Mnesia odd behaviour - delete_object

Chandrashekhar Mullaparthi <>
Tue Oct 30 14:43:42 CET 2001


Looks like a bug. When the attributes are not specified during table
creation, it assumes [key, val]. Interestingly, this problem seems to occur
only when the value for key is 'key'. I tried F1 with {a, key1, [1,2]} and
delete_object works fine.

This seems to point that the problem is in the function
erlang:db_match_erase/2

> -----Original Message-----
> From: Martin Bjorklund [mailto:]
> Sent: 30 October 2001 12:50
> To: 
> Subject: Mnesia odd behaviour - delete_object
> 
> 
> I've got a funny mnesia situation.  The problem is delete_object
> vs. delete.
> 
> I've got a simple 'set' table a:
> 
>   mnesia:create_table(a, []).
> 
> Add an object:
> 
>   mnesia:dirty_write({a, key, [1,2]}).
> 
> Now, I've got this fun:
> 
>    F1 = fun() -> 
>             mnesia:write({a, key, [1]}),  % modify the one&only object
>             [X] = mnesia:read({a, key}),  % read it
>             mnesia:delete_object(X)       % delete the one&only object
>         end.
> 
> After executing F1 within a transaction, my table still contains the
> original object.  Since 'a' is a set, I'd think that the object would
> be removed.
> 
> After executing F1 'async_dirty', the object is removed.
> 
> 
>    F2 = fun() -> 
>             mnesia:write({a, key, [1]}),  % modify the one&only object
>             mnesia:delete({a, key})       % delete the one&only object
>         end.
> 
> After executing F2 within a transaction, the object is removed.
> 
> 
> Can someone explain this behaviour??
> 
> 
> I've tested on mnesia 3.9.2 and 4.0.  It's probably not a bug, but I
> cannot come up with a interpretation that feels consistent...
> 
> 
> 
> /martin
> 



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