Merge branch 'merge-request-commits-table' into 'master'

Add table for merge request commits

Closes #30224

See merge request !12527

21 files changed, 222 insertions, 123 deletions

diff --git a/app/controllers/concerns/issuable_collections.rb b/app/controllers/concerns/issuable_collections.rb
index 650ec1e326a..693e2f6365c 100644
--- a/app/controllers/concerns/issuable_collections.rb
+++ b/app/controllers/concerns/issuable_collections.rb
@@ -47,7 +47,7 @@ module IssuableCollections
   end
 
   def merge_requests_collection
-    merge_requests_finder.execute.preload(:source_project, :target_project, :author, :assignee, :labels, :milestone, :merge_request_diff, :head_pipeline, target_project: :namespace)
+    merge_requests_finder.execute.preload(:source_project, :target_project, :author, :assignee, :labels, :milestone, :head_pipeline, target_project: :namespace, merge_request_diff: :merge_request_diff_commits)
   end
 
   def issues_finder
diff --git a/app/models/ci/build.rb b/app/models/ci/build.rb
index 48586ba8910..ba2ecbf82a2 100644
--- a/app/models/ci/build.rb
+++ b/app/models/ci/build.rb
@@ -218,7 +218,7 @@ module Ci
             .reorder(iid: :desc)
 
           merge_requests.find do |merge_request|
-            merge_request.commits_sha.include?(pipeline.sha)
+            merge_request.commit_shas.include?(pipeline.sha)
           end
         end
     end
diff --git a/app/models/commit.rb b/app/models/commit.rb
index 20206d57c4c..c7f62617c4c 100644
--- a/app/models/commit.rb
+++ b/app/models/commit.rb
@@ -138,7 +138,7 @@ class Commit
 
     safe_message.split("\n", 2)[1].try(:chomp)
   end
-  
+
   def description?
     description.present?
   end
diff --git a/app/models/merge_request.rb b/app/models/merge_request.rb
index 2752181ed79..2fc6191e785 100644
--- a/app/models/merge_request.rb
+++ b/app/models/merge_request.rb
@@ -31,7 +31,7 @@ class MergeRequest < ActiveRecord::Base
   after_create :ensure_merge_request_diff, unless: :importing?
   after_update :reload_diff_if_branch_changed
 
-  delegate :commits, :real_size, :commits_sha, :commits_count,
+  delegate :commits, :real_size, :commit_shas, :commits_count,
     to: :merge_request_diff, prefix: nil
 
   # When this attribute is true some MR validation is ignored
@@ -518,7 +518,7 @@ class MergeRequest < ActiveRecord::Base
   def related_notes
     # Fetch comments only from last 100 commits
     commits_for_notes_limit = 100
-    commit_ids = commits.last(commits_for_notes_limit).map(&:id)
+    commit_ids = commit_shas.take(commits_for_notes_limit)
 
     Note.where(
       "(project_id = :target_project_id AND noteable_type = 'MergeRequest' AND noteable_id = :mr_id) OR" +
@@ -841,15 +841,15 @@ class MergeRequest < ActiveRecord::Base
     return Ci::Pipeline.none unless source_project
 
     @all_pipelines ||= source_project.pipelines
-      .where(sha: all_commits_sha, ref: source_branch)
+      .where(sha: all_commit_shas, ref: source_branch)
       .order(id: :desc)
   end
 
   # Note that this could also return SHA from now dangling commits
   #
-  def all_commits_sha
+  def all_commit_shas
     if persisted?
-      merge_request_diffs.flat_map(&:commits_sha).uniq
+      merge_request_diffs.preload(:merge_request_diff_commits).flat_map(&:commit_shas).uniq
     elsif compare_commits
       compare_commits.to_a.reverse.map(&:id)
     else
diff --git a/app/models/merge_request_diff.rb b/app/models/merge_request_diff.rb
index 0cbf58a2325..4b141945ab4 100644
--- a/app/models/merge_request_diff.rb
+++ b/app/models/merge_request_diff.rb
@@ -11,6 +11,7 @@ class MergeRequestDiff < ActiveRecord::Base
 
   belongs_to :merge_request
   has_many :merge_request_diff_files, -> { order(:merge_request_diff_id, :relative_order) }
+  has_many :merge_request_diff_commits, -> { order(:merge_request_diff_id, :relative_order) }
 
   serialize :st_commits # rubocop:disable Cop/ActiveRecordSerialize
   serialize :st_diffs # rubocop:disable Cop/ActiveRecordSerialize
@@ -47,14 +48,13 @@ class MergeRequestDiff < ActiveRecord::Base
   # Collect information about commits and diff from repository
   # and save it to the database as serialized data
   def save_git_content
-    ensure_commits_sha
+    ensure_commit_shas
     save_commits
-    reload_commits
     save_diffs
     keep_around_commits
   end
 
