我有一个ETS表，其中的键由诸如{shell，TIME，NAME，ID}之类的记录组成，我想允许用户使用其中任何一个的组合来搜索条目。IE：其中
我了解如何使用fun2ms，但还不足以知道是否有一些干净的一线方式。我当前的解决方案是将搜索请求与6种可能的搜索类型组合进行匹配，与我广泛使用模式匹配的所有其他erlang代码相比，它感觉很脏。
你们能以更智能的方式帮助我利用fun2ms或ETS表吗？我非常确定此查询可以用一行完成。这是我用来向您展示我所拥有的6个功能之一的示例：
getShells_by_Time(Tstart, Tend) ->
Results = ets:select(schedule_row1,ets:fun2ms(
fun(A = #activity{shell = ActivityShell,activity_data = S1Data})
when (ActivityShell#activity_shell.tsched < Tend)
andalso (ActivityShell#activity_shell.tsched > Tstart) ->
ActivityShell
end)),
编辑：
因此，这是我到目前为止想要做的：
我有一条记录，我希望默认为：-record（s1shell_query，{tsched = {_ScLow，_ScHigh}，id = _ID，type = _Type}）。
这意味着用户可以为他们想要匹配的内容更改任何记录术语。问题是您不能在记录中默认未绑定变量。
我的比赛规格函数如下所示：
{ScLow,ScHigh} = ShellQuery#s3shell_query.tsched,
ets:select(Table, ets:fun2ms(
fun(#stage3Activity{shell = #activity_shell{tsched = Tsched, id = ID, type = Type}})
when Tsched < ScLow, Tsched>ScHigh,ID == ID, Type == Type ->
#activity_shell{tsched = Tsched,id = ID,type = Type}
end)).
因此，我一直试图找出如何忽略用户未放入外壳查询记录中的匹配内容的方法。
例如，您可以使用自定义匹配规格防护代替ets:fun2ms/1进行搜索：
-module(match_spec_guards).
-export([new/0, populate/0, search/1]).
-record(row, {
key :: {shell, Time :: integer(), Name :: string(), ID :: term()},
value :: term()
}).
new() ->
ets:new(?MODULE, [set, named_table, {keypos, #row.key}]).
populate() ->
[ets:insert(?MODULE, #row{key = {shell, I, integer_to_list(I), I * 1000}, value = I * 1000})
|| I <- lists:seq(1,1000)].
search(Filters) ->
Guards = [filter_to_guard(Filter) || Filter <- Filters],
MatchHead = {row, {shell, '$1', '$2', '$3'}, '_'},
Result = ['$_'],
ets:select(?MODULE, [{MatchHead, Guards, Result}]).
filter_to_guard({time_higher_than, X}) -> {'<', X, '$1'};
filter_to_guard({time_lower_than, X}) -> {'>', X, '$1'};
filter_to_guard({name_is, X}) -> {'==', '$2', X};
filter_to_guard({id_is, X}) -> {'==', '$3', X}.
您可以像这样使用它：
Erlang/OTP 22 [erts-10.7.1] [source] [64-bit] [smp:4:4] [ds:4:4:10] [async-threads:1]
Eshell V10.7.1 (abort with ^G)
1> c(match_spec_guards).
{ok,match_spec_guards}
2> match_spec_guards:new().
match_spec_guards
3> match_spec_guards:populate().
[true,true,true,true,true,true,true,true,true,true,true,
true,true,true,true,true,true,true,true,true,true,true,true,
true,true,true,true,true,true|...]
4> match_spec_guards:search([{time_higher_than, 10}, {time_lower_than, 20}]).
[{row,{shell,15,"15",15000},15000},
{row,{shell,16,"16",16000},16000},
{row,{shell,17,"17",17000},17000},
{row,{shell,12,"12",12000},12000},
{row,{shell,13,"13",13000},13000},
{row,{shell,11,"11",11000},11000},
{row,{shell,19,"19",19000},19000},
{row,{shell,14,"14",14000},14000},
{row,{shell,18,"18",18000},18000}]
5> match_spec_guards:search([{id_is, 15000}]).
