Mixins

Mixins provide field reuse for .cstack models. They are a schema authoring convenience, not a runtime inheritance feature.

Syntax

Declare a top-level mixin block and apply it inside a model with @use(...).

mixin AuditFields {
  createdAt DateTime @default(dbgenerated())
  updatedAt DateTime @default(dbgenerated())
}

model Post {
  @use(AuditFields)

  id Int @id
  title String
}

You can apply more than one mixin:

mixin AuditFields {
  createdAt DateTime @default(dbgenerated())
  updatedAt DateTime @default(dbgenerated())
}

mixin SoftDelete {
  deletedAt DateTime?
}

model Post {
  @use(AuditFields, SoftDelete)

  id Int @id
  title String
}

Semantics

CrateStack expands mixin fields into the model before semantic validation and before Rust, Dart, and TypeScript code generation.

That means:

• generated clients and generated server code see normal model fields after expansion
• validator rules run on the expanded model field set
• mixins do not create a separate generated runtime type

Rules

Current mixin support is intentionally narrow:

• mixins are only supported as top-level declarations
• @use(...) is only supported inside model blocks
• mixins contain fields, not model-level attributes
• mixins must not declare @id
• model-local fields win on name conflicts with mixin fields

Example of local override:

mixin Timestamps {
  createdAt DateTime
}

model Post {
  @use(Timestamps)

  id Int @id
  createdAt DateTime?
}

In that example, the model's createdAt DateTime? definition wins.

Non-goals

Mixins are not:

• polymorphism
• inheritance between generated model types
• a way to share model @@... attributes
• a way to declare shared primary keys