Question

I’m building a small project with SubSonic 3.0.0.3 ActiveRecord and I’m running into an issue I can’t seem to get past.

Here is the LINQ query:

var result = from r in Release.All()
             let i = Install.All().Count(x => x.ReleaseId == r.Id)
             where r.ProductId == productId
             select new ReleaseInfo
             {
                 NumberOfInstalls = i,
                 Release = new Release
                 {
                     Id = r.Id,
                     ProductId = r.ProductId,
                     ReleaseNumber = r.ReleaseNumber,
                     RevisionNumber = r.RevisionNumber,
                     ReleaseDate = r.ReleaseDate,
                     ReleasedBy = r.ReleasedBy
                 }
             };

The ReleaseInfo object is a custom class and looks like this:

public class ReleaseInfo
{
    public Release Release { get; set; }
    public int NumberOfInstalls { get; set; }
}

Release and Install are classes generated by SubSonic.

When I do a watch on result, the Release property is null.

If I make this a simpler query and watch result, the value is not null.

var result = from r in Release.All()
             let i = Install.All().Count(x => x.ReleaseId == r.Id)
             where r.ProductId == productId
             select new Release
             {
                 Id = r.Id,
                 ProductId = r.ProductId,
                 ReleaseNumber = r.ReleaseNumber,
                 RevisionNumber = r.RevisionNumber,
                 ReleaseDate = r.ReleaseDate,
                 ReleasedBy = r.ReleasedBy
             };

Is this an issue with my LINQ query or a limitation of SubSonic?

Answer 1

I think I’ve found the actual answer to this problem. I’ve been rummaging around in the SubSonic source and found that there are two types of object projection that are used when mapping the datareader to objects: one for anonymous types and groupings and one for everything else:

Here is a snippet: Line 269 – 298 of SubSonic.Linq.Structure.DbQueryProvider

IEnumerable<T> result;
Type type = typeof (T);
//this is so hacky - the issue is that the Projector below uses Expression.Convert, which is a bottleneck
//it's about 10x slower than our ToEnumerable. Our ToEnumerable, however, stumbles on Anon types and groupings
//since it doesn't know how to instantiate them (I tried - not smart enough). So we do some trickery here.
    if (type.Name.Contains("AnonymousType") || type.Name.StartsWith("Grouping`") || type.FullName.StartsWith("System.")) {
    var reader = _provider.ExecuteReader(cmd);
    result = Project(reader, query.Projector);
    } else
    {
        using (var reader = _provider.ExecuteReader(cmd))
        {
            //use our reader stuff
            //thanks to Pascal LaCroix for the help here...
            var resultType = typeof (T);
            if (resultType.IsValueType)
            {
                result = reader.ToEnumerableValueType<T>();
            }
            else
            {
                result = reader.ToEnumerable<T>();
            }
        }
    }
    return result;

Turns out that the SubSonic ToEnumerable tries to match the column names in the datareader to the properties in the object you’re trying to project to. The SQL Query from my Linq looks like this:

SELECT [t0].[Id], [t0].[ProductId], [t0].[ReleaseDate], [t0].[ReleasedBy], [t0].[ReleaseNumber], [t0].[RevisionNumber], [t0].[c0]
FROM (
  SELECT [t1].[Id], [t1].[ProductId], [t1].[ReleaseDate], [t1].[ReleasedBy], [t1].[ReleaseNumber], [t1].[RevisionNumber], (
    SELECT COUNT(*)
    FROM [dbo].[Install] AS t2
    WHERE ([t2].[ReleaseId] = [t1].[Id])
    ) AS c0
  FROM [dbo].[Release] AS t1
  ) AS t0
WHERE ([t0].[ProductId] = 2)

Notice the [t0].[c0] is not the same as my property name NumberOfInstalls. So the value of c0 never gets projected into my object.

THE FIX:
You can simply take out the if statement and use the 10x slower projection and everything will work.