Question

I am getting started with a non-SQL database (specifically, MongoDB) and Ruby on Rails because I believe flexible schemas will be an advantage. Right now, I’m confused because some things I expect to “just work” aren’t working. Specifically, I have a “method missing” error on one of my pages.

NoMethodError in Users#new

undefined method `email' for #<User _id: BSON::ObjectId('4eb8cbcaef704c02da000017')>

Extracted source (around line #13):

10:       <tbody><tr>
11:         <td><%= f.label :email %>:</td>
12:         <td>
13:           <%= f.text_field :email, :placeholder => "your email address" %>
14:         </td>
15:       </tr>
16:       <tr>

In the console:

>> User.new.email
NoMethodError: undefined method `email' for #<User _id: BSON::ObjectId('4eb8cc4def704c0358000005')>
    from /Library/Ruby/Gems/1.8/gems/activemodel-3.1.1/lib/active_model/attribute_methods.rb:385:in `method_missing'
    from (irb):5

The model looks like: (note class User does not inherit from any Active Record super class… does this matter?)

class User
  include MongoMapper::Document

  attr_accessor :password
  attr_accessible :username, :email, :password

  email_regex = /\A[\w+\-.]+@[a-z\d\-.]+\.[a-z]+\z/i

  validates :username, :presence => true,
                   :format => { :with => /^[a-zA-Z][a-zA-Z0-9_]+$/ },
                   :length => { :maximum => 32, :minimum => 4 }
  validates :email, :presence => true,
                    :format => { :with => email_regex },
                    :uniqueness => { :case_sensitive => false }
  validates :password, :presence => true,
                       :length => { :within => 5..32 },
                       :confirmation => true
  (etc...)

Answer 1

If you look at the error messages you’ll see things like this:

#<User _id: BSON::ObjectId('4eb8cc4def704c0358000005')>

so your MongoMapper backed models only have the default _id property. You’ll need to tell MongoMapper what the other properties are:

class User
  include MongoMapper::Document

  key :password, String
  key :username, String
  key :email, String
  #...

The MongoMapper documentation can be difficult to navigate but the important bits are there.

So MongoMapper does use schemas of a sort.