-  def ensure_commits_sha
+  def ensure_commit_shas
     merge_request.fetch_ref
     self.start_commit_sha ||= merge_request.target_branch_sha
     self.head_commit_sha  ||= merge_request.source_branch_sha
@@ -66,7 +66,7 @@ class MergeRequestDiff < ActiveRecord::Base
   # created before version 8.4 that does not store head_commit_sha in separate db field.
   def head_commit_sha
     if persisted? && super.nil?
-      last_commit.try(:sha)
+      last_commit_sha
     else
       super
     end
@@ -97,16 +97,11 @@ class MergeRequestDiff < ActiveRecord::Base
   end
 
   def commits
-    @commits ||= load_commits(st_commits)
+    @commits ||= load_commits
   end
 
-  def reload_commits
-    @commits = nil
-    commits
-  end
-
-  def last_commit
-    commits.first
+  def last_commit_sha
+    commit_shas.first
   end
 
   def first_commit
@@ -131,8 +126,12 @@ class MergeRequestDiff < ActiveRecord::Base
     project.commit(head_commit_sha)
   end
 
-  def commits_sha
-    st_commits.map { |commit| commit[:id] }
+  def commit_shas
+    if st_commits.present?
+      st_commits.map { |commit| commit[:id] }
+    else
+      merge_request_diff_commits.map(&:sha)
+    end
   end
 
   def diff_refs=(new_diff_refs)
@@ -207,7 +206,11 @@ class MergeRequestDiff < ActiveRecord::Base
   end
 
   def commits_count
-    st_commits.count
+    if st_commits.present?
+      st_commits.size
+    else
+      merge_request_diff_commits.size
+    end
   end
 
   def utf8_st_diffs
@@ -231,29 +234,6 @@ class MergeRequestDiff < ActiveRecord::Base
     raw.any? { |element| VALID_CLASSES.include?(element.class) }
   end
 
-  def dump_commits(commits)
-    commits.map(&:to_hash)
-  end
-
-  def load_commits(array)
-    array.map { |hash| Commit.new(Gitlab::Git::Commit.new(hash), merge_request.source_project) }
-  end
-
-  # Load all commits related to current merge request diff from repo
-  # and save it as array of hashes in st_commits db field
-  def save_commits
-    new_attributes = {}
-
-    commits = compare.commits
-
-    if commits.present?
-      commits = Commit.decorate(commits, merge_request.source_project).reverse
-      new_attributes[:st_commits] = dump_commits(commits)
-    end
-
-    update_columns_serialized(new_attributes)
-  end
-
   def create_merge_request_diff_files(diffs)
     rows = diffs.map.with_index do |diff, index|
       diff.to_hash.merge(
@@ -294,12 +274,18 @@ class MergeRequestDiff < ActiveRecord::Base
       end
   end
 
-  # Load diffs between branches related to current merge request diff from repo
-  # and save it as array of hashes in st_diffs db field
+  def load_commits
+    commits = st_commits.presence || merge_request_diff_commits
+
+    commits.map do |commit|
+      Commit.new(Gitlab::Git::Commit.new(commit.to_hash), merge_request.source_project)
+    end
+  end
+
   def save_diffs
     new_attributes = {}
 
-    if commits.size.zero?
+    if compare.commits.size.zero?
       new_attributes[:state] = :empty
     else
       diff_collection = compare.diffs(Commit.max_diff_options)
@@ -319,7 +305,13 @@ class MergeRequestDiff < ActiveRecord::Base
       new_attributes[:state] = :overflow if diff_collection.overflow?
     end
 
