如何在LINQ中编写自联接 [英] how to write self join in LINQ

问题描述

我们如何在LINQ中编写自联接？我试过这个：

 来自 coa   GL0_ChartOfAccounts 
 < span class =code-sdkkeyword> join  c  在coa.MainAccount上的GL0_ChartOfAccounts等于c.ControlAccount  into  cs 
 来自 ca   cs.DefaultIfEmpty（）
 < span class =code-sdkkeyword>选择  new  
 {
 MainAccount = coa.MainAccount，
 Title = coa.Title，
 ControlLevel = coa.ControlLevel，
 ControlAccount = coa.ControlAccount，
 ControlTitle = ca.Title 
} 

不幸的是，这给了一个匿名类型错误。



为了澄清这一点，假设有三列：

 MainAccount 
标题
 ParentAccount 

现在我想得到帐户的名称或名称，而不是ParentAccount（int）我该怎么办？在LINQ中使用这个吗？

解决方案

var q =（来自coocha in Glochartofaccount

加入c in glochartofaccount on coamainaccount equals c controlaccount

选择新的

{

MainAccount = coa.MainAccount，

Title = coa.Title，

ControlLevel = coa.ControlLevel，

ControlAccount = coa.ControlAccount，

ControlTitle = ca.Title

）.FirstOrDefault（）;

尝试使用此示例..

列表< employee> emp =  new 列表< employee>（）; 
 emp.Add（ new  Employee（）
 {
 EmpID =  1 ，
 EmpName =   a，
 City =   Pune，
 ManagerID =  11  
}）; 
 
 emp.Add（ new  Employee（）
 {
 EmpID =  2 ，
 EmpName =   b，
 City =   mumbai，
 ManagerID =  12  
}）; 
 
 emp.Add（ new  Employee（）
 {
 EmpID =  3 ，
 EmpName =   c，
 City =   Pune，
 ManagerID =  2  
}）; 
 
 emp.Add（ new  Employee（）
 {
 EmpID =  4 ，
 EmpName =   d，
 City =  德里，
 ManagerID =  14  
}）; 
 
  //   ---- Linq查询 
 
  var  q =（来自员工  emp 
  join  employee2 在 emp中，employee.EmpID等于employee2.ManagerID 
 选择员工）.FirstOrDefault（）; 
 < /  员工 >  < /  员工 >  

How do we write self join in LINQ? I have tried this:

from coa in GL0_ChartOfAccounts
  join c in GL0_ChartOfAccounts on coa.MainAccount equals c.ControlAccount into cs 
  from ca in cs.DefaultIfEmpty()
  select new 
  {
  	MainAccount = coa.MainAccount, 
	Title = coa.Title, 
	ControlLevel = coa.ControlLevel, 
	ControlAccount = coa.ControlAccount, 
	ControlTitle = ca.Title
	}

Unfortunately, this gives an anonymous type error.

To clarify this, suppose there are three columns:

MainAccount 
Title
ParentAccount

Now I want to get title or name of account instead of ParentAccount(int) how should I write this in LINQ?

解决方案

var q = (from coa in Glochartofaccount
join c in Glochartofaccount on coamainaccount equals c controlaccount
select new
{
MainAccount = coa.MainAccount,
Title = coa.Title,
ControlLevel = coa.ControlLevel,
ControlAccount = coa.ControlAccount,
ControlTitle = ca.Title
).FirstOrDefault();

try by using this sample..

List<employee> emp = new List<employee>();
emp.Add(new Employee()
{
    EmpID = 1,
    EmpName = "a",
    City = "Pune",
    ManagerID = 11
});

emp.Add(new Employee()
{
    EmpID = 2,
    EmpName = "b",
    City = "mumbai",
    ManagerID = 12
});

emp.Add(new Employee()
{
    EmpID = 3,
    EmpName = "c",
    City = "Pune",
    ManagerID = 2
});

emp.Add(new Employee()
{
    EmpID = 4,
    EmpName = "d",
    City = "Delhi",
    ManagerID = 14
});

//----Linq query

var q = (from employee in emp
        join employee2 in emp on employee.EmpID equals employee2.ManagerID
        select employee).FirstOrDefault();
</employee></employee>

这篇关于如何在LINQ中编写自联接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！