Error: An expression tree may not contain a dynamic operation

问题

I use Asp.Net 4 and C#, I use EF 4.

I have this query, I receive an error:

 An expression tree may not contain a dynamic operation

---

dynamic o = e.Item.DataItem;
var imagesContent = context.CmsImagesContents.FirstOrDefault(img => img.ContentId == o.ContentId);

It seems is imposible to Cast a Dynamic Type using a Lamba Expression.

How I can fix the problem, and able to use my object o in my Lamba? Thanks

PS: e.Item.DataItem is of Type CmsContent and o.ContentId is of type Int

回答1:

Unboxing the object will do the trick:

     int contentId = (int)o.ContentId;
     var image = context.CmsImagesContents.FirstOrDefault(img => img.ContentId == contentId);

For more info about 'boxing/unboxing' click here

回答2:

Change

dynamic o = e.Item.DataItem;

To

var o = (CmsContent)e.Item.DataItem;

来源：https://stackoverflow.com/questions/7118550/error-an-expression-tree-may-not-contain-a-dynamic-operation