来自SignalR客户端的多个呼叫

Question

on my asp.net mvc application i'm using signalR to notify db changes to application. my problem is once i page reloaded. signalR client get called multiple time.

i used SqlDependency for get sql db changes my code as below

public List<Load> GetAllReportSignalR()
{
    var loads = new List<Load>();
    var connectionString = _context.Database.Connection.ConnectionString;
    using (var connection = new SqlConnection(connectionString))
    {
        connection.Open();
        using (SqlCommand command = new SqlCommand(@"SELECT LoadId, [FileName], LoadTypeId, CreatedDate, CreatedBy, LoadStatusId FROM [dbo].[Load]", connection))
        {
            command.Notification = null;
            var dependency = new SqlDependency(command);
            dependency.OnChange +=new OnChangeEventHandler(dependency_OnChange);
            if (connection.State == ConnectionState.Closed)
                connection.Open();
            var reader = command.ExecuteReader();
            while (reader.Read())
            {
                loads.Add(
                        new Load
                        {
                            FileName = (string)reader["FileName"],
                            CreatedBy = (string)reader["CreatedBy"],
                            CreatedDate = (DateTime)reader["CreatedDate"],
                            LoadId = (int)reader["LoadId"],
                            LoadStatusId = (int)reader["LoadStatusId"],
                            LoadTypeId = (short)reader["LoadTypeId"]
                        });
            }
        }

    }
    return loads;
}


private void dependency_OnChange(object sender, SqlNotificationEventArgs e)
{

    if (e.Type == SqlNotificationType.Change)
    {
        Notifier.UpdateDataTable();
    }

}

On my hub

[HubMethodName("updateDataTable")]
public void UpdateDataTable()
{
    IHubContext context = GlobalHost.ConnectionManager.GetHubContext<Notifier>();
    context.Clients.All.updateData();
}

then i call signalR client

   var notifier = $.connection.notifier;
notifier.client.updateData = function () {
    $.ajax({
        type: 'POST',
        url: '/Home/LoadData',
        success: function (d) {
            reloadTbl(d)
        }
    });
};

$.connection.hub.start().done(function () {
    $.ajax({
        type: 'POST',
        url: '/Home/LoadData',
        success: function (d) {
            reloadTbl(d)
        }
    });
}).fail(function(e) {

});

I started and stopped SqlDependency on Application_Start() and Application_End()

i did follow below example and that has the same problem ( CodeProject Tutorial )

Answer 1

When your page is loaded you did

$.connection.hub.start().done(function () {
    $.ajax({
        type: 'POST',
        url: '/Home/LoadData',
        success: function (d) {
            reloadTbl(d)
        }
    });
})

which called back to the server to load data.

In addition, you had

var dependency = new SqlDependency(command);
dependency.OnChange +=new OnChangeEventHandler(dependency_OnChange);
private void dependency_OnChange(object sender, SqlNotificationEventArgs e)
{

    if (e.Type == SqlNotificationType.Change)
    {
        Notifier.UpdateDataTable();
    }

}

which registered to data changed. For the callback above, it would trigger dependency_OnChange , which then called back to the client side.

Therefore, your page was refreshed twice. One was from server pushed, and the other from client pulled.

Solution: You may choose to push from server to client when the page is loaded and remove the client pulls code.