Upgrade error

Upgrade Error
Could not create foreign key constraint. There are 'ASSIGNED_TO' values of entity 'REQUESTS' with no corresponding value in entity 'EMPLOYEE_DETAILS'.   Help me to fix this error..! I have attached my oml....
Hi there!

If you don't mind loosing data, the best thing to follow what is explained in this post.

"Delete the espace via servicecenter (while keeping it open in your service studio)
then publish it again. This will remove your whole datamodel and such, so you can start with a clean sheet."