-    update_columns_serialized(new_attributes)
+    update(new_attributes)
+  end
+
+  def save_commits
+    MergeRequestDiffCommit.create_bulk(self.id, compare.commits.reverse)
+
+    merge_request_diff_commits.reload
   end
 
   def repository
@@ -332,29 +324,6 @@ class MergeRequestDiff < ActiveRecord::Base
     project.merge_base_commit(head_commit_sha, start_commit_sha).try(:sha)
   end
 
-  #
-  # #save or #update_attributes providing changes on serialized attributes do a lot of
-  # serialization and deserialization calls resulting in bad performance.
-  # Using #update_columns solves the problem with just one YAML.dump per serialized attribute that we provide.
-  # As a tradeoff we need to reload the current instance to properly manage time objects on those serialized
-  # attributes. So to keep the same behaviour as the attribute assignment we reload the instance.
-  # The difference is in the usage of
-  # #write_attribute= (#update_attributes) and #raw_write_attribute= (#update_columns)
-  #
-  # Ex:
-  #
-  #   new_attributes[:st_commits].first.slice(:committed_date)
-  #   => {:committed_date=>2014-02-27 11:01:38 +0200}
-  #   YAML.load(YAML.dump(new_attributes[:st_commits].first.slice(:committed_date)))
-  #   => {:committed_date=>2014-02-27 10:01:38 +0100}
-  #
-  def update_columns_serialized(new_attributes)
-    return unless new_attributes.any?
-
-    update_columns(new_attributes.merge(updated_at: current_time_from_proper_timezone))
-    reload
-  end
-
   def keep_around_commits
     [repository, merge_request.source_project.repository].each do |repo|
       repo.keep_around(start_commit_sha)
diff --git a/app/models/merge_request_diff_commit.rb b/app/models/merge_request_diff_commit.rb
new file mode 100644
index 00000000000..cafdbe11849
--- /dev/null
+++ b/app/models/merge_request_diff_commit.rb
@@ -0,0 +1,38 @@
+class MergeRequestDiffCommit < ActiveRecord::Base
+  include ShaAttribute
+
+  belongs_to :merge_request_diff
+
+  sha_attribute :sha
+  alias_attribute :id, :sha
+
+  def self.create_bulk(merge_request_diff_id, commits)
+    sha_attribute = Gitlab::Database::ShaAttribute.new
+
+    rows = commits.map.with_index do |commit, index|
+      # See #parent_ids.
+      commit_hash = commit.to_hash.except(:parent_ids)
+      sha = commit_hash.delete(:id)
+
+      commit_hash.merge(
+        merge_request_diff_id: merge_request_diff_id,
+        relative_order: index,
+        sha: sha_attribute.type_cast_for_database(sha)
+      )
+    end
+
+    Gitlab::Database.bulk_insert(self.table_name, rows)
+  end
+
+  def to_hash
+    Gitlab::Git::Commit::SERIALIZE_KEYS.each_with_object({}) do |key, hash|
+      hash[key] = public_send(key)
+    end
+  end
+
+  # We don't save these, because they would need a table or a serialised
+  # field. They aren't used anywhere, so just pretend the commit has no parents.
+  def parent_ids
+    []
+  end
+end
diff --git a/app/services/merge_requests/refresh_service.rb b/app/services/merge_requests/refresh_service.rb
index e0e7c43f802..c5f959a1874 100644
--- a/app/services/merge_requests/refresh_service.rb
+++ b/app/services/merge_requests/refresh_service.rb
@@ -68,7 +68,7 @@ module MergeRequests
         if merge_request.source_branch == @branch_name || force_push?
           merge_request.reload_diff(current_user)
         else
-          mr_commit_ids = merge_request.commits_sha
+          mr_commit_ids = merge_request.commit_shas
           push_commit_ids = @commits.map(&:id)
           matches = mr_commit_ids & push_commit_ids
           merge_request.reload_diff(current_user) if matches.any?
@@ -128,7 +128,7 @@ module MergeRequests
       return unless @commits.present?
 
       merge_requests_for_source_branch.each do |merge_request|
-        mr_commit_ids = Set.new(merge_request.commits_sha)
+        mr_commit_ids = Set.new(merge_request.commit_shas)
 
         new_commits, existing_commits = @commits.partition do |commit|
           mr_commit_ids.include?(commit.id)
@@ -144,7 +144,7 @@ module MergeRequests
       return unless @commits.present?
 
