mnesia orm

使用mneisa存储数据不想每次mneisa:table的调用 所以写了个简单的orm只有查询

defined.hrl

%% 定义记录结构
-record(shop,{item,quantity,cost}).
-record(cost,{name,price}).

init_data.erl

 

-module(init_data).
 -compile(export_all).

 -include("defined.hrl").
 -include_lib("stdlib/include/qlc.hrl").


 start() ->
     mnesia:start(),
     %% 等待表的加载
     mnesia:wait_for_tables([shop,cost],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: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}
     ].

common_query.erl

 

-module(common_query).
 -compile(export_all).

 -include("defined.hrl").
 -include_lib("stdlib/include/qlc.hrl").


 %% 指定表的数据量
 count(Table) ->
     case list(Table) of
         {error,Msg} -> {error,Msg};
         {ok,[]} -> 0;
         {ok,L} -> length(L)
     end.

 %% 按条件查询指定表满足条件的数据的数量
 count(Table,Where) ->
     case list(Table,Where) of
         {error,Msg} -> {error,Msg};
         {ok,[]} -> 0;
         {ok,L} -> length(L)
     end.


 %% 查看指定Table中的所有数据
 list(Table) ->
     F = fun() ->
         qlc:e(qlc:q([X||X<-mnesia:table(Table)]))
     end,
     {atomic,L} = mnesia:transaction(F),
     {ok,L}.

 %% 按条件查询指定表满足条件的所有数据
 list(Table,Where) ->
     case query_func(Table,Where) of
         {error,Msg} -> {error,Msg};
         {ok,F} ->
             {atomic,L} = mnesia:transaction(F),
             {ok,L}
     end.

 %% 分页取表信息
 %% @type Table = atom()
 %% @type Offset = integer() > 0
 %% @type Limit = integer() > 0
 %% @spec list(site,1,20) -> [L] | {error,badarg}
 list(Table,Offset,Limit) ->
     if
         is_integer(Offset) and is_integer(Limit) and (Offset > 0) and (Limit > 0) ->
             F=fun() ->
                   QH=qlc:q([X||X<-mnesia:table(Table)]),
                   Qc=qlc:cursor(QH),
                   case Offset of
                       1 -> skip;
                       _ -> qlc:next_answers(Qc,Offset-1)
                   end,
                   qlc:next_answers(Qc,Limit)
             end,
             {atomic,L} = mnesia:transaction(F),
             {ok,L};
         true -> {error,badarg}
     end.

 %% 按Where条件搜索分页取表信息
 %% @type Table = atom()
 %% @type Offset = integer() > 0
 %% @type Limit = integer() > 0
 %% @type Where = [{agent,Agent}] | [{creator,Creator}]
 %% @spec list(site,1,20,[{agent,shopex}]) -> [L] | {error,badarg}
 list(Table,Offset,Limit,Where) ->
     if
         is_integer(Offset) and is_integer(Limit) and (Offset > 0) and (Limit > 0) ->
             case query_func(Table,Offset,Limit,Where) of
                 {error,Msg} -> {error,Msg};
                 {ok,F} ->
                     {atomic,L} = mnesia:transaction(F),
                     L
             end;
         true -> {error,badarg}
     end.

 %% 查询方法 翻页使用
 query_func(Table,Offset,Limit,Where) ->
     case query_cond(Table,Where) of
         {ok,QH} ->
             {ok,fun() ->
                   Qc=qlc:cursor(QH),
                   case Offset of
                       1 -> skip;
                       _ -> qlc:next_answers(Qc,Offset-1)
                   end,
                   qlc:next_answers(Qc,Limit)
             end};
         {error,Msg} -> {error,Msg}
     end.

 %% 查询方法(count使用)
 query_func(Table,Where) ->
     case query_cond(Table,Where) of
         {ok,QH} ->
             {ok,fun() -> qlc:e(QH) end};
         {error,Msg} -> {error,Msg}
     end.

 %% 查询商品(shop)
 query_cond(shop,Where) ->
     case Where of
             %% 按Item查询
             [{item,Item}] ->
                 QH=qlc:q([X || X <- mnesia:table(shop),
                                     X#shop.item =:= Item]),
                 {ok,QH};
             [_] ->
                 {error,badarg}
         end;


 %% 没有相关表的query_cond 都是报错的
 query_cond(_,_) ->
     {error,badarg}.

原文来自:

http://www.cnblogs.com/bluefrog/archive/2012/06/13/2548405.html