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C# .NET MySql - handling null fields

Posted on 2008-06-14
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Last Modified: 2013-12-17
In my MySQL table I allow NULL values in some fields.
When I itterate through the result set I get an error whenever the reader hits such a NULL value.
Here is the code:
IDataReader reader = dbcmd.ExecuteReader();

                while (reader.Read())
                {

                    string[] catalog_info = {
                (string)reader["tab_name"], (string)reader["document_name"], (string)reader["comment_text"]};

                    dataGridViewCurrentSessionPatientDocuments.Rows.Add(catalog_info);

                }

Here is the error: "Unable to cast object of type 'System.DBNull' to type 'System.String'."
What I need is to instruct the reader to substitute an emplty string ("") for a NULL value


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Question by:eugene-g
2 Comments
 
LVL 142

Accepted Solution

by:
Guy Hengel [angelIII / a3] earned 50 total points
ID: 21786744
or do it directly in the query? ...
COALESCE(yourfield, '' )

in the .net code:
string[] catalog_info = { 
                (string) (reader["tab_name"] == DBNull.Value ? "" : reader["tab_name"] )
              , (string) (reader["document_name"] == DBNull.Value ? "" : reader["document_name"] )
              , (string) (reader["comment_text"] == DBNull.Value ? "" : reader["comment_text"] )
               };

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Author Closing Comment

by:eugene-g
ID: 31467258
Veru ellegant and convinient. Thanks
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