Should I use composite primary keys or not?

Question

There seems to only be 2nd class support for composite database keys in Java\'s JPA (via EmbeddedId or IdClass annotations). And when I read up on composite keys, regardless

Answer 1

I would only ever use them in join tables. The only way to absolutely ensure that every record identifier is unique and consistent over time is to use a synthetic key.

Composite keys seem OK in theory, which is why they are tempting to use, but practice has shown that they usually indicate that there is a flaw in your data model. Worse still, in many cases they will fail to guarantee uniqueness, given a large enough data set. And data sets always grow over time, so using them may mean that you have planted a bomb in your application which will only explode when the application has been in production use for a while.

I think that people are underplaying ORMs. Every mainstream programming language has a defacto ORM, and has had for years, because they solve the fundamental incompatibility between OO and relational structures. Trying to write any complex, testable OO software against SQL databases without an ORM is very inefficient, at best.

Good ORMs also provide practices and tooling that make it much easier to create and maintain consistent high-quality database schema, so on average, a team will come out well ahead by working with an ORM. Handcrafting schema is rather like writing C++ ...people can do it, but in the real world it is so hard to maintain quality over time that the average product is not good.