Annotations

@EventType

Marks a data class as a Chronicle event type.

Parameter	Type	Default	Description
id	String	""	Stable identifier. Defaults to class name.
generation	Int	1	Schema version. Increment when shape changes.
tombstone	Boolean	false	Signals event source retirement.

@EventType
data class OrderPlaced(val orderId: String, val totalAmount: Double)

Omitting id is the common case — Chronicle uses OrderPlaced as the identifier automatically.

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@Reactor

Marks a class as a Chronicle reactor. Each public method becomes a handler for the event type of its first parameter.

Parameter	Type	Default	Description
id	String	""	Stable identifier. Defaults to class name.

@Reactor
class OrderNotifications { ... }

Supply an explicit id only when you need the identifier to survive class renames.

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@Reducer

Marks a class as a reducer. Each public method folds one event type into the read model.

Parameter	Type	Default	Description
id	String	""	Stable identifier. Defaults to class name.

@Reducer
class OrderSummaryReducer { ... }

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@ReadModel

Marks a data class as a Chronicle read model.

Parameter	Type	Default	Description
id	String	""	Stable identifier. Defaults to class name.
displayName	String	""	Human-readable label. Defaults to name.

@ReadModel
data class OrderSummary(val orderId: String = "", val status: String = "pending")

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@Projection

Marks a class as a Chronicle projection. The class must implement IProjectionFor<T> or be used with declarative field annotations.

Parameter	Type	Default	Description
id	String	""	Stable identifier. Defaults to class name.
readModel	KClass<*>	Any::class	From IProjectionFor<T>

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@Constraint

Marks a class as a Chronicle constraint definition. The class must implement IConstraint.

Parameter	Type	Default	Description
id	String	""	Stable identifier. Defaults to class name.

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@Seeder

Marks a class as a Chronicle event seeder. The class must implement ICanSeedEvents.

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@Pii

Marks a property as personally identifiable information. Chronicle encrypts annotated fields at rest using a per-subject key. See PII Attribute for the full compliance model this participates in.

@EventType
data class CustomerRegistered(
    val customerId: String,
    @Pii val email: String
)

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@FromEvent

Applied to a read model class to declare that its fields are mapped from an event type. Part of the annotation-based projection style.

Parameter	Type	Description
eventType	KClass<*>	The source event class.
key	String	Event property key. Default: "EventSourceId".

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@SetFrom

Applied to a read model property to declare which event field populates it.

Parameter	Type	Description
propertyPath	String	Event field name. Defaults to the property name.