IRowsetLocateImpl Class

Implements the OLE DB IRowsetLocate interface, which fetches arbitrary rows from a rowset.

Syntax

template <
   class T,
   class RowsetInterface,
   class RowClass = CSimpleRow,
   class MapClass = CAtlMap < RowClass::KeyType, RowClass* >,
   class BookmarkKeyType = LONG,
   class BookmarkType = LONG,
   class BookmarkMapClass = CAtlMap < RowClass::KeyType, RowClass* >>
class ATL_NO_VTABLE IRowsetLocateImpl : public IRowsetImpl<
       T,
       RowsetInterface,
       RowClass,
       MapClass>

Parameters

T
A class derived from IRowsetLocateImpl.

RowsetInterface
A class derived from IRowsetImpl.

RowClass
The storage unit for the HROW.

MapClass
The storage unit for all row handles held by the provider.

BookmarkKeyType
The type of the bookmark, such as a LONG or a string. Ordinary bookmarks must have a length of at least two bytes. (Single-byte length is reserved for the OLE DB standard bookmarksDBBMK_FIRST, DBBMK_LAST, and DBBMK_INVALID.)

BookmarkType
The mapping mechanism for maintaining bookmark-to-data relationships.

BookmarkMapClass
The storage unit for all row handles held by the bookmark.

Requirements

Header: atldb.h

Members

Interface Methods

Name	Description
Compare	Compares two bookmarks.
GetRowsAt	Fetches rows starting with the row specified by an offset from a bookmark.
GetRowsByBookmark	Fetches the rows that match the specified bookmarks.
Hash	Returns hash values for the specified bookmarks.

Data Members

Name	Description
m_rgBookmarks	An array of bookmarks.

Remarks

IRowsetLocateImpl is the OLE DB Templates implementation of the IRowsetLocate interface. IRowsetLocate is used to fetch arbitrary rows from a rowset. A rowset that does not implement this interface is a sequential rowset. When IRowsetLocate is present on a rowset, column 0 is the bookmark for the rows; reading this column will obtain a bookmark value that can be used to reposition to the same row.

IRowsetLocateImpl is used to implement bookmark support in providers. Bookmarks are placeholders (indices on a rowset) that enable the consumer to return quickly to a row, allowing high-speed access to data. The provider determines what bookmarks can uniquely identify a row. Using IRowsetLocateImpl methods, you can compare bookmarks, fetch rows by offset, fetch rows by bookmark, and return hash values for bookmarks.

To support OLE DB bookmarks in a rowset, make the rowset inherit from this class.

For information on implementing bookmark support, see Provider Support for Bookmarks in the Visual C++ Programmer's Guide and Bookmarks in the OLE DB Programmer's Reference in the Platform SDK.

IRowsetLocateImpl::Compare

Compares two bookmarks.

Syntax

STDMETHOD (Compare )(HCHAPTER /* hReserved */,
   DBBKMARK cbBookmark1,
   const BYTE* pBookmark1,
   DBBKMARK cbBookmark2,
   const BYTE* pBookmark2,
   DBCOMPARE* pComparison);

Parameters

See IRowsetLocate::Compare in the OLE DB Programmer's Reference.

Remarks

Either of the bookmarks can be a standard OLE DB-defined standard bookmark (DBBMK_FIRST, DBBMK_LAST, or DBBMK_INVALID). The value returned in pComparison indicates the relationship between the two bookmarks:

• DBCOMPARE_LT (cbBookmark1 is before cbBookmark2.)

• DBCOMPARE_EQ (cbBookmark1 is equal to cbBookmark2.)

• DBCOMPARE_GT (cbBookmark1 is after cbBookmark2.)

• DBCOMPARE_NE (The bookmarks are equal and not ordered.)

• DBCOMPARE_NOTCOMPARABLE (The bookmarks cannot be compared.)

IRowsetLocateImpl::GetRowsAt

Fetches rows starting with the row specified by an offset from a bookmark.

Syntax

STDMETHOD (GetRowsAt )(HWATCHREGION /* hReserved1 */,
   HCHAPTER hReserved2,
   DBBKMARK cbBookmark,
   const BYTE* pBookmark,
   DBROWOFFSET lRowsOffset,
   DBROWCOUNT cRows,
   DBCOUNTITEM* pcRowsObtained,
   HROW** prghRows);

Parameters

See IRowsetLocate::GetRowsAt in the OLE DB Programmer's Reference.

Remarks

To fetch from the cursor position instead, use IRowset::GetRowsAt.

IRowsetLocateImpl::GetRowsAt does not change the cursor position.

IRowsetLocateImpl::GetRowsByBookmark

Fetches one or more rows that match the specified bookmarks.

Syntax

STDMETHOD (GetRowsByBookmark )(HCHAPTER /* hReserved */,
   DBCOUNTITEM cRows,
   const DBBKMARK rgcbBookmarks[],
   const BYTE* rgpBookmarks,
   HROW rghRows[],
   DBROWSTATUS* rgRowStatus[]);

Parameters

hReserved
[in] Corresponds to hChapter parameter to IRowsetLocate::GetRowsByBookmark.

For other parameters, see IRowsetLocate::GetRowsByBookmark in the OLE DB Programmer's Reference.

Remarks

The bookmark can be a value you define or an OLE DB standard bookmarks (DBBMK_FIRST or DBBMK_LAST). Does not change the cursor position.

IRowsetLocateImpl::Hash

Returns hash values for the specified bookmarks.

Syntax

STDMETHOD (Hash )(HCHAPTER /* hReserved */,
   DBBKMARK cbBookmarks,
   const DBBKMARK* rgcbBookmarks[],
   const BYTE* rgpBookmarks[],
   DBHASHVALUE rgHashValues[],
   DBROWSTATUS rgBookmarkStatus[]);

Parameters

hReserved
[in] Corresponds to hChapter parameter to IRowsetLocate::Hash.

For other parameters, see IRowsetLocate::Hash in the OLE DB Programmer's Reference.

IRowsetLocateImpl::m_rgBookmarks

An array of bookmarks.

Syntax

CAtlArray<DBROWCOUNT> m_rgBookmarks;

See also

OLE DB Provider Templates
OLE DB Provider Template Architecture
IRowsetLocate:IRowset Provider Support for Bookmarks
Bookmarks