RikerES

一个旨在比“照本宣科”更实用的、基于事件溯源和CQRS的抽象。它建立在轻量级actor框架Riker之上。
警告 目前质量相当初阶，功能尚不完整，API仍在变化。

如何使用

此库为Riker添加了一些额外的事件溯源相关概念，实体代表一个领域，并且是处理外部命令和业务逻辑的入口点。使用通常的Riker机制（见创建actor）通过Entity actor创建。

let entity = actor_system.actor_of_args::<Entity<MyEntity>, _>("my-entity", SomeArgs)`;

定义您的实体

MyEntity 是一个用户提供的、实现了 ES 特质的结构体。

struct MyEntity;

#[async-trait]
impl ES for MyEntity {
  type Args = SomeArgs; // the arguments passed to the constructor
  type Model = MyData; // The "aggregate" is the data that is to be persisted along with its updates.
  type Cmd = MyEntityCommands; // The external command or commands(often in the form of an enum) this entity can handle.
  // type Event = (); // TODO: Similar to commands but for handling events emitted by other entities.
  type Error = MyEntityError; // Error produced by the handler functions.
  
  // Used to construct an entity, receives the `Entity` actor's context 
  // to be able to create other actors and hold their references
  fn new(_cx: &Context<CQRS<Self::Cmd>>, _args: Self::Args) -> Self {
    MyEntity
  }
  
  async fn handle_command(
    &mut self,
    cmd: Self::Cmd,
  ) -> Result<Commit<Self::Model>, Self::Error> {
    // do your command handling here and return a commit that will be persited
    // to the configured store(a simple memory store atm).
    
    // when entities are created for the first time
    Ok(Event::Create(MyData).into())
    // or to update an existing entity
    // Ok(Event::Change("some id".into(), MyDataUpdate).into())
  }
}

聚合和重新加载实体的状态

定义您的聚合（数据模型），它可以处理的更新以及如何应用它们。

struct MyData {
  some_id: String,
  some_field: String,
  other_field: Option<String>
}

enum MyDataUpdate {
  TheChange(String, String),
  LittleChange(String),
}

impl Model for MyData {
  type Change = MyDataUpdate;
  
  fn id(&self) -> EntityId {
    self.some_id.into()
  }
  
  fn apply_change(&mut self, change: Self::Change) {
    match change {
      MyDataUpdate::TheChange(field, other) => {
        self.some_field = field;
        self.other_field = Some(other);
      },
      MyDataUpdate::LittleChange(field) => {
        self.some_field = field;
      },
    }
  }
}

分发命令和查询

RikerES提供了一个实体管理器，它将保留对已注册实体的引用，并提供一个更简单的API来向正确的实体发送命令和查询。

let mgr = Manager::new(actor_system).register::<MyEntity>(SomeArgs);

let id = mgr.command(MyEntityCommands::DoSomething).await;
let data = mgr.query::<MyEntity>(id).await.unwrap();