iQueryable and Expression Tree

Question

Can anybody explain me how to use (1) iQueryable (2) Expression Tree in C# by providing a very basic example? Both are not correlated, instead of making two separate questions, I wish to clear my doubt in a single question.

Advanced Thanks.

Answer 1

Expression trees are very simple to make:

Expression<Func<int,int,int>> addExp = (a,b) => a + b;

or

var paramA = Expression.Parameter(typeof(int), "a");
var paramB = Expression.Parameter(typeof(int), "b");
Expression<Func<int,int,int>> addExp = Expression.Lambda<Func<int,int,int>>(
    Expression.Add(paramA, paramB),
    paramA,
    paramB);

Building an IQueryable provider is fairly difficult. However, Matt Warren has a very indepth series that walks you through creating an IQueryable provider.

Answer 2

I generally don't like just linking stuff, but this is a more complicated topic. I suggest watching this video:

http://channel9.msdn.com/shows/Going+Deep/Erik-Meijer-and-Bart-De-Smet-LINQ-to-Anything/

Erik does a great job of explaining this, and gives a neat Linq to Simpsons example.

Answer 3

Expression<Func<T, string, PropertyInfo>> expression = (obj, str) => 
    obj.GetType()
       .GetProperty(
           obj.GetType()
              .GetProperties()
              .ToList()
              .Find(prop =>
                    prop.Equals(str, StringComparison.OrdinalIgnoreCase).Name.ToString());
var obj = expression.Compile()(rowsData.FirstOrDefault(), sortIndex);