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Python Django how to retrieve specific objects

I've got this Post model at the moment:
class Post(models.Model):
title = models.CharField(max_length = 140)
body = models.TextField()
date = models.DateTimeField()
def __unicode__(self):
return self.title
If I've got different parts of a website (or a forum rather) that contain different posts, e.g. Discussion about basketball, and Discussion about football, if I wanted to return just posts concerning basketball or just posts concerning football, is the easiest way to just make a specific basketball_post model/football_post model or is there a more efficient way? Should I perhaps be storing the values differently?
Thanks

Django has a really good tutorial. It is about making a Poll app. In the first chapter the thing you want is discussed. It is about a Question that can have multiple Choices.:
class Question(models.Model):
question_text = models.CharField(max_length=200)
pub_date = models.DateTimeField('date published')
class Choice(models.Model):
question = models.ForeignKey(Question)
choice_text = models.CharField(max_length=200)
votes = models.IntegerField(default=0)
The foreignKey creates a relation between two models. The same can be done for a blog:
class Category(models.Model):
title = models.CharField(max_length=200)
class Post(models.Model):
category = models.ForeignKey(Category) # This is the important part.
title = models.CharField(max_length=200)
body = models.TextField()
date = models.DateTimeField()
def __unicode__(self):
return self.title
The ForeignKey relation lets you do really nice things:
basketball_posts = Post.objects.filter(category_title='Basketball')
But before we all tell you how it is done, I really recommend to do the tutorial. It introduces you to all important Django concepts: https://docs.djangoproject.com/en/1.7/intro/tutorial01/
Update
If you have a fixed set of categories that are not likely to change, than you can hardcode them and use field choices:
class Post(models.Model):
FOOTBALL = 'F' # Variable name and db_value
CRICKET = 'C'
INTRODUCTION = 'I'
CATEGORY_CHOICES = (
(FOOTBALL, 'Soccer'), # Variable name and display value
(CRICKET, 'Cricket'),
(INTRODUCTION, 'Hello my name is'),
)
category = models.CharField(max_length=1,
choices=CATEGORY_CHOICES,
default=INTRODUCTION)
...
https://docs.djangoproject.com/en/dev/ref/models/fields/#choices
One of the advantages of this 'choice machinery' over a CharField without pre defined choices is that you are sure what values end up in your database. This lets you query them, without worrying if your data is sane:
Post.objects.filter(category=Post.CRICKET)
Use the extra table if you need the freedom to create new categories in the future. Use field choices if you don't want (or need) that freedom.

I would suggest to just add a field which makes the post relevant to that certain topic:
class Post(models.Model):
title = models.CharField(max_length = 140)
body = models.TextField()
date = models.DateTimeField()
type = models.CharField(max_length=20) #<--- new field: e.g 'basketball','hockey'..
def __unicode__(self):
return self.title
example query:
#basketball posts
qs = Post.objects.filter(type__icontains="basketball")
then you dont need to have multiple models which also would be redundant.

Assuming all of the posts are in the same format, you could add another field to your model like "type". Different discussion forums could send a different values for that field when the post is added.
type = models.CharField(max_length=140, choices=['Football', 'Basketball', 'Baseball'])
Storing this would make it easy to filter which posts are which.
Post.objects.filter(type = 'Football')

Assuming that one post can be about only one sport, the better approach would be to have a foreign key relation between a model that stores data about a post with another model that stores the data about sports.
Something like this
class Sport(models.Model):
name = models.CharField(max_length = 200)
description = models.TextField()
def __unicode__(self):
return self.name
class Post(models.Model):
title = models.CharField(max_length = 140)
body = models.TextField()
date = models.DateTimeField()
sport = models.ForeignKey(Sport)
def __unicode__(self):
return self.title
This gives you the advantage of isolating the 'Sport' and the 'Post' models.You can add as many sports as you want, without any posts referring to it.
One more advantage is that you can add relevant information to the relevant models.
Eg:Suppose you want to add the information about "how many players are there in a team for sport x?". You can easily achieve this by adding a field "number_of_players" in the 'Sport' model without affecting the 'Post' model.
If you had to do this in one model, 'Post', then it would create lot of issues in terms of data consistency and other undesirable things.
Also, the query will look something like this:
posts = Post.objects.filter(sport__name = "Basketball")
PS:If your requirement is that a post can be tagged to multiple sports, then you can use ManyToMany field instead of a simple foreign key.
https://docs.djangoproject.com/en/dev/topics/db/examples/many_to_many/

You could assign your posts tags or category, and filter on those.
If you use the model approach what happens when you add more sports? You'll need manually add the sports in your code, using a tags or category approach allows you to handle it in the db, and would then allow you to filter on the tags/categories in your system

Django one-to-many, add fields dynamically in Admin

I have the following code:
class Item(models.Model):
name = models.CharField(max_length=100)
keywords = models.CharField(max_length=255)
type = models.ForeignKey(Type)
class Meta:
abstract = True
class Variant(models.Model):
test_field = models.CharField(max_length=255)
class Product(Item):
price = models.DecimalField(decimal_places=2, max_digits=8,null=True, blank=True)
brand = models.ForeignKey(Brand)
variant = models.ForeignKey(Variant)
def get_fields(self):
return [(field.name, field.value_to_string(self)) for field in Product._meta.fields]
def __unicode__(self):
return self.name
Im using Grappelli.
I want my Product to have multiple Variations. Should I use a manytomanyfield?
I want to be able to add Variants to my Product directly in the Admin. Now I get an empty dropwdown with no variants(because they doesnt exists).
I thought Django did this automatically when u specified a Foreign Key?
How can I get the Variant fields to display directly on my Product page in edit?
I've read someting about inline fields in Admin?

