Rails PG::Error Presentation and Handling of Unique Constraint - devise

Question

I am developing on Rails 4 with postgres and devise. I have the following User model:
# user model
class User < ActiveRecord::Base
extend FriendlyId
friendly_id :username, :use => :slugged
rolify
devise :database_authenticatable, :registerable, :recoverable, :rememberable, :trackable
validates :username, :presence => true, :uniqueness => {:case_sensitive => false}, :length => { :minimum => 3 },
:format => { :with => /\A[A-Z0-9a-z\w\b\ \-\_\'\!&##\.]+\z/i,
:message => "may contain only alphanumeric characters and common special characters." }
validates :email, :uniqueness => {:case_sensitive => false}, :presence => true,
:format => { :with => Devise.email_regexp, :message => "isn't valid"}
validates :password, length: { in: 6..128 }, on: :create
validates :password, length: { in: 6..128 }, on: :update, allow_blank: true
validates :slug, :presence => true
end
# in schema
create_table "users", force: true do |t|
t.string "email", default: "", null: false
t.string "encrypted_password", default: "", null: false
t.string "reset_password_token"
t.datetime "reset_password_sent_at"
t.datetime "remember_created_at"
t.integer "sign_in_count", default: 0
t.datetime "current_sign_in_at"
t.datetime "last_sign_in_at"
t.string "current_sign_in_ip"
t.string "last_sign_in_ip"
t.datetime "created_at"
t.datetime "updated_at"
t.string "username"
t.string "slug"
end
add_index "users", ["email"], name: "index_users_on_email", unique: true
add_index "users", ["reset_password_token"], name: "index_users_on_reset_password_token", unique: true
add_index "users", ["slug"], name: "index_users_on_slug", unique: true
add_index "users", ["username"], name: "index_users_on_username", unique: true
The fields email and username are unique indices of the users table. My user registration view was created from devise. I create a test account, for instance, with username "test", email "test#example.com", password "123456". I sign out and try to sign up with the same information. I am expecting that the :uniqueness validations to trigger and be rendered on a list of errors alongside the signup form, but instead I get a full-page error with:
ERROR: duplicate key value violates unique constraint "index_users_on_email"
DETAIL: Key (email)=(test#example.com) already exists.
How can I allow this error to bubble up to Rails and be shown as friendly single-line error like "Email is already registered with an account" alongside the sign up form instead of being caught with a big Rails error page?

Answer 1

I've identified the problem. The plugin friendly_id turned out not so friendly. It breaks uniqueness validation and results in 500 internal server errors. I have removed it from my application. Consider using something like ActsAsUrl in the Stringex library. I have removed
extend FriendlyId
friendly_id :username_copy, :use => :slugged
and am now using
acts_as_url :username, :sync_url => true, :url_attribute => :slug
to generate friendly urls.