Mnesia - 检查表中任一键的值

Question

我有一个使用以下记录创建的记忆表“用户”

-record(users,{username,nickname,age})

假设我有如下记录的 mnesia 表

users | username | nickname | age

users | John     | baddy    | 25 

users | Monk     | John     | 26

我有一个与表格匹配的名称...（比如“John”）..我想选择或匹配具有“John”作为用户名或昵称的行...我怎样才能做到这一点？如果有人能建议我一个方法，我会很高兴...

谢谢

Answer 1

查看 QLC - there's a simple example here on Learn You Some Erlang 或 man page here。您可以使用布尔值进行匹配，例如（在伪代码中）（用户名 == John 或昵称 == John）。

Answer 2

选择（Q）-> 案例记忆：is_transaction() 的 假-> F = fun(QH)-> qlc:e(QH) 结束， mnesia:activity(transaction,F,[Q],mnesia_frag); 真-> qlc:e(Q) 结尾。 read_by_name_or_nickname（姓名）-> 数据 = select(qlc:q([X || X

Answer 3

-module(wy).
-compile(export_all).

-record(users, {username, nickname, age}).
-include_lib("stdlib/include/ms_transform.hrl").

create_table()->
    mnesia:create_schema(node()),
    mnesia:start(),
    mnesia:create_table(users, [{attributes, record_info(fields, users)}]).

test()->
    Fun = fun()->
              mnesia:write(#users{username = "John", nickname = "baddy", age = 25}),
              mnesia:write(#users{username = "DaDa", nickname = "KaKa", age = 24}),
              mnesia:write(#users{username = "Monk", nickname = "John", age = 24})
          end,
    mnesia:transaction(Fun),

    Fun2 = ets:fun2ms(fun({users, UserName, NickName, Age}) when
                       UserName == "John" orelse NickName == "John" ->
                            {users, UserName, NickName, Age}
                  end), 

    mnesia:transaction(fun() -> mnesia:select(users, Fun2) end).