More Complex Join with Rails/ActiveRecord


I have an Articles model.
And a Moderations model.
And a Users model.

Articles have many Users (moderators) through Moderations.
Users have many Articles (moderated articles) through Moderations.

This works fine so far. I can link up a user with all their moderated
articles etc.

But, I’d like a find which would select all the Articles, except it
hides (does not return) the articles the current user has moderated. I
am currently doing this in Ruby in two stages like this:

@articles_list = Article.find(:all, :conditions => [“start_date >= ?”,
today], :order => ‘start_date’)
@articles_list -= current_user.moderated_articles if current_user

And then displaying the articles list.

This works, but I fully suspect it is cripplingly slow, and I’d also
like to paginate these articles and all the pagination tutorials seem to
warn against fetching everything in one go. This seems like good advice.

So I am seeking guidance on a join condition that would do what I want.
I’m guessing I need an inner join on the article_id on the moderations
table, but need to make sure that the user_id of those records are the
same as the current user only. So this is confusing me a bit.

Many thanks for any help you may offer!

  • N

Just a quick try (you haven’t showed up your database schema):

@articles = Article.all( :conditions => [“start_date >= ? AND id NOT
IN ( SELECT m.article_id from moderations m WHERE m.user_id = ? )”,
today,], :order => ‘start_date’)

Maurício Linhares (pt-br) |

On Tue, Apr 7, 2009 at 4:53 PM, Peter L.

This is awesome - exactly what I was after and I learned some SQL as
well (which is clearly my weakness here).

Thanks for taking the time to type that up, you’ve really helped me out.

  • N

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