Validate on report that post or comment does exist

app/models/report.rb

@@ -6,6 +6,7 @@ class Report < ActiveRecord::Base
   validates :text, presence: true
 
   validate :entry_does_not_exist, :on => :create
+  validate :post_or_comment_does_exist, :on => :create
 
   belongs_to :user
   belongs_to :post
@@ -19,6 +20,12 @@ class Report < ActiveRecord::Base
     end
   end
 
+  def post_or_comment_does_exist
+    if Post.find_by_id(item_id).nil? && Comment.find_by_id(item_id).nil?
+      errors[:base] << 'Post or comment was already deleted or doesn\'t exists.'
+    end
+  end
+
   def destroy_reported_item
     if item_type == 'post'
       delete_post

spec/models/report_spec.rb

@@ -25,11 +25,27 @@ describe Report do
 
   describe '#validation' do
     it 'validates that post ID is required' do
-      @user.reports.build(:item_type => 'post', :text => 'blub').should_not be_valid
+      report = @valid_post_report
+      report.delete(:item_id)
+      @user.reports.build(report).should_not be_valid
     end
     
     it 'validates that post type is required' do
-      @user.reports.build(:item_id => 666, :text => 'blub').should_not be_valid
+      report = @valid_post_report
+      report.delete(:item_type)
+      @user.reports.build(report).should_not be_valid
+    end
+
+    it 'validates that post does exist' do
+      report = @valid_post_report
+      report[:item_id] = 666;
+      @user.reports.build(report).should_not be_valid
+    end
+
+    it 'validates that comment does exist' do
+      report = @valid_comment_report
+      report[:item_id] = 666;
+      @user.reports.build(report).should_not be_valid
     end
 
     it 'validates that entry does not exist' do