![]() ![]() What’s in an IHierarchicalDataSource ? The documentation says ” The interface defines a single method, GetHierarchicalView, which retrieves a strongly typed HierarchicalDataSourceView object.” Our HierarchicalDataSourceView implementation, in turn, must override HierarchicalDataSourceView.Select and return a collection implementing IHierarchicalEnumerable. I don’t know what those application developers go on about. Really, we’ve defined the table, so the heavy lifting is done. So, now, all that’s left to do is write some helper functions for the IHierarchicalDataSource, the IHierarchicalDataSource itself, and tie it to a TreeView. Any practical implementation is going to provide Create/Review/Update/Delete features, but since the TreeView doesn’t provide a way to use them, they’re out of scope here. The third section adds some data, leaning on some free icons I found on the web.It provides the ‘select’ functionality for the TreeView control, for which we’ll shortly get to providing a client. This section starts with the GetParentPath function.Note that for a production implementation, you might want security, auditing and historical state functions, which are not included here This can be one table for simple implementations. We make one table to contain the data and another to locate it in the tree. That code contains a few different sections Now, we’ll just make one, with data enough to populate a TreeView. NET TreeView, so I’ll refer you to Celko’s “ SQL for Smarties” or “ Trees and Hierarchies in SQL For Smarties” for a discussion. However, this article is about showing them in a. ![]() There is a lot more to nested sets, and many wonderful reasons to use them. If one node’s lft is less than another node’s lft, and the first node’s rgt is greater than the next node’s rgt, the first node is an ancestor of the second node. rgt is always greater than lft, but only one greater for leaf nodes. In the nested set model, every node has two integer values which (after Celko) I call lft and rgt. Populating a Treeview with Nested sets The Database bit. The point of this article, though, is to fill that gap. It seems nested sets aren’t so pervasive that. However, if you try to do this through the GUI, you’ll see there is no way that is provided to add a connection to a SQL Server database.įigure 1 TreeView control in Toolbox under ‘Navigation’įigure 2: Options for a TreeView data source NET control for hierarchical data is the TreeView, and the TreeView requires an IHierarchicalDataSourceobject. We have to give up middle layer logic and tie our user interface directly to the database objects, which is not generally a good idea, but not always worth avoiding. Data-binding handles a lot of the functional requirements for you, but you have to do it pretty much the way that Microsoft expects you to, which you’ll understand if you try to set the DataSource on a FormView control. So you have an easy way of expressing hierarchical data in SQL, with ordered sibling nodes, no less.Ī decade or so later, we find ourselves trying to integrate our database design patterns with the. Kamfonas’ Nested Sets model for trees in SQL on the Usenet, and it changed your life. If you’re like me, one day Joe Celko exposed you to Michael J. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |