2 files changed, 20 insertions, 7 deletions
diff --git a/app/models/merge_request.rb b/app/models/merge_request.rb
index 422f138c4ea..26a3388602a 100644
--- a/app/models/merge_request.rb
+++ b/app/models/merge_request.rb
@@ -8,6 +8,7 @@ class MergeRequest < ActiveRecord::Base
   include ManualInverseAssociation
   include EachBatch
   include ThrottledTouch
+  include Gitlab::Utils::StrongMemoize
 
   ignore_column :locked_at,
                 :ref_fetched
@@ -53,6 +54,7 @@ class MergeRequest < ActiveRecord::Base
 
   after_create :ensure_merge_request_diff, unless: :importing?
   after_update :reload_diff_if_branch_changed
+  after_update :clear_memoized_shas
 
   # When this attribute is true some MR validation is ignored
   # It allows us to close or modify broken merge requests
@@ -387,13 +389,17 @@ class MergeRequest < ActiveRecord::Base
   end
 
   def source_branch_head
-    return unless source_project
-
-    source_project.repository.commit(source_branch_ref) if source_branch_ref
+    strong_memoize(:source_branch_head) do
+      if source_project && source_branch_ref
+        source_project.repository.commit(source_branch_ref)
+      end
+    end
   end
 
   def target_branch_head
-    target_project.repository.commit(target_branch_ref)
+    strong_memoize(:target_branch_head) do
+      target_project.repository.commit(target_branch_ref)
+    end
   end
 
   def branch_merge_base_commit
@@ -525,6 +531,13 @@ class MergeRequest < ActiveRecord::Base
     end
   end
 
+  def clear_memoized_shas
+    @target_branch_sha = @source_branch_sha = nil
+
+    clear_memoization(:source_branch_head)
+    clear_memoization(:target_branch_head)
+  end
+
   def reload_diff_if_branch_changed
     if (source_branch_changed? || target_branch_changed?) &&
         (source_branch_head && target_branch_head)
diff --git a/app/models/merge_request_diff.rb b/app/models/merge_request_diff.rb
index c37aa0a594b..e35de9b97ee 100644
--- a/app/models/merge_request_diff.rb
+++ b/app/models/merge_request_diff.rb
@@ -104,19 +104,19 @@ class MergeRequestDiff < ActiveRecord::Base
   def base_commit
     return unless base_commit_sha
 
-    project.commit(base_commit_sha)
+    project.commit_by(oid: base_commit_sha)
   end
 
   def start_commit
     return unless start_commit_sha
 
-    project.commit(start_commit_sha)
+    project.commit_by(oid: start_commit_sha)
   end
 
   def head_commit
     return unless head_commit_sha
 
-    project.commit(head_commit_sha)
+    project.commit_by(oid: head_commit_sha)
   end
 
   def commit_shas