[y1426i]

There are many reasons to not use foreign keys, but it also depends on the kind of application. For small databases, foreign keys do make things simpler from a validation standpoint.

When building systems for scale where the databases may grow large, foreign keys can cause many issues -

- ORM features around foreign keys can easily bring your system down when joining large tables with incorrect/missing indexes during heavy loads

- As the table grows, not having foreign keys makes it simple in taking out large tables into big-data solutions in the future

- The schemas and relations are sometimes hard to understand during the initial phases of application development. Not having those relations makes changing schemas simpler and faster.

- Sharding tables is much simpler when there are no foreign keys

- It helps to add some of the reference logic in the application rather than the database. Databases are the bottlenecks when it comes to IOPS and scaling. The more processing you move to your application server, the better scalability you can achieve.