FactoryGirl and validations on embeds_many in Mongoid

[Nitish Upreti]

I have a complex model relationship hierarchy setup, Here are the relevant parts ( Channel and ChannelTagWeight model) as:

class Channel
  include Mongoid::Document

  embeds_many :channel_tag_weights

  def sum_of_channel_tag_weights
    sum = 0
    self.channel_tag_weights.each {  |ctw| sum = sum + ctw.weight }
    errors.add(:channel_tag_weight,"sum for all MasterTags should equal 10") unless sum == 10 
  end
end

I have ChannelTagWeights as

class ChannelTagWeight
  include Mongoid::Document
  embedded_in :channel

  field :weight, type: Integer
  belongs_to :mastertag
  validates :weight, :presence => true

end

I have my Factory setup for Channel as:

  factory :playtex_website, :class => Channel do
    url 'http://www.playtexplayon.com/'

    after(:build) do |channel|
        channel.channel_tag_weights << FactoryGirl.create(:playtex_tag_weight,channel: channel)
        channel.channel_tag_weights << FactoryGirl.create(:playtex_tag_weight2,channel: channel)
    end
  end

For ChannelTagWeights :

  factory :playtex_tag_weight, :class => ChannelTagWeight  do
    weight 8
    after(:build) do |channel_tag_weight|
        channel_tag_weight.mastertag = channel_tag_weight.channel.company.project.mastertags.first
    end
  end

  factory :playtex_tag_weight2, :class => ChannelTagWeight  do
    weight 2
    after(:build) do |channel_tag_weight|
        channel_tag_weight.mastertag = channel_tag_weight.channel.company.project.mastertags.last 
    end
  end

I always end up with :

Mongoid::Errors::Validations: 
Problem:
  Validation of Website failed.
Summary:
  The following errors were found: Channel tag weight sum for all MasterTags should equal 10
Resolution:
  Try persisting the document with valid data or remove the validations.

Where am I going wrong? How to solve this issue?