Foreign keys and constraints sometimes are disabled during bulk data loads. Simply re-enabling the foreign key or constraint leaves it in an untrusted state. In order for SQL Server to utilize the key or constraint in query plans, it must be verified. This script will find all enabled, untrusted foreign keys and attempt to verify them and make them trusted. It will report counts of the number of foreign keys it could and could not re-trust.
The same script can be used to validate constraints by changing the first table in the cursor FROM clause from sys.foreign_keys to sys.check_constraints.