Using Parameters with a DataAdapter 

The DataAdapter has four properties that are used to retrieve data from and update data to the data source: the SelectCommand property returns data from the data source; the InsertCommand, UpdateCommand, and DeleteCommand properties are used to manage changes at the data source. The SelectCommand property must be set before calling the Fill method of the DataAdapter. The InsertCommand, UpdateCommand, or DeleteCommand properties must be set before the Update method of the DataAdapter is called, depending on what changes were made to the data in the DataSet. For example, if rows have been added, the InsertCommand must be set before calling Update. When Update is processing an inserted, updated, or deleted row, the DataAdapter uses the respective Command property to process the action. Current information about the modified row is passed to the Command object through the Parameters collection.

When updating a row at the data source, you call the UPDATE statement, which uses a unique identifier to identify the row in the table be updated. The unique identifier is commonly the value of a primary key field. The UPDATE statement uses parameters that contain both the unique identifier, and the columns and values to be updated, as shown in the following Transact-SQL statement.

UPDATE Customers SET CompanyName = @CompanyName 
  WHERE CustomerID = @CustomerID

In this Visual Basic example, the CompanyName field is updated with the value of the @CompanyName parameter for the row where CustomerID equals the value of the @CustomerID parameter. The parameters retrieve information from the modified row using the SourceColumn property of the SqlParameter object. Following are the parameters for the preceding sample UPDATE statement. The code assumes that the variable adapter represents a valid SqlDataAdapter object.

adapter.Parameters.Add( _
  "@CompanyName", SqlDbType.NChar, 15, "CompanyName")
Dim parameter As SqlParameter = _
  adapter.UpdateCommand.Parameters.Add("@CustomerID", _
  SqlDbType.NChar, 5, "CustomerID")
parameter.SourceVersion = DataRowVersion.Original

The Add method of the Parameters collection takes the name of the parameter, the DataAdapter specific type, the size (if applicable to the type), and the name of the SourceColumn from the DataTable. Notice that the SourceVersion of the @CustomerID parameter is set to Original. This ensures that the existing row in the data source is updated if the value of the identifying column or columns has been changed in the modified DataRow. In that case, the Original row value would match the current value at the data source, and the Current row value would contain the updated value. The SourceVersion for the @CompanyName parameter is not set and will use the default, Current row value.

SqlClient Example

The following example shows sample SQL statements to be used as the CommandText for the SelectCommand, InsertCommand, UpdateCommand, and DeleteCommand properties of the SqlDataAdapter. For the SqlDataAdapter object, you must use named parameters.

Dim selectSQL As String = _
  "SELECT CustomerID, CompanyName FROM Customers " & _
  "WHERE CountryRegion = @CountryRegion AND City = @City"
Dim insertSQL As String = _
  "INSERT INTO Customers (CustomerID, CompanyName) " & _
  "VALUES (@CustomerID, @CompanyName)"
Dim updateSQL As String = _
  "UPDATE Customers SET CustomerID = @CustomerID, & _
  "CompanyName = @CompanyName " & _
  "WHERE CustomerID = @OldCustomerID"
Dim deleteSQL As String = _
  "DELETE FROM Customers WHERE CustomerID = @CustomerID"

string selectSQL = 
  "SELECT CustomerID, CompanyName FROM Customers WHERE CountryRegion = " +
  "@CountryRegion AND City = @City";
string insertSQL = "INSERT INTO Customers (CustomerID, CompanyName) " +
  "VALUES (@CustomerID, @CompanyName)";
string updateSQL = "UPDATE Customers SET CustomerID = @CustomerID, " +
  "CompanyName = @CompanyName WHERE CustomerID = @OldCustomerID";
string deleteSQL = 
  "DELETE FROM Customers WHERE CustomerID = @CustomerID";

OleDb or Odbc Example

For the OleDbDataAdapter and OdbcDataAdapter objects, you must use question mark (?) placeholders to identify the parameters.

