I am trying to build a deb package A that depends on another deb package B that is downloaded from URL and then installed.

The obvious solution I tried was putting the script that downloads and installs package B in the postinst/preinst scripts of package A.

wget package_url
dpkg -i package_name.deb

But it gives me an error dpkg: error: dpkg database lock is locked by another process because the lock is already locked when installing package A.

How can manage to do this? Is there a way to declare dependencies from the deb URL in the package control file?