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| icimjs at loop.com |
 Posted: Fri Jun 18, 1999 6:46 am |
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Guest
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Hi everyone,
first of all, thank you all for the useful responses.
Torbjorn Tornkvist wrote:
>Great ! How did it go ?
We're still waiting for their new computers to arrive, which gives me a
little time to improve my code.
We've decided to use Linux instead of MS Windows :-)
Here's what I'm currently wrestling with:
Right now I have the following "generic" function:
list_glue() ->
Fun = fun() ->
Q = query [G.product_name || G <- table(glue)] end,
mnemosyne:eval(Q)
end,
mnesia:transaction(Fun).
Fine.
What I'd like to do is something like this (which doesn't work):
list_generic(Table, Tuple, Condition) ->
Fun = fun() ->
Q = query( Tuple || ??? <- table(Table),
Condition ] end,
mnemosyne:eval(Q)
end,
mnesia:transaction(Fun).
Then I would want to be able to call it with something like this ... from
the shell
list_generic(glue,
{glue, Product_Name, _ , _ , _ ,},
{glue, _ , _ , _ , "Some glue manufacturer here"} ).
where the record is
-record(glue, {name, id, reference, manufacturer}).
in order to get all glue products this particular manufacturer carries. On
a different occasion I want to use the same function list_generic, to
identify the type of glue I need to use for a certain type of floor
covering, something like this
list_generic(linoleum,
{linoleum, Glue_ID, _ , _ },
{linoleum, _ , "00134", _ } ).
where the record is
-record(linoleum, {glue_reference, linoleum_id, manufacturer}).
How could something like this be implemented? Is it at all possible? Will I
need to use
record_info(fields, Rec) -> [Names].
in the list_generic/3 function in order to construct a record and assign
the values from the tuples Tuple and Condition to the record? How do I do
that dynamically, i.e. during runtime?
I think I'm close to the solution, but I'm still struggling with the
documentation to get it right.
Is there a better way to achieve the same effect?
TIA,
Elan
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| ulf.wiger at etx.ericsson |
| Posted: Fri Jun 18, 1999 8:29 am |
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I'll just address one piece of the puzzle, since it's one that I know
off the top of my head.
Elan wrote:
>
[...]
> list_generic(glue,
> {glue, Product_Name, _ , _ , _ ,},
> {glue, _ , _ , _ , "Some glue manufacturer here"} ).
>
> where the record is
> -record(glue, {name, id, reference, manufacturer}).
>
If you want such a simple query, you can skip mnemosyne and use
match_object directly. I'm afraid that you'll have to use some kind of
parser otherwise (haven't kept up with mnemosyne lately).
Take the following code for example
(written in all haste, apologies):
-module(mntest).
-export([q/3]).
q(Tab, Fields, Select) ->
Fs = fields_info(Tab),
Wild = mnesia:table_info(Tab, wild_pattern),
Sel = insert_select(Fs, Select, Wild, 2),
Proj = calc_project_positions(Fs, Fields, 2),
{atomic, Objs} = mnesia:transaction(
fun() ->
mnesia:match_object(Sel)
end),
[project(Proj, O) || O <- Objs].
insert_select([H|T], Sel, Rec, Pos) ->
case lists:keysearch(H, 1, Sel) of
{value, {_, Val}} ->
insert_select(T, Sel, setelement(Pos, Rec, Val), Pos+1);
false ->
insert_select(T, Sel, Rec, Pos+1)
end;
insert_select([], _, Rec, _) ->
Rec.
calc_project_positions(_, all, _) -> all;
calc_project_positions([H|T], Fields, Pos) ->
case lists:member(H, Fields) of
true ->
[Pos|calc_project_positions(T, Fields, Pos+1)];
false ->
calc_project_positions(T, Fields, Pos+1)
end;
calc_project_positions([], _, _) ->
[].
project(all, O) -> O;
project(Flds, O) ->
P = project1(Flds, O),
case P of
[X] -> X;
_ ->
list_to_tuple(project1(Flds, O))
end.
project1([H|T], O) ->
[element(H, O)|project1(T, O)];
project1([], _) ->
[].
fields_info(glue) -> record_info(fields, glue);
fields_info(linoleum) -> record_info(fields, linoleum).
- - - - - - - -
Example:
(foo_at_avc343)44> mntest:q(glue, [name], [{manufacturer,m1}]).
[g2,g1]
(foo_at_avc343)45> mntest:q(glue, [name,id], [{manufacturer,m1}]).
[{g2,2},{g1,1}]
(foo_at_avc343)46> mntest:q(glue, all, []).
[{glue,g4,4,undefined,m4},
{glue,g3,3,undefined,m3},
{glue,g2,2,undefined,m1},
{glue,g1,1,undefined,m1}]
--
Ulf Wiger, Chief Designer AXD 301 <ulf.wiger_at_etx.ericsson.se>
Ericsson Telecom AB tfn: +46 8 719 81 95
Varuv |
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| icimjs at loop.com |
| Posted: Mon Jun 21, 1999 12:32 am |
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Guest
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Ulf wrote:
>Take the following code for example
>(written in all haste, apologies):
>
Thanks, Ulf. May have been written in all haste, but it certainly compiles
and does does everything I need it to.
Still, I think it should be possible to do something like this using
Mnemosyne.
Does anyone know how Menomsyne could be used to do something similar?
Elan
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| hakan at erix.ericsson.se |
| Posted: Mon Jun 21, 1999 1:15 pm |
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Guest
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On Sun, 20 Jun 1999, Elan <icimjs_at_loop.com> wrote:
Elan> Still, I think it should be possible to do something like this using
Elan> Mnemosyne.
Elan>
Elan> Does anyone know how Menomsyne could be used to do something similar?
There is an UNSUPPORTED function in the API that takes a Mnemosyne
query as a string and converts it into a Mnemosyne query handle:
Q = mnemosyne:string_to_handle(
"query [ X || X <- table(q),Y <- table(r),X.b = Y.f1] end. "),
mnesia:transaction(fun() -> mnemosyne:eval(Q) end).
It may still work, but perhaps it is too limited to be useful for you.
There also exists an experimental SQL compiler that generates the
internal form of Mnemosyne from SQL. This work was performed as a
master thesis.
/H |
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| icimjs at loop.com |
| Posted: Mon Jun 21, 1999 5:22 pm |
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| hakan at erix.ericsson.se |
| Posted: Tue Jun 22, 1999 2:07 pm |
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Guest
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On Mon, 21 Jun 1999, Elan <icimjs_at_loop.com> wrote:
>>There also exists an experimental SQL compiler that generates the
>>internal form of Mnemosyne from SQL. This work was performed as a
>>master thesis.
>
>Very interesting. Is there more information available? (A URL perhaps, or
>an email address?)
A good starting point is to read Ronny Andersson's master thesis report.
It is available at:
http://www.erlang.se/erlang/sure/main/club/university/xjobb/sql_compiler_report.pdf
It was an experimental work where a complete SQL parser was
implemented in Erlang using yecc, but only a minor subset of SQL was
mapped to Mnesia and Mnemosyne. I can dig up the code, but I don't
think that it works today.
/H |
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