The changes in midPoint schema and functionality is mostly limited to data items that were already deprecated for a long time, some of them going back even to midPoint 2.x. Those elements were removed or significantly changed. All such changes were marked as "planned removal in 4.0" in midPoint 3.9 schema. This plan was documented in midPoint 3.9 release notes therefore the users had sufficient time to prepare. You should be able to upgrade without any major issues if you haven't used any deprecated properties or if you have avoided the use of removed elements at the very least. But even in that case there may be some updates that need to be done manually. Please refer to the section that deals with midPoint schema for details. Please be especially careful about the
iterationSpecification element described below.
Upgrade from midPoint 4.0
Both midPoint 4.0.1 data model (schema) and database schema are compatible with midPoint 4.0. No special migration steps are needed to migrate the data. Upgrade of software packages is enough to upgrade to midPoint 4.0 to midPoint 4.0.1.
Upgrade from midPoint 3.x
Upgrade path from MidPoint 3.x goes through midPoint 3.9. Upgrade to midPoint 3.9 first by using the documented upgrade techniques. Then upgrade from midPoint 3.9 to 4.0.