       merge_requests_for_source_branch.each do |merge_request|
-        commit_shas = merge_request.commits_sha
+        commit_shas = merge_request.commit_shas
 
         wip_commit = @commits.detect do |commit|
           commit.work_in_progress? && commit_shas.include?(commit.sha)
diff --git a/db/migrate/20170616133147_create_merge_request_diff_commits.rb b/db/migrate/20170616133147_create_merge_request_diff_commits.rb
new file mode 100644
index 00000000000..616464cb470
--- /dev/null
+++ b/db/migrate/20170616133147_create_merge_request_diff_commits.rb
@@ -0,0 +1,20 @@
+class CreateMergeRequestDiffCommits < ActiveRecord::Migration
+  DOWNTIME = false
+
+  def change
+    create_table :merge_request_diff_commits, id: false do |t|
+      t.datetime_with_timezone :authored_date
+      t.datetime_with_timezone :committed_date
+      t.belongs_to :merge_request_diff, null: false, foreign_key: { on_delete: :cascade }
+      t.integer :relative_order, null: false
+      t.binary :sha, null: false, limit: 20
+      t.text :author_name
+      t.text :author_email
+      t.text :committer_name
+      t.text :committer_email
+      t.text :message
+
+      t.index [:merge_request_diff_id, :relative_order], name: 'index_merge_request_diff_commits_on_mr_diff_id_and_order', unique: true
+    end
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index f12fdf903c5..a47a6ae9a98 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -693,6 +693,21 @@ ActiveRecord::Schema.define(version: 20170703102400) do
   add_index "members", ["source_id", "source_type"], name: "index_members_on_source_id_and_source_type", using: :btree
   add_index "members", ["user_id"], name: "index_members_on_user_id", using: :btree
 
+  create_table "merge_request_diff_commits", id: false, force: :cascade do |t|
+    t.datetime "authored_date"
+    t.datetime "committed_date"
+    t.integer "merge_request_diff_id", null: false
+    t.integer "relative_order", null: false
+    t.binary "sha", null: false
+    t.text "author_name"
+    t.text "author_email"
+    t.text "committer_name"
+    t.text "committer_email"
+    t.text "message"
+  end
+
+  add_index "merge_request_diff_commits", ["merge_request_diff_id", "relative_order"], name: "index_merge_request_diff_commits_on_mr_diff_id_and_order", unique: true, using: :btree
+
   create_table "merge_request_diff_files", id: false, force: :cascade do |t|
     t.integer "merge_request_diff_id", null: false
     t.integer "relative_order", null: false
@@ -1563,6 +1578,7 @@ ActiveRecord::Schema.define(version: 20170703102400) do
   add_foreign_key "labels", "projects", name: "fk_7de4989a69", on_delete: :cascade
   add_foreign_key "lists", "boards", name: "fk_0d3f677137", on_delete: :cascade
   add_foreign_key "lists", "labels", name: "fk_7a5553d60f", on_delete: :cascade
+  add_foreign_key "merge_request_diff_commits", "merge_request_diffs", on_delete: :cascade
   add_foreign_key "merge_request_diff_files", "merge_request_diffs", on_delete: :cascade
   add_foreign_key "merge_request_diffs", "merge_requests", name: "fk_8483f3258f", on_delete: :cascade
   add_foreign_key "merge_request_metrics", "ci_pipelines", column: "pipeline_id", on_delete: :cascade
diff --git a/lib/gitlab/cycle_analytics/metrics_tables.rb b/lib/gitlab/cycle_analytics/metrics_tables.rb
index 9d25ef078e8..f5d08c0b658 100644
--- a/lib/gitlab/cycle_analytics/metrics_tables.rb
+++ b/lib/gitlab/cycle_analytics/metrics_tables.rb
@@ -13,6 +13,10 @@ module Gitlab
         MergeRequestDiff.arel_table
       end
 
