IMAPITable::QueryRows

The IMAPITable::QueryRows method returns one or more rows from a table, beginning at the current cursor position.

Quick Info

See IMAPITable : IUnknown.

HRESULT QueryRows(
  LONG lRowCount,          
  ULONG ulFlags,           
  LPSRowSet FAR * lppRows  
);
 

Parameters

lRowCount

[in] Maximum number of rows to be returned.

ulFlags

[in] Bitmask of flags that controls how rows are returned. The following flag can be set:

TBL_NOADVANCE

Prevents the cursor from advancing as a result of the row retrieval. If the TBL_NOADVANCE flag is set, the cursor points to the first row returned. If the TBL_NOADVANCE flag is not set, the cursor points to the row following the last row returned.

lppRows

[out] Pointer to a pointer to an SRowSet structure holding the table rows.

Return Values

S_OK

The rows were successfully returned.

MAPI_E_BUSY

Another operation is in progress that prevents the row retrieval operation from starting. Either the operation in progress should be allowed to complete or it should be stopped.

MAPI_E_INVALID_PARAMETER

The lRowCount parameter is set to zero.

Remarks

The IMAPITable::QueryRows method gets one or more rows of data from a table. The value of the lRowCount parameter affects the starting point for the retrieval. If lRowCount is positive, rows are read in a forward direction, starting at the current position. If lRowCount is negative, QueryRows resets the starting point by moving backward the indicated number of rows. After the cursor is reset, rows are read in forward order.

The cRows member in the SRowSet structure pointed to by the lppRows parameter indicates the number of rows returned. If zero rows are returned:

• The cursor was already positioned at the beginning of the table and the value of IRowCount is negative.

  -Or-

• The cursor was already positioned at the end of the table and the value of IRowCount is positive.

The number of columns and their ordering is the same for each row. If a property does not exist for a row or there is an error reading a property, the SPropValue structure for the property in the row contains the following values:

• PT_ERROR for the property type in the ulPropTag member.
• MAPI_E_NOT_FOUND for the Value member.

Memory used for the SPropValue structures in the row set pointed to by the lppRows parameter must be separately allocated and freed for each row. Use MAPIFreeBuffer to free the property value structures and to free the row set. When a call to QueryRows returns zero, however, indicating the beginning or end of the table, only the SRowSet structure itself needs to be freed. For more information about how to allocate and free memory in an SRowSet structure, see Managing Memory for ADRLIST and SRowSet Structures.

The rows that are returned and the order in which they are returned depend on whether or not successful calls have been made to IMAPITable::Restrict and IMAPITable::SortTable. Restrict filters rows from the view, causing QueryRows to return only the rows that match the criteria specified in the restriction. SortTable establishes a standard or categorized sort order, affecting the sequence of rows returned by QueryRows. The returned rows are in the order specified in the SSortOrderSet structure passed to SortTable.

The columns returned for each row and the order in which they are returned depend on whether or not a successful call has been made to IMAPITable::SetColumns. SetColumns establishes a column set, specifying the properties to be included in columns in the table and the order in which they should be included. If a SetColumns call has been made, the particular columns in each row and the order of those columns match the column set specified in the call. If no SetColumns call has been made, the table returns its default column set.

If none of these calls has been made, QueryRows returns all of the rows in the table. Each row contains the default column set in default order.

When the column set established in a call to IMAPITable::SetColumns includes columns set to PR_NULL, the SPropValue array within the row set returned in lppRows will contain empty slots.

Notes to Implementers

You can allow a caller to request an unsupported column to be included in the column set. When this occurs, place PT_ERROR in the property type portion of the property tag and MAPI_E_NOT_FOUND in the property value for the unsupported column.

Treat the row count as a request rather than a requirement. You can return anywhere from zero rows, if there are no rows in the direction of the query, to the number requested.

Return only the rows that the user will see when rows are requested from a categorized table view, allowing the caller to make valid assumptions about the scope of the data and avoid extra work.

Notes to Callers

Usually you will end up with as many rows as you have specified in the lRowCount parameter. However, when memory or implementation limits are an issue or when the operation reaches the beginning or end of the table prematurely, QueryRows will return less rows than requested.

If QueryRows returns MAPI_E_BUSY, call the IMAPITable::WaitForCompletion method and retry the call to QueryRows when the asynchronous operation is complete.

When calling QueryRows, be aware that the timing of asynchronous notifications can potentially cause the row set that you get back from QueryRows not to accurately represent the underlying data. For example, a call to QueryRows to a folder's contents table following the deletion of a message but prior to the receipt of the corresponding notification will cause the deleted row to be returned in the row set. Always wait for a notification to arrive before updating the user's view of the data.

For more information about retrieving rows from tables, see Retrieving Data from Table Rows.

See Also

ADRENTRY, FreeProws, HrQueryAllRows, IMAPIProp::GetProps, IMAPITable::SetColumns, IMAPITable::WaitForCompletion, MAPIFreeBuffer, SRow, SRowSet