Constraints

Constraints are shared Chronicle behavior. The shared docs cover constraint concepts, model-bound constraints, declarative constraints, and client-tabbed examples.

• Constraints
• Understanding constraints
• Kotlin and Java client setup

Kotlin client: constraint scoping

IConstraintBuilder (passed into IConstraint.define) can scope every constraint added through it to a narrower uniqueness dimension than the whole event store:

Member	Scopes uniqueness checking per…
perEventSourceType	Event source type
perEventStreamType	Event stream type
perEventStreamId	Event stream id

Combine any of the three; by default (none called) a constraint is checked globally across the whole event store:

import io.cratis.chronicle.constraints.Constraint
import io.cratis.chronicle.constraints.IConstraint
import io.cratis.chronicle.constraints.IConstraintBuilder
import io.cratis.chronicle.events.EventType

@EventType
data class ConstraintsBridgeUserRegistered(
    val userId: String = "",
    val email: String = ""
)

@Constraint
class ConstraintsBridgeUniqueEmail : IConstraint {
    override fun define(builder: IConstraintBuilder) {
        builder
            .perEventSourceType()
            .unique { unique ->
                unique
                    .on(
                        ConstraintsBridgeUserRegistered::class,
                        ConstraintsBridgeUserRegistered::email
                    )
                    .withMessage("Email must be unique per event source type.")
            }
    }
}