ruby on rails - After validation fails and a form redirects back to itself, why are instance variables empty? -

in rails 3.2 app, when form fails save (validation fails) , redirects form error:

undefined method `map' nil:nilclass 

this form not display errors when navigating directly new or edit paths.

the error coming select field custom options_from_collection_for_select method.

<%= f.select(:user_ids, options_from_collection_for_select_with_attributes(@users, :id, :name, 'data-attributes', :attributes ), {include_blank:true}, {multiple:true}) %> 

if replace instance variable @users user.all don't error after redirect.

i guess @users empty after redirect, hence error. why? @users defined in new , edit controllers.

my controller is:

def create   --bunch of stuff   if @model.save     --bunch of stuff     respond_to |format|       format.html { render :text => model_url(@model) }       format.html { redirect_to(@model, :notice => 'success!.') }       format.xml  { render :xml => @model, :status => :created, :location => @model }     end    else     respond_to |format|       format.html { render :action => "new" }       format.xml  { render :xml => @model.errors, :status => :unprocessable_entity }     end   end end 

it's because don't execute "new" action if fails. here's typical controller structure

class potscontroller < applicationcontroller    def new     @pot = pot.new     @users = user.all   end    def create     @pot = pot.new(params[:pot])     if @pot.create       redirect_to @pot, notice: "created"     else       #****you here****       render :new     end   end end 

in above, if pot.create fails, renders new template. should instance variables in case too

  def create     @pot = pot.new(params[:pot])     if @pot.create       redirect_to @pot, notice: "created"     else       @users = user.all #this important line       render :new     end   end