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定义面向业务的命令而不是通用CRUD。命令将领域语言带入你的API，并启用命令查询职责分离（CQRS）模式。

快速开始

#[derive(Entity)]
#[entity(table = "users", commands)]
#[command(Register)]
#[command(UpdateEmail: email)]
#[command(Deactivate, requires_id)]
pub struct User {
    #[id]
    pub id: Uuid,

    #[field(create, update, response)]
    pub email: String,

    #[field(create, response)]
    pub name: String,

    #[field(response)]
    pub active: bool,
}

生成的代码

命令结构体

/// User上Register操作的命令载荷。
#[derive(Debug, Clone)]
pub struct RegisterUser {
    pub email: String,
    pub name: String,
}

/// User上UpdateEmail操作的命令载荷。
#[derive(Debug, Clone)]
pub struct UpdateEmailUser {
    pub id: Uuid,
    pub email: String,
}

/// User上Deactivate操作的命令载荷。
#[derive(Debug, Clone)]
pub struct DeactivateUser {
    pub id: Uuid,
}

命令枚举

/// User实体的命令枚举。
#[derive(Debug, Clone)]
pub enum UserCommand {
    Register(RegisterUser),
    UpdateEmail(UpdateEmailUser),
    Deactivate(DeactivateUser),
}

impl EntityCommand for UserCommand {
    fn kind(&self) -> CommandKind {
        match self {
            UserCommand::Register(_) => CommandKind::Create,
            UserCommand::UpdateEmail(_) => CommandKind::Update,
            UserCommand::Deactivate(_) => CommandKind::Custom,
        }
    }

    fn name(&self) -> &'static str {
        match self {
            UserCommand::Register(_) => "Register",
            UserCommand::UpdateEmail(_) => "UpdateEmail",
            UserCommand::Deactivate(_) => "Deactivate",
        }
    }
}

结果枚举

/// User命令执行的结果枚举。
#[derive(Debug, Clone)]
pub enum UserCommandResult {
    Register(User),
    UpdateEmail(User),
    Deactivate,
}

Handler Trait

/// 处理User命令的异步trait。
#[async_trait]
pub trait UserCommandHandler: Send + Sync {
    type Error: std::error::Error + Send + Sync;
    type Context: Send + Sync;

    /// 将命令分派到适当的处理器。
    async fn handle(&self, cmd: UserCommand, ctx: &Self::Context)
        -> Result<UserCommandResult, Self::Error>;

    /// 处理Register命令。
    async fn handle_register(&self, cmd: RegisterUser, ctx: &Self::Context)
        -> Result<User, Self::Error>;

    /// 处理UpdateEmail命令。
    async fn handle_update_email(&self, cmd: UpdateEmailUser, ctx: &Self::Context)
        -> Result<User, Self::Error>;

    /// 处理Deactivate命令。
    async fn handle_deactivate(&self, cmd: DeactivateUser, ctx: &Self::Context)
        -> Result<(), Self::Error>;
}

命令语法参考

基本命令

使用所有 #[field(create)] 字段：

#[command(Register)]
// 生成：RegisterUser { email, name }

特定字段

仅使用指定字段（自动添加 requires_id）：

#[command(UpdateEmail: email)]
// 生成：UpdateEmailUser { id, email }

#[command(UpdateProfile: name, bio, avatar)]
// 生成：UpdateProfileUser { id, name, bio, avatar }

仅ID命令

只添加ID字段：

#[command(Deactivate, requires_id)]
// 生成：DeactivateUser { id }

#[command(Delete, requires_id, kind = "delete")]
// 生成：DeleteUser { id }，返回 ()

自定义载荷

使用外部结构体：

pub struct TransferPayload {
    pub from_account: Uuid,
    pub to_account: Uuid,
    pub amount: i64,
}

#[command(Transfer, payload = "TransferPayload")]
// 直接使用TransferPayload

自定义结果

使用自定义结果类型：

pub struct TransferResult {
    pub transaction_id: Uuid,
    pub success: bool,
}

#[command(Transfer, payload = "TransferPayload", result = "TransferResult")]
// 返回TransferResult而不是实体

Source选项

控制使用哪些字段：

#[command(Create, source = "create")]     // 使用#[field(create)]字段（默认）
#[command(Modify, source = "update")]     // 使用#[field(update)]字段（可选）
#[command(Ping, source = "none")]         // 无载荷字段

Kind提示

影响结果类型推断：

#[command(Create, kind = "create")]   // 返回实体（默认）
#[command(Update, kind = "update")]   // 返回实体
#[command(Remove, kind = "delete")]   // 返回 ()
#[command(Process, kind = "custom")]  // 从source推断

实现示例

use async_trait::async_trait;

struct UserHandler {
    pool: PgPool,
    email_service: EmailService,
}

struct RequestContext {
    user_id: Option<Uuid>,
    correlation_id: Uuid,
}

#[async_trait]
impl UserCommandHandler for UserHandler {
    type Error = AppError;
    type Context = RequestContext;

    async fn handle(&self, cmd: UserCommand, ctx: &Self::Context)
        -> Result<UserCommandResult, Self::Error>
    {
        match cmd {
            UserCommand::Register(c) => {
                let user = self.handle_register(c, ctx).await?;
                Ok(UserCommandResult::Register(user))
            }
            UserCommand::UpdateEmail(c) => {
                let user = self.handle_update_email(c, ctx).await?;
                Ok(UserCommandResult::UpdateEmail(user))
            }
            UserCommand::Deactivate(c) => {
                self.handle_deactivate(c, ctx).await?;
                Ok(UserCommandResult::Deactivate)
            }
        }
    }

    async fn handle_register(&self, cmd: RegisterUser, ctx: &Self::Context)
        -> Result<User, Self::Error>
    {
        // 验证
        if cmd.email.is_empty() {
            return Err(AppError::Validation("邮箱必填".into()));
        }

