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I needed a way to let my users know when something new arrived. For this I need to check an external system. The only way to do this is to pole the existing system every so often. I could easily do this on the clients, but this would create a lot of traffic if you had lots of clients. I decided have my server do the polling and then let the clients know when something new has arrived.
The best way I have found to this was to use Quartz.Net and SignalR.
The server
To start you can make an empty ASP.Net project.
Normally you would make a service to something like this. But I kinda need my webserver for the SignalR part. But Quartz.Net can deal with this.
First thing to do is to make our Quartz.Net Job.
- Option Strict Off
- Imports Microsoft.AspNet.SignalR
- Imports Quartz
- Imports Dapper
- Namespace Server
- Public Class NewCases
- Implements IJob
- Private ReadOnly _context As Object
- Public Sub New()
- _context = GlobalHost.ConnectionManager.GetHubContext(Of Server.BeCare)()
- End Sub
- Public Sub Execute(context As IJobExecutionContext) Implements IJob.Execute
- Try
- Using con = New SqlConnection("connectionstring")
- dim newCases = con.Query(Of String)("select * from newcases where status = 'new'").ToList
- If newCases.Count > 0 Then
- _context.Clients.All.newCases(newCases)
- End If
- End Using
- Catch ex As Exception
- _context.Clients.All.newCases(New List(Of String) From {ex.Message})
- End Try
- End Sub
- End Class
- End Namespace
I'm using dapper to get my data and I'm using the globalhost to get the context for SignalR so I can send a message to all my clients whenever there are new cases available.
Now I just have to schedule this.
I can do the configuration in code in the Global.asax
- Private Shared _scheduler As IScheduler
- Sub Application_Start(ByVal sender As Object, ByVal e As EventArgs)
- RouteTable.Routes.MapHubs()
- Dim factory = New StdSchedulerFactory()
- _scheduler = factory.GetScheduler()
- Dim startTime = DateBuilder.NextGivenSecondDate(Nothing, 10)
- Dim job = JobBuilder.Create(Of NewCases)().WithIdentity("job6", "group1").Build()
- Dim trigger As ISimpleTrigger = TriggerBuilder.Create().WithIdentity("trigger6", "group1").StartAt(startTime).WithSimpleSchedule(Function(x) x.WithIntervalInSeconds(5).RepeatForever()).Build()
- _scheduler.ScheduleJob(job, trigger)
- _scheduler.Start()
- End Sub
SO I create a scheduler, then a job and a trigger and add those to the scheduler after which I can Start the scheduler. I made a trigger with an interval of 5 seconds here. And I made it start 10 seconds after our application starts.
I also made a Hub so that our clients have something to connect to.
- Option Strict Off
- Imports Microsoft.AspNet.SignalR.Hubs
- Imports System.Data.SqlClient
- Imports Dapper
- Namespace Server
- Public Class BeCare
- Inherits Hub
- Public Sub Refresh()
- Try
- Using con = New SqlConnection("connectionstring")
- Dim newCases = con.Query(Of String)("select * from newcases where status = 'new'").ToList
- If newCases.Count > 0 Then
- Clients.All.newCases(newCases)
- End If
- End Using
- Catch ex As Exception
- Clients.All.newCases(New List(Of String) From {ex.Message})
- End Try
- End Sub
- End Class
- End Namespace
The client
I made a basic client to test if this works.
- Dim connection = New HubConnection("http://localhost:54155/")
- Dim becare= connection.CreateHubProxy("BeCare")
- becare.On(Of IList(Of String))("newCases", Sub(data)
- If data IsNot Nothing Then
- Console.WriteLine(DateTime.Now.ToString("dd/MM/yyyy HH:mm:ss") & " - Found " & data.Count & " new cases.")
- For Each s In data
- Console.WriteLine(s)
- Next
- Else
- Console.WriteLine("No records found")
- End If
- End Sub)
- connection.Start().Wait()
- Dim line As String = Nothing
- Console.WriteLine("type exit + enter to exit.")
- While line <> "exit"
- line = Console.ReadLine()
- End While
And that's it.
Chris is awesome.
Ever thought of 'long polling' or comet programming.
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