Batch load only data from same repository when lazy object is accessed

By specifying `key`, we get a different lazy batch loader for each
repository, which means that accessing a lazy object from one repository
will only result in that repository's objects being fetched, not those
of other repositories, saving us some unnecessary Gitaly lookups.

2 files changed, 8 insertions, 6 deletions

diff --git a/app/graphql/resolvers/full_path_resolver.rb b/app/graphql/resolvers/full_path_resolver.rb
index 8d3da33e8d2..0f1a64b6c58 100644
--- a/app/graphql/resolvers/full_path_resolver.rb
+++ b/app/graphql/resolvers/full_path_resolver.rb
@@ -11,10 +11,11 @@ module Resolvers
     end
 
     def model_by_full_path(model, full_path)
-      BatchLoader.for(full_path).batch(key: "#{model.model_name.param_key}:full_path") do |full_paths, loader|
+      BatchLoader.for(full_path).batch(key: model) do |full_paths, loader, args|
         # `with_route` avoids an N+1 calculating full_path
-        results = model.where_full_path_in(full_paths).with_route
-        results.each { |project| loader.call(project.full_path, project) }
+        args[:key].where_full_path_in(full_paths).with_route.each do |project|
+          loader.call(project.full_path, project)
+        end
       end
     end
   end
diff --git a/app/graphql/resolvers/merge_request_resolver.rb b/app/graphql/resolvers/merge_request_resolver.rb
index b87c95217f7..d047ce9e3a1 100644
--- a/app/graphql/resolvers/merge_request_resolver.rb
+++ b/app/graphql/resolvers/merge_request_resolver.rb
@@ -14,9 +14,10 @@ module Resolvers
     def resolve(iid:)
       return unless project.present?
 
-      BatchLoader.for(iid.to_s).batch(key: project.id) do |iids, loader|
-        results = project.merge_requests.where(iid: iids)
-        results.each { |mr| loader.call(mr.iid.to_s, mr) }
+      BatchLoader.for(iid.to_s).batch(key: project) do |iids, loader, args|
+        args[:key].merge_requests.where(iid: iids).each do |mr|
+          loader.call(mr.iid.to_s, mr)
+        end
       end
     end
     # rubocop: enable CodeReuse/ActiveRecord