1 files changed, 83 insertions, 0 deletions
diff --git a/db/migrate/20170516153305_migrate_assignee_to_separate_table.rb b/db/migrate/20170516153305_migrate_assignee_to_separate_table.rb
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+++ b/db/migrate/20170516153305_migrate_assignee_to_separate_table.rb
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+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class MigrateAssigneeToSeparateTable < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  # Set this constant to true if this migration requires downtime.
+  DOWNTIME = false
+
+  # When a migration requires downtime you **must** uncomment the following
+  # constant and define a short and easy to understand explanation as to why the
+  # migration requires downtime.
+  # DOWNTIME_REASON = ''
+
+  # When using the methods "add_concurrent_index", "remove_concurrent_index" or
+  # "add_column_with_default" you must disable the use of transactions
+  # as these methods can not run in an existing transaction.
+  # When using "add_concurrent_index" or "remove_concurrent_index" methods make sure
+  # that either of them is the _only_ method called in the migration,
+  # any other changes should go in a separate migration.
+  # This ensures that upon failure _only_ the index creation or removing fails
+  # and can be retried or reverted easily.
+  #
+  # To disable transactions uncomment the following line and remove these
+  # comments:
+  # disable_ddl_transaction!
+
+  def up
+    drop_table(:issue_assignees) if table_exists?(:issue_assignees)
+
+    if Gitlab::Database.mysql?
+      execute <<-EOF
+        CREATE TABLE issue_assignees AS
+          SELECT assignee_id AS user_id, id AS issue_id FROM issues WHERE assignee_id IS NOT NULL
+      EOF
+    else
+      ActiveRecord::Base.transaction do
+        execute('LOCK TABLE issues IN EXCLUSIVE MODE')
+
+        execute <<-EOF
+          CREATE TABLE issue_assignees AS
+            SELECT assignee_id AS user_id, id AS issue_id FROM issues WHERE assignee_id IS NOT NULL
+        EOF
+
+        execute <<-EOF
+            CREATE OR REPLACE FUNCTION replicate_assignee_id()
+            RETURNS trigger AS
+            $BODY$
+            BEGIN
+              if OLD IS NOT NULL AND OLD.assignee_id IS NOT NULL THEN
+                  DELETE FROM issue_assignees WHERE issue_id = OLD.id;
+              END IF;
+
+              if NEW.assignee_id IS NOT NULL THEN
+                  INSERT INTO issue_assignees (user_id, issue_id) VALUES (NEW.assignee_id, NEW.id);
+              END IF;
+
+              RETURN NEW;
+            END;
+            $BODY$
+            LANGUAGE 'plpgsql'
+            VOLATILE;
+
+            CREATE TRIGGER replicate_assignee_id
+            BEFORE INSERT OR UPDATE OF assignee_id
+            ON issues
+            FOR EACH ROW EXECUTE PROCEDURE replicate_assignee_id();
+        EOF
+      end
+    end
+  end
+
+  def down
+    drop_table(:issue_assignees) if table_exists?(:issue_assignees)
+
+    if Gitlab::Database.postgresql?
+      execute <<-EOF
+        DROP TRIGGER IF EXISTS replicate_assignee_id ON issues;
+        DROP FUNCTION IF EXISTS replicate_assignee_id();
+      EOF
+    end
+  end
+end