Nested LINQ IQueryable and WCF WebApi - wcf

Question

I have a method like this that works as expected.
[WebGet]
public IQueryable<BuildJobModel> GetCustomers()
{
var context = new MyDataContext(); // ADO.NET Entity Data Model
var query = from c in context.Customers
select new CustomerModel {
Id = c.Id,
Name = c.Name
};
return query;
}
But when I try to create a more complex query like this, it doesn't work.
[WebGet]
public IQueryable<BuildJobModel> GetCustomers()
{
var context = new MyDataContext(); // ADO.NET Entity Data Model
var query = from c in context.Customers
select new CustomerModel {
CustomerId = c.CustomerId,
Name = c.Name,
Orders = from o in c.Orders
select new OrderModel {
OrderId = o.OrderId,
Details = o.Details
}
};
return query;
}
The Models look like this:
public class CustomerModel
{
public int CustomerId { get; set; }
public string Name { get; set; }
public IEnumerable<OrderModel> Orders { get; set; }
}
public class OrderModel
{
public int OrderId { get; set; }
public string Details { get; set; }
}
The Exception:
Cannot serialize member Proj.CustomerModel.Logs of type System.Collections.Generic.IEnumerable`1[[Proj.OrderModel, Proj, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]] because it is an interface.
My Goals:
I want to be able to expose an IQueryable interface.
I want to return nested data.
I want to use my own Models, not the ado.net entities
I want to hit the database with as few queries as possible (one would be best).

Answer 1

I would strongly recommend not exposing IQueryable as a return type of a WCF service.
WCF was designed to return data not queries
You lose control over the nature of the query: someone might potentially use this query in a way that is resource-intensive
Ideally, if you want to return collections use array or a generic list.
With respect to your list of goals:
Can you explain this? I don't see what IQueryable interface has to do with nested data.
You can still return arrays or lists of your models
You have better control over performance if you execute query locally and return results instead
Update: Have a look at WCF Data Services - that might be able to do what you want.

Answer 2

In case you're trying to return JSON: the build in JsonFormatter is not able to (de)serialize interfaces. You should try the JSON.NET Formatter from WebApiContrib.

Answer 3

I think you just need to use an array rather than IEnumerable, like so...
public class CustomerModel
{
public int CustomerId { get; set; }
public string Name { get; set; }
public OrderModel[] Orders { get; set; }
}
public class OrderModel
{
public int OrderId { get; set; }
public string Details { get; set; }
}
If you're serializing this to json/xml I suspect the built-in serializers don't know what to do with IEnumerable.