+      def mr_diff_commits_table
+        MergeRequestDiffCommit.arel_table
+      end
+
       def mr_closing_issues_table
         MergeRequestsClosingIssues.arel_table
       end
diff --git a/lib/gitlab/cycle_analytics/plan_event_fetcher.rb b/lib/gitlab/cycle_analytics/plan_event_fetcher.rb
index 7d342a2d2cb..b260822788d 100644
--- a/lib/gitlab/cycle_analytics/plan_event_fetcher.rb
+++ b/lib/gitlab/cycle_analytics/plan_event_fetcher.rb
@@ -2,40 +2,59 @@ module Gitlab
   module CycleAnalytics
     class PlanEventFetcher < BaseEventFetcher
       def initialize(*args)
-        @projections = [mr_diff_table[:st_commits].as('commits'),
+        @projections = [mr_diff_table[:id],
+                        mr_diff_table[:st_commits],
                         issue_metrics_table[:first_mentioned_in_commit_at]]
 
         super(*args)
       end
 
       def events_query
-        base_query.join(mr_diff_table).on(mr_diff_table[:merge_request_id].eq(mr_table[:id]))
+        base_query
+          .join(mr_diff_table)
+          .on(mr_diff_table[:merge_request_id].eq(mr_table[:id]))
 
         super
       end
 
       private
 
+      def merge_request_diff_commits
+        @merge_request_diff_commits ||=
+          MergeRequestDiffCommit
+            .where(merge_request_diff_id: event_result.map { |event| event['id'] })
+            .group_by(&:merge_request_diff_id)
+      end
+
       def serialize(event)
-        st_commit = first_time_reference_commit(event.delete('commits'), event)
+        commit = first_time_reference_commit(event)
 
-        return unless st_commit
+        return unless commit
 
-        serialize_commit(event, st_commit, query)
+        serialize_commit(event, commit, query)
       end
 
-      def first_time_reference_commit(commits, event)
+      def first_time_reference_commit(event)
+        return nil unless event && merge_request_diff_commits
+
+        commits =
+          if event['st_commits'].present?
+            YAML.load(event['st_commits'])
+          else
+            merge_request_diff_commits[event['id'].to_i]
+          end
+
         return nil if commits.blank?
 
-        YAML.load(commits).find do |commit|
+        commits.find do |commit|
           next unless commit[:committed_date] && event['first_mentioned_in_commit_at']
 
           commit[:committed_date].to_i == DateTime.parse(event['first_mentioned_in_commit_at'].to_s).to_i
         end
       end
 
-      def serialize_commit(event, st_commit, query)
-        commit = Commit.new(Gitlab::Git::Commit.new(st_commit), @project)
+      def serialize_commit(event, commit, query)
+        commit = Commit.new(Gitlab::Git::Commit.new(commit.to_hash), @project)
 
