Merge branch 'fix-migration' into 'master'

Delete rename trigger before creating to prevent error

See merge request gitlab-org/gitlab-ce!32147

lib/gitlab/database/migration_helpers.rb

@@ -746,6 +746,11 @@ module Gitlab
         VOLATILE
         EOF
 
+        execute <<-EOF.strip_heredoc
+        DROP TRIGGER IF EXISTS #{trigger}
+        ON #{table}
+        EOF
+
         execute <<-EOF.strip_heredoc
         CREATE TRIGGER #{trigger}
         BEFORE INSERT OR UPDATE

spec/lib/gitlab/database/migration_helpers_spec.rb

@@ -618,11 +618,19 @@ describe Gitlab::Database::MigrationHelpers do
       expect(model).to receive(:execute)
         .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