Re: Using ContentType to link two different objects together

On 05/11/2014 18:16, Carl Meyer wrote:
> Hi,
>
> On 11/05/2014 11:09 AM, Some Developer wrote:
>> I'm trying to write my own implementation of the Django comments
>> framework for various reasons and am wondering how one would link
>> comments to a particular object (model) of another type. For instance I
>> could have a ForeignKey in the Comment model pointing to a Blog post
>> article but that would mean that you could only leave comments on Blog
>> post articles. I want to be able to configure my Comment model so that
>> it can link to any other object of any type.
>>
>> Does anyone know how to do that? I think it has something to do with the
>> ContentType framework that comes with Django but I have never used it
>> before so I'm not entirely sure.
> I think this is what you're looking for:
> https://docs.djangoproject.com/en/1.7/ref/contrib/contenttypes/#generic-relations
>
> However, by using GenericForeignKey you give up some valuable things:
> the database can no longer enforce referential integrity on those
> relationships, and joins become more complex and often slower. So I
> would recommend at least considering alternatives.
>
> One possible alternative is to instead provide the bulk of your Comment
> model as an abstract base model class, and then have users of your
> comment app create their own Comment model inheriting from your abstract
> base, and adding a single FK to whatever model they want comments on.
> (This presumes that most users of your comments app will only need
> comments on a single model in a given system; or if they want comments
> on more than one model, they don't mind having two separate Comment
> models to handle that.)
>
> Carl

Thanks for the info. You make some interesting points about the database
not being able to enforce referential integrity.

I hadn't thought of providing the comment model as a base class and
having the users specialise it themselves. How would that work in
regards to template tags? For instance if I had a template tag like this:

{% get_comments for obj as var %}

how would one hook in a user provided object with its own model which is
not known ahead of time or would you suggest using a template tag such
as this instead? I guess letting the user explicitly state the
application and the model themselves offers the best flexibility in the
long run.

{% get_comments for [app].[model] [object_id] %}

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