将LINQ返回类型转换为C＃类

Question

I have a LINQ query against my DBModel classes which is returning an anonymous type. I have to convert it to a known C# class type.

I can directly use the known type in DBModel class but it's not allowed to use any known types in my project architecture.

Example:

static dynamic getEmployees()
{
    SampleDB db = new SampleDB();
    var result = (from x in db.Employes
    select new
    {
        name = x.FirstName + " " + x.LastName,
        department = x.DepartmentId
    });
    return result;
}

My known type:

public class Emp
{
    public string name { set; get; }
    public int department { set; get; }
}

Program:

dynamic d = getEmployees();
List<Emp> result = d.cast<Emp>();
//Other code....

How can I cast the dynamic type to List? In getEmployees I can't use like

static List<Emp> getEmployees()
{
    SampleDB db = new SampleDB();
    var result = (from x in db.Employes
    select new Emp
    {
        name = x.FirstName + " " + x.LastName,
        department = x.DepartmentId
    }).ToList();

    return result;
}

Can anybody tell me how can I cast the LINQ return type to a known type?

Answer 1

There's no cast method on the dynamic type. What you should do is explicitly cast your dynamic to the required type and because in the dynamic method you have an anonimous object you'll have to do an intermediate step. Something like:

var serializer = new System.Web.Script.Serialization.JavaScriptSerializer();
var json = serializer.Serialize(d);
List<Emp> result = serializer.Deserialize<List<Emp>>(json);

Answer 2

Cast<> is an extension method, and those are not directly supported on dynamic objects.

You can get around that, by calling the extension method like this: Enumerable.Cast<Emp>(d) , but this still would not work, there is no known cast from an anonymous type to Emp.

You could try something similar with .Select() , that should work. However the easiest way is a simple for loop

dynamic d = getEmployees();
var emps = new List<Emp>();
foreach (var emp in d)
{
    emps.Add(new Emp(){name = emp.name, department = emp.department};
}

if you want to consume the collection on-demand as an IEnumerable, instead of putting it in a List, you could wrap this in a helper method:

IEnumerable<Emp> getEmps(dynamic d)
{
    foreach (var emp in d)
    {
        yield return new Emp(){name = emp.name, department = emp.department};
    }
}