Instead of using a public API, what are the ways to connect a website and mobile to a database?

I'll like to connect my website and app to a cloud database. I know that one way is to connect them both individually through a database connection, but I would prefer to reuse the same code to get the same data.

I know building an API can help in this, but the database contains private data. I've searched online for ways to privatise the api, but it looks like it can be reversed engineered.

Are there other ways that I don't know about?