As mentioned here there is a separate download for the template that is required to migrate LLBLGen Pro v2.x project files to the new format The download does include a V2xToV3Migration_readme.txt which has the usage and instructions in it which are very simple to follow.
I just ran through this process now with a project we are currently developing and the actual migration went fine, but I received an error when opening the new project file in the v3.0 Beta designer. The error (which was not copy and pasteable) was...
"In entity 'x', the field 'y' overrides an inherited field, foreign key field or field-mapped-onto-related-field, which leads to ambiguistic data-mapping."
Somehow we had managed to put a field on a subtype with the same name as the entity it was inheriting from, rather embarrassing. What should be mentioned as well is the very helpful "Possible correction action/hints" which was available when drilling down into the error, it provided 2 choices with "Go there" and "Perform" type suggestions on how to solve the problem. Click on the suggestions actually performed the suggestions which was rather awesome as well. I took this route (as I had to correct the errors with the model before the designer allowed me to refresh the metadata, which surprised me as I had already deleted the offending column from the subtype within the database).I then refreshed the Meta-data (equivalent of v2.x Catalog refresh)...
...which then cleared up the Error List except for a list of warnings regarding tables which had not been added as project elements yet which is also quite useful. I then generated the source code and tried to build only to get a whole lot of errors like..
'x.DatabaseSpecific.DataAccessAdapter' does not implement inherited abstract member 'SD.LLBLGen.Pro.ORMSupportClasses.DataAccessAdapterBase.InsertPersistenceInfoObjects(SD.LLBLGen.Pro.ORMSupportClasses.IPredicateExpression)'
'x.DataAccessAdapter' does not implement inherited abstract member 'SD.LLBLGen.Pro.ORMSupportClasses.DataAccessAdapterBase.CreateNewPhysicalDataAdapter
'x.EntityClasses.OrderStatusEntity' does not implement inherited abstract member 'SD.LLBLGen.Pro.ORMSupportClasses.EntityBase2.FieldsCustomPropertiesOfType.get'
...why? Because I didn't RTFM, so make sure you read the aptly named README1st.pdf. The actual errors though were because we were referencing the runtime libraries out of a \lib directory which is committed to source control as opposed to the GAC, copying the new versions from the v3.0 beta directory over these then fixed the above. I then however had a number of errors such as...
'x.Data.EntityClasses.ProviderEntity' does not contain a definition for 'ProviderId' and no extension method 'ProviderId' accepting a first argument of type x.Data.EntityClasses.ProviderEntity' could be found (are you missing a using directive or an assembly reference?)
...where ProviderId was the PK on an entity Provider which was a subtype of Contact. I looked at the properties available on the class and to my surprise only the supertype's PK was available, i.e. ContactId rather than ProviderId. The FK was also not visible when exploring the entity within the designer. Looked through the new Designer and Project Preferences/Properties (Which I will go into further in another post) and although I tried a few different options, I couldn't seem to change this behaviour. In the interests of getting the code working, I modified the existing code to use the PK on the supertype as needed on the subtype.
This then allowed my code to build and when running it, it seems all good with one noticeable bug thus far. The bug is regarding a property on an Anonymous Type within a LINQ query which is built by concatenating other fields on the entities retrieved by the query. Going to post on the LLBLGen forums regarding this and the above PK-FK scenario.
Overall though, even in its beta state the documentation required to install v3.0 Beta, upgrading the existing 2.x project and get it running was good and I am quite impressed thus far. Will be delving into the new features etc soon.