validate_presence_of on 'has_many' and 'belongs_to' association, how to write factory

I have a two models. Both having validate_presence_of .

 class Company < ActiveRecord::Base
   has_many :projects
   validate_presence_of :projects

   def save_projects(projects)
     projects.each do |project|
       project.company = self
       project.save(:validate => false)
     end
   end
 end

In method saving_projects(projects) is called before saving company in controller. Means I am saving company after the project.

   class Project < ActiveRecord::Base
       belongs_to :company
       validate_presence_of :company
    end

These are my models.

I am saving projects in model with validation => false. So I want to write factory for company.

What I have tried:

factory :company do
  name 'Test'
  user
  before_create do |company|
    FactoryGirl.build(:project, :company => company)
  end
end

And also tried this

factory :company do
  name 'Test'
  user
  after_build do |company|
    company.projects << FactoryGirl.build(:project, :company => company)
  end
end

I am getting this error:

Failure/Error: company = FactoryGirl.build(:company, :user=>user,:name => "test")
NoMethodError:
  undefined method `company=' for #<Project:0x000000106c3030>

Problem track: The problem with validate_presence_of on both the model that causing issue.