This class represents a parameter for a Command
object. Parameters are accessed using the
IDbCommand.Parameters collection. Parameters are
identified using the ParameterName property. With
the SQL Server provider, parameter names are required, and the SQL
statement takes the form:
SELECT * FROM Customers WHERE CustomerID = @CustomerID
and the parameter must be named @CustomerID . With
the OLE DB provider, however, a question mark placeholder is used
instead. Order is important, but the parameter name
isn't. The SQL statement takes the form:
SELECT * FROM Customers WHERE CustomerID = ?
(and the CustomerID value must be first in the
parameter collection).
The IDataParameter interface also defines several
other important properties. DbType indicates the
underlying database data type (although individual ADO.NET providers
usually provide an enumeration specific to the data source), and
Direction determines whether the parameter is sent
to the stored procedure, retrieve from it, or both. You can set the
value for the parameter directly using the Value
property. You can map it to a column in the
DataSet by setting the name of the column in the
SourceColumn property. This is primarily useful
when you are defining a generic update, insert, or delete command for
use with a data adapter. Because this command must work with any
modified row, you can't directly code a parameter
value. Instead, the value must be retrieved from the appropriate
DataRow . You can also specify the version of the
value using the SourceVersion property. For
example, if the parameter corresponds to a WHERE clause that selects
the row that needs to be updated, you use the original value. If the
parameter corresponds to the SET clause in an UPDATE statement, use
the current value to apply the new information to the data source.
public interface IDataParameter {
// Public Instance Properties
public DbType DbType{set; get; }
public ParameterDirection Direction{set; get; }
public bool IsNullable{get; }
public string ParameterName{set; get; }
public string SourceColumn{set; get; }
public DataRowVersion SourceVersion{set; get; }
public object Value{set; get; }
}
