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Defines the particular properties and order of properties to appear as columns in the table.
The column set of a table is the group of properties that make up the columns for the rows in the table. There is a default column set for each type of table. The default column set is made up of the properties that the table implementer automatically includes. Table users can alter this default set by calling the IMAPITable::SetColumns method. They can request that other columns be added to the default set if the table implementer supports them that columns be removed, or that the order of columns be changed. SetColumns specifies the columns that are returned with each row and the order of these columns within the row.
The success of the SetColumns operation is apparent only after a subsequent call has been made to retrieve the data of the table. It is then that any errors are reported.
Some providers allow a SetColumns call to order only table columns that are part of the available columns for a table view. Other providers allow a SetColumns call to order all table columns, including those containing properties not in the original column set.
When TBL_BATCH is set for asynchronous operations, providers should return a property type of PT_ERROR and a property value of NULL for columns that are not supported.
You do not need to respond to the TBL_ASYNC flag requesting that the operation be asynchronous. If you do not support asynchronous column set definition, perform the operation synchronously. If you can support the TBL_ASYNC flag and another asynchronous operation is still in progress, return MAPI_E_BUSY. Otherwise, return S_OK regardless of whether or not you support all of the properties included in the property tag array. Errors resulting from unsupported properties should be returned from IMAPITable methods that retrieve data, such as QueryRows.
Do not generate notifications for table rows that are hidden from view by calls to Restrict.
When sending table notifications, the order of the properties in the row member of the TABLE_NOTIFICATION structure and the order specified by the most recent SetColumns call must be the same as of the time that the notification request was sent.
Another flag, TBL_BATCH, allows callers to specify that the table implementer can defer evaluating the results of the operation until a later time. Whenever possible, callers should set this flag because batched operation improves performance.
It is often convenient for callers to reserve some columns in the retrieved row set for values to be added later. Callers do this by placing PR_NULL (PidTagNull) at the desired positions in the property tag array passed to SetColumns; the table will then pass back PR_NULL at those positions in all rows retrieved with QueryRows.
When building the property tag array for the lpPropTagArray parameter, order the tags in the order that you want the columns to appear in the table view.
You can specify multivalued properties to be included in the column set by applying the multivalued instance flag, or MVI_FLAG constant, to the property tag. Set this flag by passing the property tag for the single-valued version of the property as a parameter to the MVI_PROP macro as follows:
The MVI_PROP macro will set MVI_FLAG for the property, turning the tag into a multivalued tag. If you erroneously try to call MVI_PROP on a single-valued property, MAPI will ignore the call and leave the property tag unchanged.
You can include property tags set to PR_NULL in the property tag array to reserve space in the column set. Reserving space allows you to add to a column set without having to allocate a new property tag array.
When your call to SetColumns causes a change to the order of a table's columns and one or more of these columns represent a multivalued property, it is possible for the number of rows in the table to increase. If this occurs, all of the bookmarks for the table are discarded. For more information about how multivalued columns affect tables, see Working with Multivalued Columns.
Setting columns is by default a synchronous operation. However, you can allow the table to postpone the operation until such time as the data is needed by setting the TBL_BATCH flag. Setting this flag can improve performance. Another flag, TBL_ASYNC, makes the operation asynchronous, allowing SetColumns to return before the operation is complete. To determine when completion occurs, call IMAPITable::GetStatus.
If a call to SetColumns returns MAPI_E_BUSY, indicating that another operation is preventing your operation from starting, you can call IMAPITable::Abort to stop the operation in progress.
You can also call HrAddColumnsEx to change a column set. The difference between HrAddColumnsEx and IMAPITable::SetColumns is that HrAddColumnsEx is less flexible; it can only add columns. The additional columns are placed at the beginning of the column set; all existing columns appear following these columns.