Re: Help with defining Models for ManyToMany and OneToMany relationships...

On 23/04/2016 11:22 PM, Bruce Whealton wrote:
> Hello all,
> Â Â Â Â Â So, I setup django in a virtualenv on my Ubuntu
> environment. Â I was reading the docs and thought I had things rightÂ
> for creating the 3 models I wanted with this application. I am using
> Postgresql. Â I have the Postgresql driver for Python/Django installed
> in the virtualenv. Â It is a "Contacts" app. Â
> First question: Do django model fields default to required unless you
> use blank=True, null=True?
> Many of my fields, I want to have optional.
>
> I have a class called Contact, a class called Organization and a class
> called Connection. Â

I think you should rethink your Contact and Organization classes and see
if you can eliminate one or the other. A single table for both would
simplify the problem because the Connection class can implement as many
connections as you like.

For example ...

class ContactOrOrganization(etc):
various detail fields ...

class Connection(etc):
organization = ForeignKey("ContactOrOrganization",
related_name="organization")
contact = ForeignKey("ContactOrOrganization",
related_name="contact")

Just because I used related_name that way means nothing. You can connect
contacts together or organizations together. Also, you can add other
fields to Connection with which to describe the relationship.

Mike

> I wanted to use the Organization as a foreign key on the Contact model.
> Â I could have more than one contact from
> an Organization. Â The Connection model is inspired by the Google Plus
> idea of "Circles" - e.g. friends,
> family, following, etc. Â So, this would be a many-to-many relationship. Â
>
> My problems are (1) I cannot create connections without specifying a
> contact. Â
> (2) If I was adding a contact using the admin interface, how do I allow
> no value for that foreign field
> or allow for some kind of ajax type of text completion? Â If a person is
> family or friend, I may not need
> to list an Organization for them.
> (3) I would like to support multiple connection types - e.g. following,
> employer, etc.
>
> So, here is my apps models.py file:
> >>>>
>
> from django.db import models
>
>
> class Contact(models.Model):
> Â Â name = models.CharField(max_length=40)
> Â Â Organization = models.CharField(max_length=50)
> Â Â street_line1 = models.CharField("Street Line 1", max_length=50)
> Â Â street_line2 = models.CharField("Street Line 2", max_length=50)
> Â Â city = models.CharField(max_length=40)
> Â Â state = models.CharField(max_length=40)
> Â Â zipcode = models.CharField(max_length=20, blank=True, null=True)
> Â Â phone1 = models.CharField(max_length=20)
> Â Â phone2 = models.CharField(max_length=20)
> Â Â email = models.EmailField(max_length=60)
>
>
> class Organization(models.Model):
> Â Â name = models.CharField(max_length=60)
> Â Â street_line1 = models.CharField("Street Line 1", max_length=50)
> Â Â street_line2 = models.CharField("Street Line 2", max_length=50)
> Â Â city = models.CharField(max_length=40)
> Â Â state = models.CharField(max_length=40)
> Â Â zipcode = models.CharField(max_length=20, blank=True, null=True,)
> Â Â phone = models.CharField(max_length=20)
> Â Â email = models.EmailField(max_length=60)
> Â Â website = models.URLField(max_length=90)
> Â Â contact_name = models.ForeignKey(Contact, on_delete=models.CASCADE)
>
>
> class Connection(models.Model):
> Â Â type = models.CharField(max_length=60)
> Â Â contact_name = models.ManyToManyField(Contact) Â Â
>
> >>>
> Thanks in advance for any suggestions,
> BruceÂ
>
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