有没有一种方法可以将运算符指定为LINQ中的参数? [英] Is there a way to specify an operator as an argument in LINQ?
问题描述
我有一段这样的代码:
var emptyKeys = (from recs in allRecords
where recs.Key == string.Empty
orderby recs.Key
select recs).ToList();
这仅给我那些以空字符串作为键值的记录.
this gives me only those recs which have an empty string as key values.
要获得具有所有更改值的记录,就是将==更改为!=
To get the recs with values all that changes is the == to !=
因此可以将这段代码放入一种方法中,该方法将根据需要将比较从==更改为!=,或者我像这样重复查询以做到这一点:
So is it possible to put this piece of code in a method which will change the comparison from == to != based on what's required or do I repeat the query to do it like so:
var emptyKeys = (from recs in allRecords
where recs.Key != string.Empty
orderby recs.Key
select recs).ToList();
致谢.
推荐答案
不完全是,但是,如果您对LINQ查询稍加修改,则可以执行以下操作:
Not quite, but if you slightly modify your LINQ query, you can do something of the sort:
Func<string, string, bool> selectorFunc = (a, b) => a == b;
var emptyKeys = (from recs in allRecords
where selectorFunc(recs.Key, string.Empty)
orderby recs.Key
select recs).ToList();
这将是equals函数.
That will be the equals function.
我要做的是将它们放在字典中:
What I would do is put them in a dictionary:
Dictionary<string, Func<string, string, bool>> selectorDictionary =
new Dictionary<string, Func<string, string, bool>>()
{ {"==", (a, b) => a == b}, {"!=", (a, b) => a != b} };
然后像这样使用它:
Dictionary<string, Func<string, string, bool>> selectorDictionary =
new Dictionary<string, Func<string, string, bool>>()
{ {"==", (a, b) => a == b}, {"!=", (a, b) => a != b} };
Func<string, string, bool> selectorFunc = selectorDictionary[operator];
var emptyKeys = (from recs in allRecords
where selectorFunc(recs.Key, string.Empty)
orderby recs.Key
select recs).ToList();
这比其他答案要好,因为它也可以扩展到其他运算符.
This is better than the other answers as it's expandable to other operators, too.
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