RFC: Introduce GraphGen into Simulacrum

Motivation

Simulacrum has the concept of a state atom. It's a unified data store that is used by all simulators. Simulators consume this state and contribute to it based on their specific functionality. This concept is not unique to Simulacrum. Tools like Mirage.js have an Object-relational mapping (ORM) that is used to describe the data stored in the server. Server handlers use this ORM to generate the response payload.

The concept of an ORM is well known and established in our industry. Patterns and APIs around ORMs are familiar as well. All ORMs have a concept of a Model which gives name to data of a certain shape. Models have fields of different types. One of those types is relationships that represent connections between data. These models can be constructed using factories that control how objects are created from models. Factory APIs are different in ORM but they have one quality in common. They are designed to easily create models but they leave wiring up relationships up to the user via factory configuration. For example, in Mirage.js you can easily create 100 records with createList API, but if you would like those records to automatically create relationships you need to define how to construct those relationships in afterCreate hook.

Manually creating relationships is tedious but manageable when you’re simulating a single server. When you’re managing multiple simulators with all of their data models, wiring up all of the relationships becomes onerous and limiting. It’s onerous when the logic of relationship-creating code becomes more complicated than a very basic relationship - especially when you want to support multiple scenarios. It’s limiting because changing the rules that govern how relationships are created requires changing code which is not possible in low code environments like automated testing.

What all of these tools are missing is a way to declaratively describe the rules that control how relationship data is created. That mechanism needs to be higher level so you declare how the relationships are created without writing any code to connect those relationships. This is what frontside/graphgen project was designed to do. The API that it exposes is currently a little too low level to be truly declarative - think React.createElement before JSX was introduced. This goal of this RFC is to describe what introducing the graphgen into Simulacrum might look like.

Approach

WIP

The issue names no implementation files, tests, or entry points, and its Approach section is still WIP. Start by reading Simulacrum's state atom and simulator data-model code, then review the linked GraphGen project and the RFC requirements. Done would require an agreed design for declarative relationship creation and an implementation plan.