Seek 方法是客户端对 Microsoft SQL Server Compact 4.0 中的索引使用最广泛的方法。使用 Seek，您可以依据游标快速地查找行。
使用 Seek
为了使 Seek 方法能够正常工作，必须在搜索键中的列上定义索引。大多数查找操作都是针对特定的值，但也可以使用其他比较运算符（如“大于”或“小于”）进行查找。
IRowsetIndex::Seek 通过使用 OLE DB 中用于获取和设置数据的取值函数机制向访问接口传递值。相对于用于 IRowset::GetData 和 IRowset::SetData 的取值函数，用于 Seek方法的取值函数具有更多的限制。取值函数必须按照列出现在索引键中的顺序对其进行绑定。
只有可滚动游标支持 IRowsetPosition 接口。
示例
下面的示例说明了如何通过 OLE DB Provider for SQL Server Compact 4.0 对索引使用 IRowsetIndex::Seek。该示例仅包含与 Seek 方法有关的函数部分。
对于 32 位和 64 位平台，已更新下面的示例。64 位兼容类型来自 sqlce_oledb.h 本机头文件。可以在 %ProgramFiles%\Microsoft SQL Server Compact Edition\v3.5\Include 文件夹中找到 sqlce_oledb.h 本机头文件。有关详细信息，请参阅 Microsoft 网站上“OLE DB 编程人员指南”中的“OLE DB 64 位信息”主题。
TableID.eKind = DBKIND_NAME;
TableID.uName.pwszName = (WCHAR*)TABLE_EMPLOYEE;
IndexID.eKind = DBKIND_NAME;
IndexID.uName.pwszName = L"PK_Employees";
// Request ability to use IRowsetChange interface.
rowsetpropset[0].cProperties = 1;
rowsetpropset[0].guidPropertySet = DBPROPSET_ROWSET;
rowsetpropset[0].rgProperties = rowsetprop;
rowsetprop[0].dwPropertyID = DBPROP_IRowsetIndex;
rowsetprop[0].dwOptions = DBPROPOPTIONS_REQUIRED;
rowsetprop[0].colid = DB_NULLID;
rowsetprop[0].vValue.vt = VT_BOOL;
rowsetprop[0].vValue.boolVal = VARIANT_TRUE;
// Open the table using the index.
hr = pIOpenRowset->OpenRowset(NULL, &TableID, &IndexID,
IID_IRowsetIndex, sizeof(rowsetpropset)/sizeof(rowsetpropset[0]),
rowsetpropset, (IUnknown**) &pIRowsetIndex);
if(FAILED(hr))
{
goto Exit;
}
// Get the IRowset interface.
hr = pIRowsetIndex->QueryInterface(IID_IRowset, (void**) &pIRowset);
if(FAILED(hr))
{
goto Exit;
}
///////////////////////////////////////////////////////////////////////
// Steps to get column data using IcolumnsInfo have been removed
///////////////////////////////////////////////////////////////////////
// Create a DBBINDING array.
dwBindingSize = sizeof(pwszEmployees)/sizeof(pwszEmployees[0]);
prgBinding = (DBBINDING*)CoTaskMemAlloc(sizeof(DBBINDING)*dwBindingSize);
if (NULL == prgBinding)
{
hr = E_OUTOFMEMORY;
goto Exit;
}
// Set initial offset for binding position.
dwOffset = 0;
// Prepare structures to create an accessor for each index.
for (dwIndex = 0; dwIndex < dwBindingSize; ++dwIndex)
{
if (!GetColumnOrdinal(pDBColumnInfo, ulNumCols, pwszEmployees[dwIndex], &dwOrdinal))
{
hr = E_FAIL;
goto Exit;
}
prgBinding[dwIndex].iOrdinal = dwOrdinal;
prgBinding[dwIndex].dwPart = DBPART_VALUE | DBPART_STATUS | DBPART_LENGTH;
prgBinding[dwIndex].obLength = dwOffset;
prgBinding[dwIndex].obStatus = prgBinding[dwIndex].obLength + sizeof(DBLENGTH);
prgBinding[dwIndex].obValue = prgBinding[dwIndex].obStatus + sizeof(DBSTATUS);
prgBinding[dwIndex].pTypeInfo = NULL;
prgBinding[dwIndex].pBindExt = NULL;
prgBinding[dwIndex].dwMemOwner = DBMEMOWNER_CLIENTOWNED;
prgBinding[dwIndex].dwFlags = 0;
prgBinding[dwIndex].bPrecision = pDBColumnInfo[dwOrdinal].bPrecision;
prgBinding[dwIndex].bScale = pDBColumnInfo[dwOrdinal].bScale;
///////////////////////////////////////////////////////////////////////
// Case-specific binding information has been removed.
///////////////////////////////////////////////////////////////////////
prgBinding[dwIndex].pObject NULL;
prgBinding[dwIndex].wType = pDBColumnInfo[dwOrdinal].wType;
if(DBTYPE_WSTR == pDBColumnInfo[dwOrdinal].wType)
{
prgBinding[dwIndex].cbMaxLen = pDBColumnInfo[dwOrdinal].ulColumnSize
* sizeof(WCHAR);
}
else
{
prgBinding[dwIndex].cbMaxLen = pDBColumnInfo[dwOrdinal].ulColumnSize;
}
// Calculate and align the offset.
}
// Get IAccessor interface.
hr = pIRowset->QueryInterface(IID_IAccessor, (void**)&pIAccessor);
if(FAILED(hr))
{
goto Exit;
}
// Create the accessor.
hr = pIAccessor->CreateAccessor(DBACCESSOR_ROWDATA, dwBindingSize,
prgBinding, 0, &hAccessor, NULL);
if(FAILED(hr))
{
goto Exit;
}
// Allocate data buffer for seek and retrieve operation.
pData = (BYTE*)CoTaskMemAlloc(dwOffset);
if (NULL == pData)
{
hr = E_OUTOFMEMORY;
goto Exit;
}
// Set data buffer to zero.
//
memset(pData, 0, dwOffset);
// Set data buffer for seek operation by specifying the
// dwEmployeeID variable that is passed to the function.
*(DBLENGTH*)(pData+prgBinding[0].obLength) = 4;
*(DBSTATUS*)(pData+prgBinding[0].obStatus) = DBSTATUS_S_OK;
*(int*)(pData+prgBinding[0].obValue) = dwEmployeeID;
// Seek for the first row where the value of the selected column
// is dwEmployeeID.
hr = pIRowsetIndex->Seek(hAccessor, 1, pData, DBSEEK_FIRSTEQ);
if(FAILED(hr))
{
goto Exit;
}
// Retrieve a row handle for the row resulting from the seek.
hr = pIRowset->GetNextRows(DB_NULL_HCHAPTER, 0, 1, &cRowsObtained,
&prghRows);
if(FAILED(hr))
{
goto Exit;
}
///////////////////////////////////////////////////////////////////////
// Perform programming logic here on the
// returned rowset, and then release the rowset.
///////////////////////////////////////////////////////////////////////
Exit:
///////////////////////////////////////////////////////////////////////
// This is where the resources are released.
///////////////////////////////////////////////////////////////////////
return hr;