Including child resources in a Django Tastypie API

Question

I'm planning a site with Django and Tastypie for the REST API, and I'm having a tough time figuring out the "right" way to include child resources in a returned resource.

As a sandbox, I made a small app with a Ticket model and a TicketComment model, where comments belong to a ticket. I looked at the Tastypie Cookbook recipe on nested resources (http://django-tastypie.readthedocs.org/en/latest/cookbook.html#nested-resources), but I'm having a hard time understanding why I should do that. The code below uses django.forms.models.model_to_dict() to get the comments into the ticket, but I'm thinking there must be a "gotcha" here somewhere.

Is there a reason I shouldn't do what I'm doing now? Also, is there a cleaner-feeling pattern for this than what's listed in the cookbook?

Models are as follows:

# tickets/models.py

from django.db import models

class Ticket(models.Model):
    title = models.CharField(max_length=200)
    create_ts = models.DateTimeField(auto_now_add=True)
    submitter_email = models.EmailField()
    PRIORITY_CHOICES = (
        ('H', 'High'),
        ('M', 'Medium'),
        ('L', 'Low'),)
    priority = models.CharField(max_length=1, choices=PRIORITY_CHOICES)
    description = models.TextField()
    STATUS_CHOICES = (
        ('NEW', 'New & Unclaimed'),
        ('WIP', 'Work In Progress'),
        ('RES', 'Resolved'),
        ('CLS', 'Closed'),)
    status = models.CharField(max_length=3, choices=STATUS_CHOICES)

    def __unicode__(self):
        return "<Ticket:%d:%s>" % (self.id, self.title,)

class TicketComment(models.Model):
    ticket = models.ForeignKey(Ticket)
    comment_ts = models.DateTimeField(auto_now_add=True)
    commenter_email = models.EmailField()
    comment = models.TextField()

    def __unicode__(self):
        return "<TicketComment:%d:%d>" % (self.ticket.id, self.id,)

Resources are as follows:

# tickets/api.py

from tastypie import fields
from tastypie.resources import ModelResource
from tickets.models import Ticket, TicketComment
from django.forms.models import model_to_dict

class TicketResource(ModelResource):

    class Meta:
        queryset = Ticket.objects.all()
        resource_name = 'ticket'

    def dehydrate(self, bundle):
        comments = TicketComment.objects.filter(ticket=bundle.data['id'])
        bundle.data['comments'] = [model_to_dict(c) for c in comments]
        return bundle

class TicketCommentResource(ModelResource):
    ticket = fields.ForeignKey(TicketResource, 'ticket')

    class Meta:
        queryset = TicketComment.objects.all()
        resource_name = 'comment'

Output is as follows:

{
   comments: [
        {
            comment: "This is the first comment.",
            commenter_email: "[email protected]",
            id: 1,
            ticket: 1
        },
        {
            comment: "This is the second comment.",
            commenter_email: "[email protected]",
            id: 2,
            ticket: 1
        }
    ],
    create_ts: "2011-10-17T15:55:11.372000",
    description: "This is the first ticket.",
    id: "1",
    priority: "M",
    resource_uri: "/api/v1/ticket/1/",
    status: "NEW",
    submitter_email: "[email protected]",
    title: "First Ticket"
}

Sultanate

Answer 1

You're looking for related fields: http://django-tastypie.readthedocs.org/en/latest/fields.html#relationship-fields

Evaporation

Thanks, this makes a lot more sense, however all I'm getting is the URL to the child comments. If I want the serialized resources instead, is there a clean way to get them? – Sultanate

use the full=True argument in your declaration – Evaporation

Perfect, exactly what I wanted. Thanks! – Sultanate

Answer 2

Can you post your solution?

I have the same use case/models (a foreign key relation ship established in the "child table" pointing back to the parent table) but cannot resolve it.

The solution I have seen is to add this line to your TicketResource a the class level NOT within the meta subclass:

comments = fields.ToManyField('TicketCommentResource', 'ticket', full=True)

Then possibly also add this to TicketCommentResource, again at the class level:

event = fields.ForeignKey('TicketResource', 'event')

But I always get the error that my parent object resource (in your example TicketResource) does not have the attribute 'ticket' which is the second term sent to ToManyField.

I have tried to play with this a lot but can't seem to get the winning combo. The solution you originally posted works but as you yourself pointed out it not ideal.

Thanks!

Niedersachsen

Wanted to add this as comment but did not have the option. – Niedersachsen