How to prevent double round trip with Linq and ToArray() Method

Question

I am trying to use an Array instead of a list in my query. But I must get the count first before I can iterate through the objects returned from the database. Here is my code:

        var FavArray = favorites.OrderByDescending(y => y.post_date).Skip((page - 1) * config.MaxRowsPerPage).Take(config.MaxRowsPerPage).ToArray();
        int FavArrayCount = FavArray.Count();  //Is this a round trip to the database?

        for (int y = 0; y < FavArrayCount; y++)
        {
            q = new PostType();
            q.Title = FavArray[y].post_title;
            q.Date = FavArray[y].post_date;
            q.PostID = FavArray[y].post_id;
            q.Username = FavArray[y].user_username;
            q.UsernameLowered = FavArray[y].user_username.ToLower();
            q.CategoryID = FavArray[y].catid;
            q.CategoryName = FavArray[y].name;
            q.TitleSlug = FavArray[y].post_titleslug;
        }

As you can see I need the count before I start iterating and I am worried that getting the count my make a trip to the database. Is this true?

Answer 1

FavArray.Count() will not round trip, because you have already converted it to an array, which is no longer "LINQ-ified".

Answer 2

Once you call ToArray, any operations on the array that it returns will not go back to the server. (Unless you use a foreign key)

LINQ methods such as Count() that you call on the array will use regular LINQ to Objects and will be completely unaware of SQL Server.

Answer 3

In addition to other comments (it definitely won't round trip; it's just an array), you can just use favArray.Length.