🐛 Bug / Feature Request: `inputModel = true` fails on relations to join models with composite IDs

[tsegreto]

🐛 Bug / Feature Request: inputModel = true fails on relations to join models with composite IDs

Summary

When inputModel = true is enabled, prismabox generation fails if a relation points to an explicit join model that does not have a single scalar @id (e.g., it uses a composite primary key @@id([…])).

This seems like a generator limitation: prismabox InputModels appear to assume that related records can be identified with a single scalar ID for connect / disconnect.

Error

Unsupported ID type: Membership on model User in relation memberships

Minimal Reproduction (brief example)

Prisma schema

model User {
  id          String       @id @default(uuid())
  memberships Membership[]
}

model Team {
  id          String       @id @default(uuid())
  memberships Membership[]
}

// Explicit join model with composite primary key
model Membership {
  userId String
  teamId String

  user   User @relation(fields: [userId], references: [id])
  team   Team @relation(fields: [teamId], references: [id])

  @@id([userId, teamId])
}

Generator config

generator prismabox {
  provider   = "prismabox" // or the correct provider string
  inputModel = true
}

Command

prisma generate

Expected behavior

One of the following would be ideal:

1. Support composite IDs / compound uniques for relation connect / disconnect shapes in InputModels (generate a schema compatible with Prisma’s compound-unique connect format), or

2. If composite IDs aren’t supported, skip or disable connect/disconnect generation for such relations (with a documented option), or

3. At minimum, fail with a clearer error message like:

   inputModel=true requires the related model to have a single scalar @id field (composite @@id not supported yet)

Actual behavior

Generation fails with:

Unsupported ID type: Membership on model User in relation memberships

Why this matters

Composite-key join tables are a common Prisma pattern. With inputModel = true, projects that model many-to-many relationships using explicit join models cannot generate InputModels unless they introduce a surrogate id.

Workarounds

• Add a surrogate scalar id to the join model and keep a @@unique([userId, teamId]), or
• Hide the relation from input generation (if supported), and manage join records through a dedicated endpoint/model, or
• Disable inputModel.

Proposed implementation idea

When generating InputModels for relation fields, prismabox could:

• Detect whether the related model is identified by:

  • scalar @id, or
  • composite @@id, or
  • compound @@unique

• If composite/compound is present, generate connect / disconnect schemas that accept a compound “where” object (as Prisma does), or allow a config option to select which unique constraint to use.