how to code spec file to install a file on system only if a file is missing

I am new to rpm building and for the past week I am trying to code a spec file to install a file on the system only if a specific files is missing. Here is a snippet %global homedir %{_var}/lib/test Source10: main.db Source11: back.db %files data %defattr(-,%{updateuser},%{updateuser},-) %config(noreplace) %verify(not size md5 mtime) %{homedir}/*.db I would like to add a condition where, If file /var/lib/test/file1.txt is missing, install /var/lib/test/back.db I am aware I need to use the %files macro but so far I am not able to figure out how to write the if condition