Modify LINQ output AnonymousType cannot be assigned

Question

Hi i have a problem and ive been hacking at it for hours i keep getting the error

Property or indexer 'AnonymousType#1.XP' cannot be assigned to -- it is read only

The problem occurs on the a.XP here

    foreach (var a in comments)
    {
        a.XP = score.getLevel(a.XP);
    }

and as a comment pointed out i never say what i want done, i whould like to substitute a.XP with the improved value score.getLevel(a.XP).

Here is the full code

protected void GetComments()
{
    TimberManiacsDataContext db = new TimberManiacsDataContext();
    Score score = new Score();
    var comments = (from fComment in db.Comments
                    where fComment.PublishID == Convert.ToInt32(Request.QueryString["Article"])
                    orderby fComment.DateTime descending
                    select new
                    {
                        UserName = fComment.User.UserLogin.Username,
                        PostTime = fComment.DateTime,
                        UserImage = fComment.User.UserGeneralInfo.ProfilePicture,
                        Comment = fComment.Comment1,
                        UserID = fComment.UserID,
                        XP = fComment.User.CommunityScore
                    }).Take(10).ToList();

    foreach (var a in comments)
    {
        a.XP = score.getLevel(a.XP);
    }
    Commentlist.DataSource = comments;
    Commentlist.DataBind();
}

Answer 1

Anonymously-typed objects are read only, but given your code sample, there is little need to try this modification in the loop, simply make it part of your query execution.

XP = score.getLevel(fComment.User.CommunityScore)

If you find yourself in need of performing changes after the query has executed, then you should go ahead and define a class that allows such mutations and then select into that class instead of the anonymous type.

class CommentData { ... } // define this type with your properties

// then use it for the query projection

select new CommentData 
{
    // ...
}

Answer 2

Anonymous types in C# are immutable and there is nothing you can do about it. As I see it, you have two options:

1. Create a normal (named) type that has a mutable property XP.

2. Copy the contents of the old object into new one, except XP:

   var modifiedComments = comments.Select(
       c => new
       {
           c.UserName,
           c.PostTitle,
           c.UserImage,
           c.Comment,
           c.UserID,
           XP = score.getLevel(c.XP)
       });