Hi all…
I can't come up with a syntax to order by a field of the `trough` table in
a many to many relationship and how to combine it with `prefetch_related`.
I have two models — _Note_ and _Pinboard_ — with a many to many
relationship. Those two models are related trough another model — _Pin_ —
so I can store additional information about the relationship.
I want to show the related _Note_ instances in the `DetailView` for
_Pinboard_. That's not the problem. But I want to __prefetch__ the notes
and also __order__ them on the `position` field from the `through` table.
Any hints on how to archive this (prefetch + ordering on `trough` table)?
# Example
This is what I have so far… it works in the sense, that I don't have to
query for each entry, but I found no way to order the _Note_ instances by
their `position` without more queries for each instance.
__Models__
from django.db import models
class Note(models.Model):
title = models.CharField(max_lenght=200)
content = models.TextField()
class Pinboard(models.Model):
title = models.CharField(max_lenght=200)
notes = models.ManyToManyField(
Note, blank=True, related_name='pinboards', through='Pin'
)
class Pin(models.Model):
class Meta:
ordering = ['position', ]
get_latest_by = 'position'
pinboard = models.ForeignKey(Pinboard, related_name='note_pins')
note = models.ForeignKey(Note, related_name='pinboard_pins')
position = models.PositiveSmallIntegerField(default=0)
__View__
from django.views.generic import DetailView
class PinboardDetailView(DetailView):
model = Pinboard
# THIS is the part, where I want the notes ordered by the position in
queryset = Pinboard.objects.prefetch_related('notes')
__Template__
{% extends 'base.html' %}
{% block content %}
{{ pinboard.title }}
{% if pinboard.notes.all.exists %}
{% for note in pinboard.notes %}
{{ note.title }}
{% endfor %}
{% else %}
Nothing here yet…
{% endif %}
{% endblock content %}
# What else did I try
Right now I'm using the `Pin` Model for my query (with `select_related`).
It's a workaround. I'm thinking there must be a better way, using
`Pinboard` and `prefetch_related` seems more straight forward, but I can't
figure out how.
BTW: It's on SO here:
http://stackoverflow.com/questions/35410834/how-to-order-by-a-field-from-the-through-table-for-a-m2m-relationship-in-djang
Regards
-brutus
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