Ruby on Rails -- multiple selection in f.select

I have the following select box in my form:

Related Type: &nbsp; <%= f.select(:TYPE, [['Type A', 'Type A'],
                                  ['Type B', 'Type B'],
                                  ['Type C', 'Type C'],
                                  ['Type D', 'Type D'],
                                  ['Type E', 'Type E']
                                 ],{ :prompt => "Please select"}
                                 ) %>

I want to allow the user to make multiple selections and also make the size of the select box 5.

How to do that for the code above?

After your { :prompt => "Please select"} add another hash with html options e.g.

<%= f.select(:TYPE, [['Type A', 'Type A'],
                                  ['Type B', 'Type B'],
                                  ['Type C', 'Type C'],
                                  ['Type D', 'Type D'],
                                  ['Type E', 'Type E']
                                 ],{ :prompt => "Please select"},
                                   { :multiple => true, :size => 5 }
                                 ) %>

Once you've done this you might want to move your :prompt option (keep the empty {} though so that html attributes don't get treated as Rails options.)

Also you'll need to ensure your controller code is correctly accepting and handling multiple values.

In case of collection, try

    <%= f.select(:TYPE, Categories.collect {|p| [ p.name, p.id ] }, 
                                           { :prompt => "Please select"}, 
                                           { :multiple => true, :size => 5 }) %>

I have a fully working example (including preselection when editing the object), when:

• Object is the considered object
• similar_ids is the key to relations, and is a string

In the form:

form_for(@object) do |f|
  = f.select :similar_ids, options_from_collection_for_select(Object.all, :id, :name, {:selected => @object.similar_ids.split(';')}), {}, {:multiple => true, :size => 4, :name => 'object[similar_ids][]'}

And in the Object.rb model:

class Object < ActiveRecord::Base
  before_save :handle_similars

  def handle_similars
    self.similar_ids = self.similar_ids.select(&:present?).join(';') 
    # .select(&:present?) is necessary to avoid empty objects to be stored
  end

  def similars
    self.class.find(self.similar_ids.split(';'))
  end

end

These posts helped me out:

• https://stackoverflow.com/questions/21667251/select-tag-with-multiple-values-pre-selected-values-inserted-manually-in-datab
• https://stackoverflow.com/questions/3089849/ruby-on-rails-submitting-an-array-in-a-form

Hope it helps

HTML

<%= form.select(:product_ids, Product.all.collect {|p| [ p.name, p.id ] }, 
                                                   { :prompt => "Please select"}, 
                                                   { :multiple => true, :size => 5  }) %>

Controller

@category = Category.new(category_params) 

def category_params
    params.require(:category).permit(:name, product_ids: [])
end

{ :prompt => "Please select"}, { :multiple => true, :size => 5 } {} is important when f.select

with bootstrap selectpicker and pre selected values:

    = simple_form_for [:backend, @user], html: { autocomplete: 'off' } do |f|
      = f.select :role_ids, options_for_select(Role.all.map{|role| [role.name, role.id]}, @user.role_ids), {},  {:multiple => true, inlcude_blank: false, class: "form-control input-sm selectpicker"}

in controller:

def user_params
      params.require(:user).permit(:id, role_ids: [])
end

# only if you havent build in new action
def new
  # set user
  @user.roles.any?
end

<%= f.select :tag_ids, Tag.all.collect {|t| [t.name, t.id]}, { :prompt => "Please select"}, { :multiple => true, :size => 5 } %>