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<  Erlang  ~  How do you write an mnesia update query?
LRP
Posted: Mon Oct 13, 2008 3:04 am Reply with quote
Joined: 08 Oct 2008 Posts: 8 Location: Boston, MA.
Hello,

At risk of sounding desperate (fast getting there), I'm rephrasing the question I posted on October 8.

Suppose I have the following record structure:

-record(news,
{newsID,
head,
copy,
dateline}).

...where head and copy are binaries. How do I write a mnesia query to update the head and/or copy fields?

Table is initialized as follows:

init_newswire() ->
% Initialize database
mnesia:create_schema([node()]),
mnesia:start(),
try
mnesia:table_info(news, type)
catch
exit: _ ->
mnesia:create_table(news, [
{attributes, record_info(fields, news)},
{type, set},
{disc_copies, [node()] }
])
end.


Seems to me that every good erlang programmer would know how to do this, but there were no responses to my post and I come up blank in my Google searches.

Many thanks,

LRP
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klaar
Posted: Wed Oct 15, 2008 10:18 pm Reply with quote
User Joined: 06 Oct 2008 Posts: 11 Location: Göteborg/Sweden
It depends upon which type of table that is used. If you are using (set|ordered_set) then just write it again, just like you did the first time. The old version will be overwritten, so make sure that you have read out _all_ of the data before you do this Smile

http://www.erlang.org/doc/apps/mnesia/index.html
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LRP
Posted: Wed Oct 15, 2008 10:28 pm Reply with quote
Joined: 08 Oct 2008 Posts: 8 Location: Boston, MA.
Many thanks.

I did scour the menesia reference manual. But must have missed... or misunderstood how to update records.

Thanks again,

LRP
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Mazen
Posted: Thu Oct 16, 2008 7:30 am Reply with quote
User Joined: 20 Jul 2006 Posts: 164 Location: London
My excuse:

The word "query" threw me off...

Very Happy
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