Which ORM framework can best handle an MVCC database design?

I might consider implementing the MVCC tier purely in the DB, using stored procs and views to handle my data operations. Then you could present a reasonable API to any ORM that was capable of mapping to and from stored procs, and you could let the DB deal with the data integrity issues (since it's pretty much build for that). If you went this way, you might want to look at a more pure Mapping solution like IBatis or IBatis.net.

I designed a database similarly (only INSERTs — no UPDATEs, no DELETEs). Almost all of my SELECT queries were against views of only the current rows for each table (highest revision number). The views looked like this… SELECT dbo.tblBook.

BookId, dbo.tblBook. RevisionId, dbo.tblBook. Title, dbo.tblBook.

AuthorId, dbo.tblBook. Price, dbo.tblBook. Deleted FROM dbo.

TblBook INNER JOIN ( SELECT BookId, MAX(RevisionId) AS RevisionId FROM dbo. TblBook GROUP BY BookId ) AS CurrentBookRevision ON dbo.tblBook. BookId = CurrentBookRevision.

BookId AND dbo.tblBook. RevisionId = CurrentBookRevision. RevisionId WHERE dbo.tblBook.

Deleted = 0 And my inserts (and updates and deletes) were all handled by stored procedures (one per table). The stored procedures looked like this… ALTER procedure dbo. Sp_Book_CreateUpdateDelete @BookId uniqueidentifier, @RevisionId bigint, @Title varchar(256), @AuthorId uniqueidentifier, @Price smallmoney, @Deleted bit as insert into tblBook ( BookId, RevisionId, Title, AuthorId, Price, Deleted ) values ( @BookId, @RevisionId, @Title, @AuthorId, @Price, @Deleted ) Revision numbers were handled per-transaction in the Visual Basic code… Shared Sub Save(ByVal UserId As Guid, ByVal Explanation As String, ByVal Commands As Collections.Generic.

Queue(Of SqlCommand)) Dim Connection As SqlConnection = New SqlConnection(System.Configuration. ConfigurationManager. ConnectionStrings("Connection").

ConnectionString) Connection.Open() Dim Transaction As SqlTransaction = Connection. BeginTransaction Try Dim RevisionId As Integer = Nothing Dim RevisionCommand As SqlCommand = New SqlCommand("sp_Revision_Create", Connection) RevisionCommand. CommandType = CommandType.

StoredProcedure RevisionCommand.Parameters. AddWithValue("@RevisionId", 0) RevisionCommand. Parameters(0).

SqlDbType = SqlDbType. BigInt RevisionCommand. Parameters(0).

Direction = ParameterDirection. Output RevisionCommand.Parameters. AddWithValue("@UserId", UserId) RevisionCommand.Parameters.

AddWithValue("@Explanation", Explanation) RevisionCommand. Transaction = Transaction LogDatabaseActivity(RevisionCommand) If RevisionCommand.ExecuteNonQuery() = 1 Then 'rows inserted RevisionId = CInt(RevisionCommand. Parameters(0).

Value) 'generated key Else Throw New Exception("Zero rows affected. ") End If For Each Command As SqlCommand In Commands Command. Connection = Connection Command.

Transaction = Transaction Command. CommandType = CommandType. StoredProcedure Command.Parameters.

AddWithValue("@RevisionId", RevisionId) LogDatabaseActivity(Command) If Command.ExecuteNonQuery() 0 Then Return New Book(Database. Find(Command). Rows(0)) Else Return Nothing End If End Function Such a system preserves all past versions of each row, but can be a real pain to manage.

PROS: Total history preserved Fewer stored procedures CONS: relies on non-database application for data integrity huge amount of code to be written No foreign keys managed within database (goodbye automatic Linq-to-SQL-style object generation) I still haven't come up with a good user interface to retrieve all that preserved past versioning. CONCLUSION: I wouldn't go to such trouble on a new project without some easy-to-use out-of-the-box ORM solution. I'm curious if the Microsoft Entity Framework can handle such database designs well.

Jeff and the rest of that Stack Overflow team must have had to deal with similar issues while developing Stack Overflow: Past revisions of edited questions and answers are saved and retrievable. I believe Jeff has stated that his team used Linq to SQL and MS SQL Server. I wonder how they handled these issues.

To the best of my knowledge, ORM frameworks are going to want to generate the CRUD code for you, so they would have to be explicitly designed to implement a MVCC option; I don't know of any that do so out of the box. From an Entity framework standpoint, CSLA doesn't implement persistence for you at all -- it just defines a "Data Adapter" interface that you use to implement whatever persistence you need. So you could set up code generation (CodeSmith, etc.) templates to auto-generate CRUD logic for your CSLA entities that go along with a MVCC database architecture.

This approach would work with any entity framework, most likely, not just CSLA, but it would be a very "clean" implementation in CSLA.

Check out the Envers project - works nice with JPA/bernate applications and basically does that for you - keeps track of different versions of each Entity in another table and gives you SVN-like possibilities ("Gimme the version of Person being used 2008-11-05...") jboss.org/envers/ /Jens.

I always figured you'd use a db trigger on update and delete to push those rows out into a TableName_Audit table. That'd work with ORMs, give you your history and wouldn't decimate select performance on that table. Is that a good idea or am I missing something?

What we do, is just use a normal ORM ( hibernate ) and handle the MVCC with views + instead of triggers. So, there is a v_emp view, which just looks like a normal table, you can insert and update into it fine, when you do this though, the triggers handle actually inserting the correct data into the base table. Not.. I hate this method :) I'd go with a stored procedure API as suggested by Tim.

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