Need data from rails join table, has_many :through

Question

I have 3 tables - users, things, and follows. Users can follow things through the follows table, associating a user_id with a things_id. This would mean:

class User
  has_many :things, :through => :follows
end

class Thing
  has_many :users, :through => :follows
end

class Follow
  belongs_to :users
  belongs_to :things
end

So I can retrieve thing.users with no problem. My issue is if in the follows table, I have a column named "relation", so I can set a follower as an "admin", I want to have access to that relation. So in a loop I can do something like:

<% things.users.each do |user| %>
  <%= user.relation %>
<% end %>

Is there a way to include relation into the original user object? I have tried :select => "follows.relation", but it doesn't seem to join the attribute.

Its a really bad idea to name a relation "relation"... This may break some ruby internals and you will get unexpected behaviour! — BvuRVKyUVlViVIc7, Jan 16 '12 at 00:44
Alright, thanks. Lets say the column is named "is_admin" and has a type of boolean.. — Matt Gaidica, Jan 16 '12 at 00:57

score 22 · Accepted Answer · answered Jan 16 '12 at 01:09

22

To do this you need to use a bit of SQL in the has_many. Something like this should hopefully work. has_many :users, :through => :follows, :select => 'users.*, follows.is_admin as is_follow_admin'

Then in the loop you should have access to user.is_follow_admin

answered Jan 16 '12 at 01:09

Bradley Priest

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Definitely works, and is essentially what I was trying before. My hangup was that the SQL dump when doing this on the command line doesn't show the is_admin attribute anywhere.. it just shows the follows object. Thank you! – Matt Gaidica Jan 16 '12 at 01:20
2

Rails4 deprecated :select I think. How is this accomplished now? – index Jul 25 '13 at 07:26
8

I'm using rails 4 and this format works `has_many :users, -> { select('users.*, members.role as member_role') }, through: :members` – index Dec 11 '13 at 06:51
@Matt Gaidica, you should add this to your User model (to make attribute accessible) - `def is_follow_admin attributes['is_follow_admin'] end` – Richard Peck Dec 30 '13 at 18:35

Seoman · Answer 2 · 2014-11-03T09:06:03.990

8

For people using rails 4, the usage of :order, :select, etc has been deprecated. Now you need to specify as follows:

has_many :users, -> { select 'users.*, follows.is_admin as is_follow_admin' }, :through => :follows

edited Nov 03 '14 at 09:06

answered Nov 03 '14 at 07:42

Seoman

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score 0 · Answer 3 · edited Mar 07 '14 at 00:24

0

You might be able to do something like:

<% things.follows.each do |follow| %>
  <%= follow.relation %>
  <%= follow.user %>
<% end %>

edited Mar 07 '14 at 00:24

jvperrin

3,368
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answered Jan 16 '12 at 01:16

Johnny Brown

1,000
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Need data from rails join table, has_many :through

3 Answers3

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