[erlang-questions] Mnemosyne query problem

Ulf Wiger (TN/EAB) <>
Fri Jan 11 16:36:09 CET 2008


One way to do this is to use the exprecs parse transform,
http://forum.trapexit.org/viewtopic.php?p=21790#21790

which would allow you to write:

Q = query
     [ Entity
     || Entity <- table(TableName),
        [AttributeValue] == M:'#get-'([AttributeName], Entity)
     ]

where M is some module in which you've declared and
exported the record definition of Entity.

(Not that I've tested this, but I believe it should work.
It's been a few years since I played with Mnemosyne
queries.)

BTW, for this type of query, you should really use QLC
instead, since Mnemosyne is no longer supported.

BR,
Ulf W

Matej Kosik skrev:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> Friends,
> 
> I would like to perform the following query:
> 
>     TableName = circuit,
>     AttributeValue = ipe_od,
>     AttributeName = type,
>     F = fun() ->
>          Q = query
>             [  Entity
>             || Entity <- table(TableName),
>                Entity.AttributeName=AttributeValue
>             ]
>          end,
>          mnemosyne:eval(Q)
>     end,
>     {atomic, Entities} = mnesia:transaction(F).
> 
> Unfortunatelly, compilator rejects its. I would like to write a code that selects particular
> entities from a given TableName whose AttributeName has a given AttributeValue.
> 
> Since Erlang does not accept bound variables here
> 
> 	Entity.AttributeName=AttributeValue
> 
> I must literally hard-wire particular attribute name. For example
> 
> 	Entity.od_id=AttributeValue





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