WCF Data Services Expand as Linq Statement

问题

at the moment I am trying myself with WCF Data Services. Now I am trying to query my Servie for some objects similar to the EF ( which is my datasource of the Service ) with an Include Statement, to get an objecttree.

My statement looks like this at this moment :

var query = this.Entities.Veranstaltung.Expand( "VeranstaltungMaterial/Material/Template" ).Expand( "Ort,Dozent" );

var k = query.Where( z => z.DauerTage > 5 && z.TemplateID == null );

Is it possible to write the Expandstatement via LINQ so it gets translated automatically ?

回答1:

Gert's answer is correct, just wanted to expand on it (and can't fit it into a comment): You can express even the first query with the Expand just using LINQ:

Order_Details.Take(1).Select(od =>
    new Order_Detail
    {
        Order = new Order
        {
            Customer = od.Order.Customer
        },
        Product = new Product
        {
            Order_Details = od.Product.Order_Details
        },
    });

You can do a similar trick with m:n relationships. This sample follows a 1:n relationship but from the opposite direction:

Customers.Select(c =>
    new Customer
    {
        Orders = c.Orders.Select(o =>
            new Order
            {
                Order_Details = o.Order_Details
            });
    });

This is equivalent to ~/Customers?$expand=Orders/Order_Details&$select=Orders/Order_Details.

回答2:

I guess that your question is: can I get to the navigation properties through regular linq statements in stead of the WCF-DS-specific Expand statement? If so, the answer is "yes, we can".

Of course I can't use your example but if I connect to the Northwind OData service¹ I can do:

Order_Details.Expand("Order/Customer").Expand("Product/Order_Details").Take (1)

Order_Details.Take(1).Select(o => 
                      new { o.Order.Customer, o.Product.Order_Details })

Not entirely equivalent (and hardly useful), but OK.

In the URL's you'll see that the second statement is translated to expand as well.

http://services.odata.org/V3/Northwind/Northwind.svc/

来源：https://stackoverflow.com/questions/12438481/wcf-data-services-expand-as-linq-statement

标签

wcf

linq

wcf-data-services

expand