linq之多表连接

1、左连接：

var LeftJoin = from emp in ListOfEmployees 
join dept in ListOfDepartment 
on emp.DeptID equals dept.ID into JoinedEmpDept 
from dept in JoinedEmpDept.DefaultIfEmpty() 
select new  
{ 
EmployeeName = emp.Name, 
DepartmentName = dept != null ? dept.Name : null  
};

如果想实现右连接，就把两个表换一下位置。

2、右连接：

var RightJoin = from dept in ListOfDepartment 
join employee in ListOfEmployees 
on dept.ID equals employee.DeptID into joinDeptEmp 
from employee in joinDeptEmp.DefaultIfEmpty() 
select new  
{ 
EmployeeName = employee != null ? employee.Name : null,          //重点
DepartmentName = dept.Name 
};

左链接或右链接，使用DefaultIfEmpty()语法，采用些语法前需要用到into语法

3、内连接：

var query = from t in entitiy.TB_GCGL_ADA_USER 
join p in entitiy.TB_GCGL_ZY_ZYK 
on t.ETPRS_CODE equals p.ETPRS_CODE

select new TB_USER_ZYK 
{ 
USER_ID = t.USER_ID, 
USER_NAME = t.USER_NAME, 
USER_PASSWORD = t.USER_PASSWORD,

};