如果传入值，则仅执行Where条件 [英] Only do Where condition if a value is passed in

问题描述

我有以下在date和LabID上的where上执行的LINQ语句.

I have the following LINQ statement that does on where on the date and a LabID.

我要传递LABS和日期的列表，但是不是必需的，并且我可能只传递日期，而没有实验，在这种情况下，我想获得所有实验的结果那个特定的实验室.

I'm passing in a list of LABS and a date, however they are not required, and I could potentially only pass in a date, and no lab, in which case I'd like to get results for all labs for that particular lab.

这是我现在拥有的:

List<dExp> lstDatExp = (from l in ctx.dExp.Include("datLab")
                        where values.Contains(l.datL.Lab_ID)
                            && l.reportingPeriod == reportingPeriod
                        select l).ToList<dExp>();

但是，如果传入的值不存在，这将中断.如何更改此设置以确保我的两个where语句都是可选的?

But this breaks if the value getting passed in is not there. How do I change this to make sure both of my where statements are optional?

推荐答案

使用IQueryable，您可以简单地在步骤中添加条件:

With IQueryable you can simply add conditions in steps:

int? reportingPeriod = ...;

IQueryable<dExp> resultsQuery =         // don't use `var` here.
        ctx.dExp.Include("datLab");   

if (values != null)
   resultsQuery = resultsQuery.Where(exp => values.Contains(exp.datL.Lab_ID));

if (reportingPeriod.Hasvalue)
   resultsQuery = resultsQuery.Where(exp => exp.reportingPeriod == reportingPeriod.Value);

// additional .Where(), .OrderBy(), .Take(), .Skip() and .Select()

// The SQL query is made and executed on the line below
// inspect the string value in the debugger
List<dExp> results = resultsQuery.ToList();

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