Dim selectSQL As String = _
  "SELECT CustomerID, CompanyName FROM Customers " & _
  "WHERE CountryRegion = ? AND City = ?"
Dim insertSQL AS String = _
  "INSERT INTO Customers (CustomerID, CompanyName) VALUES (?, ?)"
Dim updateSQL AS String = _
  "UPDATE Customers SET CustomerID = ?, CompanyName = ? " & _
  WHERE CustomerID = ?"
Dim deleteSQL As String = "DELETE FROM Customers WHERE CustomerID = ?"

string selectSQL = 
  "SELECT CustomerID, CompanyName FROM Customers " +
  "WHERE CountryRegion = ? AND City = ?";
string insertSQL = 
  "INSERT INTO Customers (CustomerID, CompanyName) " +
  "VALUES (?, ?)";
string updateSQL = 
  "UPDATE Customers SET CustomerID = ?, CompanyName = ? " +
  "WHERE CustomerID = ? ";
string deleteSQL = "DELETE FROM Customers WHERE CustomerID = ?";

The parameterized query statements define which input and output parameters must be created. To create a parameter, use the Parameters.Add method or the Parameter constructor to specify the column name, data type, and size. For intrinsic data types, such as Integer, you do not need to include the size, or you can specify the default size.

The following code example creates the parameters for the SQL statement from the preceding example and fills a DataSet.

SqlClient

' Assumes that connection is a valid SqlConnection object.
Dim adapter As SqlDataAdapter = New SqlDataAdapter

Dim selectCMD AS SqlCommand = New SqlCommand(selectSQL, connection)
adapter.SelectCommand = selectCMD

' Add parameters and set values.
selectCMD.Parameters.Add( _
  "@CountryRegion", SqlDbType.NVarChar, 15).Value = "UK"
selectCMD.Parameters.Add( _
  "@City", SqlDbType.NVarChar, 15).Value = "London"

Dim customers As DataSet = New DataSet
adapter.Fill(customers, "Customers")

// Assumes that connection is a valid SqlConnection object.
SqlDataAdapter adapter = new SqlDataAdapter();         

SqlCommand selectCMD = new SqlCommand(selectSQL, connection);
adapter.SelectCommand = selectCMD;

// Add parameters and set values.
selectCMD.Parameters.Add(
  "@CountryRegion", SqlDbType.NVarChar, 15).Value = "UK";
selectCMD.Parameters.Add(
  "@City", SqlDbType.NVarChar, 15).Value = "London";

DataSet customers = new DataSet();
adapter.Fill(customers, "Customers");

OleDb

' Assumes that connection is a valid OleDbConnection object.
Dim adapter As OleDbDataAdapter = New OleDbDataAdapter 

Dim selectCMD AS OleDbCommand = New OleDbCommand(selectSQL, connection)
adapter.SelectCommand = selectCMD

' Add parameters and set values.
selectCMD.Parameters.Add( _
  "@CountryRegion", OleDbType.VarChar, 15).Value = "UK"
selectCMD.Parameters.Add( _
  "@City", OleDbType.VarChar, 15).Value = "London"

Dim customers As DataSet = New DataSet
adapter.Fill(customers, "Customers")

// Assumes that connection is a valid OleDbConnection object.
OleDbDataAdapter adapter = new OleDbDataAdapter();

OleDbCommand selectCMD = new OleDbCommand(selectSQL, connection);
adapter.SelectCommand = selectCMD;

// Add parameters and set values.
selectCMD.Parameters.Add(
  "@CountryRegion", OleDbType.VarChar, 15).Value = "UK";
selectCMD.Parameters.Add(
  "@City", OleDbType.VarChar, 15).Value = "London";

DataSet customers = new DataSet();
adapter.Fill(customers, "Customers");

Odbc

' Assumes that connection is a valid OdbcConnection object.
Dim adapter As OdbcDataAdapter = New OdbcDataAdapter

Dim selectCMD AS OdbcCommand = New OdbcCommand(selectSQL, connection)
adapter.SelectCommand = selectCMD

' Add Parameters and set values.
selectCMD.Parameters.Add("@CountryRegion", OdbcType.VarChar, 15).Value = "UK"
selectCMD.Parameters.Add("@City", OdbcType.VarChar, 15).Value = "London"

