Add build_relations method in Chain::Populate

lib/gitlab/ci/pipeline/chain/create.rb

@@ -6,9 +6,6 @@ module Gitlab
           include Chain::Helpers
           def perform!
-            # Allocate next IID outside of transaction
-            pipeline.ensure_project_iid!
-
             ::Ci::Pipeline.transaction do
               pipeline.save!

lib/gitlab/ci/pipeline/chain/populate.rb

@@ -8,10 +8,7 @@ module Gitlab
           PopulateError = Class.new(StandardError)
           def perform!
-            ##
-            # Populate pipeline with block argument of CreatePipelineService#execute.
-            #
-            @command.seeds_block&.call(pipeline)
+            build_relations
             ##
             # Populate pipeline with all stages, and stages with builds.
@@ -34,6 +31,18 @@ module Gitlab
           def break?
             pipeline.errors.any?
           end
+
+          private
+
+          def build_relations
+            ##
+            # Populate pipeline with block argument of CreatePipelineService#execute.
+            #
+            @command.seeds_block&.call(pipeline)
+
+            # Allocate next IID. This operation must be outside of transactions of pipeline creations.
+            pipeline.ensure_project_iid!
+          end
         end
       end
     end