name=like_articles)

relate_name should be specified
Otherwise, in the upper case, the dereference manager name(user.article_set) would be duplicated.

forms.py

class ArticleForm(models.ModelForm):

    class Meta:
        model = Article
        exclude = ('user', 'like_users', )

urls.py

app_name = 'articles',
urlpatterns = [
    ...,
    path('<int:article_pk>/likes/', views.likes, name='likes')
]

views.py

@require_POST
def likes(request, article_pk):
    if request.user.is_authenticated:
        article = Article.objects.get(pk=article_pk)
        if article.like_usres.filter(pk=request.user.pk).exists():
        # if request.user in article.like_users.all():
        # get을 쓰면 객체가 없을 때 Error 발생
            article.like_users.remove(request.user)
        else:
            article.like_users.add(request.user)
        return redirect('articles:index')
    return redirect('accounts:login')

exists()
Returns True if the QuerySet has value, or False

index.html

{% block content %} {% for article in articles %}
<p><b>작성자 : {{ article.user }}</b></p>
<p>글 번호: {{ article.pk }}</p>
<p>글 제목: {{ article.title }}</p>
<p>글 내용: {{ article.content }}</p>
<div>
  <form action="{% url 'article:likes' article.pk %}" method="POST">
    {% csrf_token %} {% if request.user in article.like_users.all %}
    <input type="submit" value="좋아요취소" />
    {% else %}
    <input type="submit" value="좋아요" />
    {% endif %}
  </form>
</div>
<a href="{% url 'articles:detail' article.pk %}">DETAIL</a>
<hr />
{% endfor %} {% endblock content %}

3. Follow (User-User)

3.1. Profile Page

urls.py
```
app_name='accounts'
urlpatterns = [
    path('profile/<str:username>/', views.profile, name='profile'),
]
```
- if you name the path as path('<str:username>/', views.profile, name='profile'), you should consider the order of the url paths carefully.

views.py

from django.contrib.auth import get_user_model

def profile(request, username):
    User = get_user_model()
    person = User.objects.get(username=username)
    context = {
        'person': person,
    }
    return render(request, 'accounts/prfile.html', context)

profile.html

{% block content %}
<h1>{{ person.username }}'s profile</h1>

<h4>{{ person.username }}'s articles</h4>
{% for article in person.article_set.all %}
<div>{{ article.title }}</div>
{% endfor %}
<hr />
<h4>{{ person.username }}'s comments</h4>
{% for comment in person.comment_set.all %}
<div>{{ comment.content }}</div>
{% endfor %}
<hr />
<h4>{{ person.username }}'s liked articles</h4>
{% for article in person.like_articles.all %}
<div>{{ article.title }}</div>
{% endfor %} {% endblock content %}

base.html

<a href="{% url 'accounts:profile' user.username %}">My Profile</a>

index.html

{% block content %} {% for article in articles %}
<p>
  <b
    >작성자 :
    <a href="{% url 'accounts:profile' article.user.username %}"
      >{{ article.user }}</a
    ></b
  >
</p>
<p>글 번호: {{ article.pk }}</p>
<p>글 제목: {{ article.title }}</p>
<p>글 내용: {{ article.content }}</p>
<a href="{% url 'articles:detail' article.pk %}">DETAIL</a>
<hr />
{% endfor %} {% endblock content %}

3.2. Follow

models.py

class User(AbstractUser):
    followings = models.ManyToManyField('self', symmetrical=False, related_name='followers')

urls.py

app_name = 'accounts',
urlpatterns = [
    ...,
    path('<int:user_pk>/follow/', views.follow, name='follow')
]

views.py

@require_POST
def follow(request, user_pk):
    if request.user.is_authenticated:
        if request.user.pk != user_pk:
            User = get_user_model()
            person = User.objects.get(pk=user_pk)
            if person.followers.filter(pk=reqeust.user.pk).exists():
            # if reuqest.user in person.followers.all():
                person.followers.remove(request.user)
            else:
                person.followers.add(request.user)
        return redirect('accounts:profile' person.username)
    return redirect('accounts:login')

profile.html

{% block content %}
<h1>{{ person.username }}'s profile</h1>
<div>
  Followers: {{ person.followers.all|length }} Followings:{{
  erson.followings.all|length }}
</div>
{% if request.user != person %}
<div>
  <form action="{% url 'accounts:follow' person.pk %}" method="POST">
    {% csrf_token %} {% if request.user in person.followers.all %} <input
    type="submit" value=="Follow"> {% else %} <input type="submit"
    value=="Unfollow"> {% endif %}
  </form>
</div>
... {% endblock content %}

Django N:M Realationship

1. Intro

1.1. Terms

1.2. The limits of N:1 Relationship

1.3. Intermediary Model

1.4. Many To Many Field

1.5. Many To Many Table

1.6. with Extra Fields

2. Like (Article-User)

3. Follow (User-User)

3.1. Profile Page

3.2. Follow

Django N:1 Realationship

Django REST API