Anonymous Type with Linq and Guid

Question

I have a simple table:

ID | Value

When I do this:

var sequence = from c in valuesVault.GetTable()
               select new {RandomIDX = Guid.NewGuid(), c.ID, c.Value};

each element in the projection has the value of the same guid... How do I write this so that I get a different random guid value for each of my element in the projection?

Edit

To clarify on the issue. The GetTable() method simply calls this:

        return this.context.GetTable<T>();

where the this.contenxt is the DataContext of type T.

The itteration is done as it's always done, nothing fancy:

     foreach (var c in seq) 
     {
          Trace.WriteLine(c.RandomIDX + " " + c.Value);
     }

Output:

bf59c94e-119c-4eaf-a0d5-3bb91699b04d What is/was your mother's maiden name?
bf59c94e-119c-4eaf-a0d5-3bb91699b04d What was the last name of one of your high school English teachers?
bf59c94e-119c-4eaf-a0d5-3bb91699b04d In elementary school, what was your best friend's first and last name?

Edit 2 Using out the box linq2Sql Provider. I had built some generic wrappers around it but they do not alter the way IQuaryable or IEnumerable function in the code.

Answer 1

What is underneath valuesVault.GetTable()?

You probably have a Linq provider such as Linq 2 SQL.

That means that valuesVault.GetTable() is of type IQueryable which in turn means that the entire query becomes an expression.

An expression is a query that is defined but not yet executed.

When sequence is being iterated over, the query is executed using the Linq provider and that Linq provider and one of the steps it has to perform is to execute this expression: Guid.NewGuid(). Most Linq providers cannot pass that expression to the underlying source (SQL Server wouldn't know what to do with it) so it gets executed once and the result of the execution returned with the rest of the result.

What you could do is to force the valuesVault.GetTable() expression to become a collection by calling the .ToList() or .ToArray() methods. This executes the expression and returns an IEnumerable which represents an in-memory collection.

When performing queries against an IEnumerable, the execution is not passed to the Linq provider but executed by the .NET runtime.

In your case this means that the expression Guid.NewGuid() can be executed correctly.

Try this:

var sequence = from c in valuesVault.GetTable().ToArray()
               select new {RandomIDX = Guid.NewGuid(), c.ID, c.Value};

Notice the .ToArray() there. That is what will make the statement go from IQueryable to IEnumerable and that will change its behaviour.