LINQ 中的动态 where 条件

问题描述

我有一个场景，我必须在 LINQ 中使用动态 where 条件.

I have a scenario where I have to use a dynamic where condition in LINQ.

我想要这样的东西:

public void test(bool flag)
{
   from e in employee
   where e.Field<string>("EmployeeName") == "Jhom"
   If (flag == true)
   {
       e.Field<string>("EmployeeDepartment") == "IT"
   }
   select e.Field<string>("EmployeeID")
}

我知道我们不能在 Linq 查询中间使用If"，但是对此有什么解决方案?

I know we can't use the 'If' in the middle of the Linq query but what is the solution for this?

请帮忙...

推荐答案

所以，如果 flag 是 false 你需要所有 Jhoms，如果 flag 是的，您只需要 IT 部门的 Jhoms

So, if flag is false you need all Jhoms, and if flag is true you need only the Jhoms in the IT department

这个条件

!flag || (e.Field<string>("EmployeeDepartment") == "IT"

满足该标准(如果标志为假，则总是为真，等等)，因此查询将变为:

satisfies that criterion (it's always true if flag is false, etc..), so the query will become:

from e in employee    
where e.Field<string>("EmployeeName") == "Jhom"
  && (!flag || (e.Field<string>("EmployeeDepartment") == "IT")
select e.Field<string>("EmployeeID") 

还有，这个 e.Field("EmployeeID") 业务，闻起来像 软编码，可能会考虑一下.我猜

also, this e.Field<string>("EmployeeID") business, smells like softcoding, might take a look into that. I guess

from e in employee    
where e.EmployeeName == "Jhom"
  && (!flag || (e.EmployeeDepartment == "IT")
select e.EmployeeID

会更紧凑，更不容易出现打字错误.

would be more compact and less prone to typing errors.

此答案适用于此特定场景.如果您有很多此类查询，请务必投资其他答案中提出的模式.

This answer works for this particular scenario. If you have lots of this kinds of queries, by all means investingate the patterns proposed in the other answers.