Better `typeKey` support in TypeScript, or drop support for it in TypeScript altogether

[vkarpov15]

Re: #9927, #11241

The fact that type is optional in SchemaTypeOptions causes unpredictable behavior, because incorrect type definitions often end up as valid SchemaTypeOptions because of

mongoose/types/index.d.ts

Line 1582 in 3dd0461

[other: string]: any;

. Something to think about.

[Uzlopak]

Yeah, that should be removed imho, as it indicates that the schema type can handle more values.

Was this added, because than people can add more attributes for their custom types?

Probably instead of having that big T extends bla stuff, we should use type as discriminator.

[vkarpov15]

We added it because Mongoose supports schema definitions like this:

new Schema({
  name: {
    $type: String // Notice '$type` here instead of `type`... because of `typeKey`
  }
}, { typeKey: '$type' });

The original rationale for this was to make it easier to define schemas that have properties named 'type'. Unfortunately, this sort of pattern doesn't work well with TypeScript, and we made type optional in SchemaTypeOptions to avoid completely blocking using typeKey in TypeScript.

Also, I linked to the wrong line. [other: string]: any is correct, because plugins often use additional schema type options. Like the autopopulate option from mongoose-autopopulate.

[vkarpov15]

We have this in #11487 now, just need some docs.

[agus-condro-speedoc]

We added it because Mongoose supports schema definitions like this:

new Schema({
  name: {
    $type: String // Notice '$type` here instead of `type`... because of `typeKey`
  }
}, { typeKey: '$type' });

The original rationale for this was to make it easier to define schemas that have properties named 'type'. Unfortunately, this sort of pattern doesn't work well with TypeScript, and we made type optional in SchemaTypeOptions to avoid completely blocking using typeKey in TypeScript.

Also, I linked to the wrong line. [other: string]: any is correct, because plugins often use additional schema type options. Like the autopopulate option from mongoose-autopopulate.

Has this been resolved?

In NestJs Typescript declaring the schema's field like that doesn't work, and the recommended way here also doesn't work meaning to say VSCode doesn't detect the sibling fields

[vkarpov15]

@agus-condro-speedoc docs haven't been done, but everything else has been resolved. Can you provide an example of how you're defining schema fields?

[vkarpov15]

We can close this since the typeKey option works as expected in TypeScript right now.