[erlang-bugs] Documentation error for mnesia:activity/4

Bernard Duggan <>
Fri Jun 21 07:57:00 CEST 2013


Hi list,
This isn't strictly a bug per se, not in the code, anyway, but it it
will certainly lead to them (take my word for it ;)). The documented
list of functions that an AccessMod passed to mnesia:activity/4 needs to
implement is incomplete. It appears, at the very least, to need select/5
added to it. A glance through the code suggests to me that all of the
following need to be added:

foldl/6
foldr/6
select/5,6
select_cont/3
clear_table/4

I discovered this while moving our code to R16 - previously I'd used
-extends(mnesia) in our AccessMod, so anything implemented in the mnesia
module was automatically provided by my module. However when I removed
the -extends and explicitly provided pass-through implementations for
the functions I hadn't implemented (based on the list in the docs) I
ended up getting an undef crash on a call to my_access_mod:select/5.
(For what it's worth, I ended up going back to -extends, using the
pmod_pt parse transform).

I'm happy to fix the docs myself, I partly just wanted to double check
that I'd read the code correctly and that all those functions really are
required.

Cheers,

Bernard

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