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<  Advanced Erlang/OTP  ~  Mnesia - is thera generic way to show a tables content ?
brett hallett
Posted: Mon Aug 27, 2007 12:22 am Reply with quote
User Joined: 21 Aug 2007 Posts: 21
I'm working my way thru the Mnesia manual, and cant figure out if there is a generic way to list a tables content.

The examples are very specific in that they select
a particular record(s) eg: the 'all-Females' example.

What I want is to be able to simply list off all records (and fields)
in a particular table using the least complex 'query',


The equivalent of SQL's "Select * from tablename", and NO I'm not wanting to use SQl Laughing
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michal
Posted: Mon Aug 27, 2007 7:42 pm Reply with quote
User Joined: 20 Jul 2006 Posts: 44 Location: London
Hi,
You can get all the keys of some table using mnesia:dirty_all_keys/1 function ( http://www.erlang.org/doc/man/mnesia.html#dirty_all_keys/1 ). If you want to get not only the keys but also whole records you can call mnesia:dirty_read/2 for each key. Combining the above two functions in a list comprehension could look like this:

[mnesia:dirty_read(TableName, Key) || Key <- mnesia:dirty_all_keys(TableName)].

If you work in Erlang shell, you have mnesia running and you simply want to print out all the records you can use:

ets:tab2list(TableName).

Michal

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brett hallett
Posted: Mon Aug 27, 2007 11:45 pm Reply with quote
User Joined: 21 Aug 2007 Posts: 21
Thanks , thats exactly what I need.
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khigia
Posted: Tue Aug 28, 2007 8:47 am Reply with quote
User Joined: 27 Mar 2007 Posts: 52
I often use the tv module to inspect ETS or Mnesia tables.
Code:
(erlnode@erlhost)1> tv:start().
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