Constants

Constant properties are set once during creation and never change afterward. Any value provided for them during creation or updates is ignored.

Defining a constant

A constant field requires two rules:

• constant: true
• value: a fixed value or a sync/async function that generates the value

import { Schema, type SetterFnData } from "ivo";

type Input = {
  userName: string;
};

type Output = {
  dateJoined: Date;
  id: string;
  role: string;
};

type SetterData = SetterFnData<Input, Output, CtxOptions>;

const userSchema = new Schema<Input, Output>({
  dateJoined: { constant: true, value: () => new Date() },
  id: {
    constant: true,
    value: ({ ctx }: SetterData) => `${ctx.userName}-${Date.now()}`,
  },
  role: { constant: true, value: "user" },
  userName: { required: true, validator: validateUserName },
});

Note: If the value function throws, the constant's value becomes null.

Lifecycle hooks

Constants support only onDelete and onSuccess lifecycle handlers:

• onSuccess runs once after a successful creation.
• onDelete runs once when the model's delete method is invoked.

const schema = new Schema({
  id: {
    constant: true,
    value: generateId,
    onSuccess: ({ ctx }) => console.log("created", ctx.id),
    onDelete: (data) => console.log("deleted", data.id),
  },
});

API summary

Option	Type	Required	Description
constant	true	Yes	Marks the property as constant.
value	any | function	Yes	Fixed value or resolver that produces the constant value.
onDelete	function | function[]	No	Handler(s) invoked when the model instance is deleted.
onSuccess	function | function[]	No	Handler(s) invoked after a successful create operation.