        // 创建用户
        let user = User {
            id: Uuid::now_v7(),
            email: cmd.email.to_lowercase(),
            name: cmd.name,
            active: true,
        };

        // 持久化
        sqlx::query(
            "INSERT INTO users (id, email, name, active) VALUES ($1, $2, $3, $4)"
        )
        .bind(user.id)
        .bind(&user.email)
        .bind(&user.name)
        .bind(user.active)
        .execute(&self.pool)
        .await?;

        // 副作用
        self.email_service.send_welcome(&user.email).await?;

        Ok(user)
    }

    async fn handle_update_email(&self, cmd: UpdateEmailUser, ctx: &Self::Context)
        -> Result<User, Self::Error>
    {
        // 授权检查
        if ctx.user_id != Some(cmd.id) {
            return Err(AppError::Forbidden("无法更新其他用户的邮箱".into()));
        }

        // 更新
        let user: User = sqlx::query_as(
            "UPDATE users SET email = $1 WHERE id = $2 RETURNING *"
        )
        .bind(&cmd.email.to_lowercase())
        .bind(cmd.id)
        .fetch_one(&self.pool)
        .await?;

        // 发送验证
        self.email_service.send_verification(&user.email).await?;

        Ok(user)
    }

    async fn handle_deactivate(&self, cmd: DeactivateUser, ctx: &Self::Context)
        -> Result<(), Self::Error>
    {
        sqlx::query("UPDATE users SET active = false WHERE id = $1")
            .bind(cmd.id)
            .execute(&self.pool)
            .await?;

        Ok(())
    }
}

使用命令

async fn register_user(
    handler: &impl UserCommandHandler,
    email: String,
    name: String,
) -> Result<User, AppError> {
    let cmd = RegisterUser { email, name };
    let ctx = RequestContext {
        user_id: None,
        correlation_id: Uuid::new_v4(),
    };

    match handler.handle(UserCommand::Register(cmd), &ctx).await? {
        UserCommandResult::Register(user) => Ok(user),
        _ => unreachable!(),
    }
}

// 或直接调用特定handler
async fn update_email(
    handler: &impl UserCommandHandler,
    user_id: Uuid,
    new_email: String,
    ctx: &RequestContext,
) -> Result<User, AppError> {
    let cmd = UpdateEmailUser {
        id: user_id,
        email: new_email,
    };

    handler.handle_update_email(cmd, ctx).await
}

EntityCommand Trait

所有命令枚举都实现 EntityCommand trait：

use entity_derive::{EntityCommand, CommandKind};

let cmd = UserCommand::Register(register_data);

// 获取命令元数据
assert_eq!(cmd.name(), "Register");
assert!(matches!(cmd.kind(), CommandKind::Create));

// 模式匹配
match cmd.kind() {
    CommandKind::Create => println!("创建实体"),
    CommandKind::Update => println!("更新实体"),
    CommandKind::Delete => println!("删除实体"),
    CommandKind::Custom => println!("自定义操作"),
}

命令钩子

当同时启用 commands 和 hooks 时：

#[derive(Entity)]
#[entity(table = "orders", commands, hooks)]
#[command(Place)]
#[command(Cancel, requires_id)]
pub struct Order { /* ... */ }

生成的钩子：

#[async_trait]
pub trait OrderHooks: Send + Sync {
    type Error: std::error::Error + Send + Sync;

    // 标准CRUD钩子...

    // 命令特定钩子
    async fn before_command(&self, cmd: &OrderCommand) -> Result<(), Self::Error>;
    async fn after_command(&self, cmd: &OrderCommand, result: &OrderCommandResult) -> Result<(), Self::Error>;
}

最佳实践

  1. 领域语言 — 使用业务术语：RegisterUser 而不是 CreateUser
  2. 单一职责 — 一个命令 = 一个业务操作
  3. 明确意图 — 命令名应描述操作
  4. 在handler中验证 — 将验证逻辑保留在命令handler中
  5. 尽可能幂等 — 设计命令以便安全重试
  6. 使用上下文 — 通过上下文传递请求元数据（用户、关联ID）

CQRS模式

命令是CQRS的一半。与投影结合用于查询端：

#[derive(Entity)]
#[entity(table = "orders", commands)]
#[projection(Summary: id, status, total_cents, created_at)]
#[projection(Details: id, status, items, shipping_address, total_cents)]
#[command(Place)]
#[command(Ship, requires_id)]
#[command(Cancel, requires_id)]
pub struct Order { /* ... */ }

// 命令（写入端）
let result = handler.handle(OrderCommand::Place(place_order), &ctx).await?;

// 查询（读取端）
let summary = repo.find_by_id_summary(order_id).await?;
let details = repo.find_by_id_details(order_id).await?;

另见

  • [[钩子|钩子]] — 生命周期钩子包括命令钩子
  • [[事件|事件]] — 用于审计日志的事件生成
  • [[属性|属性]] — 完整属性参考