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Bug: ZenStack v2 loses type information in TypeScript types for delegated polymorphic models

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Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
45/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Stale
Tech stack
typescript
Domain
tooling

Research direction

Reproduce with the three-model schema above and inspect the generated TypeScript types: the discriminator literal survives on the Base union but widens to string on Foo and Bar. The cause is in ZenStack's schema-to-TypeScript emitter for @@delegate models — trace where the discriminator field type is inferred for each concrete model and why the literal is dropped there but not in the base union. Done means Foo emits type: "Foo" and Bar type: "Bar", so the Extract<Base, ...> workaround is no longer needed; verify against the regenerated types and the existing delegate type tests.

Written by the indexing model from the issue text.

Description

Description and expected behavior
There is a mismatch between the TypeScript type generated for the base model and all of its delegated submodels.

Consider the following schema:

model Base {
  id String @id @default(cuid(2))
  type String
  @@delegate(type)
}

model Foo extends Base {
  foo Number
}

model Bar extends Base {
  bar String
}

The types generated are as follows:

type Base = {
  id: string
  type: "Foo"
  foo: number
} | {
  id: string
  type: "Bar"
  bar: string
}

type Foo = {
  id: string
  type: string // Expected: "Foo"
  foo: number
}

type Bar = {
  id: string
  type: string // Expected: "Bar"
  bar: string
}

The types of the submodels Foo and Bar lose their discriminator, while the Base union does not. As a workaround, I use the following pattern everywhere:

type Foo = Extract<Base, { type: "Foo" }>
type Bar = Extract<Base, { type: "Bar" }>

Environment (please complete the following information):

  • ZenStack version: 2.21.0
  • Prisma version: 6.18.0
  • Database type: PostgreSQL

Additional context

Dominant language
TypeScript
Stars
2.9k
Forks
157
Avg merge
11h 42m
Merged PRs (30d)
20

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