Hello Benoit Nesme

DataObjects 5 had had problems with build under VS 2015 too before we fixed them in 5.0.7 RC.

Upgrading to PostSharp 3.1 or 4.1 depends on changes in new version of PostSharp, I thing. We'll think about it.

Speaking of upgrade to DataObjects 5, we've changed some APIs and you might have to change your code.

1. We've reworked validation framework. Some parts of legacy framework are supported but API changed a lot.
2. We've changed ClientProfile mode. It affected EntitySet end Entity classes but not much. Some session options were deleted.
3. We've removed support for .Net Framework 3.5.
4. Xtensive.Core and Xtensive.Aspects are no loger exist, we merged them with Xtensive.Orm.
5. Obsolete Transaction.OpenAuto() methods were removed.
6. Logging framework was reworked.

Probably there are other changes which might affect your solution like removed methods or something like that. Amount of changes you have to do depends on what you use in the solution.

DO 5 have some improvements. Queries supports new methods. Added support for DateTimeOffset. Added support for non-transactional queries. Optimized persist actions. If you build several domains with same model than you defenetely should migrate to 5.0. We've implemented storage nodes. It allows you to build domain on different databases (or schemes) which use same model (have same structure) and switch between them easly. Also it saves memory. If you are interested in it I'll tell you more about storage nodes.

Anyway I'll help you with upgrade and answer your questions.