Validations on extra column in devise not working - ruby-on-rails

Question

While inserting some thing in firstName field its show error that firstName should not be blank....
Any Suggestion why this will be happening......?
Model
members.rb file
class Member < ActiveRecord::Base
# Include default devise modules. Others available are:
# :confirmable, :lockable, :timeoutable and :omniauthable
devise :database_authenticatable, :registerable,
:recoverable, :rememberable, :trackable, :validatable
validates :firstName, :presence => true
end
View
new.html.erb file
<h2>Sign up</h2>
<%= form_for(resource, :as => resource_name, :url => registration_path(resource_name)) do |f| %>
<%= devise_error_messages! %>
<div><%= f.label :firstName %><br />
<%= f.email_field :firstName, :autofocus => true %></div>
<div><%= f.label :email %><br />
<%= f.email_field :email, :autofocus => true %></div>
<div><%= f.label :password %><br />
<%= f.password_field :password %></div>
<div><%= f.label :password_confirmation %><br />
<%= f.password_field :password_confirmation %></div>
<div><%= f.submit "Sign up" %></div>
<% end %>
<%= render "devise/shared/links" %>

Answer 1

In Rails 4, you need to make a list of the parameters you are expecting a form to submit to you. this is called "strong parameters".
Devise has its own way that you can do this, called "sanitizing".
Look up those two terms.
See this answer: https://stackoverflow.com/a/20756469/2308190

Answer 2

Is it possible even you didn't input first name, but in params it still has value as empty string ""? If you use following, could it work？
validates :firstName, length: { minimum: 2 }
You can chage 2 to any other number.

Answer 3

Update your devise view with this.
<h2>Sign up</h2>
<%= form_for(resource, :as => resource_name, :url => registration_path(resource_name)) do |f| %>
<%= devise_error_messages! %>
<div><%= f.label :firstName %><br />
<%= f.text_field :firstname, :autofocus => true %></div>
<div><%= f.label :email %><br />
<%= f.email_field :email%></div>
<div><%= f.label :password %><br />
<%= f.password_field :password %></div>
<div><%= f.label :password_confirmation %><br />
<%= f.password_field :password_confirmation %></div>
<div><%= f.submit "Sign up" %></div>
<% end %>
<%= render "devise/shared/links" %>
And model
validates :firstname, :presence => true