If i have a product.
var p = new Product { Price = 30 };
and i have the following linq query.
var q = repo.Products().Where(x=>x.Price == p.Price).ToList()
In an IQueryable provider, I get a MemberExpression back for the p.Price which contains a Constant Expression, however I can't seem to get the value "30" back from it.
Update I have tried this but it doesn't seem to work.
var memberExpression = (MemberExpression)GetRootConstantExpression(m);
var fi = (PropertyInfo)memberExpression.Member;
var val = fi.GetValue(((ConstantExpression)memberExpression.Expression).Value, null);
Cheers.
You can compile and invoke a lambda expression whose body is the member access:
private object GetValue(MemberExpression member)
{
var objectMember = Expression.Convert(member, typeof(object));
var getterLambda = Expression.Lambda<Func<object>>(objectMember);
var getter = getterLambda.Compile();
return getter();
}
Local evaluation is a common technique when parsing expression trees. LINQ to SQL does this exact thing in quite a few places.