In Rails, is it possible to display an alert without calling redirect_to or render?

Question

I have a form:

<%= form_tag generate_report_path(:header => true) do |f| % >
<div class="container-fluid">
  <div style="padding-right:10px">

    <%= select_tag(:report_id, options_for_select(
      [["Select Report Type", 0],
      ["Report1", 1],
      ["Report2", 2],
      ["Report3", 3]]), id: "report_selection") %>


      <%= hidden_field_tag :format, :pdf %>

I have a submit button and a checkbox right next to it:

<%= button_tag "Generate Report", class: 'btn btn-sm btn-primary'%>
<%= label_tag do %>
  <%= check_box_tag "format_reqd", "format_reqd", false %>
  Check for Numeric format 
<% end %>

When the user selects the checkbox and clicks on the Generate Report button, I would like to display an alert to the user "your report would be emailed to you in a few minutes"; but the page should not be refreshed.

How can I achieve these two:

1. Disable page refresh?
2. Display a flash message?

Please help!

UPDATE:

1. I added this to my controller (called report_controller):

    def reportgen

            respond_to do |format|
              format.js { flash.now[:alert] = "Report generation has been initiated. You will receive an email in approximately 4 - 5 minutes with a link to download the report."}
            end

    end

2. \app\views\report\reportgen.js.erb

    $("#flash").html('<%= j render partial: "shared/notice_banner" %>');

3. application.html.erb

  <div id="flash">
    <% if alert.present? %>
      <%= render partial: "shared/notice_banner" %>
    <% end %>
  </div>

  <% flash.each do |key, value| %>
    <% if key.to_s == "alert" %>
      <div style= "color: #FF0000" class="text-center <%= flash_class(key) %>">
      <%= value %>
    </div>
    <% else %>
      <div class="lead text-center <%= flash_class(key) %>">
      <%= value %>
    </div>
    <% end %>    
  <% end %>



  <%= yield %>

4. app\views\shared\_notice_banner.html.erb

<div data-alert class="alert-box">
  <%= alert %>
  <a href="#" class="close">&times;</a>
</div>

5. And this is my code to add the button and checkbox in my form:

                  <div id="generate_button" style="display: none; float:left;">
                    <%= button_tag "Generate Report", class: 'btn btn-sm btn-primary'%>
                  </div>
                  &nbsp;
                  <div id="report_type_drop" style="display: none;padding-top:5px;padding-left:5px">


                    <%= label_tag do %>
                      <%= check_box_tag "format_reqd", "format_reqd", false %>
                      Check for Numeric format
                    <% end %>
                    </div>

With the above code these are the results for my 2 issues in my original question right now:

1. Disable page refresh - this works perfectly fine now
2. Display flash message - this does not work!

UPDATE:

I also see this error now (not sure what's causing this though):

ActionController::UnknownFormat (ReportController#reportgen is missing a template for this request format and variant.

request.formats: ["application/vnd.openxmlformats-officedocument.spreadsheetml.sheet"]
request.variant: []):

actionpack (5.0.7.1) lib/action_controller/metal/implicit_render.rb:43:in `default_render'
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actionpack (5.0.7.1) lib/action_controller/metal/basic_implicit_render.rb:4:in `send_action'
actionpack (5.0.7.1) lib/abstract_controller/base.rb:188:in `process_action'
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activesupport (5.0.7.1) lib/active_support/callbacks.rb:448:in `block (2 levels) in around'
activesupport (5.0.7.1) lib/active_support/callbacks.rb:286:in `block (2 levels) in halting'
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activesupport (5.0.7.1) lib/active_support/callbacks.rb:285:in `block in halting'
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actionpack (5.0.7.1) lib/action_controller/metal/instrumentation.rb:32:in `block in process_action'
activesupport (5.0.7.1) lib/active_support/notifications.rb:164:in `block in instrument'
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activerecord (5.0.7.1) lib/active_record/railties/controller_runtime.rb:18:in `process_action'
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omniauth (1.4.2) lib/omniauth/strategy.rb:186:in `call!'
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rack (2.0.6) lib/rack/runtime.rb:22:in `call'
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activesupport (5.0.7.1) lib/active_support/cache/strategy/local_cache_middleware.rb:28:in `call'
newrelic_rpm (6.3.0.355) lib/new_relic/agent/instrumentation/middleware_tracing.rb:99:in `call'
actionpack (5.0.7.1) lib/action_dispatch/middleware/executor.rb:12:in `call'
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actionpack (5.0.7.1) lib/action_dispatch/middleware/static.rb:136:in `call'
newrelic_rpm (6.3.0.355) lib/new_relic/agent/instrumentation/middleware_tracing.rb:99:in `call'
rack (2.0.6) lib/rack/sendfile.rb:111:in `call'
newrelic_rpm (6.3.0.355) lib/new_relic/agent/instrumentation/middleware_tracing.rb:99:in `call'
railties (5.0.7.1) lib/rails/engine.rb:522:in `call'
newrelic_rpm (6.3.0.355) lib/new_relic/agent/instrumentation/middleware_tracing.rb:99:in `call'
puma (3.12.0) lib/puma/configuration.rb:225:in `call'
puma (3.12.0) lib/puma/server.rb:658:in `handle_request'
puma (3.12.0) lib/puma/server.rb:472:in `process_client'
puma (3.12.0) lib/puma/server.rb:332:in `block in run'
puma (3.12.0) lib/puma/thread_pool.rb:133:in `block in spawn_thread'

UPDATE: (update 3)

If I change my controller code to this:

• the above stacktrace error goes away
• page refresh does not happen - this is good
• but the flash message still does not appear

            respond_to do |format|
              format.json { flash.now[:alert] = "Report generation has been initiated. You will receive an email in approximately 4 - 5 minutes with a link to download the report."}
            end

Answer 1

You should use remote: true in your form.

<%= form_tag generate_report_path(:header => true), remote: true do |f| % >
<div class="container-fluid">
  <div style="padding-right:10px">
   <%= select_tag(:report_id, options_for_select(
      [["Select Report Type", 0],
      ["Report1", 1],
      ["Report2", 2],
      ["Report3", 3]]), id: "report_selection") 
   %>
   <%= hidden_field_tag :format, :pdf %>
   <%= button_tag "Generate Report", class: 'btn btn-sm btn-primary'%>
   <%= label_tag do %>
     <%= check_box_tag "format_reqd", "format_reqd", false %>
     Check for Numeric format 
   <% end %>

<% end  %>

Above remote: true is responsible for sending ajax request to your controller method. Here is a complete guide for form_for and remote requests.

In your method of the controller:

def generate_report
  ... #Whatever you want to add here.
  render js: "alert('Your report would be emailed to you in a few minutes')"
end

Update with the flash message:

Your controller method will now look like:

def generate_report
  ... #Whatever you want to add here.
  respond_to do |format|
    format.js { flash[:notice] = "Your report would be emailed to you in a few minutes" }
  end
end

Rendered view:

# app/views/users/generate_report.js.erb
$("#flash").html('<%= j render partial: "shared/notice_banner" %>');

# app/views/layouts/application.html.erb
<div id="flash">
  <% if notice.present? %>
    <%= render partial: "shared/notice_banner" %>
  <% end %>
</div>


# app/views/shared/_notice_banner.html.erb
<div data-alert class="alert-box">
  <%= notice %>
  <a href="#" class="close">&times;</a>
</div>

Here is the detailed answer present. Hope this will help.