Unpermitted parameter in HABTM relationship - ruby-on-rails

Question

So I'm building an HABTM relationship and I always get this error back in the terminal when I submit the form:
Unpermitted parameter: :color_ids
No other errors. The app works fine, except that the associations are always an empty array.
Schema.rb:
create_table "colors", force: :cascade do |t|
t.string "color"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
end
create_table "colors_products", id: false, force: :cascade do |t|
t.integer "color_id", null: false
t.integer "product_id", null: false
end
create_table "products", force: :cascade do |t|
t.string "title"
t.decimal "price"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
end
color.rb:
class Color < ApplicationRecord
has_and_belongs_to_many :products
end
product.rb:
class Product < ApplicationRecord
has_and_belongs_to_many :colors
end
_form.html.erb:
<div class="field">
<%= form.label :color %>
<%= form.collection_select :color_ids, Color.all, :id, :color, {:multiple => true}, class: "input-field-data" %>
</div>
product_controller.rb
def product_params
params.require(:product).permit(:title, :price, color_ids: [])
end
changing the param hash from color ids to color_ids:[:id, :color]
makes no difference.
This example is obviously just something I recreated to see if I did something else wrong in my original app, probably also easier to debug.
Any ideas what's wrong with that setup? I actually have another project with the exact same setup and it works? Because of that, I think that I'm missing something, but I don't actually find anything wrong with my code.
Thanks in advance for any input!
Edit:
As requested, here is the terminal log when submitting a new product with a collection_select as shown above:
Started POST "/products" for 127.0.0.1 at 2019-02-10 14:02:59 +0100
Processing by ProductsController#create as HTML
Parameters: {"authenticity_token"=>"+f+GJaN58M029eGICvMqlwtjYB4Qmv/KNBY0OnymrxyFy+zNYXKfZtCXR0NM3kLY16QIzfLb+takhNjgIQXeEw==", "product"=>{"title"=>"abc", "price"=>"9.99", "color_ids"=>"1"}, "commit"=>"Create Product"}
Unpermitted parameter: :color_ids
(0.1ms) begin transaction
↳ app/controllers/products_controller.rb:30:in `block in create'
Product Create (1.0ms) INSERT INTO "products" ("title", "price", "created_at", "updated_at") VALUES (?, ?, ?, ?) [["title", "abc"], ["price", 9.99], ["created_at", "2019-02-10 13:02:59.634965"], ["updated_at", "2019-02-10 13:02:59.634965"]]
↳ app/controllers/products_controller.rb:30:in `block in create'
(1.1ms) commit transaction
↳ app/controllers/products_controller.rb:30:in `block in create'
Redirected to http://localhost:3000/products/15
Completed 302 Found in 14ms (ActiveRecord: 2.3ms | Allocations: 3885)
Started GET "/products/15" for 127.0.0.1 at 2019-02-10 14:02:59 +0100
Processing by ProductsController#show as HTML
Parameters: {"id"=>"15"}
Product Load (0.4ms) SELECT "products".* FROM "products" WHERE "products"."id" = ? LIMIT ? [["id", 15], ["LIMIT", 1]]
↳ app/controllers/products_controller.rb:67:in `set_product'
Rendering products/show.html.erb within layouts/application
Rendered products/show.html.erb within layouts/application (Duration: 1.1ms | Allocations: 302)
Completed 200 OK in 23ms (Views: 16.0ms | ActiveRecord: 0.4ms | Allocations: 8945)
Also:
Submitting via rails console works fine, so this has definitely something to do with the form i guess:
irb(main):010:0> p = Product.last
=> #<Product id: 15, title: "abc", price: 0.999e1, created_at: "2019-02-10 13:02:59", updated_at: "2019-02-10 13:02:59">
irb(main):011:0> p.colors
=> #<ActiveRecord::Associations::CollectionProxy []>
irb(main):012:0> p.colors << [Color.last]
=> #<ActiveRecord::Associations::CollectionProxy [#<Color id: 2, col: "Red", created_at: "2019-02-10 09:04:42", updated_at: "2019-02-10 09:04:42">]>
irb(main):013:0> p.colors
=> #<ActiveRecord::Associations::CollectionProxy [#<Color id: 2, col: "Red", created_at: "2019-02-10 09:04:42", updated_at: "2019-02-10 09:04:42">]>
_form.html.erb (generated by scaffold and adjusted with the collection_select field)
<%= form_with(model: product, local: true) do |form| %>
<% if product.errors.any? %>
<div id="error_explanation">
<h2><%= pluralize(product.errors.count, "error") %> prohibited this product from being saved:</h2>
<ul>
<% product.errors.full_messages.each do |message| %>
<li><%= message %></li>
<% end %>
</ul>
</div>
<% end %>
<div class="field">
<%= form.label :title %>
<%= form.text_field :title %>
</div>
<div class="field">
<%= form.label :price %>
<%= form.text_field :price %>
</div>
<div class="field">
<%= form.label :color_ids %>
<%= form.collection_select( :color_ids, Color.all, :id, :col, {multiple: true}) %>
</div>
<div class="actions">
<%= form.submit %>
</div>
<% end %>
Greetings!

Answer 1

You are expecting an array/hash but you are receiving a single string. It looks like the helper is not creating a multiple select, do you see the multiple="true" attr on the select tag? If not, try changing the method to this:
form.collection_select( :color_ids, Color.all, :id, :col, {}, {multiple: true})
Note the extra {}. The helper expect the first hash to be the options for the helper and the second hash to be the options for the tag.