C# expression tree for ordinary code

Question

It's possible to create an expression tree, if you declare it as such.

But is it possible to get an expression tree for an ordinary chunk of code such as a method or property getter?

What I'm trying to do is, let's say for an order processing system, I have a class for order items:

class Item : Entity
{
    [Cascade]
    public Document document { get; set; }
    public int line { get; set; }

    public Product product { get; set; }
    public string description { get; set; }
    public decimal qty { get; set; }
    public decimal price { get; set; }
    public decimal net
    {
        get
        {
            return qty * price;
        }
    }
    public VatCode vat_code { get; set; }
}

where the net value equals qty * price, so I'd like to declare it as such, either with a property or method, and then also have the framework introspect that expression so it can generate appropriate SQL for defining a corresponding calculated column in a corresponding database view.

The most obvious way to do this would be to get the expression tree for a property getter or a method, but I can't find any indication how to do this, or that it is possible. (I have found a way to get a method body as a byte stream, but that's not what's desired here.)

If that isn't possible, I suppose the recommended solution would be to declare something like a static field that is an expression tree, and compile/run it at run time for internal use, and also introspect as normal for SQL generation?

Answer 1

No, not possible - normal code is bytecode, there is no mechanism to turn that into an expression tree.What you can do is use reflection - but that basically is it.

Answer 2

I've been looking for a similar thing before, and I haven't found a perfect way to do this, tbh.

The other problem that you might run into, is that even if you will have an expression tree that you'd want to inject in a linq query - it's not straightforward and as easy as it sounds...

For what it's worth, one way to do this is have a static expression stored that will allow getting your "net" out, and let the getter of the "net" property run this expression against this.

And how to inject an expression in a regular linq query? I've written a blog post about it. Basically, I create an expression extender that will update the L2S expression tree with the custom expression :) Extending LINQ selectors with custom expressions