[{row,{shell,15,"15",15000},15000}]
6> match_spec_guards:search([{name_is, "15000"}]).
[]
7> match_spec_guards:search([{name_is, "15"}]).
[{row,{shell,15,"15",15000},15000}]
您在ets:select/2中具有有关比赛规格语法的更多信息，>
我建议使用
MatchHead = #row{key = {shell, '$1', '$2', '$3'}, value = '_'},即使您需要调整记录定义以允许
'$x'和'_'原子。
[此外，如果您使用大表，请考虑编译匹配说明和/或使用延续。
编辑
通过滥用erlang术语和搜索记录中有用的'_'默认值之间的完整顺序，您可以获得所需的内容：-module(match_spec_guards). -export([new/0, populate/0, search/1]). -record(row, { key :: {shell, Time :: integer(), Name :: string(), ID :: term()}, value :: term() }). -record(s1shell_query, { tsched_low = 0, tsched_high = undefined, id = '_', name = '_' }). new() -> ets:new(?MODULE, [set, named_table, {keypos, #row.key}]). populate() -> [ets:insert(?MODULE, #row{key = {shell, I, integer_to_list(I), I * 1000}, value = I * 1000}) || I <- lists:seq(1,1000)]. search(#s1shell_query{tsched_low = Low, tsched_high = High} = Query) -> MatchHead = #row{key = {shell, '$1', Query#s1shell_query.name, Query#s1shell_query.id}, value = '_'}, Guards = [{'>', High, '$1'}, {'=<', Low, '$1'}], ets:select(?MODULE, [{MatchHead, Guards, ['$_']}]).
id和name如果已定义，将从记录中获取（如果未定义，则使用'_'），如果定义了保护，则守卫自然执行过滤，并使用complete order如果不是，则为上限（原子总是大于数字，而与原子和数字无关）。
用法示例如下：
Erlang/OTP 22 [erts-10.7.1] [source] [64-bit] [smp:4:4] [ds:4:4:10] [async-threads:1]
Eshell V10.7.1 (abort with ^G)
1> c(match_spec_guards).
{ok,match_spec_guards}
2> match_spec_guards:new().
match_spec_guards
3> match_spec_guards:populate().
[true,true,true,true,true,true,true,true,true,true,true,
true,true,true,true,true,true,true,true,true,true,true,true,
true,true,true,true,true,true|...]
4> rr(match_spec_guards).
[row,s1shell_query]
7> match_spec_guards:search(#s1shell_query{id = 14000}).
[#row{key = {shell,14,"14",14000},value = 14000}]
8> match_spec_guards:search(#s1shell_query{name = "14"}).
[#row{key = {shell,14,"14",14000},value = 14000}]
9> match_spec_guards:search(#s1shell_query{tsched_high = 20}).
[#row{key = {shell,1,"1",1000},value = 1000},
#row{key = {shell,15,"15",15000},value = 15000},
#row{key = {shell,6,"6",6000},value = 6000},
#row{key = {shell,16,"16",16000},value = 16000},
#row{key = {shell,8,"8",8000},value = 8000},
#row{key = {shell,2,"2",2000},value = 2000},
#row{key = {shell,9,"9",9000},value = 9000},
#row{key = {shell,17,"17",17000},value = 17000},
#row{key = {shell,12,"12",12000},value = 12000},
#row{key = {shell,7,"7",7000},value = 7000},
#row{key = {shell,13,"13",13000},value = 13000},
#row{key = {shell,10,"10",10000},value = 10000},
#row{key = {shell,3,"3",3000},value = 3000},
#row{key = {shell,11,"11",11000},value = 11000},
#row{key = {shell,19,"19",19000},value = 19000},
#row{key = {shell,14,"14",14000},value = 14000},
#row{key = {shell,5,"5",5000},value = 5000},
#row{key = {shell,4,"4",4000},value = 4000},
#row{key = {shell,18,"18",18000},value = 18000}]
10> match_spec_guards:search(#s1shell_query{tsched_low = 998}).
[#row{key = {shell,998,"998",998000},value = 998000},
#row{key = {shell,999,"999",999000},value = 999000},
#row{key = {shell,1000,"1000",1000000},value = 1000000}]