Mongoid add field but don't exist in mongodb - mongodb

Question

I use Mongoid to query db in a rails project.
When i add a field "scope" to a User Model
class User
include Mongoid::Document
field :scope, type: String
end
When use rails console, we can find this field have add to User model.
But when we go to mongodb console to view users data, use db.users.find(), it don't have scope field yet.
also when i want update scope field in rails console. It always have below error.
pry(main)> user = User.first
=> #<User _id: 521dcd4464fad29a74000009, scope: "private", xxx_id: "521dcd4464fad29a74000008">
pry(main)> user.update_attributes(scope: "public")
Moped::Errors::OperationFailure: The operation: #<Moped::Protocol::Command
#length=84
#request_id=17
#response_to=0
#op_code=2004
#flags=[]
#full_collection_name="blog_development.$cmd"
#skip=0
#limit=-1
#selector={:getlasterror=>1, :safe=>true}
#fields=nil>
failed with error 11000: "E11000 duplicate key error index: blog_development.users.$_id_ dup key: { : ObjectId('521dcd4464fad29a74000009') }"
Any one can tell me why?

Answer 1

Just adding field :scope, type: String to your model won't add it to the underlying MongoDB collection, that just tells Mongoid that it should allow the model to have a scope for accessors, mutators, validations, mass-assignment, ... Keep in mind that different documents in a MongoDB collection can have entirely different properties so the schema is really a fiction that is applied by Mongoid.
If you want all your users to have a scope then you'd have to say something like this:
User.collection.find().update_all(:$set => { :scope => 'whatever it should be' })
to manually add it to all the documents.

Answer 2

The field exists in your saved objects. But to be able to find one with your asked value, you have to create one.
class User
include Mongoid::Document
field :name, type: String
field :age, type: Integer
end
User.find(name: 'John')
# => nil
User.create({ name: 'John', age: '18' })
# => User 284692 :name => 'John', :age => 18
User.find(name: 'John')
# => User 284692 :name => 'John', :age => 18
Hope it helps.
edit after 'mu is too short' post :
To fill all existing objects in db, just provide a :default value to your field
class User
field :name, type: String, default: 'Martin Dupont'
end

Answer 3

Thanks for reply.
The reason is in this model, i have overwrite new_record? method. So cause this error.