Skip to content

Instantly share code, notes, and snippets.

@stoshiya
Last active August 29, 2015 14:01
Show Gist options
  • Save stoshiya/c390844c634d1a088df8 to your computer and use it in GitHub Desktop.
Save stoshiya/c390844c634d1a088df8 to your computer and use it in GitHub Desktop.
-module(test_mnesia).
-import(lists, [foreach/2]).
-compile(export_all).
-include_lib("stdlib/include/qlc.hrl").
-record(shop, {item, quantity, cost}).
-record(cost, {name, price}).
-record(design, {id, plan}).
do_this_once() ->
mnesia:create_schema([node()]),
mnesia:start(),
mnesia:create_table(shop, [{attributes, record_info(fields, shop)}]),
mnesia:create_table(cost, [{attributes, record_info(fields, cost)}]),
mnesia:create_table(design, [{attributes, record_info(fields, design)}]),
mnesia:stop().
start() ->
mnesia:start(),
mnesia:wait_for_tables([shop, cost, design], 20000).
demo(select_shop) ->
do(qlc:q([X || X <- mnesia:table(shop)]));
demo(select_some) ->
do(qlc:q([{X#shop.item, X#shop.quantity} || X <- mnesia:table(shop)]));
demo(reorder) ->
do(qlc:q([X#shop.item || X <- mnesia:table(shop), X#shop.quantity < 250]));
demo(join) ->
do(qlc:q([X#shop.item || X <- mnesia:table(shop),
X#shop.quantity < 250,
Y <- mnesia:table(cost),
X#shop.item =:= Y#cost.name,
Y#cost.price < 2])).
do(Q) ->
F = fun() -> qlc:e(Q) end,
{atomic, Val} = mnesia:transaction(F),
Val.
example_tables() ->
[
{shop, apple, 20, 2.3},
{shop, orange, 100, 3.8},
{shop, pear, 200, 3.6},
{shop, banana, 420, 4.5},
{shop, potato, 2456, 1.2},
{cost, apple, 1.5},
{cost, orange, 2.4},
{cost, pear, 2.2},
{cost, banana, 1.5},
{cost, potato, 0.6}
].
add_shop_item(Name, Quantity, Cost) ->
Row = #shop{item=Name, quantity=Quantity, cost=Cost},
F = fun() -> mnesia:write(Row) end,
mnesia:transaction(F).
remove_shop_item(Item) ->
Oid = {shop, Item},
F = fun() -> mnesia:delete(Oid) end,
mnesia:transaction(F).
farmer(Nwant) ->
F = fun() ->
[Apple] = mnesia:read({shop, apple}),
NApples = Apple#shop.quantity,
Apple1 = Apple#shop{quantity = NApples + 2 * Nwant},
mnesia:write(Apple1),
[Orange] = mnesia:read({shop, orange}),
NOranges = Orange#shop.quantity,
if
NOrange >= Nwant ->
N1 = NOrange - Nwant,
Orange1 = Orange#shop{quantity=N1},
mnesia:write(Orange1);
true -> mnesia:abort(oranges)
end
end,
mnesia:transaction(F).
reset_tables() ->
mnesia:clear_table(shop),
mnesia:clear_table(cost),
F = fun() -> foreach(fun mnesia:write/1, example_tables()) end,
mnesia:transaction(F).
add_plans() ->
D1 = #design{id = {joe, 1}, plan = {circle, 10}},
D2 = #design{id = fred, plan = {rectangle, 10, 5}},
D3 = #design{id = {jane, {house, 23}}, plan = {house, [
{floor, 1, [{doors, 3}, {window, 2}, {room, 5}]},
{floor, 2, [{doors, 2}, {rooms, 4}, {windows, 15}]}]}},
F = fun() ->
mnesia:write(D1),
mnesia:write(D2),
mnesia:write(D3)
end,
mnesia:transaction(F).
get_plan(PlanId) ->
F = fun() -> mnesia:read({design, PlanId}) end,
mnesia:transaction(F).
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment