Data Validation and Transformation

Validation

Just like with authorization rules, we can validate data using functions. For example:

import "./validators.js" as validators { runtime = "nodejs:14" }

@onWrite(function: validators.validateBook)
@1 model Book {
  @1 id: String @uuid @primary
  @2 title: String
  @2 authors: [String]
}

where validateBook is a JavaScript function in validators.js, defined as:

const validateBook = ({ book }) => {
  if(book.authors.length < 1) {
    throw new Error("A book must have at least one author")
  }
  return { book }
}

Transformation

Let's say that we want every book's title to be in uppercase automatically on every read, we can pass a function to @onRead directive on the Book model

import "./transformers.js" as transformers { runtime = "nodejs:14" }

@onRead(function: transformers.transformBook)
@1 model Book {
  @1 id: String @uuid @primary
  @2 title: String
  @3 authors: [String]
}

transformBook is a JavaScript function defined in transformers.js as:

const transformBook = ({ book }) => ({ ...book, title: book.title.toUpperCase() })

The result of the transformation is then returned to the user, or passed to the next @onRead. The same composition mechanism applies to other types of directives that take function arguments, i.e. onWrite, onLogin, and onDelete.

Validation#

Transformation#

Validation

Transformation