Prevent Duplicate Entries and alert via a alert box if user insert duplicate entry.

Question

How i Prevent Duplicate Entries in database at the time of form submit and display an alert box and stop form submission if entry is duplicate.

Answer 1

You can add a validates_uniqueness_of validation to your model:

class Model < ActiveRecord::Base
  validates_uniqueness_of :column
end

• ActiveRecord Validations and Callbacks

Answer 2

The more idiomatic Rails approach is to have a model validation for a set of attributes and then display the validation error messages after the form is submitted. By failing the validation the model is not saved to the database.

In the model

validates_uniqueness_of :some_attribute

In the form view

<% form_for @model do |f| %>
  <%= f.error_messages %>


<% end %>

If you really want an alert box (which is a very in-your-face approach IMHO) then you might be better off using an AJAX submit in which you hook the form submit, make an AJAX call to the server to check the form validity by some means of your own, then process the server returned result. JQuery and its form plugin make this relatively easy to do