cannot be called with instance of type 'System.Data.Entity.Core.Objects.ObjectQuery

Question

I want to Find Username by userId

this code snippet working

Discussion_CreateBy = db.AspNetUsers.Find(discussion.CreatedBy).UserName,

Answer 1

Discussion_CreateBy = db.AspNetUsers.Find(discussion.CreatedBy).UserName

Works because discussion is an in-memory object because you are executing a query by calling FirstOrDefault on it:

var discussion = db.AB_Discussion.Where(d => d.Discussion_ID == Discussion_ID).FirstOrDefault();

On the other hand in the following statement:

db.AspNetUsers.Find(c.CreatedBy).UserName

c is not queried yet because

db.AB_DiscussionComments.Where(c => c.Discussion_ID == Discussion_ID)

returns an IQueriable and not the actual collection of comments

The easiest way to fix it is to bring all your comments into memory (since you are anyway need them all) :

var comments = db.AB_DiscussionComments.Where(c => c.Discussion_ID == Discussion_ID).ToList();