I have the same question : is there any way in concrete5 to manage table relation in customs blocks ? Like a simple employees->company relation ?
Thanks

You basically need to manage relationships yourself. Concrete5 does include the ADODB library for database access, which has a basic ActiveRecord implementation, but it is woefully incomplete (kind of buggy, doesn't have many-to-many relationships, etc.). You can check out the free "Email List Signup" addon which I created a while back and used the ActiveRecord stuff for it. But now I just find that most blocks are so simple it's not too bad to just use SQL statements to manage relationships. Check out the built-in "Slideshow" block for an example of how to deal with related records (basically declare a second table in the block's db.xml file, then you need to manually create/update/delete those secondary records in the controller's save(), duplicate(), and delete() methods).

I don't know if you're still looking for an answer, but what I've done is include php ActiveRecord in the package's libraries, load it in the controller, and then manage relations in the models. You do have to set up the foreign keys in your db.xml file, though.