How to validate .csv file in rails 4

Question

I am using rails 4. I am having employee attendance model. In that I have to upload .csv file alone. It won't allow any other format. So, How to validate file format. whether imported file was other than csv.

Model

class EmpAttendance < ActiveRecord::Base
    attr_accessible :emp_id,:in_time,:out_time,:date,:status


    def self.import(file)
            CSV.foreach(file.path, headers: true) do |row|
            @emp_attendance  = EmpAttendance.find_by_emp_id_and_date(row['emp_id'],row['date']) || EmpAttendance.new
            @emp_attendance.emp_id                = row['emp_id']
            @emp_attendance.in_time               = row['in_time']
            @emp_attendance.out_time              = row['out_time']
            @emp_attendance.status                = row['status']
            @emp_attendance.date                  = row['date']
            @emp_attendance.save!
        end
    end
end

Controller

def import
    if params[:file].present?   
     EmpAttendance.import(params[:file])
     flash[:notice] = "Sucessfully Created."
     redirect_to emp_attendances_path
    else 
     flash[:error] = "No File Chosen"
     redirect_to emp_attendances_path
    end 
 end

View (Index.html.erb)

<div class='row-fluid clear'>
  <div class='box gradient'>
    <div class='title'>
      <h3 style='margin-left:1em'>Add Driver Details</h3>
    </div>
    <div class='content'>

     <% if flash[:notice].present? %>
    <div class="alert alert-success">
        <button type="button" class="close" data-dismiss="alert">&times;</button>
        <%= flash[:notice] %>
    </div>
<% end %>
<% if flash[:error].present? %>

    <div class="alert alert-danger">
        <button type="button" class="close" data-dismiss="alert">&times;</button>
        <%= flash[:error] %>
    </div>
<% end %>
<div>
    <h3>Employee Attendance</h3>
    <p>
</div>
<%= form_tag import_emp_attendances_path, multipart: true do %>
<%= file_field_tag :file %>
  <%= submit_tag "Import", :class => 'btn btn-primary' %>
<% end %>
    </div>
  </div>
</div>                   

Please Help me..

Answer 1

The API Docs mentions the accept option:

file_field_tag :file, accept: 'text/csv'

:accept - If set to one or multiple mime-types, the user will be suggested a filter when choosing a file. You still need to set up model validations.

Answer 2

When I do csv imports, I do two things:

1. put the data-rows into intermediate hash-objects. Then I check basic things like that nr of columns is big enough. Also this decouples the csv-format from the format in the database.

2. insert all data in one transaction. When an object does not validate, nothing is imported, and there is a clear state. The user is not left with half imported data. writing many objects in one transactions also tend to be faster.