refactoring of Membership create

refactor.patch

diff --git a/app/controllers/admin/users_controller.rb b/app/controllers/admin/users_controller.rb
index 5747a13..c5c9a05 100644
--- a/app/controllers/admin/users_controller.rb
+++ b/app/controllers/admin/users_controller.rb
@@ -12,8 +12,7 @@ class Admin::UsersController < AdminController
       @email = Email.new(email: @identity.email, confirmed: true)
       @user = User.create!(name: @identity.name, nickname: @identity.nickname,
                            emails: [@email])
-      # create the membership for other domain user.
-      Membership.create!(:account => account, :email => @email) unless account.membership_for(@user)
+      Membership.for!(account, @email)
       flash[:notice] = "User created successfully"
     else
       error_msg = existing_email.blank? ? @identity.errors.full_messages.join(', ') : "This email address (#{@identity.email}) is already registered with Socialspring."
diff --git a/app/models/email.rb b/app/models/email.rb
index 5f9b533..2c5753c 100644
--- a/app/models/email.rb
+++ b/app/models/email.rb
@@ -83,9 +83,7 @@ class Email < ActiveRecord::Base
   def activate_domain_membership
     unless domain_membership?
       account = Account.for_domain(self.domain)
-      unless account.membership_for(user)
-        Membership.create!(:account => account, :email => self)
-      end
+      Membership.for!(account, self)
     end
   rescue ActiveRecord::RecordInvalid
     Rails.logger.info "Email#activate_domain_membership: account/membership not created - #{$!}"
diff --git a/app/models/invitation.rb b/app/models/invitation.rb
index b15462f..d1bc5e3 100644
--- a/app/models/invitation.rb
+++ b/app/models/invitation.rb
@@ -41,7 +41,7 @@ class Invitation < ActiveRecord::Base
       the_email = Email.new(email: self.email, confirmed: true, accounts: [self.account])
     end
     if the_email.user.try(:persisted?)
-      Membership.create!(:account => self.account, :email => the_email) unless account.membership_for(the_email.user)
+      Membership.for!(account, the_email)
       user = the_email.user
     else
       user = User.create(emails: [the_email])
diff --git a/app/models/membership.rb b/app/models/membership.rb
index 4e71fb9..3a66079 100644
--- a/app/models/membership.rb
+++ b/app/models/membership.rb
@@ -22,6 +22,10 @@ class Membership < ActiveRecord::Base
   validate :email_is_confirmed
   validate :unique_user_to_account
 
+  def self.for!(account, email)
+    account.membership_for(email.user) || create!(account: account, email: email)
+  end
+
   def email_is_confirmed
     errors.add(:email, "must be confirmed") unless email.try(:confirmed?)
   end
diff --git a/spec/models/membership_spec.rb b/spec/models/membership_spec.rb
index 2c80fbb..ba6c6d2 100644
--- a/spec/models/membership_spec.rb
+++ b/spec/models/membership_spec.rb
@@ -6,6 +6,25 @@ describe Membership do
     lambda{ m.update_attributes(disabled: true) }.should change(Membership, :count).by(-1)
   end
 
+  describe ".for!" do
+    before do
+      @account = Factory(:account)
+      @user = Factory(:user)
+      @email = Factory(:email, :user => @user)
+    end
+
+    it "should find existing membership" do
+      m = Membership.create!(account: @account, email: @email)
+      Membership.for!(@account, @email).should == m
+    end
+
+    it "should create new membership" do
+      m = Membership.for!(@account, @email)
+      m.email.should == @email
+      m.account.should == @account
+    end
+  end
+
   describe "#clean_old_invitations" do
     before do
       @account = Factory(:account)