Validates self relation

app/models/related_issue.rb

@@ -5,4 +5,15 @@ class RelatedIssue < ActiveRecord::Base
   validates :issue, presence: true
   validates :related_issue, presence: true
   validates :issue, uniqueness: { scope: :related_issue_id, message: 'is already related' }
+  validate :check_self_relation
+
+  private
+
+  def check_self_relation
+    return unless issue || related_issue
+
+    if issue == related_issue
+      errors.add(:issue, 'cannot be related to itself')
+    end
+  end
 end