Views

Providers that do not support full command syntax can still expose simple operations such as sorting or filtering a rowset by applying a view. Views may be applied when opening a rowset, or they may be applied to an existing rowset in order to return either a new chapter on that rowset or a completely new rowset with the additional functionality.

Views are similar to commands, with the following restrictions:

• The source of the rowset is a single table, fixed at the time the view is created.
  
  
• Views support only simple operations such as filtering and sorting. They do not support complex semantics such as subqueries, joins, or dynamic parameters.
  
  
• View operations are expressed through method calls as opposed to textual statements.

Views:

   CoType TView {
      [mandatory] interface IColumnsInfo;
      [optional]  interface IAccessor;
      [optional]  interface ISupportErrorInfo;
      [optional]  interface IViewChapter;
      [optional]  interface IViewFilter;
      [optional]  interface IViewRowset;
      [optional]  interface IViewSort;
   };

Views are created in one of two ways:

• Applying a view when opening a rowset. In order to apply a view when opening a rowset, the following steps occur:
  1. The consumer requests that IID_IViewRowset be supported when executing a method that returns a rowset, either by setting the DBPROP_IViewRowset property, or by requesting IID_IViewRowset on the returned rowset. The method returns a view object in place of the rowset.
     
     
  2. The consumer applies operations such as filtering and sorting to the view object through interfaces such as IViewFilter and IViewSort.
     
     
  3. The consumer calls IViewRowset::OpenViewRowset on the view object in order to return the actual rowset.
• Applying a view to an existing rowset. In order to apply a view to an existing rowset, the following steps occur:
  1. The consumer calls IRowsetView::CreateView on the rowset.
     
     
  2. The consumer applies operations such as filtering and sorting to the view object through interfaces such as IViewFilter and IViewSort.
     
     
  3. The consumer calls IViewChapter::OpenViewChapter on the view to return a new chapter on the original rowset that reflects the view operations.
     - or -
     The consumer calls IViewRowset::OpenViewRowset on the view in order to return a new rowset with the view operations applied.