1 files changed, 38 insertions, 0 deletions
diff --git a/app/models/issue_link.rb b/app/models/issue_link.rb
new file mode 100644
index 00000000000..9740b009396
--- /dev/null
+++ b/app/models/issue_link.rb
@@ -0,0 +1,38 @@
+# frozen_string_literal: true
+
+class IssueLink < ApplicationRecord
+  include FromUnion
+
+  belongs_to :source, class_name: 'Issue'
+  belongs_to :target, class_name: 'Issue'
+
+  validates :source, presence: true
+  validates :target, presence: true
+  validates :source, uniqueness: { scope: :target_id, message: 'is already related' }
+  validate :check_self_relation
+
+  scope :for_source_issue, ->(issue) { where(source_id: issue.id) }
+  scope :for_target_issue, ->(issue) { where(target_id: issue.id) }
+
+  TYPE_RELATES_TO = 'relates_to'
+  TYPE_BLOCKS = 'blocks'
+  TYPE_IS_BLOCKED_BY = 'is_blocked_by'
+
+  enum link_type: { TYPE_RELATES_TO => 0, TYPE_BLOCKS => 1, TYPE_IS_BLOCKED_BY => 2 }
+
+  def self.inverse_link_type(type)
+    type
+  end
+
+  private
+
+  def check_self_relation
+    return unless source && target
+
+    if source == target
+      errors.add(:source, 'cannot be related to itself')
+    end
+  end
+end
+
+IssueLink.prepend_if_ee('EE::IssueLink')