         AnalyticsCommitSerializer.new(project: @project, total_time: event['total_time']).represent(commit)
       end
diff --git a/lib/gitlab/import_export/import_export.yml b/lib/gitlab/import_export/import_export.yml
index 1860352c96d..c8ad3a7a5e0 100644
--- a/lib/gitlab/import_export/import_export.yml
+++ b/lib/gitlab/import_export/import_export.yml
@@ -27,6 +27,7 @@ project_tree:
       - :author
       - :events
     - merge_request_diff:
+      - :merge_request_diff_commits
       - :merge_request_diff_files
     - :events
     - :timelogs
diff --git a/spec/lib/gitlab/import_export/all_models.yml b/spec/lib/gitlab/import_export/all_models.yml
index a5f09f1856e..562f0c2991c 100644
--- a/spec/lib/gitlab/import_export/all_models.yml
+++ b/spec/lib/gitlab/import_export/all_models.yml
@@ -88,7 +88,10 @@ merge_requests:
 - head_pipeline
 merge_request_diff:
 - merge_request
+- merge_request_diff_commits
 - merge_request_diff_files
+merge_request_diff_commits:
+- merge_request_diff
 merge_request_diff_files:
 - merge_request_diff
 pipelines:
diff --git a/spec/lib/gitlab/import_export/project.json b/spec/lib/gitlab/import_export/project.json
index 98c117b4cd8..469a014e4d2 100644
--- a/spec/lib/gitlab/import_export/project.json
+++ b/spec/lib/gitlab/import_export/project.json
@@ -2741,13 +2741,12 @@
       "merge_request_diff": {
         "id": 27,
         "state": "collected",
-        "st_commits": [
+        "merge_request_diff_commits": [
           {
-            "id": "bb5206fee213d983da88c47f9cf4cc6caf9c66dc",
+            "merge_request_diff_id": 27,
+            "relative_order": 0,
+            "sha": "bb5206fee213d983da88c47f9cf4cc6caf9c66dc",
             "message": "Feature conflcit added\n\nSigned-off-by: Dmitriy Zaporozhets \u003cdmitriy.zaporozhets@gmail.com\u003e\n",
-            "parent_ids": [
-              "5937ac0a7beb003549fc5fd26fc247adbce4a52e"
-            ],
             "authored_date": "2014-08-06T08:35:52.000+02:00",
             "author_name": "Dmitriy Zaporozhets",
             "author_email": "dmitriy.zaporozhets@gmail.com",
@@ -2756,11 +2755,10 @@
             "committer_email": "dmitriy.zaporozhets@gmail.com"
           },
           {
-            "id": "5937ac0a7beb003549fc5fd26fc247adbce4a52e",
+            "merge_request_diff_id": 27,
+            "relative_order": 1,
+            "sha": "5937ac0a7beb003549fc5fd26fc247adbce4a52e",
             "message": "Add submodule from gitlab.com\n\nSigned-off-by: Dmitriy Zaporozhets \u003cdmitriy.zaporozhets@gmail.com\u003e\n",
-            "parent_ids": [
-              "570e7b2abdd848b95f2f578043fc23bd6f6fd24d"
-            ],
             "authored_date": "2014-02-27T10:01:38.000+01:00",
             "author_name": "Dmitriy Zaporozhets",
             "author_email": "dmitriy.zaporozhets@gmail.com",
@@ -2769,11 +2767,10 @@
             "committer_email": "dmitriy.zaporozhets@gmail.com"
           },
           {
-            "id": "570e7b2abdd848b95f2f578043fc23bd6f6fd24d",
+            "merge_request_diff_id": 27,
+            "relative_order": 2,
+            "sha": "570e7b2abdd848b95f2f578043fc23bd6f6fd24d",
             "message": "Change some files\n\nSigned-off-by: Dmitriy Zaporozhets \u003cdmitriy.zaporozhets@gmail.com\u003e\n",
-            "parent_ids": [
-              "6f6d7e7ed97bb5f0054f2b1df789b39ca89b6ff9"
-            ],
             "authored_date": "2014-02-27T09:57:31.000+01:00",
             "author_name": "Dmitriy Zaporozhets",
             "author_email": "dmitriy.zaporozhets@gmail.com",
@@ -2782,11 +2779,10 @@
             "committer_email": "dmitriy.zaporozhets@gmail.com"
           },
           {
-            "id": "6f6d7e7ed97bb5f0054f2b1df789b39ca89b6ff9",
+            "merge_request_diff_id": 27,
+            "relative_order": 3,
+            "sha": "6f6d7e7ed97bb5f0054f2b1df789b39ca89b6ff9",
             "message": "More submodules\n\nSigned-off-by: Dmitriy Zaporozhets \u003cdmitriy.zaporozhets@gmail.com\u003e\n",
-            "parent_ids": [
-              "d14d6c0abdd253381df51a723d58691b2ee1ab08"
-            ],
             "authored_date": "2014-02-27T09:54:21.000+01:00",
             "author_name": "Dmitriy Zaporozhets",
             "author_email": "dmitriy.zaporozhets@gmail.com",
@@ -2795,11 +2791,10 @@
             "committer_email": "dmitriy.zaporozhets@gmail.com"
           },
           {
-            "id": "d14d6c0abdd253381df51a723d58691b2ee1ab08",
+            "merge_request_diff_id": 27,
+            "relative_order": 4,
+            "sha": "d14d6c0abdd253381df51a723d58691b2ee1ab08",
             "message": "Remove ds_store files\n\nSigned-off-by: Dmitriy Zaporozhets \u003cdmitriy.zaporozhets@gmail.com\u003e\n",
-            "parent_ids": [
-              "c1acaa58bbcbc3eafe538cb8274ba387047b69f8"
-            ],
             "authored_date": "2014-02-27T09:49:50.000+01:00",
             "author_name": "Dmitriy Zaporozhets",
             "author_email": "dmitriy.zaporozhets@gmail.com",
@@ -2808,11 +2803,10 @@
             "committer_email": "dmitriy.zaporozhets@gmail.com"
           },
           {
-            "id": "c1acaa58bbcbc3eafe538cb8274ba387047b69f8",
+            "merge_request_diff_id": 27,
+            "relative_order": 5,
+            "sha": "c1acaa58bbcbc3eafe538cb8274ba387047b69f8",
             "message": "Ignore DS files\n\nSigned-off-by: Dmitriy Zaporozhets \u003cdmitriy.zaporozhets@gmail.com\u003e\n",
-            "parent_ids": [
-              "ae73cb07c9eeaf35924a10f713b364d32b2dd34f"
-            ],
             "authored_date": "2014-02-27T09:48:32.000+01:00",
             "author_name": "Dmitriy Zaporozhets",
             "author_email": "dmitriy.zaporozhets@gmail.com",
diff --git a/spec/lib/gitlab/import_export/project_tree_restorer_spec.rb b/spec/lib/gitlab/import_export/project_tree_restorer_spec.rb
index c11b15a811b..d50d238ddcd 100644
--- a/spec/lib/gitlab/import_export/project_tree_restorer_spec.rb
+++ b/spec/lib/gitlab/import_export/project_tree_restorer_spec.rb
@@ -95,6 +95,11 @@ describe Gitlab::ImportExport::ProjectTreeRestorer, services: true do
         expect(MergeRequestDiffFile.where.not(diff: nil).count).to eq(9)
       end
 
