If the BrandId column in a "car" entity has DeleteRule=Protect, what happens if a brand is deleted?

When the DeleteRule for a column, like BrandId in a "car" entity, is set to Protect, it prohibits the deletion of the brand if any associated records exist in the linked entity (in this case, cars). This means that if an attempt is made to delete a brand that still has cars referencing it, the system will raise a database exception. The integrity of the data is maintained by preventing the deletion of a parent record when there are dependent child records, thereby ensuring that the relationship between entities is consistent.

This rule is critical in database design as it protects against orphaned records, which could lead to data integrity issues. Therefore, when an attempt to delete a brand occurs while there are still cars that reference this brand, the protective rule triggers an exception, effectively blocking the deletion and ensuring that the relationships within the data model remain intact.