如何在sql中使用的linq中使用Left join? [英] How can I use Left join in linq that we use in sql?
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问题描述
如何在编写SQL查询的Linq中使用左联接?
How can I use Left join in Linq that I write SQL query?
select
p.Name, p.Family,
E.EmployTypecode, E.employtypeName, E.EmplytyppeTye
from
personnel as p
left join
Employee as E on E.EmployTypecode = p.EmployTypecode
推荐答案
使用Join关键字而不是Left join,并且必须使用"INTO"关键字和"DefaultIfEmpty()"方法,因为右表将返回空值.
Use Join keyword instead of Left join and it is mandatory to use "INTO" keyword and "DefaultIfEmpty()" method as right table returns null value.
var query = from p in personnel
join e in Employee on p.EmployTypecode equals e.EmployTypecode into t
from nt in t.DefaultIfEmpty()
orderby p.Name
select new
{
p.Name, p.Family,
EmployTypecode=(int?)nt.EmployTypecode, // To handle null value if Employtypecode is specified as not null in Employee table.
nt.employtypeName, nt.EmplytyppeTye
}.ToList();
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