django - How to prepare a list for queryset (select2) from multiple m2m filed

Question

One of my models has three columns which are M2M fields and each of these three M2M fields has different models.

I want to get a dataset from this product attribute model as shown in the output SQU below. And this is the dataset I want to get as the queryset of the model form.

I would be very grateful if someone could give me a little idea on how to do this. Or I'm not sure if the model design is right in the field of getting such a dataset, because I'm brand new to Django.

class ProductAttributes(models.Model):
    product     = models.ForeignKey('Product', blank=True, null=True, on_delete=models.SET_NULL)
    size        = models.ManyToManyField('ProductSize', related_name = "productsize")
    colour      = models.ManyToManyField('ProductColour', related_name="productcolour")
    cupsize     = models.ManyToManyField('ProductCupSize', related_name="productcupsize")

class ProductSize(models.Model):
    name = models.CharField(max_length=10)

class ProductColour(models.Model):
    name = models.CharField(max_length=25)
    colour = models.CharField(max_length=15, blank=True, null=True)

class ProductCupSize(models.Model):
    name = models.CharField(max_length=1)

The way I query data from these three models.

attrs = ProductAttributes.objects.filter(product=product_id).values('product', 'size__name', 'colour__name',
                                                                        'cupsize__name')
        sku = []
        for attr in attrs:
            att = {'id': '-'.join([str(attr['product']), str(attr['size__name']), str(attr['cupsize__name']),
                                   str(attr['colour__name'])]),
                   'text': '-'.join(
                       [str(attr['size__name']), str(attr['cupsize__name']), str(attr['colour__name'])])}
            sku.append(att)

output sku:

[{'id': '108-32-B-Grey', 'text': '32-B-Grey'}, {'id': '108-32-C-Grey', 'text': '32-C-Grey'}, {'id': '108-32-B-White', 'text': '32-B-White'}, {'id': '108-32-C-White', 'text': '32-C-White'}, {'id': '108-34-B-Grey', 'text': '34-B-Grey'}, {'id': '108-34-C-Grey', 'text' : '34-C-Grey'}, {'id': '108-34-B-White', 'text': '34-B-White'}, {'id': '108-34-C-White', 'text': '34-C-White'}]

Updated:

self.fields['product_attr'].queryset = ProductAttributes.objects.filter(product_id=108).values("id").annotate(
                id_dummy=Concat(
                    'product', V('-'), 'size__name', V('-'), 'cupsize__name', V('-'), 'colour__name',
                    output_field=CharField()
                ),
                text=Concat(
                    'size__name', V('-'), 'cupsize__name', V('-'), 'colour__name',
                    output_field=CharField()
                )
            ).values("id_dummy", "text").annotate(id=F('id_dummy')).values_list("id", "text")

question from:https://stackoverflow.com/questions/65892149/how-to-prepare-a-list-for-queryset-select2-from-multiple-m2m-filed

Answer 1

You can do that with Concat and Value() expressions

The following code should do what you want:

from django.db.models import CharField, F, Value as V
from django.db.models.functions import Concat

attrs = list(ProductAttributes.objects.values("id").annotate(
    id_dummy=Concat(
        'product', V('-'), 'size__name', V('-'), 'cupsize__name', V('-'), 'colour__name',
        output_field=CharField()
    ),
    text=Concat(
        'size__name', V('-'), 'cupsize__name', V('-'), 'colour__name',
        output_field=CharField()
    )
).values("id_dummy", "text").annotate(id=F('id_dummy')).values_list("id", "text")

In your place i would use django-select2

my_choice = forms.ChoiceField(widget=Select2Widget(attrs={'data-placeholder': 'Your placeholder'}), choices=YOURE_CHOICES, required=False)