-module(test_mnesia).
-compile(export_all).-include_lib("stdlib/include/qlc.hrl").%% 定义记录结构
-record(shop,{item,quantity,cost}).
-record(cost,{name,price}).
-record(design,{id,plan}).start() ->mnesia:start(),%% 等待表的加载mnesia:wait_for_tables([shop,cost,design],20000).%% 初始化mnesia表结构
init() ->mnesia:create_schema([node()]),mnesia:start(),%% 表创建 mnesia:create_talbe(TableName,[Args])%% {type,Type}  set,ordered_set,bag 表类型%% {ram_copies,NodeList} NodeList每个节点都有内存备份　默认为这个{ram_copies,[node()]}%% {disc_copies,NodeList} NodeList每个节点都有内存备份和磁盘备份 %% {disc_only_copies,NodeList} NodeList每个节点有磁盘备份 %% {attributes,AtomList} 要保存的列名称 一般和record有关　record_info(fields,RecordName)mnesia:create_table(shop,[{attributes,record_info(fields,shop)}]), %% 创建shop表
    mnesia:create_table(cost,[{attributes,record_info(fields,cost)}]),mnesia:create_table(design,[{attributes,record_info(fields,design)}]),mnesia:stop().%% 加载测试数据
reset_tables() ->mnesia:clear_table(shop),mnesia:clear_table(cost),F = fun() ->lists:foreach(fun mnesia:write/1,example_tables())end,mnesia:transaction(F).%% 测试数据
example_tables() ->[%% shop table{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 table{cost,apple,1.5},{cost,orange,2.4},{cost,pear,2.2},{cost,banana,1.6},{cost,potato,0.6}].%%== 查询 =============================================================

do(Q) ->F = fun() -> qlc:e(Q) end,{atomic,Val} = mnesia:transaction(F),Val.%% SELECT * FROM shop
%% 选取所有列
demo(select_shop) ->do(qlc:q([X || X <- mnesia:table(shop)]));%% SELECT  item,quantity FROM shop
%% 选取指定列
demo(select_some) ->do(qlc:q([{X#shop.item, X#shop.quantity} || X <- mnesia:table(shop)]));%% SELECT * FROM shop WHERE shop.quantity < 250
%% 选取指定条件的数据
demo(where) ->do(qlc:q([X || X <- mnesia:table(shop),X#shop.quantity < 250]));%% 关联查询
%% SELECT shop.* FROM shop,cost wHERE shop.item = cost.name AND cost.price < 2 AND shop.quantity < 250
demo(join) ->do(qlc:q([X || X <- mnesia:table(shop),X#shop.quantity < 250,Y <- mnesia:table(cost),X#shop.item =:= Y#cost.name,Y#cost.price < 2])).%% == 数据操作 ===============================================%% 增加一行
add_shop_item(Name,Quantity,Cost) ->Row = #shop{item = Name,quantity = Quantity, cost = Cost},F = fun() ->mnesia:write(Row)end,mnesia:transaction(F).%% 删除一行
remove_shop_item(Item) ->Oid = {shop,Item},F = fun() ->mnesia:delete(Oid)end,mnesia:transaction(F).%% 取消一个事务
former(Nwant) ->F = fun() ->%% find the num of apples[Apple] = mnesia:read({shop,apple}),Napples = Apple#shop.quantity,%% update the databaseNewApple = Apple#shop{quantity = Napples + 2 * Nwant},mnesia:write(NewApple),%% find the num of oranges[Orange] = mnesia:read({shop,orange}),Noranges = Orange#shop.quantity,if Noranges >= Nwant ->%% update the databaseNum = Noranges - Nwant,NewOrange = Orange#shop{quantity = Num},mnesia:write(NewOrange);true ->%% no enough oranges 取消事务
                    mnesia:abort(oranges)endend,mnesia:transaction(F).%% 保存复杂数据
add_plans() ->D1 = #design{id = {joe,1},plan = {circle,10}},D2 = #design{id = fred,plan = {rectangle,[10,5]}},F = fun() ->mnesia:write(D1),mnesia:write(D2)end,mnesia:transaction(F).%% 获复杂数据
get_plans(PlanId) ->F = fun() -> mnesia:read({design,PlanId}) end,mnesia:transaction(F).