Dim customers As DataSet = New DataSet
adapter.Fill(customers, "Customers")

// Assumes that connection is a valid OdbcConnection object.
OdbcDataAdapter adapter = new OdbcDataAdapter();

OdbcCommand selectCMD = new OdbcCommand(selectSQL, connection);
adapter.SelectCommand = selectCMD;

//Add Parameters and set values.
selectCMD.Parameters.Add("@CountryRegion", OdbcType.VarChar, 15).Value = "UK";
selectCMD.Parameters.Add("@City", OdbcType.VarChar, 15).Value = "London";

DataSet customers = new DataSet();
adapter.Fill(customers, "Customers");

Parameter.DbType

The type of a Parameter is specific to the .NET Framework data provider. Specifying the type converts the value of the Parameter to the .NET Framework data provider type before passing the value to the data source. You may also specify the type of a Parameter in a generic fashion by setting the DbType property of the Parameter object to a particular DbType.

The .NET Framework data provider type of a Parameter object is inferred from the .NET Framework type of the Value of the Parameter object, or from the DbType of the Parameter object. The following table shows the inferred Parameter type based on the object passed as the Parameter value or the specified DbType.

Parameter.Direction

The following table shows the values you can use with the ParameterDirection enumeration to set the Direction of the Parameter.

The following code example shows how to set the Direction of the Parameter.

parameter.Direction = ParameterDirection.Output

Parameter.SourceColumn, Parameter.SourceVersion

The SourceColumn and SourceVersion may be passed as arguments to the Parameter constructor, or set as properties of an existing Parameter. The SourceColumn is the name of the DataColumn from the DataRow where the value of the Parameter will be retrieved. The SourceVersion specifies which DataRow version the DataAdapter uses to retrieve the value.

The following table shows the DataRowVersion enumeration values available for use with SourceVersion.

The following code example defines an UPDATE statement in which the CustomerID column is used as a SourceColumn for two parameters: @CustomerID (SET CustomerID = @CustomerID), and @OldCustomerID (WHERE CustomerID = @OldCustomerID). The @CustomerID parameter is used to update the CustomerID column to the current value in the DataRow. As a result, the CustomerID SourceColumn with a SourceVersion of Current is used. The @OldCustomerID parameter is used to identify the current row in the data source. Because the matching column value is found in the Original version of the row, the same SourceColumn (CustomerID) with a SourceVersion of Original is used.

SqlClient

adapter.UpdateCommand.Parameters.Add( _
  "@CustomerID", SqlDbType.NChar, 5, "CustomerID")

adapter.UpdateCommand.Parameters.Add( _
  "@CompanyName", SqlDbType.NVarChar, 40, "CompanyName")

Dim parameter As SqlParameter = _
  adapter.UpdateCommand.Parameters.Add("@OldCustomerID", _
  SqlDbType.NChar, 5, "CustomerID")
parameter.SourceVersion = DataRowVersion.Original

adapter.UpdateCommand.Parameters.Add(
  "@CustomerID", SqlDbType.NChar, 5, "CustomerID");

adapter.UpdateCommand.Parameters.Add(
  "@CompanyName", SqlDbType.NVarChar, 40, "CompanyName");

SqlParameter parameter = 
  adapter.UpdateCommand.Parameters.Add(
  "@OldCustomerID", SqlDbType.NChar, 5, "CustomerID");
parameter.SourceVersion = DataRowVersion.Original;

UpdatedRowSource

You can control how the values returned from the data source are mapped back to the DataSet by using the UpdatedRowSource property of the Command object. By setting the UpdatedRowSource property to one of the UpdateRowSource enumeration values, you can control whether parameters returned by the DataAdapter command are ignored or applied to the changed row in the DataSet. You can also specify whether the first returned row (if it exists) is applied to the changed row in the DataSet.

The following table describes the different values of the UpdateRowSource enumeration and how they affect the behavior of a command used with a DataAdapter.

See Also

Concepts

Specifying Parameters and Return Values
Mapping Data Provider Data Types to .NET Framework Data Types

Other Resources

Working with DataAdapters
Working with SqlTypes