linq实现左连接

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,
DepartmentName = dept.Name
};

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,

};

 

 

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