+      it 'has the correct data for merge request diff commits in serialised and table formats' do
+        expect(MergeRequestDiff.where.not(st_commits: nil).count).to eq(7)
+        expect(MergeRequestDiffCommit.count).to eq(6)
+      end
+
       it 'has the correct time for merge request st_commits' do
         st_commits = MergeRequestDiff.where.not(st_commits: nil).first.st_commits
 
diff --git a/spec/lib/gitlab/import_export/project_tree_saver_spec.rb b/spec/lib/gitlab/import_export/project_tree_saver_spec.rb
index e52f79513f1..22a65e24f26 100644
--- a/spec/lib/gitlab/import_export/project_tree_saver_spec.rb
+++ b/spec/lib/gitlab/import_export/project_tree_saver_spec.rb
@@ -87,6 +87,10 @@ describe Gitlab::ImportExport::ProjectTreeSaver, services: true do
         expect(saved_project_json['merge_requests'].first['merge_request_diff']['merge_request_diff_files']).not_to be_empty
       end
 
+      it 'has merge request diff commits' do
+        expect(saved_project_json['merge_requests'].first['merge_request_diff']['merge_request_diff_commits']).not_to be_empty
+      end
+
       it 'has merge requests comments' do
         expect(saved_project_json['merge_requests'].first['notes']).not_to be_empty
       end
diff --git a/spec/lib/gitlab/import_export/safe_model_attributes.yml b/spec/lib/gitlab/import_export/safe_model_attributes.yml
index 697ddf52af9..b4a7e956686 100644
--- a/spec/lib/gitlab/import_export/safe_model_attributes.yml
+++ b/spec/lib/gitlab/import_export/safe_model_attributes.yml
@@ -172,6 +172,17 @@ MergeRequestDiff:
 - real_size
 - head_commit_sha
 - start_commit_sha
+MergeRequestDiffCommit:
+- merge_request_diff_id
+- relative_order
+- sha
+- authored_date
+- committed_date
+- author_name
+- author_email
+- committer_name
+- committer_email
+- message
 MergeRequestDiffFile:
 - merge_request_diff_id
 - relative_order
diff --git a/spec/models/ci/build_spec.rb b/spec/models/ci/build_spec.rb
index 2b10791ad6d..431fcda165d 100644
--- a/spec/models/ci/build_spec.rb
+++ b/spec/models/ci/build_spec.rb
@@ -863,7 +863,7 @@ describe Ci::Build, :models do
         pipeline2 = create(:ci_pipeline, project: project)
         @build2 = create(:ci_build, pipeline: pipeline2)
 
