How do I order a has_many through association in Ruby on Rails?

Question

Given the following AR models, I would like to sort users alphabetically by last name when given a handle to a task:

#user
has_many :assignments
has_many :tasks, :through => :assignments    

#assignment
belongs_to :task
belongs_to :user

#task
has_many :assignments
has_many :users, :through => :assignments

I would like to get a task then navigation to its assigned users, and sort the user list alphabetically.

I keep thinking that I should be able to add the :order clause to has_many :users, :through => :assignments like this:

#task.rb
has_many :assignments
has_many :users, :through => :assignments, :order => 'last_name, first_name'

however this does not work.

How can I sort users by last_name when given a task?

score 72 · Answer 1 · answered Oct 02 '13 at 13:56

72

Since condition arguments are deprecated in Rails 4, one should use scope blocks:

has_many :users, -> { order 'users.last_name, users.first_name' }, :through => :assignments

answered Oct 02 '13 at 13:56

Daniel

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1

It looks like there is currently a bug in Rails 4 with this https://github.com/rails/rails/issues/17904 "In Rails 4.0, the order clause was ignored. In Rails 4.1, invalid SQL is generated." – Nate Dec 29 '14 at 13:35
It doesn't even give me that, just completely ignores the order clause with no message. – Wylliam Judd Aug 03 '16 at 18:04

Martin T. · Answer 2 · 2017-02-21T10:29:29.937

37

Rails 3.x version:

has_many :users, :through => :assignments, :order => 'users.last_name, users.first_name'

UPDATE: This only works in Rails 3.x (maybe before that too). For 4+, see other answers.

edited Feb 21 '17 at 10:29

answered Oct 18 '11 at 11:19

Martin T.

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Works fine for me as well. Clean solution that doesn't affect other functions of the sorted model as the first answer does. – barancw Aug 05 '12 at 14:04
2

not working, it says :order is not a key. Below answer of Denial IS working. – RohitPorwal Jun 30 '14 at 09:57

score 12 · Answer 3 · answered Sep 24 '12 at 05:17

12

The M.G.Palmer's approach works well, however table name is involved. There is a better way to do it:

has_many :users, :through => :assignments, :order => [ :last_name, :first_name ]

answered Sep 24 '12 at 05:17

denis.peplin

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but what if the order is determined by the join table? e.g. assignments ... but without defining a default scope on assignments.. – Tilo Feb 27 '18 at 07:28

edx · Answer 4 · 2015-07-31T16:03:05.873

This works for me (Rails 4.2)

Applying an ordering on the through map is not preserved, aka this is not enough to have the genres ordered:

has_many    :disk_genre_maps,
            -> {order('disk_genre_map.sort_order')},
            :inverse_of => :disk,
            :dependent  => :destroy,
            :autosave   => true


has_many    :genres,    # not sorted like disk_genre_maps
            :through    => :disk_genre_maps,
            :source     => :genre,
            :autosave   => true

So I overwrite this per instance:

def genres  # redefine genres per instance so that the ordering is preserved
    self.disk_genre_maps.map{|dgm|dgm.genre}
end

To make that work for assignments, this should be something like this (untested)

def genres= some_genres
    self.disk_genre_maps = some_genres.map.with_index do |genre, index|
        DiskGenreMap.new(disk:self, genre:genre, sort_order:index)
    end
end

score 7 · Answer 5 · edited Feb 27 '18 at 07:30

7

I am using Rails (5.0.0.1) and could make the sort with this syntax in my model Group that has many users through group_users:

# Associations.
has_many :group_users
has_many :users, -> { order(:name) }, through: :group_users

Adjust the code to your need that will work.

edited Feb 27 '18 at 07:30

Tilo

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answered Dec 27 '16 at 16:28

Ricardo Emerson

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Antony Sastre · Answer 6 · 2010-02-05T11:55:24.377

6

Would this work for you?

# User.rb

class User < ActiveRecord::Base
 default_scope :order => 'last_name ASC'
 ...
end

You can define other named scopes for when sorting needs to be different.

http://ryandaigle.com/articles/2008/11/18/what-s-new-in-edge-rails-default-scoping

edited Feb 05 '10 at 11:55

answered Feb 05 '10 at 07:45

Antony Sastre

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2

Sorry to bump an old question, but this might be relevant to future readers: Some plugins (acts_as_list for example) don't work properly with default_scope. – May 08 '11 at 14:56
Also bumping this as I had a similar issue, but needed to sort on a field IN the :through table — the awesome thing is that default_scope works in the :through table as well, and records retrieved via that relationship will respect the order. – MBHNYC May 19 '12 at 21:04
1

Having `default_scope` is a very bad practice. There are many aricles written on this topic, for example: https://piechowski.io/post/why-is-default-scope-bad-rails/ – dpaluy Apr 09 '20 at 20:08

score 2 · Answer 7 · answered Jan 16 '13 at 06:27

2

You could also create a new 'sort_order' column on the assignment table, and add a default scope like

default_scope { order('sort_order desc')}

to your assignments model.

answered Jan 16 '13 at 06:27

Yogzzz

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score 1 · Answer 8 · answered Apr 16 '19 at 16:59

1

has_many :users, -> { order(:last_name, :first_name) }, :through => :assignments, source: 'user'

answered Apr 16 '19 at 16:59

user223697

193
7

How do I order a has_many through association in Ruby on Rails?

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