How to wrap app with data? (for db migration)

Help
1

For self-hosting i would like to wrap a db migration application like dbmate
with data (sql scripts); my goal is to write a one-off migration systemd service. I tried

pkgs.stdenv.mkDerivation {
          pname = "dbmigrate";
          version = "1.0.0";
          src = ./.; 
          buildInputs = [ pkgs.dbmate pkgs.makeWrapper ];
          installPhase = ''
            mkdir -p $out/db/migrations
            cp -r ${./db/migrations}/* $out/db/migrations/
          '';
          postFixup = ''
            makeWrapper "${pkgs.dbmate}/bin/dbmate" $out/bin/dbmigrate \
              --set DBMATE_MIGRATIONS_DIR $out/db/migrations \
              --add-flags "--no-dump-schema" \
              --add-flags "--wait" \
              --add-flags "up"
          '';
        };

which builds ./result folder structure that looks correct, but doesn’t do anything when run (or at least i don’t receive any error message). What am i doing wrong or rather what is the best approach for such a setup?