-        allow(@merge_request).to receive(:commits_sha)
+        allow(@merge_request).to receive(:commit_shas)
           .and_return([pipeline.sha, pipeline2.sha])
         allow(MergeRequest).to receive_message_chain(:includes, :where, :reorder).and_return([@merge_request])
       end
diff --git a/spec/models/merge_request_diff_commit_spec.rb b/spec/models/merge_request_diff_commit_spec.rb
new file mode 100644
index 00000000000..dbfd1526518
--- /dev/null
+++ b/spec/models/merge_request_diff_commit_spec.rb
@@ -0,0 +1,15 @@
+require 'rails_helper'
+
+describe MergeRequestDiffCommit, type: :model do
+  let(:merge_request) { create(:merge_request) }
+  subject { merge_request.commits.first }
+
+  describe '#to_hash' do
+    it 'returns the same results as Commit#to_hash, except for parent_ids' do
+      commit_from_repo = merge_request.project.repository.commit(subject.sha)
+      commit_from_repo_hash = commit_from_repo.to_hash.merge(parent_ids: [])
+
+      expect(subject.to_hash).to eq(commit_from_repo_hash)
+    end
+  end
+end
diff --git a/spec/models/merge_request_diff_spec.rb b/spec/models/merge_request_diff_spec.rb
index 4ad4abaa572..edc2f4bb9f0 100644
--- a/spec/models/merge_request_diff_spec.rb
+++ b/spec/models/merge_request_diff_spec.rb
@@ -98,7 +98,7 @@ describe MergeRequestDiff, models: true do
     end
 
     it 'saves empty state' do
-      allow_any_instance_of(MergeRequestDiff).to receive(:commits)
+      allow_any_instance_of(MergeRequestDiff).to receive_message_chain(:compare, :commits)
         .and_return([])
 
       mr_diff = create(:merge_request).merge_request_diff
@@ -107,14 +107,14 @@ describe MergeRequestDiff, models: true do
     end
   end
 
-  describe '#commits_sha' do
+  describe '#commit_shas' do
     it 'returns all commits SHA using serialized commits' do
       subject.st_commits = [
         { id: 'sha1' },
         { id: 'sha2' }
       ]
 
-      expect(subject.commits_sha).to eq(%w(sha1 sha2))
+      expect(subject.commit_shas).to eq(%w(sha1 sha2))
     end
   end
 
diff --git a/spec/models/merge_request_spec.rb b/spec/models/merge_request_spec.rb
index d91f1f1a11c..ea405fabff0 100644
--- a/spec/models/merge_request_spec.rb
+++ b/spec/models/merge_request_spec.rb
@@ -720,14 +720,14 @@ describe MergeRequest, models: true do
     subject { create :merge_request, :simple }
   end
 
-  describe '#commits_sha' do
+  describe '#commit_shas' do
     before do
-      allow(subject.merge_request_diff).to receive(:commits_sha)
+      allow(subject.merge_request_diff).to receive(:commit_shas)
         .and_return(['sha1'])
     end
 
     it 'delegates to merge request diff' do
-      expect(subject.commits_sha).to eq ['sha1']
+      expect(subject.commit_shas).to eq ['sha1']
     end
   end
 
@@ -752,7 +752,7 @@ describe MergeRequest, models: true do
   describe '#all_pipelines' do
     shared_examples 'returning pipelines with proper ordering' do
       let!(:all_pipelines) do
-        subject.all_commits_sha.map do |sha|
+        subject.all_commit_shas.map do |sha|
           create(:ci_empty_pipeline,
                  project: subject.source_project,
                  sha: sha,
@@ -794,16 +794,16 @@ describe MergeRequest, models: true do
     end
   end
 
-  describe '#all_commits_sha' do
+  describe '#all_commit_shas' do
     context 'when merge request is persisted' do
-      let(:all_commits_sha) do
+      let(:all_commit_shas) do
         subject.merge_request_diffs.flat_map(&:commits).map(&:sha).uniq
       end
 
       shared_examples 'returning all SHA' do
         it 'returns all SHA from all merge_request_diffs' do
           expect(subject.merge_request_diffs.size).to eq(2)
-          expect(subject.all_commits_sha).to eq(all_commits_sha)
+          expect(subject.all_commit_shas).to eq(all_commit_shas)
         end
       end
 
@@ -834,7 +834,7 @@ describe MergeRequest, models: true do
         end
 
         it 'returns commits from compare commits temporary data' do
-          expect(subject.all_commits_sha).to eq [commit, commit]
+          expect(subject.all_commit_shas).to eq [commit, commit]
         end
       end
 
@@ -842,7 +842,7 @@ describe MergeRequest, models: true do
         subject { build(:merge_request) }
 
         it 'returns array with diff head sha element only' do
-          expect(subject.all_commits_sha).to eq [subject.diff_head_sha]
+          expect(subject.all_commit_shas).to eq [subject.diff_head_sha]
         end
       end
     end