code: async function show(ctx) {
    let { Model } = ctx.state;
    let code = Model.api.show;
    if (code > _alaska.PUBLIC && !ctx.user) {
      //未登录,需要认证
      ctx.status = 401;
      return;
    }
  
    const scope = ctx.state.scope || ctx.query._scope || 'show';
  
    let doc = await Model.showByContext(ctx, { scope });
    if (!doc) {
      //404
      return;
    }
    // $Flow 已经确认ctx.user存在
    if (code === _alaska.OWNER && doc[Model.userField].toString() !== ctx.user.id) {
      //404
      return;
    }
    ctx.state.record = doc;
    ctx.body = doc.data(ctx.state.scope || ctx.query._scope || scope);
  }
docs: 获取单个对象详细信息