返回linq查询的结果时方法的输出类型是什么？

Question

I use Linq query instead of using Sqlserver's view. I want to put it in method .what is my output type? thanks for helping

public ???? InsuranceWorkerView()
{
    var InsuranceWorkers =(from ins_insuranceworkers in db.INS_InsuranceWorkers
         join dv in db.DivisionCountry on new { InsWorkerCityID = ins_insuranceworkers.InsWorkerCityID } equals new { InsWorkerCityID = dv.DivisionID } into divisioncountry_1_join
         from dv in divisioncountry_1_join.DefaultIfEmpty()
         join divisioncountry in db.DivisionCountry on new { InsWorkerStateID = ins_insuranceworkers.InsWorkerStateID } equals new { InsWorkerStateID = divisioncountry.DivisionID } into divisioncountry_join
         from divisioncountry in divisioncountry_join.DefaultIfEmpty()
         select new 
         {
            ins_insuranceworkers.InsWorkerID,
            ins_insuranceworkers.InsWorkerCreateUserID,
             ins_insuranceworkers.InsWorkerTypeID,
             ins_insuranceworkers.InsWorkerFirstName,
             ins_insuranceworkers.InsWorkerLastName,  
            ins_insuranceworkers.InsWorkerNationalCode,
             ins_insuranceworkers.InsWorkerMobileNum,
             ins_insuranceworkers.InsWorkerAddress,
             ins_insuranceworkers.InsWorkerEmail,
              City = dv.DivisionName,
              State = divisioncountry.DivisionName,
             InsWorkerStateID =(Int32?)ins_insuranceworkers.InsWorkerStateID,
             InsWorkerCityID = (Int32?)ins_insuranceworkers.InsWorkerCityID
         }).ToList();

    return InsuranceWorkers;
}

Answer 1

Unfortunately you can't return anonymous types from methods:

You cannot declare a field, a property, an event, or the return type of a method as having an anonymous type. Similarly, you cannot declare a formal parameter of a method, property, constructor, or indexer as having an anonymous type. To pass an anonymous type, or a collection that contains anonymous types, as an argument to a method, you can declare the parameter as type object.

So, either create some specific type for this data and return it:

public List<Foo> InsuranceWorkerView()
{
    return (from i in db.INS_InsuranceWorkers
            select new Foo {
                InsWorkerID = i.InsWorkerID,
                InsWorkerCreateUserID = i.InsWorkerCreateUserID
                // etc
            }).ToList();
}

Or return object (which I find a little useless):

public object InsuranceWorkerView()
{
    return (from i in db.INS_InsuranceWorkers
            select new {
                i.InsWorkerID,
                i.InsWorkerCreateUserID
                // etc
            }).ToList();
}

Answer 2

That's the case when dynamic may come in handy.

public IEnumerable<dynamic> InsuranceWorkerView()
{
    var InsuranceWorkers =(from ins_insuranceworkers in db.INS_InsuranceWorkers
         join dv in db.DivisionCountry on new { InsWorkerCityID = ins_insuranceworkers.InsWorkerCityID } equals new { InsWorkerCityID = dv.DivisionID } into divisioncountry_1_join
         from dv in divisioncountry_1_join.DefaultIfEmpty()
         join divisioncountry in db.DivisionCountry on new { InsWorkerStateID = ins_insuranceworkers.InsWorkerStateID } equals new { InsWorkerStateID = divisioncountry.DivisionID } into divisioncountry_join
         from divisioncountry in divisioncountry_join.DefaultIfEmpty()
         select new 
         {
            ins_insuranceworkers.InsWorkerID,
            ins_insuranceworkers.InsWorkerCreateUserID,
             ins_insuranceworkers.InsWorkerTypeID,
             ins_insuranceworkers.InsWorkerFirstName,
             ins_insuranceworkers.InsWorkerLastName,  
            ins_insuranceworkers.InsWorkerNationalCode,
             ins_insuranceworkers.InsWorkerMobileNum,
             ins_insuranceworkers.InsWorkerAddress,
             ins_insuranceworkers.InsWorkerEmail,
              City = dv.DivisionName,
              State = divisioncountry.DivisionName,
             InsWorkerStateID =(Int32?)ins_insuranceworkers.InsWorkerStateID,
             InsWorkerCityID = (Int32?)ins_insuranceworkers.InsWorkerCityID
         }).ToList();

    return InsuranceWorkers;
}

And then you can use something like:

foreach (var worker in InsuranceWorkerView()) {
   var id = (int)worker.InsWorkerID;
}

Answer 3

You can return the new list as IList.

public IList InsuranceWorkerView()
{
    var InsuranceWorkers =(from ins_insuranceworkers in db.INS_InsuranceWorkers
         join dv in db.DivisionCountry on new { InsWorkerCityID = ins_insuranceworkers.InsWorkerCityID } equals new { InsWorkerCityID = dv.DivisionID } into divisioncountry_1_join
         from dv in divisioncountry_1_join.DefaultIfEmpty()
         join divisioncountry in db.DivisionCountry on new { InsWorkerStateID = ins_insuranceworkers.InsWorkerStateID } equals new { InsWorkerStateID = divisioncountry.DivisionID } into divisioncountry_join
         from divisioncountry in divisioncountry_join.DefaultIfEmpty()
         select new 
         {
            ins_insuranceworkers.InsWorkerID,
            ins_insuranceworkers.InsWorkerCreateUserID,
             ins_insuranceworkers.InsWorkerTypeID,
             ins_insuranceworkers.InsWorkerFirstName,
             ins_insuranceworkers.InsWorkerLastName,  
            ins_insuranceworkers.InsWorkerNationalCode,
             ins_insuranceworkers.InsWorkerMobileNum,
             ins_insuranceworkers.InsWorkerAddress,
             ins_insuranceworkers.InsWorkerEmail,
              City = dv.DivisionName,
              State = divisioncountry.DivisionName,
             InsWorkerStateID =(Int32?)ins_insuranceworkers.InsWorkerStateID,
             InsWorkerCityID = (Int32?)ins_insuranceworkers.InsWorkerCityID
         }).ToList();

And to access the item

   foreach(var item in InsuranceWorkers)
   {
      var a=   item.InsWorkerID; // to access the anonymous items
   }
}

Answer 4

To simplify things, I would suggest you to create a kind of a POCO class with the required properties in order to represent the required projection properly instead of selecting it as anonymous type and get involved with annoying dangerous castings.

Create your POCO class as:

public class InsuranceWorker
{
  public int InsWorkerId {get;set;}
  public int InsWorkerCreateUserId {get;set;}

  //Keep add the necessary properties here...
}

Usage:

Replace your anonymous selection ( select new ) statement with the known type which we've just created above:

 select new InsuranceWorker
 {
    InsWorkerId = ins_insuranceworkers.InsWorkerID,
    InsWorkerCreateUserId = ins_insuranceworkers.InsWorkerCreateUserID,
    //....
 }).ToList();

and return IList<InsuranceWorker> :

public IList<InsuranceWorker> InsuranceWorkerView()
{
  ....
}