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Command/Event Patterns

Introduction To Messages

If you are not familiar with the concept of Messages as it pertains to RIDDL, see here. This document pertains only to Commands and Events.

Backend v Gateway

This design spec considers only designing services themselves. As such it ignores usability features like fine-grained command parameters for updating data, unless justified. In a gateway service more consideration would have to be made for usability.

Problem Statement

There are implementation designs to be made regarding the arrangement of input (Command) and output (Event) data across Handlers. This documents pertains to all types of Command Handlers.

Preliminary Definitions

In this section we will be trying to figure out how to structure commands for creating, modifying, and deleting fields on User entities.

Here are the riddl specs we will be assuming for each example (borrowed from the evolving improving.app:

entity Organization is {
    state Active is {
        info: Info,
        members: MemberId*,
        contacts: Contacts,

type Contacts is {
    primaryContacts: MemberId+,
    billingContacts: MemberId*,
    distributionContacts: MemberId*

type Info is {
    name: String,
    address: Address?,
    isPrivate: Boolean,

type OrganizationId is Id (Organization)
type MemberId is Id (Member) briefly 
"Member is not relevant here, so it will not be shown here."

type Address is {
    line1: String,
    line2: String,
    city: String,
    stateProvince: String,
    country: String,
    postalCode: PostalCode

type MobileNumber is Pattern("\(([0-9]{3})\)([0-9]{3})-([0-9]{4})") 
described as "North American Phone Number standard"

type EmailAddress is String

type CAPostalCode is Pattern("[A-Z]\d[A-Z]\d[A-Z]\d")

type USPostalCode is Pattern("\d{5}(-\d{4})?")

type PostalCode is one of { CAPostalCode, USPostalCode }

### We will be trying to find Events for the following Commands:

command EstablishOrganization {
    info: Info,
    contacts: Contacts

command ModifyUserInfo {
    id: OrganizationId,
    info: Info

command AddMembersToUser {
    userId: OrganizationId,
    members: MemberId*

command ModifyUserContacts {
    userId: MemberId,
    contacts: Contacts

Solutions To Consider