state-change-slice

name	state change slice
description	Knows how to build state change slices

STATE_CHANGE Slice Skill

Overview

A STATE_CHANGE slice represents a business operation that modifies aggregate state through commands and events. This is the core CQRS/Event Sourcing pattern.

Input Structure

{
  "sliceType": "STATE_CHANGE",
  "title": "slice: <Name>",
  "context": "<BoundedContext>",
  "commands": [...],
  "events": [...],
  "readmodels": [...],
  "screens": [...],
  "processors": [...],
  "specifications": [...]
}

Flow Pattern

Screen (UI) → Command → Aggregate (@CommandHandler) → Event → ReadModel (via @EventHandler Projector)
                                                    ↓
                                              Automation (if processors exist)

Code Generation Steps

Step 1: Create Command

Location: src/main/kotlin/de/alex/<module>/domain/commands/<commandname>/<CommandName>Command.kt

Template:

package de.alex.<module>.domain.commands.<commandname>

import de.alex.common.Command
import org.axonframework.modelling.command.TargetAggregateIdentifier
import java.util.UUID

data class <CommandName>Command(
    @TargetAggregateIdentifier var aggregateId: UUID,
    // Add fields from slice command definition
    // Map types: UUID, String, Date → LocalDate, Integer → Int, Boolean, Decimal → BigDecimal
    // Handle cardinality: Single → regular type, Multiple → List<type>
) : Command

Field Mapping Rules:

Slice Type	Kotlin Type
UUID	UUID
String	String
Date	LocalDate
Integer	Int
Boolean	Boolean
Decimal	BigDecimal
Multiple cardinality	List
optional: true	Nullable (T?)

Step 2: Create Event(s)

Location: src/main/kotlin/de/alex/events/<EventName>Event.kt

Template:

package de.alex.events

import de.alex.common.Event
import java.util.UUID

data class <EventName>Event(
    var aggregateId: UUID,
    // Add fields from slice event definition
    // Fields typically mirror command fields
) : Event

Step 3: Add CommandHandler to Aggregate

Location: src/main/kotlin/de/alex/domain/<Aggregate>Aggregate.kt

Template for existing aggregate:

@CommandHandler
fun handle(command: <CommandName>Command): CommandResult {
    // Business validation logic
    AggregateLifecycle.apply(
        <EventName>Event(
            command.aggregateId,
            // Map command fields to event fields
        )
    )
    return CommandResult(command.aggregateId.toString(), AggregateLifecycle.getVersion())
}

Template for new aggregate creation (when createsAggregate: true):

@CreationPolicy(AggregateCreationPolicy.ALWAYS)
@CommandHandler
fun handle(command: <CommandName>Command): CommandResult {
    AggregateLifecycle.apply(
        <EventName>Event(
            command.aggregateId,
            // Map command fields to event fields
        )
    )
    return CommandResult(command.aggregateId.toString(), AggregateLifecycle.getVersion())
}

Step 4: Add EventSourcingHandler to Aggregate

@EventSourcingHandler
fun on(event: <EventName>Event) {
    // Update aggregate state from event
    this.aggregateId = event.aggregateId
    // Update other state fields
}

Example: Processing "slice: Assign Clerk to Case"

Input:

{
  "sliceType": "STATE_CHANGE",
  "title": "slice: Assign Clerk to Case",
  "commands": [{
    "title": "Assign Clerk to Case",
    "aggregate": "Case",
    "fields": [
      {"name": "caseId", "type": "UUID", "idAttribute": true},
      {"name": "clerkId", "type": "UUID"},
      {"name": "hourlyRate", "type": "Decimal"}
    ]
  }],
  "events": [{
    "title": "Clerk Assigned to Case",
    "fields": [...]
  }]
}

Generated Files:

1. src/main/kotlin/de/alex/cases/domain/commands/assignclerktocase/AssignClerkToCaseCommand.kt
2. src/main/kotlin/de/alex/events/ClerkAssignedToCaseEvent.kt
3. Update src/main/kotlin/de/alex/domain/CaseAggregate.kt with handlers

Processing Group Configuration

Ensure the module has a ProcessingGroups file:

Location: src/main/kotlin/de/alex/<module>/ProcessingGroups.kt

package de.alex.<module>

class ProcessingGroups {
    companion object {
        const val <MODULE> = "<MODULE>"
    }
}