JSONSchemaType incorrectly requires optional properties to be nullable

What version of Ajv are you using? Does the issue happen if you use the latest version?

Ajv 8.6.0, Typescript 4.3.4

Your typescript code

import { JSONSchemaType } from 'ajv/dist/2020';

interface Example {
  foo: string;
  bar?: string;
}

const schema: JSONSchemaType<Example> = {
  additionalProperties: false,
  type: 'object',
  properties: {
    foo: {
      type: 'string'
    },
    bar: {
      type: 'string'
    }
  },
  required: ['foo']
};

Typescript compiler error messages

TS2322: Type '{ additionalProperties: false; type: "object"; properties: { foo: { type: "string"; }; bar: { type: "string"; }; }; required: "foo"[]; }' is not assignable to type 'UncheckedJSONSchemaType<Example, false>'.
  Type '{ additionalProperties: false; type: "object"; properties: { foo: { type: "string"; }; bar: { type: "string"; }; }; required: "foo"[]; }' is not assignable to type '{ type: "object"; additionalProperties?: boolean | UncheckedJSONSchemaType<unknown, false> | undefined; unevaluatedProperties?: boolean | UncheckedJSONSchemaType<unknown, false> | undefined; ... 7 more ...; maxProperties?: number | undefined; } & { ...; } & { ...; } & { ...; }'.
    Type '{ additionalProperties: false; type: "object"; properties: { foo: { type: "string"; }; bar: { type: "string"; }; }; required: "foo"[]; }' is not assignable to type '{ type: "object"; additionalProperties?: boolean | UncheckedJSONSchemaType<unknown, false> | undefined; unevaluatedProperties?: boolean | UncheckedJSONSchemaType<unknown, false> | undefined; ... 7 more ...; maxProperties?: number | undefined; }'.
      The types of 'properties.bar' are incompatible between these types.
        Type '{ type: "string"; }' is not assignable to type '{ $ref: string; } | (UncheckedJSONSchemaType<string | undefined, false> & { nullable: true; const?: undefined; enum?: readonly (string | null | undefined)[] | undefined; default?: string | ... 1 more ... | undefined; })'.
          Type '{ type: "string"; }' is not assignable to type '{ type: "string"; } & StringKeywords & { allOf?: readonly UncheckedPartialSchema<string | undefined>[] | undefined; anyOf?: readonly UncheckedPartialSchema<string | undefined>[] | undefined; ... 4 more ...; not?: UncheckedPartialSchema<...> | undefined; } & { ...; } & { ...; }'.
            Property 'nullable' is missing in type '{ type: "string"; }' but required in type '{ nullable: true; const?: undefined; enum?: readonly (string | null | undefined)[] | undefined; default?: string | null | undefined; }'.

Describe the change that should be made to address the issue?

This code will not compile unless bar is marked as nullable in the schema. However, I don’t want to accept null as a value for bar if it is present. It appears that JSONSchemaType expects all properties not mentioned in the required array to be marked as nullable. null and undefined are different values and should not be conflated.

Are you going to resolve the issue? 🤷

[reggi]

Hey future traveler 👋

I just discovering this post and was about to give up, when I saw nullable: true and it worked!

Here’s a clear example:

export const schema: JSONSchemaType<{ value: string, embed?: string, page?: string}> = {
    type: "object",
    properties: {
        value: {
            type: 'string',
        },
        embed: {
            type: 'string',
            nullable: true
        },
        page: {
            type: 'string',
            nullable: true
        },
    },
    required: ['value'],
    additionalProperties: false
}

[epoberezkin]

@erikbrinkman i think the correct way to improve it in the next major version is to only require nullable: true if the property has null as possible value in typescript, independently of whether it’s required or optional. That will be a breaking change.