Dynamic Linq on method called with generic type via reflection

Question

I have a Query Extender, which has a CustomExpression that I want to use to do some filtering on my datasource.

This is in a DynamicData website so I don't know the object type(current entity) at compile time. Say I knew the object type at compile time, then I could do something like this:

protected void GameFiltering(object sender, CustomExpressionEventArgs e)
{
        e.Query = e.Query.Cast<Resource>().Where(x => x.GameId == GameId);
}

I can get the type I need from e.Query.ElementType. Now I just to send the ElementType as a generic parameter to the Cast method and then call the linq method Where.

I'm gonna assume that every Type is going to have a GameId property which I'll want to filter by.

MethodInfo method = e.Query.GetType().GetMethod("Cast").MakeGenericMethod(new Type[] { e.Query.ElementType });
var castedQuery = method.Invoke(e.Query, null);

This is how I call the cast method with reflection, but I don't know how I can call the linq method on the resulting object.

possible duplicate of How do I invoke an extension method using reflection? — InvisiblePanda
– InvisiblePanda, Commented Aug 31, 2015 at 9:27
The answer in the link above contains a description on how to call the correct Where overload via Reflection. Basically, you have to loop through all the existing Where methods defined on System.Linq.Enumerable and search for the fitting one. Then build a Func<Resource, bool> to pass as parameter. — InvisiblePanda
– InvisiblePanda, Commented Aug 31, 2015 at 9:31
If all your types have a property GameID why not implementing a common interface and cast to that. Then you can call Where on that instance. — MakePeaceGreatAgain
– MakePeaceGreatAgain, Commented Aug 31, 2015 at 9:39
because they are generated automatically from the database via Entity Framework. — Adrian Buzea
– Adrian Buzea, Commented Aug 31, 2015 at 9:48

Robert Fricke · Accepted Answer · 2015-08-31 09:55:33Z

2

If you assume all items have the property, you don't need to cast them.

protected void GameFiltering(object sender, CustomExpressionEventArgs e)
{
    e.Query = e.Query.Where(obj => (int)obj.GetType().GetProperty("GameId").GetValue(obj, null) == GameId)
}

answered Aug 31, 2015 at 9:55

Robert Fricke

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3 Comments

Adrian Buzea Over a year ago

Interesting solution. I tried this: e.Query = e.Query.Cast<Object>().Where(x => (short)x.GetType().GetProperty("GameId").GetValue(x, null) == GameId); Still have to cast to something otherwise I can't call Where on e.Query. This works but when I try to do the DataBind() on my gridview I get an error saying it was expecting an QueryObject of type Resource but it got a QueryObject of type Object

Robert Fricke Over a year ago

What type is e.Query?

Adrian Buzea Over a year ago

{System.Data.Entity.Core.Objects.ObjectQuery<OfferManagementBackOffice.Resource>}

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