LINQ left, right, and inner connections

Little scum · Posted on 8/9/2017 10:51:26 AM

1. Left connection:
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
};

2. Right connection:
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. Internal connection:
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,
               };

When making a left join between two tables, pay attention to the use of defaultifempty, which originally meant that if it is empty, use the default value instead, the default value is NULL, and of course, you can also use another overload of defaultifempty to specify the default.

QWERTYU · Posted on 8/11/2017 6:28:43 PM

linq sorts by multiple fields: service = service. OrderByDescending(s => s.LastUpdateDate). ThenByDescending(s => s.CreateDate);

[Source] LINQ left, right, and inner connections

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