Rails 3: Multiple Select with has_many through associations
Ruby on-RailsRuby on-Rails-3Ruby on-Rails Problem Overview
I want to get possibility to select several Categories for one Post with multiple select.
I have next models: Post, Category and PostCategory.
class Post < ActiveRecord::Base
has_many :post_categories
has_many :categories, :through => :post_categories
end
class Category < ActiveRecord::Base
has_many :post_categories
has_many :posts, :through => :post_categories
end
class PostCategory < ActiveRecord::Base
has_one :post
has_one :category
belongs_to :post # foreign key - post_id
belongs_to :category # foreign key - category_id
end
In my controller I have something like @post = Post.new . I've created some categories.
And in view I have:
<%= form_for @post do |f| %>
<%= f.text_field :title %>
<%= f.select :categories, :multiple => true %>
<%= f.submit %>
<% end %>
And... where is my categories? I have only "multiple" in select options. I think it's something wrong with my form.
Ruby on-Rails Solutions
Solution 1 - Ruby on-Rails
Sorry to resurrect the dead, but I found a much simpler solution that lets one use the default controller action code and use the ActiveModel setter logic for a has_many. Yes, it's totally magic.
<%= f.select :category_ids, Category.all.collect {|x| [x.name, x.id]}, {}, :multiple => true %>
Specifically, using the :category_ids (or :your_collection_ids) param name will automagically tell Rails to call
@post.category_ids = params[:post][:category_ids]
to set the categories for that post accordingly, all without modifying the default controller/scaffold #create and #update code.
Oh, and it works with has_many :something, through: :something_else
automatically managing the join model. Freaking awesome.
So from the OP, just change the field/param name to :category_ids
instead of :categories
.
This will also automatically have the model's selected categories populate the select field as highlighted when on an edit form.
References:
From the has_many API docs where I found this.
Also the warning from the form helpers guide explains this "type mismatch" when not using the proper form-field/parameter name.
By using the proper form-field/param name, you can dry up new and edit forms and keep the controllers thin, as encouraged by the Rails way.
note for rails 4 and strong parameters:
def post_params
params.require(:post).permit(:title, :body, category_ids: [])
end
Solution 2 - Ruby on-Rails
Final solution to organize categories in your posts, I hope it will be useful.
To use multiple we need select_tag:
<%= select_tag "categories", options_from_collection_for_select(Categories.all, 'id', 'name'), :multiple => true %>
Or f.select (many thanks to Tigraine and Brent!), it's more elegant way:
<%= f.select :categories, Category.all.collect {|x| [x.name, x.id]}, {}, :multiple => true %>
In create action of our controller we need:
def create
@post = Post.new(params[:post])
if @post.save
params[:categories].each do |categories|
categories = PostCategory.new(:category_id => categories, :post_id => @post.id)
if categories.valid?
categories.save
else
@errors += categories.errors
end
end
redirect_to root_url, :notice => "Bingo!"
else
render "new"
end
end
Solution 3 - Ruby on-Rails
What you need is a list of options for the select:
<%= f.select :category_id, Category.all.collect {|x| [x.name, x.id]}, :multiple => true %>
Solution 4 - Ruby on-Rails
Tigraine almost had it, but you need to specify an additional empty hash:
<%= f.select :category_id, Category.all.collect {|x| [x.name, x.id]}, {}, :multiple => true %>
Solution 5 - Ruby on-Rails
As the @post does not have id, the from might not display categories as there is no association. You need to pass do a build on @post something like
@post = Post.new(:categories => Category.all)