[英]How does Linq projection work between Extention Method and query expression
[英]Why does this linq projection not work?
由於某些原因,注釋掉的版本不起作用? 我想做的是去掉UI中不需要的字段。這是正確的方法嗎?
public IQueryable<tMember> Get(int id)
{
var congressGroup = from m in db.tMembers
join mp in db.tMemPositions on m.MembersID equals mp.MembersID
join cmp in db.tCongressMemPositions on mp.MemPositionsID equals cmp.MemPositionsID
join c in db.tCongresses on cmp.CongressID equals c.CongressID
where c.CongressNumber == id
// select new tMember { Firstname = m.Firstname, Lastname = m.Lastname };
select m;
//testing
foreach (tMember m in congressGroup)
{
}
return congressGroup;
}
編輯1:兩種方式都可以編譯。 僅使用select m即可編譯並正常運行。 與另一行談到foreach時說
mscorlib.dll中發生類型'System.NotSupportedException'的異常,但未在用戶代碼中處理
附加信息:實體或復雜類型'CongressDb_DevModel.tMember'不能在LINQ to Entities查詢中構造。
EDIT2:構造函數是
public tMember()
{
this.tMemMilitaries = new HashSet<tMemMilitary>();
this.tMemOccupations = new HashSet<tMemOccupation>();
this.tMemPositions = new HashSet<tMemPosition>();
this.tMemRatings = new HashSet<tMemRating>();
this.tMemVoteScores = new HashSet<tMemVoteScore>();
}
只需創建一個新類型,而不要嘗試重用tMember
。
public class Name
{
public string FirstName { get; set; }
public string LastName { get; set; }
}
然后更改方法的返回類型,並將選擇更改為:
select new Name { Firstname = m.Firstname, Lastname = m.Lastname };
聲明:本站的技術帖子網頁,遵循CC BY-SA 4.0協議,如果您需要轉載,請注明本站網址或者原文地址。任何問題請咨詢:yoyou2525@163.com.