Typechecking doesn't work when insert value is instantiated outside the values function

[maktouch]

In this playground link: https://kysely.dev/docs/examples/INSERT/single-row

const result = await db
  .insertInto('person')
  .values({
    first_name: 'Jennifer',
    last_name: 'Aniston',
    age: 40,
    hello: 'world'
  })
  .executeTakeFirst()

console.log(result.insertId)

This gets correctly typechecked. Column hello doesn't exist and there's squiggly lines everywhere.
This, however, doesn't work.

const obj = {
    first_name: 'Jennifer',
    last_name: 'Aniston',
    age: 40,
    hello: 'world'
  }
  
const result = await db
  .insertInto('person')
  .values(obj)
  .executeTakeFirst()

console.log(result.insertId)

Same thing for updates.

This is quite a footgun!

[igalklebanov]

Hey 👋

This is a general TypeScript problem. I'll try to find the relevant issue/s later.
You can find the same shenanigans in anything that involves objects, see zod's pick/omit methods.

Lemme give you another weird behavior:

const values = {
    first_name: 'Jennifer',
    last_name: 'Aniston',
    age: 40,
    hello: 'world'
}

const result = await db
  .insertInto('person')
  .values([values, {
    first_name: 'Jennifer',
    last_name: 'Aniston',
    age: 40,
    hello: 'world'
  }])
  .executeTakeFirst()

no type errors.

const values = {
    first_name: 'Jennifer',
    last_name: 'Aniston',
    age: 40,
    hello: 'world'
  }

const result = await db
  .insertInto('person')
  .values([{
    first_name: 'Jennifer',
    last_name: 'Aniston',
    age: 40,
    hello: 'world'
  }, values])
  .executeTakeFirst()

again, no type-errors.

if you add as const to values, there are type-errors.
so you should always use as const when passing input "from outside" in type-safe TS libraries.

I actually had a PR that "fixes" it with a hack, but we rightfully didn't merge it as it's unhealthy. This is TypeScript's responsibility to fix.
#229

[maktouch]

hmm but even with as const it doesn't work?

const obj = {
    first_name: 'Jennifer',
    last_name: 'Aniston',
    age: 40,
    hello: 'world'
  } as const

const result = await db
  .insertInto('person')
  .values(obj)
  .executeTakeFirst()

console.log(result.insertId)

[igalklebanov]

It worked on the 2 item example, haven't checked on single value example.

Here's some related text from people who are more in the know about this issue.
https://stackoverflow.com/a/57015227
microsoft/TypeScript#12936
microsoft/TypeScript#13444 (comment)

[cmmartin]

Okay, so typescript allows additional members, which makes sense. What doesn't make sense is why this is valid...

const obj = {
    first_name: 'Jennifer',
    last_name: 'Aniston',
    age: 40,
    hello: 'world'
  }
  
const result = await db
  .insertInto('person')
  .values(obj)
  .executeTakeFirst()

but this is not...

const result = await db
  .insertInto('person')
  .values({
    first_name: 'Jennifer',
    last_name: 'Aniston',
    age: 40,
    hello: 'world'
  })
  .executeTakeFirst()

If the explanation is that the additional members are not type errors, then both of these should be valid. Something else is going on here

[igalklebanov]

What can you do, when one of TypeScript's team says: "works as intended". 🤷

1. You could do some type hackery but, it's unhealthy, hurts compile-time performance, makes the code less readable, and might break with any new TypeScript version.
2. Wait. This is TypeScript's responsibility to fix. They haven't closed the exact types issue, so there's hope.
3. Spread awareness of this TypeScript caveat and provide recommendations in documentation.
4. Provide an alternative API that doesn't use objects as inputs.

[maktouch]

I think 3. Spread awareness of this TypeScript caveat and provide recommendations in documentation. makes the most sense. I'll try to make PR for the docs in the coming days.

Thanks for everything!