Question

I have model as follows:

class User
  include Mongoid::Document
  field :name
end

After saving a few user objects to the database I added some more fields:

class User
  include Mongoid::Document
  include Mongoid::Timestamps::Created
  field :name
  field :birthdate
end

Now, I expect I can use the following snippet:

@user = User.all
@user.each do |u|
   puts u.name
   puts u.birthdate.strftime(#someFormat)
   puts u.created_at.strftime(#someFormat)
end

Unfortunately, because my old user objects don’t have birthdate keys, I receive this error: strftime called on nil class.

Question:

• How can I handle such cases with Mongoid? In MySQL, when a column is added it gets added to old rows as well. But if I see in MongoDB, it doesn’t add new fields as keys for old data.
• This problem also exists with the created_at field as old data doesn’t have that field either.

I am looking for good way to solve this, checking for nil conditions each time is not a scalable option because the number of fields will continue increasing.

Answer 1

You could also add a default to your new field, which would give all your old records a fallback value.

class User
  include Mongoid::Document
  include Mongoid::Timestamps::Created

  field :name
  field :birthdate, :type => Date, :default => Date.new(1970,1,1)
end

You can update your models which are missing created_at values, but just running something simple in your rails console:

User.all.each{ |u| u.update_attributes(:created_at => Time.now) if u.created_at.nil? }