计算Django中的外键

Question

I am doing some statistics between products and suppliers in django 1.11 with python3, the problem is that I do not know how to relate the model:

class Proveedor(models.Model):
    nombre_empresa = models.CharField(max_length=150)
    direccion = models.TextField()
    telefono = models.IntegerField()
    fecha_registro = models.DateField(auto_now_add=True)

    def __str__(self):
        return self.nombre_empresa

class Producto(models.Model):
    nombre_producto = models.CharField(max_length=150)
    descripcion = models.TextField()
    precio = models.IntegerField()
    proveedor = models.ForeignKey(Proveedor)
    fecha_registro = models.DateField(auto_now_add=True)

    def __str__(self):
        return self.nombre_producto

With the following sql statement:

select nombre_empresa,count(prod.id_proveedor) from productos prod,proveedores prov where prod.id_proveedor=prov.id_proveedor group by nombre_empresa

My code :

from app.models import Producto,Proveedor

productos = Producto.objects.all() # How do I do the filter ?
for producto in productos:
    nombre_producto = producto.nombre_producto
    proveedor = len(producto.proveedor)

I need to see the name of the suppliers with the quantity products that each supplier

How can I make the same relation to load a list with that result?

Answer 1

To get all the suppliers with the number of products of each of them you can use annotate()

sup_with_prod = Proveedor.objects.annotate(num_prod=Count('producto'))

and you can access the number of products like so:

sup_with_prod[0].num_prod

for the first supplier, and so on. Or, in your case:

for supplier in sup_with_prod:
    nr_products = supplier.num_prod