Add table for merge request commits

This is an ID-less table with just three columns: an association to the merge
request diff the commit belongs to, the relative order of the commit within the
merge request diff, and the commit SHA itself.

Previously we stored much more information about the commits, so that we could
display them even when they were deleted from the repo. Since 8.0, we ensure
that those commits are kept around for as long as the target repo itself is, so
we don't need to duplicate that data in the database.

1 files changed, 38 insertions, 0 deletions

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