How to use LINQ where clause for filtering the collection having dynamically generated type - linq

Question

I need to filter the ObservableCollection using LINQ Where clause in my Silverlight application.
The object type is dynamically created using method provided in following url.
http://mironabramson.com/blog/post/2008/06/Create-you-own-new-Type-and-use-it-on-run-time-(C).aspx
Is filtering my collection using Where clause for specific property possible?
How can I achieve it?
Thanks

Answer 1

The only way I know is using reflection, like this:
// using a list of dynamic types
var items = new List<object> { new { A = 0, B = 1 }, new { A = 1, C = 0 } };
// select ao items with A > 0
var filteredItems = items.Where(obj => (int)obj.GetType().GetField("A").GetValue(obj) > 0).ToArray();
// if you have a property instead of field, you should call GetProperty(), like this:
obj.GetType().GetProperty("PropertyName").GetValue(obj, null)

Answer 2

As you know the element type of your collection only at run time it probably is object at compile time. So the argument to the .Where method has to be a Func<object, bool>.
Here's a piece of code that will create such a delegate given a property of the actual element type and a lambda expression on the property (which i suppose you know the type of):
/// <summary>
/// Get a predicate for a property on a parent element.
/// </summary>
/// <param name="property">The property of the parent element to get the value for.</param>
/// <param name="propertyPredicate">The predicate on the property value.</param>
static Func<object, bool> GetPredicate<TProperty>(PropertyInfo property, Expression<Func<TProperty, bool>> propertyPredicate)
{
if (property.PropertyType != typeof(TProperty)) throw new ArgumentException("Bad property type.");
var pObj = Expression.Parameter(typeof(object), "obj");
// ((elementType)obj).property;
var xGetPropertyValue = Expression.Property(Expression.Convert(pObj, property.DeclaringType), property);
var pProperty = propertyPredicate.Parameters[0];
// obj => { var pProperty = xGetPropertyValue; return propertyPredicate.Body; };
var lambda = Expression.Lambda<Func<object, bool>>(Expression.Block(new[] { pProperty }, Expression.Assign(pProperty, xGetPropertyValue), propertyPredicate.Body), pObj);
return lambda.Compile();
}
Sample usage:
var items = new List<object> { new { A = 0, B = "Foo" }, new { A = 1, B = "Bar" }, new { A = 2, B = "FooBar" } };
var elementType = items[0].GetType();
Console.WriteLine("Items where A >= 1:");
foreach (var item in items.Where(GetPredicate<int>(elementType.GetProperty("A"), a => a >= 1)))
Console.WriteLine(item);
Console.WriteLine();
Console.WriteLine("Items where B starts with \"Foo\":");
foreach (var item in items.Where(GetPredicate<string>(elementType.GetProperty("B"), b => b.StartsWith("Foo"))))
Console.WriteLine(item);
Output:
Items where A >= 1:
{ A = 1, B = Bar }
{ A = 2, B = FooBar }
Items where B starts with "Foo":
{ A = 0, B = Foo }
{ A = 2, B = FooBar }