Crate fmodel_rust

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FModel Rust

When you’re developing an information system to automate the activities of the business, you are modeling the business. The abstractions that you design, the behaviors that you implement, and the UI interactions that you build all reflect the business — together, they constitute the model of the domain.

event-modeling

IOR<Library, Inspiration>

This crate can be used as a library, or as an inspiration, or both. It provides just enough tactical Domain-Driven Design patterns, optimised for Event Sourcing and CQRS.

Decider

Decider is a datatype/struct that represents the main decision-making algorithm. It belongs to the Domain layer. It has three generic parameters C, S, E , representing the type of the values that Decider may contain or use. Decider can be specialized for any type C or S or E because these types do not affect its behavior. Decider behaves the same for C=Int or C=YourCustomType, for example.

Decider is a pure domain component.

  • C - Command
  • S - State
  • E - Event
pub type DecideFunction<'a, C, S, E> = Box<dyn Fn(&C, &S) -> Vec<E> + 'a + Send + Sync>;
pub type EvolveFunction<'a, S, E> = Box<dyn Fn(&S, &E) -> S + 'a + Send + Sync>;
pub type InitialStateFunction<'a, S> = Box<dyn Fn() -> S + 'a + Send + Sync>;

pub struct Decider<'a, C: 'a, S: 'a, E: 'a> {
    pub decide: DecideFunction<'a, C, S, E>,
    pub evolve: EvolveFunction<'a, S, E>,
    pub initial_state: InitialStateFunction<'a, S>,
}

Additionally, initialState of the Decider is introduced to gain more control over the initial state of the Decider.

Event-sourcing aggregate

aggregate::EventSourcedAggregate is using/delegating a Decider to handle commands and produce new events. It belongs to the Application layer. In order to handle the command, aggregate needs to fetch the current state (represented as a list/vector of events) via EventRepository.fetchEvents async function, and then delegate the command to the decider which can produce new events as a result. Produced events are then stored via EventRepository.save async function.

It is a formalization of the event sourced information system.

State-stored aggregate

aggregate::StateStoredAggregate is using/delegating a Decider to handle commands and produce new state. It belongs to the Application layer. In order to handle the command, aggregate needs to fetch the current state via StateRepository.fetchState async function first, and then delegate the command to the decider which can produce new state as a result. New state is then stored via StateRepository.save async function.

View

View is a datatype that represents the event handling algorithm, responsible for translating the events into denormalized state, which is more adequate for querying. It belongs to the Domain layer. It is usually used to create the view/query side of the CQRS pattern. Obviously, the command side of the CQRS is usually event-sourced aggregate.

It has two generic parameters S, E, representing the type of the values that View may contain or use. View can be specialized for any type of S, E because these types do not affect its behavior. View behaves the same for E=Int or E=YourCustomType, for example.

View is a pure domain component.

  • S - State
  • E - Event
pub type EvolveFunction<'a, S, E> = Box<dyn Fn(&S, &E) -> S + 'a + Send + Sync>;
pub type InitialStateFunction<'a, S> = Box<dyn Fn() -> S + 'a + Send + Sync>;

pub struct View<'a, S: 'a, E: 'a> {
    pub evolve: EvolveFunction<'a, S, E>,
    pub initial_state: InitialStateFunction<'a, S>,
}

Materialized View

materialized_view::MaterializedView is using/delegating a View to handle events of type E and to maintain a state of denormalized projection(s) as a result. Essentially, it represents the query/view side of the CQRS pattern. It belongs to the Application layer.

In order to handle the event, materialized view needs to fetch the current state via ViewStateRepository.fetchState suspending function first, and then delegate the event to the view, which can produce new state as a result. New state is then stored via ViewStateRepository.save suspending function.

FModel in other languages

Credits

Special credits to Jérémie Chassaing for sharing his research and Adam Dymitruk for hosting the meetup.

Created with love by Fraktalio

Modules

Type Aliases