undefined method `update_all' for nil:NilClass

Question

I am trying to implement a way to update my entries through checkboxes so that via checkboxes the selected entries can be cleared with completed ones being rendered on a separate view. I have followed the railscast on updating entries through checkboxes but I am getting the above error and I can't seem to solve it.

Controller:

class Admin::DiagnosticsController < Admin::BaseController
  before_filter :diagnostic, :except => [:index, :complete]

  def index
    @diagnostics = DiagnosticInfo.all.order_by(:created_at.desc).page(params[:page]).per(50)
  end

  def show
    respond_to do |format|
      format.html
      format.json { render json: @diagnostic }
    end
  end

  def update
    if @diagnostic.update_attributes(params[:diagnostic_info])
      redirect_to admin_diagnostic_path, notice: 'Successfully updated.'
    else
      render action: "edit"
    end
  end

  def edit
  end

  def destroy
    diagnostic.destroy
    redirect_to admin_diagnostics_path
  end

  def complete
    @diagnostic.update_all(["completed_at=?", Time.now], :id => params[:diagnostics_ids]) 
  end


private

  def diagnostic
    @diagnostic = DiagnosticInfo.find(params[:id])
  end
end

View:

    %h1 Diagnostics
= form_tag complete_admin_diagnostics_path, :method => :put 
/ - for diagnostic in @diagnostics do

%table
  %tr
    %th
    %th User
    %th Message
    %th Device
    %th RELS-Mobile Version
    %th Submitted
    %th Archive
  - @diagnostics.each do |diagnostic| 
    %tr
      %td
        %strong= link_to 'show', admin_diagnostic_path(diagnostic)
      %td
        - if diagnostic.user
          = link_to diagnostic.user.email, [:admin, diagnostic.user]
        - else
          unknown
      %td
        = diagnostic.data["message"]
      %td
        %pre= JSON.pretty_generate(diagnostic.data["device"])
      %td
        = diagnostic.data["appVersion"]
      %td
        = diagnostic.updated_at
      %td
        = check_box_tag "diagnostic_ids[]", diagnostic.id
        = diagnostic.data

  = submit_tag "Mark as complete"
= paginate @diagnostics

Answer 1

You should use

Diagnostic.where(params[:diagnostics_ids]).update_all(completed_at: Time.now)