cant truncate tables with a pk/ fk relationship? I have a table called Folder with 3 fields: Id (PK), Name, UserId (FK)

and another table called User with two fields: Id (PK), UserName

i am trying to run this sql:

truncate table Folder
truncate table User


i get the following error

Cannot truncate table 'Folder' because it is being referenced by a FOREIGN KEY constraint.
Cannot truncate table 'user'   because it is being referenced by a FOREIGN KEY constraint.


...even after deleting all the records in both tables i get this. why am i not allowed to truncate my tables? 

how can i reset the seeds of the PK's easily without using truncate if there is now way to run a truncate on pk/fk relationship tables?

Edit: 
DB diagram added
To reseed, use DBCC CHECKIDENT

DBCC CHECKIDENT ('table', RESEED, 1)


Or you'd have to drop the FK, truncate, then recreate the FK.

This is by design: TRUNCATE TABLE is simple page deallocation and constraints are not checked row by row. This limitation means you can't truncate when there are FKs.. even if you disable the FK.