[#58520] added api for single hierarchy item route

docs/api/apiv3/paths/custom_field_item.yml

@@ -23,6 +23,18 @@ get:
           examples:
             'simple response':
               $ref: '../components/examples/hierarchy_item_response.yml'
+    '403':
+      description: Returned if the user is not logged in.
+      content:
+        application/hal+json:
+          schema:
+            $ref: '../components/schemas/error_response.yml'
+          examples:
+            response:
+              value:
+                _type: Error
+                errorIdentifier: urn:openproject-org:api:v3:errors:MissingPermission
+                message: You are not authorized to access this resource.
     '404':
       description: Returned if the custom field item does not exist or the user is not logged in.
       content:

lib/api/v3/custom_fields/hierarchy/item_api.rb

@@ -0,0 +1,53 @@
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+module API
+  module V3
+    module CustomFields
+      module Hierarchy
+        class ItemAPI < ::API::OpenProjectAPI
+          resource :custom_field_items do
+            route_param :id, type: Integer, desc: "Custom Field Item ID" do
+              after_validation do
+                authorize_logged_in
+
+                @custom_field_item = CustomField::Hierarchy::Item.find(params[:id])
+              end
+
+              get &::API::V3::Utilities::Endpoints::Show
+                     .new(model: CustomField::Hierarchy::Item,
+                          render_representer: HierarchyItemRepresenter,
+                          instance_generator: ->(*) { @custom_field_item })
+                     .mount
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/api/v3/root.rb

@@ -52,6 +52,7 @@ class Root < ::API::OpenProjectAPI
       mount ::API::V3::Configuration::ConfigurationAPI
       mount ::API::V3::CustomActions::CustomActionsAPI
       mount ::API::V3::CustomFields::CustomFieldsAPI
+      mount ::API::V3::CustomFields::Hierarchy::ItemAPI
       mount ::API::V3::CustomOptions::CustomOptionsAPI
       mount ::API::V3::Days::DaysAPI
       mount ::API::V3::Grids::GridsAPI