Railscasts - Find Through Association

Mar 08, 2007

Find Through Association

No need to pass foreign keys in find conditions, just do the find through a has_many association.

Tags: active-record

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# projects_controller.rb
def show
  @project = Project.find(params[:id])
  @tasks = @project.tasks.find_all_by_complete(false)
end

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11 comments

1. Klaus Paiva Jul 18, 2007 at 04:53

Nice examples! All these tips will certainly contribute to a clever and beautiful code. Thanks!

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2. bob Aug 07, 2007 at 08:15

will this work if you have @projects, i.e multiple projects?

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3. Ryan Bates Aug 07, 2007 at 09:32

@bob, nope. If you have an array of projects you'll have to fetch the tasks for all those projects using a custom find of some sort.

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4. weelkoh0 Sep 08, 2007 at 04:28

Hi Ryan,

I have been checking your website for more has_many :through articles.

I have this question which I hope you could provide your insights, as I have been checking around but to-date still could not fully understand.

I would greatly appreciate if you could look at my code on http://railsforum.com/viewtopic.php?id=10204

I have these 2 tables: groups and users, where a group can have many users and an user can have many groups.

I have this third table, roles, which contains group_id, user_id, type. The field 'type' can be Administrator, Owner and Member. A user can play the role of Owner for a group but assume the role of member for another group. I use this table as Single Table Inheritance.

I want to do such query:
Based on a given user's id, I want to
display all the groups of this user, with the respective role for that group.

I have been reading and trying the associations. The last working association I tried is (assuming the user-id I want to check is 1):

User.find(1).roles.each do |role|
<%= role.group.name %>
end

Is that the way to perform such query?

Thank you, for your great effort in sharing your knowledge with others.

Thank you very much.

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5. Yui-Ikari Nov 06, 2007 at 11:17

I have the same problem as weelkohO
would be nice to have a railcast with that specific problem ^___^
pls! ^_^

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6. kino May 23, 2008 at 01:54

By immersing ourselves meditatively in the general intentions of modes of consciousness, we discover that noematic descriptions are "in themselves".