1 files changed, 53 insertions, 0 deletions
diff --git a/app/models/work_items/parent_link.rb b/app/models/work_items/parent_link.rb
new file mode 100644
index 00000000000..3c405dbce3b
--- /dev/null
+++ b/app/models/work_items/parent_link.rb
@@ -0,0 +1,53 @@
+# frozen_string_literal: true
+
+module WorkItems
+  class ParentLink < ApplicationRecord
+    self.table_name = 'work_item_parent_links'
+
+    MAX_CHILDREN = 100
+
+    belongs_to :work_item
+    belongs_to :work_item_parent, class_name: 'WorkItem'
+
+    validates :work_item, :work_item_parent, presence: true
+    validate :validate_child_type
+    validate :validate_parent_type
+    validate :validate_same_project
+    validate :validate_max_children
+
+    private
+
+    def validate_child_type
+      return unless work_item
+
+      unless work_item.task?
+        errors.add :work_item, _('Only Task can be assigned as a child in hierarchy.')
+      end
+    end
+
+    def validate_parent_type
+      return unless work_item_parent
+
+      unless work_item_parent.issue?
+        errors.add :work_item_parent, _('Only Issue can be parent of Task.')
+      end
+    end
+
+    def validate_same_project
+      return if work_item.nil? || work_item_parent.nil?
+
+      if work_item.resource_parent != work_item_parent.resource_parent
+        errors.add :work_item_parent, _('Parent must be in the same project as child.')
+      end
+    end
+
+    def validate_max_children
+      return unless work_item_parent
+
+      max = persisted? ? MAX_CHILDREN : MAX_CHILDREN - 1
+      if work_item_parent.child_links.count > max
+        errors.add :work_item_parent, _('Parent already has maximum number of children.')
+      end
+    end
+  end
+end