Declarative constraints

The declarative API lets you define constraints in a dedicated class by implementing IConstraint. Chronicle discovers all IConstraint implementations automatically — no registration is needed.

Use declarative constraints when you need:

• Uniqueness spanning multiple event types with different property names
• A callback to compose dynamic violation messages
• More explicit control over constraint names

Constraint types

Type	Description
Unique property	Enforce that a property value is unique across one or more event types
Unique event type	Enforce that only one event of a specific type can be appended per event source

Defining a constraint

Implement IConstraint and call the builder in Define:

using Cratis.Chronicle.Events.Constraints;

public class UniqueProjectName : IConstraint
{
    public void Define(IConstraintBuilder builder) =>
        builder.Unique(unique =>
            unique
                .On<ProjectCreated>(e => e.Name)
                .RemovedWith<ProjectRemoved>());
}

Discovery

Chronicle scans all loaded assemblies for types that implement IConstraint and registers them with the Kernel automatically when the client starts. No explicit registration is required.