MySQL :: MySQL 5.0 Reference Manual :: 25.2.3.5 MySqlDataReader

MySQL 5.0 Reference Manual :: 25 Conectores :: 25.2 MySQL Connector/NET :: 25.2.3 Connector/NET Examples :: 25.2.3.5 MySqlDataReader

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25.2.3.5. MySqlDataReader

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25.2.3.5.1. GetBytes
25.2.3.5.2. GetTimeSpan
25.2.3.5.3. GetDateTime
25.2.3.5.4. GetMySqlDateTime
25.2.3.5.5. GetString
25.2.3.5.6. GetDecimal
25.2.3.5.7. GetDouble
25.2.3.5.8. GetFloat
25.2.3.5.9. GetGiud
25.2.3.5.10. GetInt16
25.2.3.5.11. GetInt32
25.2.3.5.12. GetInt64
25.2.3.5.13. GetUInt16
25.2.3.5.14. GetUInt32
25.2.3.5.15. GetUInt64

To create a MySQLDataReader, you must call the MySqlCommand.ExecuteReader method of the MySqlCommand object, rather than directly using a constructor.

While the MySqlDataReader is in use, the associated MySqlConnection is busy serving the MySqlDataReader, and no other operations can be performed on the MySqlConnection other than closing it. This is the case until the MySqlDataReader.Close method of the MySqlDataReader is called.

MySqlDataReader.IsClosed and MySqlDataReader.RecordsAffected are the only properties that you can call after the MySqlDataReader is closed. Though the RecordsAffected property may be accessed at any time while the MySqlDataReader exists, always call Close before returning the value of RecordsAffected to ensure an accurate return value.

For optimal performance, MySqlDataReader avoids creating unnecessary objects or making unnecessary copies of data. As a result, multiple calls to methods such as MySqlDataReader.GetValue return a reference to the same object. Use caution if you are modifying the underlying value of the objects returned by methods such as GetValue.

Examples

The following example creates a MySqlConnection, a MySqlCommand, and a MySqlDataReader. The example reads through the data, writing it out to the console. Finally, the example closes the MySqlDataReader, then the MySqlConnection.

Visual Basic example:

Public Sub ReadMyData(myConnString As String)
    Dim mySelectQuery As String = "SELECT OrderID, CustomerID FROM Orders"
    Dim myConnection As New MySqlConnection(myConnString)
    Dim myCommand As New MySqlCommand(mySelectQuery, myConnection)
    myConnection.Open()
    Dim myReader As MySqlDataReader
    myReader = myCommand.ExecuteReader()
    ' Always call Read before accessing data.
    While myReader.Read()
        Console.WriteLine((myReader.GetInt32(0) & ", " & myReader.GetString(1)))
    End While
    ' always call Close when done reading.
    myReader.Close()
    ' Close the connection when done with it.
    myConnection.Close()
End Sub 'ReadMyData

C# example:

public void ReadMyData(string myConnString) {
    string mySelectQuery = "SELECT OrderID, CustomerID FROM Orders";
    MySqlConnection myConnection = new MySqlConnection(myConnString);
    MySqlCommand myCommand = new MySqlCommand(mySelectQuery,myConnection);
    myConnection.Open();
    MySqlDataReader myReader;
    myReader = myCommand.ExecuteReader();
    // Always call Read before accessing data.
    while (myReader.Read()) {
       Console.WriteLine(myReader.GetInt32(0) + ", " + myReader.GetString(1));
    }
    // always call Close when done reading.
    myReader.Close();
    // Close the connection when done with it.
    myConnection.Close();
 }

25.2.3.5.1. GetBytes

GetBytes returns the number of available bytes in the field. In most cases this is the exact length of the field. However, the number returned may be less than the true length of the field if GetBytes has already been used to obtain bytes from the field. This may be the case, for example, if the MySqlDataReader is reading a large data structure into a buffer. For more information, see the SequentialAccess setting for MySqlCommand.CommandBehavior.

If you pass a buffer that is a null reference (Nothing in Visual Basic), GetBytes returns the length of the field in bytes.

No conversions are performed; therefore the data retrieved must already be a byte array.