Question

我正在使用rethinkdbdash和koa，并试图找出在应用程序首次启动时如何执行数据库设置。我试图完成类似于Instagram教程的Segphalt的猫，但使用koa。

Module Module1

    Sub Main()
        Dim result = GetData()
    End Sub

    Public Class MakeStyle
        Public Property Id As Integer
    End Class

    Public Class ModelStyle
        Public Property Id As String
    End Class

    Public Class EngineStyle
        Public Property Id As String
        Public Property RotationsPerMinute As EngineRotationsPerMinuteStyle
    End Class

    Public Class EngineRotationsPerMinuteStyle
        Public Property HorsePower As Integer
        Public Property Torque As Integer
    End Class

    Public Class Payload
        Public Property Make As MakeStyle
        Public Property Model As ModelStyle
        Public Property Engine As EngineStyle
        Public Property Colors As IEnumerable(Of ColorStyle)
    End Class

    Public Class ColorStyleOptionItem
        Public Property Id As String
        Public Property Name As String
    End Class

    Public Class ColorStyle
        Public Property Category As String
        Public Property Options As IEnumerable(Of ColorStyleOptionItem)
    End Class

    Public Class DataItem
        Public Property Category As String
        Public Property Id As String
        Public Property Name As String
    End Class


    Public Function GetData() As IEnumerable(Of DataItem)
        Dim payloadString As String = GetDemoData() ' json serialized data

        Dim serializer As System.Web.Script.Serialization.JavaScriptSerializer = New System.Web.Script.Serialization.JavaScriptSerializer()
        Dim payload = serializer.Deserialize(Of Payload)(payloadString) ' sets Property Values of Payload to 'Nothing' when the json fields are not present in the json string.

        Dim data As IEnumerable(Of DataItem) = payload.Colors.SelectMany(Function(item) item.Options.Select(Function(opt) New DataItem With {.Category = item.Category, .Id = opt.Id, .Name = opt.Name}))
        GetData = data
    End Function

    Public Function GetDemoData() As String
        Dim serializer As System.Web.Script.Serialization.JavaScriptSerializer = New System.Web.Script.Serialization.JavaScriptSerializer()

        GetDemoData = serializer.Serialize(New Payload() With {
                                       .Make = New MakeStyle() With {.Id = 200001444},
                                       .Model = New ModelStyle() With {.Id = "Honda_Pilot"},
                                       .Engine = New EngineStyle With {.Id = "200058127", .RotationsPerMinute = New EngineRotationsPerMinuteStyle() With {.HorsePower = 5700, .Torque = 4800}},
                                       .Colors = New ColorStyle() {
                                           New ColorStyle() With {
                                               .Category = "Interior",
                                               .Options = New ColorStyleOptionItem() {
                                                   New ColorStyleOptionItem() With {.Id = "200058068", .Name = "Blue"}
                                               }
                                           },
                                           New ColorStyle() With {
                                               .Category = "Exterior",
                                               .Options = New ColorStyleOptionItem() {
                                                   New ColorStyleOptionItem() With {.Id = "200058073", .Name = "Crystal Black Pearl"},
                                                   New ColorStyleOptionItem() With {.Id = "200058072", .Name = "Polished Metal Metallic"}
                                               }
                                           }
                                       }
                                   })

    End Function

End Module

我试图屈服而不是链接承诺，但由于语法无效而引发错误。

var conn;
r.connect(config.database).then(function(c) {
  conn = c;
  return r.dbCreate(config.database.db).run(conn);
})
.then(function() {
  return r.tableCreate("instacat").run(conn);
})
.then(function() {
  return q.all([
    r.table("instacat").indexCreate("time").run(conn),
    r.table("instacat").indexCreate("place", {geo: true}).run(conn)
  ]);
})
.error(function(err) {
  if (err.msg.indexOf("already exists") == -1)
    console.log(err);
})
.finally(function() {
  r.table("instacat").changes().run(conn)
  .then(function(cursor) {
    cursor.each(function(err, item) {
      if (item && item.new_val)
        io.sockets.emit("cat", item.new_val);
    });
  })
  .error(function(err) {
    console.log("Error:", err);
  });

执行此类设置的最佳方法是什么，包括执行在koa中运行.changes（）的查询，以便它只在服务器启动时执行，而不是在每个请求周期中执行。或者在koa有更好的方法来实现这一目标吗？

Answer 1

您只能在生成器函数内使用yield关键字（签名中带星号的关键字）。通常，如果要使用yield等待promise的完成，则可以使用基于生成器的协程包装整组操作。

您可以使用两个库：

Co：https://www.npmjs.com/package/co
蓝鸟：https://www.npmjs.com/package/bluebird

Co是Koa在其所有中间件处理程序中使用的内容，但我个人更喜欢Bluebird，因为根据我的经验，它似乎有更好的错误处理。

您可以将设置代码包装在Bluebird协程中，然后将其调用到位：

bluebird.coroutine(function *() {
  try {
    yield r.dbCreate(config.database.db).run();
    yield r.tableCreate('user').run();
  }
  catch (err) {
    if (err.message.indexOf("already exists") == -1)
      console.log(err.message);
  }
})();

如何使用rethinkdb在koa中执行初始设置

1 个答案: