LINQ：使用三元（？：）与LINQ let是不够的，需要一个“IF”但似乎不能让它上班 [英] LINQ: Using a ternary ( ?: ) with LINQ let is not enough, need an "IF" but can't seem to get it to work

问题描述

我试图在LINQ的LET中包含一个IF，但是我不能让它工作，似乎对三元运算符起作用，但这是TRUE或FALSE，我需要有两个以上的选项。

我认为这很好解释

基本上我有一个选择，使用数据库连接来选择项目。然后我得到每个记录的状态，但是我必须根据products.type的类型，在单独的表中进行加入。

  var tst = from p in products join i in info on p.id equals i.pid 
 
 // if p.type =homethen ... 
 
 let status = from s in homestatus 
 select new {status = s.status} 
 
 //如果p.type =offshore然后
 
 
 let status = from s in offshorestatus 
 select new {status = s.status} 
 
 
 //如果p.type =internal则
 
 
 let status = from s in internalestatus 
 select new {status = s.status} 
 
选择新的{
 name = p.name，
 status = status.StatusText 
} 
  

任何人都有任何想法如何做一个标准的IF所以我可以选择我希望执行哪个STATUS（let）。

提前感谢

解决方案

您可以使用条件运算符（1）

  var tst = from p in products join i in info on p.id equals i.pid 
 
 let status = p.type =home？ homestatus.Select（s => s.status）：
 p.type =offshore？ offshorestatus.Select（s => s.status）：
 p.type =internal？ internalestatus.Select（s => s.status）：null 
选择新的{
 name = p.name，
 status = status！= null？ status.StatusText：string.Empty; 
} 
  

如果您不使用StatusText以外的其他状态，您还可以这样做

  var tst = from p in products join i in info on p.id equals i.pid 
 
 let status =（p.type =home？homestatus.Select（s => s.status.StatusText）：
 p.type =offshore？offshorestatus.Select（s =   s.status.StatusText）：
 p.type =internal？internalestatus.Select（s => s.status.StatusText）：null）？ string.Empty 
选择新的{
 name = p.name，
 status = status; 
} 
  

（1）一个三元运算符是任何运算符这需要三个参数，其中目前在C＃中只有一个称为条件运算符

I am trying to include an IF within my LET in LINQ but i can't get it to work, it seems to work for the ternary operator, but this is TRUE or FALSE and i need to have more than 2 options.

I think this explains it well

Basically i have a select which selects items using joins from a DB. Then the i get the status for each record but i have to make a join on separate tables depending on the type from products.type

var tst = from p in products join i in info on p.id equals i.pid

// if p.type = "home" then ...

let status = from s in homestatus
select new { status = s.status }

// if p.type ="offshore" then


let status = from s in offshorestatus
select new { status = s.status }


// if p.type ="internal" then


let status = from s in internalestatus
select new { status = s.status }

select new {
name = p.name,
status = status.StatusText
}

Anybody have any ideas how to do a standard IF so i can select which STATUS (let) i wish to execute.

Thanks in advance

解决方案

You can do that with the conditional operator (1)

var tst = from p in products join i in info on p.id equals i.pid

let status = p.type = "home" ? homestatus.Select(s=>s.status) :
             p.type = "offshore" ? offshorestatus.Select(s=>s.status) :
             p.type = "internal" ? internalestatus.Select(s=>s.status) : null
select new {
name = p.name,
status = status != null ? status.StatusText : string.Empty;
}

If you are not using the status for anything else than the StatusText you could also do it like this

var tst = from p in products join i in info on p.id equals i.pid

let status = (p.type = "home" ? homestatus.Select(s=>s.status.StatusText) :
             p.type = "offshore" ? offshorestatus.Select(s=>s.status.StatusText) :
             p.type = "internal" ? internalestatus.Select(s=>s.status.StatusText) : null) ?? string.Empty
select new {
name = p.name,
status = status;
}

(1) A ternary operator is any operator that takes three arguments, of which there at present is only one in C# called the conditional operator

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