如何将新行添加到由IDataReader填充的表中？

Question

I'm trying to add a new entry to a DataTable after I load it with the info contained in an IDataReader object, a DbDataReader concretely. The loading goes fine and the query to the database is correct I think.

When trying to add a new row I get an ArgumentException with the following info:

Cannot set column 'ID'. The value violates the MaxLength limit of this column.

This is the code I have right now:

// Build the query:
DbCommand cmd = dbCon.CreateCommand();
cmd.CommandText = "SELECT ID, Name || ' ' || SurName AS FullName FROM Clients ORDER BY FullName;";
// Execute it:
DbDataReader reader = cmd.ExecuteReader();
// Construct the table out of the query result:
DataTable table = new DataTable();
table .Load(reader);
table.Rows.Add(0, "None");

In the database (SQLite) ID is of type INTEGER and both Name and SurName are VARCHAR s. Am I doing something wrong? How could 0 violate the MaxLength limit?

Answer 1

Finally you've solved the issue by using one of my favourite debugger "tricks" to un-mistify strange DataTable exceptions. From comments:

You can always look what causes the ConstraintException by using the debugger. Execute table.Load(reader) in a QuickWatch Dialog Box. Afterwards execute table.GetErrors(). Then you can look into the returned rows at their RowError property. Voilà!

Since i'm using DbDataAdapter.Fill(DataTable) in almost all cases, i've forgotten that DataTable.Load(IDataReader) infers the schema based on the result set from the imported IDataReader . But of course it needs at least one DataRow to do so. That was the reason why it works when the DataTable wasn't empty.

Answer 2

Check the MaxLength property on your ID column in your datatable

  size = dataTables(0).Columns(0).MaxLength 

http://forums.asp.net/t/306971.aspx