Cannot construct entity or complex type _ back-end in LINQ to Entities query

Yes, to make sure that EF knows your query type, personal experience, the EF query only supports the mapping entity objects generated by the table structure, and simple C # types, to return directly to the newly defined type of the individual, to be converted with an anonymous type
C # code?                               1 2 3 4 5 from T in db.projects select new { T=t,}

After the tolist is really calculated and then converted to another type

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Error code: var  orders = db. Orders.where (O => o.userid == userid). Select (c =>                    new  Order                    {                          Orderid = c.orderid,                        OrderDate  = c.orderdate,                        Total = c.total,                        orderdetails =  Db. Orderdetailss.Where (Od => od. Orderid == c.orderid). ToList ()                      }                      ). ToList ();             Correct code: var  orders = db. Orders.where (O=>o.userid==userid). ToList (). select                  (c  =>                 new  Order                  {                    orderid =  c.orderid,                     orderdate = c.orderdate,                      total = c.total,                      OrderDetails  = db. Orderdetailss.where (Od => od. Orderid == c.orderid). ToList ()               }                ). ToList ();       principle: linq  When selecting data   can not new  known objects, only anonymous.   But if you can new  a known class from a  List  list  .   http://www.cnblogs.com/studylife/p/3202616.html

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Called after the new complex type. Asnotracking () on the premise that you do not need to delete the object of change.

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The EF is not able to directly new out its own entity classes.

First query the anonymous class, and then new
var aaa = query. ToList (). Select (data => new Tb_item {num_iid = data. A.key, num = data. A.sumnum, title = data. B.firstordefault (U => u.num_iid = = data. A.key). Title}). ToList ();

Look, I've got this code a little more than yours. ToList ().
LINQ to Entities