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    <p>I have used all three methods. It's mostly a question of taste.</p> <p>I agree that hierarchy with parent-child relationships in the table is the simplest. Moving a subtree is simple and it's easy to code the recursive access with CTEs. Performance is only going to be an issue if you have very large tree structures and you are frequently accessing the hierarchical data. For the most part, recursive CTEs are very fast when you have the correct indexes on the table.</p> <p>The closure table is more like a supplement to the above. Finding all the descendants of a given node is lightning fast, you don't need the CTEs, just one extra join, so it's sweet. Yes, the number of records blows up, but I think it is no more than N-1 times the number of nodes for a tree of depth N (e.g. a tertiary tree of depth 5 would require 1 + 3 + 9 + 27 + 81 = 121 connections when storing only the parent-child relationship vs. 1 + 3 + (9 * 2) + (27 * 3) + (81 * 4) = 427 for the closure table). In addition, the closure table records are so narrow (just 2 ints at a minimum) that they take up almost no space. Generating the list of records to insert into the closure table when a new record is inserted into the hierarchy takes a tiny bit of overhead.</p> <p>I personally like HierarchyId since it really combines the benefit of the above two, which is compact storage, and lightning fast access. Once you get it set up, it is easy to query and takes very little space. As you mentioned, it's a little tricky to move subtrees around, but it's manageable. Anyway, how often do you really move a subtree in a hierarchy? There are some links you can find that will suggest some methods, e.g.:</p> <p><a href="http://sqlblogcasts.com/blogs/simons/archive/2008/03/31/SQL-Server-2008---HierarchyId---How-do-you-move-nodes-subtrees-around.aspx">http://sqlblogcasts.com/blogs/simons/archive/2008/03/31/SQL-Server-2008---HierarchyId---How-do-you-move-nodes-subtrees-around.aspx</a></p> <p>The main drawback I have found to hierarchyId is the learning curve. It's not as obvious how to work with it as the other two methods. I have worked with some very bright SQL developers who would frequently get snagged on it, so you end up with one or two resident experts who have to field questions from everyone else.</p>
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    1. COTwo drawbacks I ran into on my initial foray into hierarchyId was, first, handling bulk inserts/updates in the insert/update trigger and, second, using the hierarchyId'd table in C# through Entity Framework. Do you have any advice or info about handling either of those? Also, this answer was very helpful, but I am going to wait a bit before I select it to encourage anyone else who might have helpful information.
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