difficulty getting mnesia to work with cowboy web backend
Sun Oct 25 00:31:04 CEST 2020
i'm building a web backend using cowboy and mnesia.
at this point i'm running mnesia on only one node and don't need
distributed mnesia for the foreseeable future.
i installed cowboy and bootstrapped my cowboy app per the instructions
in the cowboy user guide on ninenines.eu.
i run my cowboy app with "make run" which uses the rather involved
"erlang.mk" makefile in the ninenines repo.
i need to specify that my cowboy app is dependent on the mnesia app.
i edited "Makefile" in my app's root directory and added "mnesia" to the
when i then execute "make run" i get "Error: Unknown or invalid
when i execute "make run", erlang.mk appears to automatically construct
ebin/<my_app>.app - no doubt using some other input which i haven't
if i manually edit ebin/<my_app>.app to add mnesia to the "applications"
tuple then mnesia runs as expected.
how do i specify that my cowboy app is dependent on mnesia such that the
<my_app>.app config file gets constructed correctly every time i execute
but wait, there's more... :(
i constructed an mnesia schema in a particular directory under the
cowboy app directory hierarchy.
i need to specify this directory to mnesia which apparently can only be
done using the "-mnesia dir <Dir>" option to erl.
is there any other way to do this?
why isn't the schema directory an argument to mnesia:start()?
that seems much more intuitive.
back again to the gigantic erlang.mk where i found where the erl command
that runs erts which in turn runs my cowboy app.
i added the "-mnesia dir <Dir>" option to the erl command line, but
mnesia is still not finding my pre-defined schema - it's running in
ram-only mode which means it didn't find a pre-defined schema.
i can run erl manually in the directory above the directory where my
pre-defined schema is located, and see that the schema is there and it's
configured as i expected.
when executing "make run" (navigating through the erlang.mk maze), how
do i get mnesia to see the schema directory when it's launched by the
do i need to pass an argument to some start() function?
does erlang.mk need to be modified or one of its inputs modified?
thanx for any assistance!
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