Mnesia bug?

Rudolph van Graan <>
Mon Feb 2 16:58:10 CET 2004


It seems as though mnesia (R9C) does not allow updates to user 
properties of a table during a transaction... Any ideas?

-module(mnesia_bug).
-export([run/0]).

run() ->
   mnesia:delete_table(abc),							%Drop Table
   {atomic,ok} = 
mnesia:create_table(abc,[{attributes,[a,b,c]}]),		%Create a simple 
table
   mnesia:write_table_property(abc,{some_value,1}),				%Write a value to 
the table properties
   {some_value,1} = mnesia:read_table_property(abc,some_value),			%Check 
that it is correct
   io:format("Value of 1written and verified\n",[]),
   F = fun() ->									%Now modify the value in the fun
	  io:format("Changing value to 2\n",[]),
	  mnesia:write_table_property(abc,{some_value,2}),
	  {some_value,New_value_1} = 
mnesia:read_table_property(abc,some_value),%Verify it is ok
	  case New_value_1 of
	    2 ->
	      io:format("Value has changed to 2 - this is ok\n",[]);
	    Other ->
	      io:format("Value is ~p - this is NOT ok\n",[Other])
	  end
       end,
   {atomic,ok} = mnesia:transaction(F),						%Run the fun
   io:format("Now read it back again...\n",[]),
   {some_value,Last_Value} = 
mnesia:read_table_property(abc,some_value),			%And read it back again
   io:format("Value is ~p\n",[Last_Value])  .


Rudolph van Graan
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