Drop existing trigger before creating new onefix-migration

- When renaming a column concurrently, drop any existing trigger before
attempting to create a new one.

When running migration specs multiple times (as it happens during
local development), the down method of previous migrations are called.
If any of the called methods contains a call to
rename_column_concurrently, a trigger will be created and not removed.
So, the next time a migration spec is run, if the same down method is
executed again, it will cause an error when attempting to create the
trigger (since it already exists). Dropping the trigger if it already
exists will prevent this problem.

2 files changed, 13 insertions, 0 deletions

diff --git a/lib/gitlab/database/migration_helpers.rb b/lib/gitlab/database/migration_helpers.rb
index 9bba4f6ce1e..8bc45f6e78c 100644
--- a/lib/gitlab/database/migration_helpers.rb
+++ b/lib/gitlab/database/migration_helpers.rb
@@ -747,6 +747,11 @@ module Gitlab
         EOF
 
         execute <<-EOF.strip_heredoc
+        DROP TRIGGER IF EXISTS #{trigger}
+        ON #{table}
+        EOF
+
+        execute <<-EOF.strip_heredoc
         CREATE TRIGGER #{trigger}
         BEFORE INSERT OR UPDATE
         ON #{table}
diff --git a/spec/lib/gitlab/database/migration_helpers_spec.rb b/spec/lib/gitlab/database/migration_helpers_spec.rb
index 2731fc8573f..fe44b09aa24 100644
--- a/spec/lib/gitlab/database/migration_helpers_spec.rb
+++ b/spec/lib/gitlab/database/migration_helpers_spec.rb
@@ -619,10 +619,18 @@ describe Gitlab::Database::MigrationHelpers do
         .with(/CREATE OR REPLACE FUNCTION foo()/m)
 
       expect(model).to receive(:execute)
+        .with(/DROP TRIGGER IF EXISTS foo/m)
+
+      expect(model).to receive(:execute)
         .with(/CREATE TRIGGER foo/m)
 
       model.install_rename_triggers_for_postgresql('foo', :users, :old, :new)
     end
+
+    it 'does not fail if trigger already exists' do
+      model.install_rename_triggers_for_postgresql('foo', :users, :old, :new)
+      model.install_rename_triggers_for_postgresql('foo', :users, :old, :new)
+    end
   end
 
   describe '#remove_rename_triggers_for_postgresql' do