Unable to access Multiselect Values in Ruby on Rails Controller - ruby-on-rails

Question

I'm trying to implement a multi-select for a many to many relationship in Ruby on Rails, however I'm unable to access the array of strings representing the selected User Ids in the user_ids field.
The following is my project_params after clicking update
"project"=>{"name"=>"Project Name",
"client"=>"Client X", "project_url"=>""},
"user_ids"=>["2", "3", "4", "5"], "commit"=>"Update Project", "id"=>"1"}
The following is my ProjectsController code
def update
puts project_params[:user_ids=>[]]
respond_to do |format|
if #project.update(project_params)
format.html { redirect_to #project, notice: 'Project was successfully updated.' }
format.json { render :show, status: :ok, location: #project }
else
format.html { render :edit }
format.json { render json: #project.errors, status: :unprocessable_entity }
end
end
end
def project_params
params.require(:project).permit(:id, :name, :client, :project_url, :user_ids => [])
end
The line puts project_params[:user_ids=>[]] prints a blank line. I've also tried puts project_params[:user_ids] and puts project_params[:user_ids[]] - none of which work
The following is my _form.html.erb Code
<%= select_tag "user_ids",
options_from_collection_for_select(User.all, "id", "name", #project.user),
{ :multiple => true, :size =>10}
%>

Answer 1

The select tag will use the first argument as the key. Hence the values is located on:
params[:user_ids]
or if you are using form builder
<%= form_for #project do |f| %>
<%= f.select :user_ids,
options_from_collection_for_select(User.all, "id", "name", #project.user),
{ :multiple => true, :size =>10}
%>
<% end %>
then it will be available in project_params