如何将 Mnesia 查询结果转换为 JSON 可用列表？

Question

我正在尝试使用 JSX 将元组列表转换为 JSON 对象。

列表项基于记录定义：

-record(player, {index, name, description}).

看起来像这样：

[
    {player,1,"John Doe","Hey there"},
    {player,2,"Max Payne","I am here"}
]

查询函数如下所示：

select_all() ->
    SelectAllFunction =
        fun() ->
            qlc:eval(qlc:q(
                [Player ||
                    Player <- mnesia:table(player)
                ]
            ))
        end,
    mnesia:transaction(SelectAllFunction).

在知道我有所用记录的模式并了解元组结构的情况下，将其转换为 JSON 的正确方法是什么？

Answer 1

您必须将记录转换为 jsx 可以正确编码为 JSON 的术语。假设您想要 JSON 中的对象数组作为 player 记录列表，您必须将每个 player 转换为映射或元组列表。您还必须将字符串转换为二进制文件，否则 jsx 会将其编码为整数列表。这是一些示例代码：

-record(player, {index, name, description}).

player_to_json_encodable(#player{index = Index, name = Name, description = Description}) ->
    [{index, Index}, {name, list_to_binary(Name)}, {description, list_to_binary(Description)}].

go() ->
    Players = [
        {player, 1, "John Doe", "Hey there"},
        % the following is just some sugar for a tuple like above
        #player{index = 2, name = "Max Payne", description = "I am here"}
    ],
    JSON = jsx:encode(lists:map(fun player_to_json_encodable/1, Players)),
    io:format("~s~n", [JSON]).

测试：

1> r:go().
[{"index":1,"name":"John Doe","description":"Hey there"},{"index":2,"name":"Max Payne","description":"I am here"}]

如何将 Mnesia 查询结果转换为 JSON 可用列表？

How to convert Mnesia query results to a JSON'able list?

json

erlang

mnesia