Saving things as string attributes is not the best way to do this: you should just create an association between your entity and System.UserRole. Then, you can create an XPath constraint on the datagrid Entity[Entity_UserRole/UserRole/UserRoles = '[%CurrentUser%]']
The advantage of this is that it supports a many to many relation between your entity and user roles and it supports a user having multiple user roles.
If you are determined to use a string attribute, then you could use a data source microf]low where you retrieve the UserRole of the current user (UserRole[UserRoles = $CurrentUser]) and retrieve Entity[userRoleString = UserRole/Name] and return that list.
Thank you for your quick response! I have managed to link my entities to user role and to show them only when the user has that role. The only reason I was using a string was that the UserRole/Name attribute is also a string, but your approach is way better!