Subsonic 3 Linq Projection Issue

问题

OK I'm banging my head against a wall with this one ;-)

Given tables in my database called Address, Customer and CustomerType, I want to display combined summary information about the customer so I create a query to join these two tables and retrieve a specified result.

 var customers = (from c in tblCustomer.All()
                        join address in tblAddress.All() on c.Address equals address.AddressId
                        join type in tblCustomerType.All() on c.CustomerType equals type.CustomerTypeId
                        select new CustomerSummaryView
                                   {
                                       CustomerName = c.CustomerName,
                                       CustomerType = type.Description,
                                       Postcode = address.Postcode
                                   });

  return View(customers);

CustomerSummaryView is a simple POCO

public class CustomerSummaryView
{
    public string Postcode { get; set; }
    public string CustomerType { get; set; }
    public string CustomerName { get; set; }
}

Now for some reason, this doesn't work, I get an IEnumerable list of CustomerSummaryView results, each record has a customer name and a postcode but the customer type field is always null.

I've recreated this problem several times with different database tables, and projected classes.

Anyone any ideas?

回答1:

I can't repro this issue - here's a test I just tried:

[Fact]
public void Joined_Projection_Should_Return_All_Values() {
    var qry = (from c in _db.Customers
                     join order in _db.Orders on c.CustomerID equals order.CustomerID
                     join details in _db.OrderDetails on order.OrderID equals details.OrderID
                     join products in _db.Products on details.ProductID equals products.ProductID
                     select new CustomerSummaryView
                     {
                         CustomerID = c.CustomerID,
                         OrderID = order.OrderID,
                         ProductName = products.ProductName
                     });

    Assert.True(qry.Count() > 0);

    foreach (var view in qry) {
        Assert.False(String.IsNullOrEmpty(view.ProductName));
        Assert.True(view.OrderID > 0);
        Assert.False(String.IsNullOrEmpty(view.CustomerID));
    }

}

This passed perfectly. I'm wondering if you're using a reserved word in there?

回答2:

This post seems to be referring to a similar issue...

http://groups.google.com/group/subsonicproject/browse_thread/thread/2b569539b7f67a34?hl=en&pli=1

回答3:

Yes, the reason Rob's example works is because his projection's property names match exactly, whereas John's original example has a difference between CustomerType and type.Description.

This shouldn't have been a problem, but it was - the Projection Mapper was looking for properties of the same name and wasn't mapping a value if it didn't find a match. Therefore, your projection objects' properties would be default values for its type if there wasn't an exact name match.

The good news is, I got the latest source today and built a new Subsonic.Core.dll and the behavior is now fixed.

So John's code above should work as expected.

回答4:

I just downloaded the latest build from 3/21/2010, which is about 2 months after the last poster on this thread, and the problem still exists in the packaged binary. Bummer.

Here what I have to do:

        var data =
            (from m in Metric.All()
             where m.ParentMetricId == parentId
             select new
                    {
                         m.MetricName,
                         m.MetricId,
                    })
                    .ToList();

        var treeData =
            from d in data
            select new TreeViewItem
                    {
                        Text = d.MetricName,
                        Value = d.MetricId.ToString(),
                        LoadOnDemand = true,
                        Enabled = true,
                    };

        return new JsonResult { Data = treeData };

If I try to do the projection directly from the Subsonic query, the Text property ends up with the ID, and the Value property ends up with the Name. Very strange.

来源：https://stackoverflow.com/questions/1105052/subsonic-3-linq-projection-issue

标签

linq

activerecord

subsonic3