reading mnesia tables where key is a tuple and the search criteria contains '_' underscores

I have a 3rd or 4th normal form mnesia database and the table in question should be a key/value hash, however, the architect put the keys and values in the key portion of the record.

It looks something like:

-record(idx,{key,value}).
...
Invoice = 1,
Date = now(),
K1 = {?NORMAL_TYPE1,Invoice,Date},
mnesia:write(#idx{key=K1}).
...

So the question 开发者_开发技巧is... if I only know the Invoice number can I still get the data from the DB in the same time as if the Invoice was the only key instead of the tuple?

K2 = {?NORMAL_TYPE1,Invoice,'_'},
Rec = mnesia:read(#idx{key=K2}).

The short answer: No.

The longer answer: You may have a chance if the table is an orderet_set or something such, but I would not count on it.

The Aside: mnesia is usually not too effective w.r.t. normalized data. It is usually better to use standard RDBMS systems for that.

You can use mnesia:match_object/1/3 and mnesia:select/2/3/4/1 where you provide a pattern which can contain '_' as a don't care variable. I assume that is what you meant.