轉換SQL左連接到LINQ Lambda表達式

Question

我有這樣的SQL查詢

select at.description, 
     a.Address1, 
     a.Address2, 
     a.City 
    from address_types at 
    left join Address a 
    on a.addresstype = at.addresstype 
    and a.addressid=24 

想它寫在LINQ的Lambda表達式，任何線索？

謝謝！

Answer 1

我寧願把它簡化以下列方式

(from at in address_types 
join a in address 
on at.addresstype equals a.addresstype into tt 
from ar in tt.DefaultIfEmpty() 
where (ar != null && ar.addressid == 24) 
select new 
{ 
    at.Description, 
    ar.Address1, 
    ar.Address2, 
    ar.City 
    }) 

爲什麼我們不需要這種檢查的理由「（JA == NULL） 「是因爲我們已經在這一行限制了我們的設置」（ar！= null & & ar.addressid == 24）「。

同時這個查詢的工作原理，我的POV是，在SQL查詢中，LEFT JOIN也是冗餘的。 http://msdn.microsoft：你會不會因爲你的條件「a.addressid = 24」，所以SQL可以改寫到INNER JOIN和LINQ查詢以及對

(from at in address_types 
    join a in address 
    on at.addresstype equals a.addresstype 
    where at.addressid == 24 
    select new 
    { 
     at.Description, 
     a.Address1, 
     a.Address2, 
     a.City 
     }) 

Answer 2

你可以嘗試這樣的事情：

var resultset = (from at in addresstypes 
        join a in addresses 
        on at.AddressType equals a.AddressType into joinaddress 
        from ja in joinaddress.DefaultIfEmpty() 
        where (ja != null && ja.AddressID == 24) 
        select new 
        { 
         AddressType = at.AddressType, 
         AddressID = ja == null ? 0 : ja.AddressID, 
         Address1 = ja== null ? string.Empty : ja.Address1 
         });