Can I make a column's value late databound?

Question

I have a table with a few columns and I'd like to add a column withouth providing it a value a first because it's a (somewhat) complex object that might not be useful everytime the table is used.

So my current code looks like this:

            var com = new SqlConnection(functions.ConnectionString).CreateCommand();
            com.CommandText = @"
SELECT
    S.id
    , S.Name
    , S.MemberID
FROM dbo.SubSets AS S
WHERE S.SubsetType = 0
AND S.MemberId > 1
";
            this.tblSubsets = new DataTable();

            new SqlDataAdapter(com).Fill(this.tblSubsets);

            this.tblSubsets.Columns.Add(new DataColumn()
            {
                AllowDBNull = true
                , ColumnName = "Member"
                , DataType = typeof(object) // ?
                , DefaultValue = DBNull.Value // late binding mechanism?
            });

How can I make that column Member stays "empty" until it's being used DoSomethingwith(table.Rows[x]["Member"])?

score 0 · Answer 1 · answered Jul 08 '13 at 09:16

I Guess you can't.

I ended up storing a Func<T> and automatically set the field whenever a row is added to the table.
Plus the dictionary in closure serves the performance goal.

            this.tblSubsets = new DataTable();

            this.tblSubsets.Columns.AddRange(new DataColumn[] {
                new DataColumn()
                {
                    AllowDBNull = false
                    , ColumnName = "Member"
                    , DataType = typeof(Func<Member>)
                }
            });

            var members = new Dictionary<int, Member>();
            this.tblSubsets.RowChanged += new DataRowChangeEventHandler((object sender, DataRowChangeEventArgs e) =>
            {
                if (e.Action != DataRowAction.Add)
                {
                    return;
                }

                e.Row["Member"] = new Func<Member>(() =>
                {
                    Member returnValue;
                    var mid = Convert.ToInt32(e.Row["MemberID"]);

                    if (!members.TryGetValue(mid, out returnValue))
                    {
                        members.Add(mid, (returnValue = new Member(mid)));
                    }

                    return returnValue;
                });
            });


            var com = new SqlConnection(functions.ConnectionString).CreateCommand();
            com.CommandText = @"
SELECT
    S.id
    , S.Name
    , S.MemberID
FROM dbo.SubSets AS S
WHERE S.SubsetType = 0
";
            new SqlDataAdapter(com).Fill(this.tblSubsets);

Can I make a column's value late databound?

1 Answers1