JSONSchemaType support for Record

Version v8

Problem Currently JSONSchemaType does not support types like Record<string, T | undefined> (or {[K in string]?: T}).

Solution

For the type for example:

type MyRecord = Record<string, number | undefined>

JSONSchema should be:

const myRecordSchema: JSONSchemaType<MyRecord> = {
  type: "object"
  additionalProperty: {type: "number"}
}

It should also allow propertyName keyword.

Possibly, below should also type check (although it can be expressed with properties but it would be more verbose:

type MyEnumRecord = Record<"a" | "b" | "c" | "d", number | undefined>

const myEnumRecordSchema: JSONSchemaType<MyEnumRecord> = {
  type: "object"
  propertyNames: {enum: ["a", "b", "c", "d"]}, // it won't check for completeness
  additionalProperty: {type: "number"}
}

(Although it would require properly supporting enum, which currently is not type checked at all)

[erikbrinkman]

A few points:

1. Typescript errors aren’t great. I agree. Unfortunately there’s not a great way to customize them. There are some proposals of making a never style type with custom errors so you can better indicate what the problem is.
2. The way JSONSchemaType is implemented, all of these extra parameters are partial, so they can exist or not, but there’s no guarantee that you fully specify the type, which is probably fine.
3. For your (2), it’s currently propertyNames?: JSONSchemaType<string> so you could instead make it Omit< JSONSchemaType<string>, "type"> & { type?: "string" }. Which would just make type optional. Note that current property names does no validation, so you can specify an enum, but you can also put whatever you want in the enum.
4. For your (1), are you just thinking that required should be optional when RequiredMembers is empty

https://github.com/ajv-validator/ajv/blob/8762e6f8b17c4e61f3d47db502b19e99f4582724/lib/types/json-schema.ts#L138-L140

I agree that you could open new issues, but I think both of these are potentially pretty simple.

[erikbrinkman]

@epoberezkin ping to get your feedback on what you had in mind