1 files changed, 40 insertions, 0 deletions
diff --git a/app/validators/nested_attributes_duplicates_validator.rb b/app/validators/nested_attributes_duplicates_validator.rb
new file mode 100644
index 00000000000..b60350a6311
--- /dev/null
+++ b/app/validators/nested_attributes_duplicates_validator.rb
@@ -0,0 +1,40 @@
+# frozen_string_literal: true
+
+# NestedAttributesDuplicates
+#
+# This validator is designed for especially the following condition
+# - Use `accepts_nested_attributes_for :xxx` in a parent model
+# - Use `validates :xxx, uniqueness: { scope: :xxx_id }` in a child model
+class NestedAttributesDuplicatesValidator < ActiveModel::EachValidator
+  def validate_each(record, attribute, value)
+    return if child_attributes.any? { |child_attribute| record.errors.include?(:"#{attribute}.#{child_attribute}") }
+
+    if options[:scope]
+      scoped = value.group_by do |variable|
+        Array(options[:scope]).map { |attr| variable.send(attr) } # rubocop:disable GitlabSecurity/PublicSend
+      end
+      scoped.each_value { |scope| validate_duplicates(record, attribute, scope) }
+    else
+      validate_duplicates(record, attribute, value)
+    end
+  end
+
+  private
+
+  # rubocop: disable CodeReuse/ActiveRecord
+  def validate_duplicates(record, attribute, values)
+    child_attributes.each do |child_attribute|
+      duplicates = values.reject(&:marked_for_destruction?).group_by(&:"#{child_attribute}").select { |_, v| v.many? }.map(&:first)
+      if duplicates.any?
+        error_message = +"have duplicate values (#{duplicates.join(", ")})"
+        error_message << " for #{values.first.send(options[:scope])} scope" if options[:scope] # rubocop:disable GitlabSecurity/PublicSend
+        record.errors.add(attribute, error_message)
+      end
+    end
+  end
+  # rubocop: enable CodeReuse/ActiveRecord
+
+  def child_attributes
+    options[:child_attributes] || %i[key]
+  end
+end