deleting records from mnesia

Serge Aleynikov <>
Wed Jul 19 19:46:54 CEST 2006


Hmm... I was hoping there was a solution using mnesia:activity call that 
wouldn't require patching.  :-(

Can this function be exported in the future OTP release?

Serge


Ulf Wiger (TN/EAB) wrote:
> I tried with my slightly patched version:
> 
> ()2> mnesia:create_table(test,[]). 
> {atomic,ok}
> ()3> [mnesia:dirty_write({test,I,v}) || I <-
> lists:seq(1,10)].
> [ok,ok,ok,ok,ok,ok,ok,ok,ok,ok]
> ()4> ets:tab2list(test).
> [{test,1,v},
>  {test,10,v},
>  {test,2,v},
>  {test,3,v},
>  {test,8,v},
>  {test,4,v},
>  {test,5,v},
>  {test,7,v},
>  {test,6,v},
>  {test,9,v}]
> ()5> mnesia_schema:schema_transaction(
>   fun() -> mnesia_schema:do_clear_table(test),
>            mnesia:write({test,1,a}) end).
> {atomic,ok}
> ()6> ets:tab2list(test).
> [{test,1,a}]
> 
> 
> The only change that's required is that 
> mnesia_schema:do_clear_table/1 is exported.
> 
> BR,
> Ulf W
>            
> 
>> -----Original Message-----
>> From:  
>> [mailto:] On Behalf Of Serge 
>> Aleynikov
>> Sent: den 19 juli 2006 18:17
>> To: Erlang Users' List
>> Subject: deleting records from mnesia
>>
>> Hi,
>>
>> Is there a way to delete all records from a table in mnesia 
>> within a transaction?
>>
>> This won't work because mnesia:clean_table/1 doesn't support nested
>> transactions:
>>
>> F = fun() ->
>>          {atomic, ok} = mnesia:clear_table(Tab),
>>          insert_records(Tab)
>>      end,
>> mnesia:transaction(F).
>>
>> I know that I could do this:
>>
>> [mnesia:delete(Tab, Key, sticky_write) || Key <- 
>> mnesia:all_keys(Tab)].
>>
>> but is there a way to truncate table in one shot within a 
>> transaction instead of iterating over all records?
>>
>> Serge
>>
> 


-- 
Serge Aleynikov
R&D Telecom, MIS, IDT Corp
Tel: +1 (973) 438-3436
Fax: +1 (973) 438-1464



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