Well, it's the other way around :)
1/ Place the foreign key field in your Variant, not in your Product (what you describe is actually a OneToMany relationship).
2/ Link the Variant to your Product in the relative ProductAdmin in admin.py as an inline (i.e VariantInline).
See the docs for further informations : https://docs.djangoproject.com/en/1.6/ref/contrib/admin/#inlinemodeladmin-objects
Hope this helps !
Regards,

Django Tag model design

I am wondering if the following is the correct way to create tagging system for images and being able to render a tag cloud:
from django.db import models
class Tag(models.Model):
word = models.CharField(max_length=35)
slug = models.CharField(max_length=250)
created_at = models.DateTimeField(auto_now_add=False)
def __unicode__(self):
return self.word
class Photo(models.Model):
slug = models.CharField(max_length=250)
filename = models.CharField(max_length=200)
extension = models.CharField(max_length=4)
size = models.IntegerField()
...
tags = models.ManyToManyField(Tag)
def __unicode__(self):
return self.slug
Note that my database table will include millions of rows and each image will have 4-8 tags.
Please advise.

If all you want to do is create a tag cloud, than that data model should be sufficient. I would make one modification:
tags = models.ManyToManyField(Tag,related_name='photos')
That will make reverse lookups in you photo views cleaner to read and easier to remember.
However, I would consider other use cases for your tags. Is a tag cloud the only thing you want to use the tagging for? Is there any meta data that the relationship should contain?
If you're planning on having millions of rows, then caching is going to be as important as the data model.
Also, to avoid reinventing the wheel, see if anyone else has built a library that serves your purposes: http://www.djangopackages.com/grids/g/tagging/

Handling tags youself could be a hard job.
You can easily use django library. Install it with pip
pip install django-taggit

django ModelForm override field has no effect

I have a ForeignKey field in a model of mine, and I'm using ModelForm with it to generate the HTML. The thing is, I want to add an Other option as well - I plan to add JavaScript with it so that a textbook appears when that's selected.
I'm looking at http://docs.djangoproject.com/en/1.2/topics/forms/modelforms/#overriding-the-default-field-types-or-widgets, and started off with trying something like
class Event(models.Model):
name = models.CharField(max_length=200)
time = models.DateField()
.
.
.
cost = models.CharField(max_length=200)
affiliation = models.ForeignKey('Affiliation')
def __unicode__(self):
return self.name
class EventForm(ModelForm):
cost = models.TextField()
class Meta:
model = Event
cost should become a text field instead of char field, so the output should be textarea instead of input[type=text]. This doesn't change, however, no errors are printed, and nothing really happens. I was hoping to proceed by doing
class EventForm(ModelForm):
affiliations = list(Affiliation.objects.all()).append('Other')
affiliation = forms.CharField(choices=affiliations)
class Meta:
model = Event
I'm using django-nonrel on GAE if it helps, but this isn't really an issue with the Model (or so I think...) so I don't think it should change anything. Any help would be much appreciated!

I haven't used django-nonrel, so take this tip with a grain of salt (YMMV).
In your EventForm definition, you're setting cost to be a model.TextField - but you actually want it to be a forms.CharField, with a textarea widget.

Your problem is that EventForm is overriding cost with a models.TextField() when it should be forms.CharField(widget=forms.Textarea())

Can a CharField have choices? Django docs show a 'ChoiceField' which would seem to be what you want...
http://docs.djangoproject.com/en/1.2/ref/forms/fields/#charfield

admin template for manytomany

I have a manytomany relationship between publication and pathology. Each publication can have many pathologies. When a publication appears in the admin template, I need to be able to see the many pathologies associated with that publication. Here is the model statement:
class Pathology(models.Model):
pathology = models.CharField(max_length=100)
def __unicode__(self):
return self.pathology
class Meta:
ordering = ["pathology"]
class Publication(models.Model):
pubtitle = models.TextField()
pathology = models.ManyToManyField(Pathology)
def __unicode__(self):
return self.pubtitle
class Meta:
ordering = ["pubtitle"]
Here is the admin.py. I have tried variations of the following, but always
get an error saying either publication or pathology doesn't have a foreign key
associated.
from myprograms.cpssite.models import Pathology
class PathologyAdmin(admin.ModelAdmin):
# ...
list_display = ('pathology', 'id')
admin.site.register(Pathology, PathologyAdmin)
class PathologyInline(admin.TabularInline):
#...
model = Pathology
extra = 3
class PublicationAdmin(admin.ModelAdmin):
# ...
ordering = ('pubtitle', 'year')
inlines = [PathologyInline]
admin.site.register(Publication,PublicationAdmin)
Thanks for any help.

Unless you are using a intermediate table as documented here http://docs.djangoproject.com/en/dev/ref/contrib/admin/#working-with-many-to-many-intermediary-models, I don't think you need to create an Inline class. Try removing the line includes=[PathologyInline] and see what happens.

I realize now that Django is great for the administration (data entry) of a website, simple searching and template inheritance, but Django and Python are not very good for complex web applications, where data is moved back and forth between a database and an html template. I have decided to combine Django and PHP, hopefully, applying the strengths of both. Thanks for you help!

That looks more like a one-to-many relationship to me, tho I'm somewhat unclear on what exactly Pathologies are. Also, so far as I understand, Inlines don't work on manytomany. That should work if you flip the order of the models, remove the manytomany and add a ForeignKey field to Publication in Pathology.
class Publication(models.Model):
pubtitle = models.TextField()
def __unicode__(self):
return self.pubtitle
class Meta:
ordering = ["pubtitle"]
class Pathology(models.Model):
pathology = models.CharField(max_length=100)
publication = models.ForeignKey(Publication)
def __unicode__(self):
return self.pathology
class Meta:
ordering = ["pathology"]