如何基于先前返回的值向LINQ查询添加条件条件 [英] How to add conditional condition to LINQ query based on a previously returned value

问题描述

例如:

var sList = from ASL in aslist
            where ASL.Description == as.ToString()
            select ASL;
as = sList.FirstOrDefault();
var rList = from ARL in arlist
            where ARL.Description == rDescription && ARL.Id == as.Id
            select ARL;

现在，如您所见，rList查询的最后条件(即&& ARL.Id == as.Id)基于从sList查询中检索到的值.我的问题是当sList是NULL时，出现错误.我只想在sList不为null的情况下包括最后一个条件(即&& ARL.Id == as.Id).

Now as you see, the last condition of rList query (i.e. && ARL.Id == as.Id) is based on the value retrieved from sList query. My problem is when sList is NULL, I get an error. I want to include last condition (i.e. && ARL.Id == as.Id) only if sList is not null.

我可以使用如下所示的其他方式来做到这一点，但如果可能的话，我希望使用LINQ来做到这一点:

I can do it using if else like as shown below, but I want to do it elegantly using LINQ if possible:

if (as != null)
{
    // include ARL.Id == as.Id condition in the query
} 
else
{
    // exclude ARL.Id == as.Id condition from the query
}

提前谢谢！

推荐答案

&& (assetsensor == null || ARL.SensorID == assetsensor.ID)

这篇关于如何基于先前返回的值向LINQ查询添加条件条件的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！