SqlCeDataReader.Seek Method

Artikel
03/29/2011

Places the SqlCeDataReader on the record with indexed values that match the specified parameters.

Namespace: System.Data.SqlServerCe
Assembly: System.Data.SqlServerCe (in System.Data.SqlServerCe.dll)

Syntax

'Declaration
<SecurityCriticalAttribute> _
<SecurityTreatAsSafeAttribute> _
<SecurityPermissionAttribute(SecurityAction.Assert, UnmanagedCode := True)> _
Public Function Seek ( _
    dbSeekOptions As DbSeekOptions, _
    ParamArray index As Object() _
) As Boolean
'Usage
Dim instance As SqlCeDataReader
Dim dbSeekOptions As DbSeekOptions
Dim index As Object()
Dim returnValue As Boolean

returnValue = instance.Seek(dbSeekOptions, _
    index)

[SecurityCriticalAttribute]
[SecurityTreatAsSafeAttribute]
[SecurityPermissionAttribute(SecurityAction.Assert, UnmanagedCode = true)]
public bool Seek(
    DbSeekOptions dbSeekOptions,
    params Object[] index
)

[SecurityCriticalAttribute]
[SecurityTreatAsSafeAttribute]
[SecurityPermissionAttribute(SecurityAction::Assert, UnmanagedCode = true)]
public:
bool Seek(
    DbSeekOptions dbSeekOptions, 
    ... array<Object^>^ index
)

[<SecurityCriticalAttribute>]
[<SecurityTreatAsSafeAttribute>]
[<SecurityPermissionAttribute(SecurityAction.Assert, UnmanagedCode = true)>]
member Seek : 
        dbSeekOptions:DbSeekOptions * 
        index:Object[] -> bool

public function Seek(
    dbSeekOptions : DbSeekOptions, 
    ... index : Object[]
) : boolean

Parameters

dbSeekOptions
Type: System.Data.SqlServerCe.DbSeekOptions
The DbSeekOptions to use.

index
Type: array<System.Object[]
The index of the record.

Return Value

Type: System.Boolean
A Boolean value; true indicates the cursor is positioned on a row.

Exceptions

Exception	Condition
SqlCeException	The value was not found, or another error occurred.

Remarks

This method is intended to be a faster alternative to a SELECT statement for retrieving a row from a base table. Instead of a WHERE clause in a SELECT statement, Seek can be used to quickly retrieve a row based on its index value. For example, to retrieve an employee with an employee ID of 5, you could execute a SELECT statement, but using Seek with a value of 5 on the employee ID index will greatly improve performance.

Seek can only be used when CommandType is set to TableDirect, CommandText is set to a valid base table name, and IndexName is set to a valid index name on the specified base table.

After using Seek, SqlCeDataReader will return the remaining rows in their index order. When Seek is used on a SqlCeDataReader that has a range specified by SetRange, Seek will only position on rows within the range. For more information, see the "IRowsetIndex::Seek" topic in the OLE DB documentation.

Examples

        Try
            Dim conn As New SqlCeConnection("Data Source = MyDatabase.sdf")
            conn.Open()

            Dim cmd As SqlCeCommand = conn.CreateCommand()
            cmd.CommandType = CommandType.TableDirect
            cmd.IndexName = "Orders_PK"
            cmd.CommandText = "Orders"

            ' We are interested in orders that match Order ID = 10020
            '
            cmd.SetRange(DbRangeOptions.Match, New Object() {10020}, Nothing)

            Dim reader As SqlCeDataReader = cmd.ExecuteReader(CommandBehavior.Default)

            While reader.Read()
                MessageBox.Show(String.Format("{0} ; {1}", reader("Order ID"), reader("Order Date")))
            End While

            ' Now we are interested in orders with Order ID between (10020, 10050)
            '
            cmd.SetRange(DbRangeOptions.InclusiveStart Or DbRangeOptions.InclusiveEnd, New Object() {10020}, New Object() {10050})

            reader = cmd.ExecuteReader(CommandBehavior.Default)

            ' Now seek to Order ID = 10045
            '
            Dim onRow As Boolean =  reader.Seek(DbSeekOptions.FirstEqual, New Object() {10045})

            ' Now ,the reader will return rows with Order ID >= 10045 <= 10050
            ' because the range was set to (10020, 10050)
            '
            If onRow Then
                While reader.Read()
                    MessageBox.Show(String.Format("{0} ; {1}", reader("Order ID"), reader("Order Date")))
                End While
            End If
        Catch e As Exception
            MessageBox.Show(e.Message)
        End Try

        try
        {
            SqlCeConnection conn = new SqlCeConnection("Data Source = MyDatabase.sdf");
            conn.Open();

            SqlCeCommand cmd = conn.CreateCommand();
            cmd.CommandType = CommandType.TableDirect;
            cmd.IndexName = "Orders_PK";
            cmd.CommandText = "Orders";

            // We are interested in orders that match Order ID = 10020
            //
            cmd.SetRange(DbRangeOptions.Match, new object[] { 10020 }, null);

            SqlCeDataReader reader = cmd.ExecuteReader(CommandBehavior.Default);

            for (int i = 1; reader.Read(); i++)
            {
                MessageBox.Show(String.Format("{0} ; {1}", reader["Order ID"], reader["Order Date"]));
            }

            // Now we are interested in orders with Order ID between (10020, 10050)
            //
            cmd.SetRange(DbRangeOptions.InclusiveStart | DbRangeOptions.InclusiveEnd,
                new object[] { 10020 }, new object[] { 10050 });

            reader = cmd.ExecuteReader(CommandBehavior.Default);

            // Now seek to Order ID = 10045
            //
            bool onRow = reader.Seek(DbSeekOptions.FirstEqual, new object[] { 10045 });

            // Now ,the reader will return rows with Order ID >= 10045 <= 10050
            // because the range was set to (10020, 10050)
            //
            if (onRow)
            {
                for (int i = 1; reader.Read(); i++)
                {
                    MessageBox.Show(String.Format("{0} ; {1}", reader["Order ID"], reader["Order Date"]));
                }
            }
        }
        catch (Exception e)
        {
            MessageBox.Show(e.Message);
        }

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