在Linq查询动态地选择属性 [英] Dynamically select property in Linq query

问题描述

我现在面临的LINQ查询一个问题在C＃中，我的LINQ查询按以下

I am facing one issue with linq query in c# , my linq query as per below

list = (from row in dt.AsEnumerable()
                            select new Perfmon
                            {
                                id = row.Field<long>("id"),
                                counter1 = row.Field<string>("counter"),

                            }).ToList();

我有一个的perfmon 类，它包含像（ID，C1​​的特性，C2的...）
有更多然后20​​个柜现在我已经开发了SQL查询，根据参数传递如要countername选择ID和反如果我已经通过了C1的那么它将选择ID，C1​​的（更名为计数器）仅

I have one perfmon class and it contains properties like (id, counter1, counter2 ...) there are more then 20 counters now i have developed sql query to select id and counter based on passed countername in parameter e.g. if i have passed counter1 then it will select id , counter1 (renamed as counter) only

如果我在这里用开关情况，那么就会有20个魔女的情况下，任何人都可以请帮助我如何可以动态地在LINQ绑定属性？

if i will use switch case here then it will have 20 witch case, can anyone please help me how can bind property dynamically in linq?

在此先感谢。

推荐答案

您可以通过字典的支持，而不是每个属性的字段的性能监视器类。这样的：

You can make your Perfmon class backed by a dictionary rather than fields per properties. like:

class Perfmon
{
    private readonly Dictionary<string, string> _counters = new Dictionary<string, string>();

    public Perfmon(params KeyValuePair<string, string>[] knownCounters)
    {
        foreach (var knownCounter in knownCounters)
        {
            SetCounter(knownCounter.Key, knownCounter.Value);
        }
    }   
    public void SetCounter(string name, string value)
    {
        _counters[name] = value;
    }

    protected string GetCounterValue(string name)
    {
        if (_counters.ContainsKey(name))
            return _counters[name];
        else
            return null;
    }

    public string Counter1 { get { return GetCounterValue("Counter1"); } }
    public string Counter2 { get { return GetCounterValue("Counter2"); } }
    public string Counter3 { get { return GetCounterValue("Counter3"); } }
}

构造函数是有这样您就可以轻松地使用它在查询像

The constructor is there so you can easily use it in your query like:

var counterName = "Counter2";
list = (from row in dt.AsEnumerable() 
                            select new Perfmon(new KeyValuePair<string, string>(counterName, row.Field<string>("counter")))
                            { 
                                id = row.Field<long>("id")
                            }).ToList();

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