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Declarative approach is excellent for many use-cases but every once in a while, we simply need to resort to custom imperative code (e.g. cryptography, payment, external tools and services, our own custom behavior, ...). This is where Gaudi hooks come in. They are the "escape hatches" which allow you to use any JS custom code or a library you need and run it inside Gaudi.

First, you need to define a runtime which contains a path to your hooks folder.

runtime MyJsRuntime {
path "./path/to/hooks"

This folder is relative to current working directory so make sure you matches your runtime settings.

Once a runtime is defined, you can add some hooks.

Hook types

You can write hooks in two different ways:

  • inline - typically, simple one-liners,
  • source - referencing a function defined in your runtime directory.

Inline hooks

Inline hooks contain entire code inlined inside a string. They have access to args as if they were variables.

hook {
arg myValue 10
inline "`value is ${myValue}`"

External hooks

External hooks are located in outside, typically native, files (e.g. .js files) and are only referenced inside Gaudi code. This allows you to use native language tools when writing hooks while still using them inside Gaudi.

hook {
arg myValue 10
source getValue from "./examples.js"

A function (in this case getValue) accepts context (varies based on hook type), and arguments passed:

export function getValue(args) {
// using lodash lib using "_" global var
return _.identity(args.myValue);

Make sure to export hooks functions so Gaudi can find them.

Hooks usage

Hooks can be used in several places.

Model hook

A model hook calculates a custom property on model. It can accept query as an argument, as well as normal expressions.

model User {
field fullName { type string }
field paymentId { type string }
hook paymentHistory {
arg maxHistLength 10
arg user query { select { id, paymentId } }
source fetchHistory from "./stripe.js"

Setter hook

A setter hook can be executed as part of the set statement with create or update actions:

create as org {
set randomInt hook {
inline "Math.floor(Math.random() * 1000)"

Execute action hook

Execute action hook is a way to define an action using completely custom JS code. Execute hook has a context with access to request and response objects.

action {
create as org {}
execute {
hook {
arg orgId
inline "console.log(orgId)"