Hello everybody !

This is a question I have already posted on Stack Overflow 
<https://stackoverflow.com/questions/35546853/sqlalchemy-dynamic-customized-collection-class>,
 
but as none is answering I decided to post it here too :) However I invite 
you to go to the Stack Overflow page, as it is maybe more clearly explained 
than here.

I have a One-To-Many relation between an Article entity and a Post entity 
(which are the comments on the article).
Each Post has a date attribute.
What I would like to do is getting the posts related to an article between 
two dates directly from this article, using the following syntax :

article.posts[start_date:end_date]

With the "lazy" argument or "relationship", I can do :

    posts = relationship('Post', back_populates='article', lazy='dynamic')

After that, the "posts" attribute isn't a list any longer, but a Query 
Object, which allows us to do:

    article.posts.filter(Post.date >= start_date, Post.date < 
end_date).all()

Which is still not exactly what I'm looking for.

I think I have to use the "collection_class" attribute of the relationship, 
by using a custom Class in which I would override the "__getitem__" method, 
but I don't know what to write in this function, because we don't have 
access to the query given by the `relationship` Object !

Does someone have an idea which could help me ?

Thank you !
Edouard

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