How to extract certain keys whose value is a certain type?

[glacial mortar]

mochoman#0777

Playground Link

Preview:```ts
type Entity = {
[key: string]: unknown
}

type ParticipantTag = {
uuid: string
name: string
colour: string | null
priority: string
}

type Relation<T> = T

type Participant = {
id: string
firstName: string
middleName: string
lastName: stri
...```

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[strange gull]

So the only relations that can be included are tags - but this still allows all values

I could be going about it all wrong

[thin ibex]

Relation is just an identity type there, so your T[K] extends Relation<T[K]> condition will be true for any possible T[K]

there needs to be some structural difference about the relation properties that you can check

i'm not sure what's up for grabs here, but possibilities include:

1. adjusting Relation to add some structure to it so you can tell just by looking at a value whether it is a Relation or not
2. change the outer structure to make relations easier to identify (e.g. put them in a sub-object under a relations key)
3. keep track of which keys are relations separately

all else being equal i'd probably vote for option 2, which could look something like this:

[glacial mortar]

mkantor#7432

Playground Link

Preview:```ts
type Entity = {
[key: string]: unknown
}

type ParticipantTag = {
uuid: string
name: string
colour: string | null
priority: string
}

type Relation<T> = T

type Participant = {
id: string
firstName: string
middleName: string
lastName: stri
...```

You can choose specific lines to embed by selecting them before copying the link.

[strange gull]

Hmm gotchya - 2 and 3 look promising

Not sure what other benefits I may getwith #2 as I am rebuilding the API as well so am open to this change