C# – Performing part of a IQueryable query and deferring the rest to Linq for Objects

cexpression-treesiqueryablelinq

I have a Linq provider that sucessfully goes and gets data from my chosen datasource, but what I would like to do now that I have my filtered resultset, is allow Linq to Objects to process the rest of the Expression tree (for things like Joins, projection etc)

My thought was that I could just replace the expression constant that contains my IQueryProvider with the result-sets IEnumerable via an ExpressionVisitor and then return that new expression. Also return the IEnumerable's provider from my IQueryable…but this does not seem to work šŸ™

Any idea's?

Edit:
Some good answers here, but given the form…

var qry = from c in MyProv.Table<Customer>()
          Join o in MyProv.Table<Order>() on c.OrderID equals o.ID
          select new 
          {
            CustID = c.ID,
            OrderID = o.ID
          }

In my provider I can easily get back the 2 resultsets from Customers and Orders, if the data was from a SQL source I would just construct and pass on the SQL Join syntax, but it this case the data is not from a SQL source so I need to do the join in code…but as I said I have the 2 result sets, and Linq to Objects can do a join…(and later the projection) it would be real nice to just substitute the Expression constants MyProv.Table<Customer> and MyProv.Table<Order> with List<Customer> and List<Order> and let a List<> provider process the expression…is that possible? how?

Best Answer

Both of the previous answers work, but it reads better if you use AsEnumerable() to cast the IQueryable to IEnumerable:

// Using Bob's code...
var result = datacontext.Table
   .Where(x => x.Prop == val)
   .OrderBy(x => x.Prop2)
   .AsEnumerable()  //  <---- anything after this is done by LINQ to Objects
   .Select(x => new { CoolProperty = x.Prop, OtherProperty = x.Prop2 });

EDIT:

// ... or MichaelGG's
var res = dc.Foos
           .Where(x => x.Bla > 0)  // uses IQueryable provider
           .AsEnumerable()
           .Where(y => y.Snag > 0); // IEnumerable, uses LINQ to Objects
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