model configuration

[frank dilorenzo]

I have the following conditions. 

A supplier can have many shipments. 

A shipment can have many species.

A shipment can have only one supplier. 

Species can belong to many shipments.

No matter how I try I can't seem to configure the models correctly.  I was hoping someone could help me on this.

Thank you.

[Mike Dewhirst]

On 4/06/2021 11:34 am, frank dilorenzo wrote:
> I have the following conditions.
> A supplier can have many shipments.
> A shipment can have many species.
> A shipment can have only one supplier.
> Species can belong to many shipments.

supplier 1:n shipment
shipment n:m species

>
> No matter how I try I can't seem to configure the models correctly.  I
> was hoping someone could help me on this.
>
> Thank you.

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[Mike Dewhirst]

On 4/06/2021 1:39 pm, Mike Dewhirst wrote:
> On 4/06/2021 11:34 am, frank dilorenzo wrote:
>> I have the following conditions.
>> A supplier can have many shipments.
>> A shipment can have many species.
>> A shipment can have only one supplier.
>> Species can belong to many shipments.
>
> supplier 1:n shipment
> shipment n:m species

shipment has FK to supplier

species has m2m field with shipment

The latter implements a connecting table between species and shipment
which can be expanded to carry additional information if you need to
include anything related to a particular shipment + species

In all this I refer to the word species in its singular sense. E.g., we
are members of the human species.

[frank dilorenzo]

Thank Mike.  I am sorry for all this code but I am including it to show the problem I can't resolve.  I have 3 apps, shipment, supplier, specie. This is the models for them.

from django.db import models

from .models import Shipment

from django.utils import timezone

# Create your models here.

# A specie can belong to many shipments

class Specie(models.Model):

shipment = models.ManyToManyField(Shipment)

name = models.CharField(max_length=120, null=True)

image = models.ImageField(upload_to="species", default="no_picture.png")

created = models.DateTimeField(default=timezone.now)

def __str__(self):

return self.name

===================

from django.db import models

from .models import Supplier

# Create your models here.

# A shipment can have many species

class Shipment(models.Model):

supplier = models.ForeignKey(Supplier, on_delete=models.CASCADE)

slabel = models.CharField(max_length=10)

received = models.PositiveIntegerField(default=0)

bad = models.PositiveIntegerField(default=0)

non = models.PositiveIntegerField(default=0)

doa = models.PositiveIntegerField(default=0)

para = models.PositiveIntegerField(default=0)

released = models.PositiveIntegerField(default=0)

entered = models.BooleanField(default=False)

created = models.DateTimeField(auto_now_add=True)

def __str__(self):

return f"{self.slabel}"

======================

from django.db import models

# Create your models here.

# Supplier can have many shipments

class Supplier(models.Model):

name = models.CharField(max_length=120, null=True)

phone = models.CharField(max_length=15, null=True)

email = models.CharField(max_length=120, null=True)

created = models.DateTimeField(auto_now_add=True)

updated = models.DateTimeField(auto_now=True)

def __str__(self):

return self.name

the error I can't resolve is:

ImportError: cannot import name 'Supplier' from partially initialized module 'shipment.models' (most likely due to a circular import) (/Users/frankd/django_projects/tryit/src/shipment/models.py)

thanks again.

[Mike Dewhirst]

Frank

You don't have to import the class for the FK. Instead do a "lazy import".

That means you just use "appname.Modelname" and Django is smart enough to fugure it out.

Cheers

Mike

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[frank dilorenzo]

Thanks Mike.  I'll give it a try.

Have a great day.

frank-

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