An even worse mistake is treating all three of those model layers as one and the same, which tools like Django REST Framework make it so easy to do. It all seems well and good for a while, as developers build up a big codebase with ease, but then are confronted with an almost insurmountable amount of work when the need to refactor arises.
The thing I’ve noticed when stepping into a codebase where this problem has been allowed to occur is the lack of layers of abstraction. Having those different models built up from the start allows for an application to shift along with the needs of the product. Having a single layer, with the endpoints talking literally directly to the ORM models, almost inevitably leads to calcification, spaghettification, and disastrous performance.
The thing I’ve noticed when stepping into a codebase where this problem has been allowed to occur is the lack of layers of abstraction. Having those different models built up from the start allows for an application to shift along with the needs of the product. Having a single layer, with the endpoints talking literally directly to the ORM models, almost inevitably leads to calcification, spaghettification, and disastrous performance.