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DbSeekOptions 枚举

  • 项目

指定 Seek 方法将如何对索引进行搜索的选项。

此枚举具有可以使用其成员值位组合的 FlagsAttribute 属性。

命名空间：  System.Data.SqlServerCe
程序集：  System.Data.SqlServerCe（在 System.Data.SqlServerCe.dll 中）

语法

声明
<FlagsAttribute> _
Public Enumeration DbSeekOptions
用法
Dim instance As DbSeekOptions

[FlagsAttribute]
public enum DbSeekOptions

[FlagsAttribute]
public enum class DbSeekOptions

[<FlagsAttribute>]
type DbSeekOptions

public enum DbSeekOptions

成员

成员名称 说明
FirstEqual 按照索引顺序，前进至索引中第一个匹配行。
LastEqual 按照索引顺序，前进至索引中最后一个匹配行。
AfterEqual 前进至索引中最后一个匹配行。如果没有匹配行，则按照索引顺序，前进至所包含的值位于查找值之后的第一行。
After 按照索引顺序，前进至所包含的值位于查找值之后的第一行。
BeforeEqual 前进至索引中第一个匹配行。如果没有匹配行，则按照索引顺序，前进至所包含的值位于查找值之前的最后一行。
Before 按照索引顺序，前进至所包含的值位于查找值之前的最后一行。

示例

在此示例中，为对索引执行的 Seek 操作指定了 FirstEqual 选项。

        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);
        }

请参阅

参考

System.Data.SqlServerCe 命名空间