ManytoMany query and template rendering from one model to another

Question

I'm new to Django. I had two different questions.

I can't query between one of my model and another model (ManyToMany). I can do this with the shell, but I couldn't handle it in the template.
I cannot assign a default value from one model to another model's field.

For the first question;

What I want to do is show values for multiple options. For this, I could make a query similar to this in the shell:

room[0].room_type_id.all()

But I can't do this in the template. On the other hand, when I want to show it with display, it returns empty. What I want to do here; returning the room types for each room or or accessing the room_cost of the RoomType class and displaying it in the template, repeated for each room type.

{% for room in rooms %}
     {{room.room_type_id_display}} 
{% endfor %}

My second question is;

To set the value from the property of a different model as default in the other model field. That is, to assign the value returned from the total_price of the Booking model to the price field in the Payment model by default.

I would appreciate it if anyone could provide documentation or resources on the subject.

class RoomType(models.Model):
    ROOM_CHOICES = (
        ('1', 'O),
        ('2','T'),
        ('3', 'Th'),
        ('4','F'),
        ('5','Fi')
    )
    room_type = models.CharField(max_length=50,choices=ROOM_CHOICES)
    room_type_des = models.TextField(blank=True,null=True)
    room_cost = models.IntegerField()

    def __str__(self):
        return str(self.room_type)

class Room(models.Model):
    room_number = models.IntegerField()
    room_des = models.TextField(blank=True,null=True)
    room_availabe = models.BooleanField(default=True)
    room_type_id = models.ManyToManyField(RoomType)

    def __str__(self):
        return str(self.room_number)

class Booking(models.Model):
    room_number_id = models.ForeignKey(Room,on_delete=models.DO_NOTHING)
    customer_id = models.ManyToManyField(Customer)
    check_in = models.DateTimeField(auto_now_add=True)
    check_out = models.DateTimeField(auto_now_add=False,auto_now=False,auto_created=False, null=True)
    status = models.BooleanField(default=False)
    @property
    def calculate_day(self):
        day = self.check_out - self.check_in
        return str(day.days)
    
    @property
    def total_price(self):
        day = self.check_out - self.check_in
        price = self.room_number_id.room_type_id.room_cost
        return price*day.days
        

class Payment(models.Model):
    booking_id = models.ForeignKey(Booking,on_delete=models.DO_NOTHING)
    ACCEPT_CHOICES = (
        ('N','N'),
        ('K','K'), 
    )
    payment_type = models.CharField(max_length=1,choices=ACCEPT_CHOICES)
    price = models.IntegerField()
    payment_detail = models.TextField()

user_106140 · Answer

Here's a small modification: don't use "_id", because it's not an id, it's a real instance of the foreign model. Then, use "related_name", and think like "if I start from the opposite side, what name should I use?" (it's always plural). And for your (2), you can't set a default value for a "in-between table": a ManyToMany field create a "join" table to join the two other tables. You can only set a default value for OneToOne and ForeignKey fields.

class RoomType(models.Model):
    ROOM_CHOICES = (
        ('1', 'O),
        ('2','T'),
        ('3', 'Th'),
        ('4','F'),
        ('5','Fi')
    )
    room_type = models.CharField(max_length=50,choices=ROOM_CHOICES)
    room_type_des = models.TextField(blank=True,null=True)
    room_cost = models.IntegerField()

    def __str__(self):
        return str(self.room_type)

class Room(models.Model):
    room_number = models.IntegerField()
    room_des = models.TextField(blank=True,null=True)
    room_availabe = models.BooleanField(default=True)
    room_type = models.ManyToManyField(RoomType, related_name="rooms")

    def __str__(self): 
        return str(self.room_number)

class Booking(models.Model):
    room = models.ForeignKey(Room, related_name="bookings", on_delete=models.DO_NOTHING)
    customer = models.ManyToManyField(Customer, related_name="bookings")
    check_in = models.DateTimeField(auto_now_add=True)
    check_out = models.DateTimeField(auto_now_add=False,auto_now=False,auto_created=False, null=True)
    status = models.BooleanField(default=False)
    @property
    def calculate_day(self):
        day = self.check_out - self.check_in
        return str(day.days)
    
    @property
    def total_price(self):
        day = self.check_out - self.check_in
        price = self.room_number.room_type.room_cost
        return price * day.days
        

class Payment(models.Model):
    booking = models.ForeignKey(Booking, related_name="payments", on_delete=models.DO_NOTHING)
    ACCEPT_CHOICES = (
        ('N','N'),
        ('K','K'), 
    )
    payment_type = models.CharField(max_length=1,choices=ACCEPT_CHOICES)
    price = models.IntegerField()
    payment_detail = models.TextField()

If you want all your room types, it's:

RoomType.objects.all()

If you want to "send" all types to a template, use get_context_data like this:

def get_context_data(self, **kwargs):
    context = super().get_context_data(**kwargs)
    context["room_types"] = RoomType.objects.all()
    return context

and in your template:

 {% for room_type in room_types %}
     {{ room_type }}
 {% endfor %}

For your template (and with my models code above), you could do:

{% for room in rooms %}
     {{ room.room_type }} 
{% endfor %}

And if you want to show all options in a form, it's another subject, too long for a simple answer here, read the official documentation here.

ManytoMany query and template rendering from one model to another

1 Answers