User-961853402 posted
I am trying to create a page that updates data in real time when ever something changes in the database. I have used SignalR. There is only one hub, here is the code to the hub:
public class MyHub : Hub
{
public static int prodId { get; set; }
public void setProdID(int pid)
{
prodId = pid;
}
public BidDetailViewModel GetChanges()
{
string conStr = ConfigurationManager.ConnectionStrings["DefaultConnection"].ConnectionString;
SqlConnection connection = new SqlConnection(conStr);
SqlDependency.Start(conStr);
string query = @"select Id,
BidDate,
BidAmount,
BidStatusId,
BidderId,
ProductId
from [dbo].[Bids]
where ProductId = " + prodId +
" order by BidDate desc ";
SqlCommand command = new SqlCommand(query, connection);
command.Notification = null;
SqlDependency dependency = new SqlDependency(command);
//If Something will change in database and it will call dependency_OnChange method.
dependency.OnChange += new OnChangeEventHandler(dependency_OnChange);
connection.Open();
SqlDataReader dr = command.ExecuteReader();
var bid = new Bid();
while (dr.Read())
{
bid.Id = dr.GetInt32(0);
bid.BidDate = DateTime.Now; //fake value, dont need it
bid.BidAmount = dr.GetFloat(2);
bid.BidStatusId = dr.GetInt32(3);
bid.BidderId = dr.GetString(4);
bid.ProductId = dr.GetInt32(5);
//Break after reading the first row
//Using this becasue we can not use TOP(1) in the query due to SignalR restrictions
break;
}
connection.Close();
var vm = new BidDetailViewModel
{
HighestBid = bid,
NoOfBids = -1
//NoOfBids is no longer needed, assigning a random value of -1
//will remove it later, just testing rn
};
return vm;
}
private void dependency_OnChange(object sender, SqlNotificationEventArgs e)
{
if (e.Type == SqlNotificationType.Change) SendNotifications();
}
private void SendNotifications()
{
BidDetailViewModel vm = GetChanges();
IHubContext context = GlobalHost.ConnectionManager.GetHubContext<MyHub>();
//Will update all the client with new bid values
context.Clients.All.broadcastMessage(vm);
}
}
I am calling the hub in two different pages. First one is `/Home/About` and second is `/Home/About2`. They both have the same JS code except for one change, the prodId being passed in `/Home/About` is `40`, and for `/Home/About2` it's `41`. The JS code is:
(This is the code for `/Home/About` as you can see it's sending `40`. Again, `/Home/About2` has the exact same code but with `41`).
<script>
$(function () {
// Declare a proxy to reference the hub.
var ew = $.connection.myHub;
//This method will fill all the Messages in case of any database change.
ew.client.broadcastMessage = function (response) {
//Changing HTML content here using document.getElementById()
};
//This method will fill all the Messages initially
$.connection.hub.start().done(function () {
ew.server.setProdID(40);
//Hardcoding the prodID for now, will get it using document.getElementById() later
//ProdId will be different for each page
ew.server.getChanges().done(function(response) {
//Changing HTML content here using document.getElementById()
});
});
});
</script>
As you can see, I'm setting the `ProdId` in `MyHub` hub by calling the `SetProdID` function. I've set `ProdId` to a static member so I can set it without making an object of the hub. Now If visit `/Home/About`, it sets the `prodId` to `40` (as expected) and
I get the results from the query. But, when I visit `\Home\About2` it sets `prodId` to `41` (again, as expected) and I get the results from the query that correspond to parameter `41`.
Now if I update the item with id `41` in the database, both the `/Home/About` and `/Home/About2` pages are updated in real time but with the data that corresponds to item with id `41`. I know this post is gettting really long, but my question is, shouldn't
SignalR be making a completely separate instance of `MyHub1` for the two different pages? Is this happening because I've made the `ProdId` a static member? If that's it, how do I set it without making it a static member? I basically want multiple instances
of the same `MyHub`, each instance for a completely different `prodId`. Is this possible? or do I have to write multiple hubs (MyHub1, MyHub2, .... MyHubn). The problem with writing multiple hubs is that I don't know how many items there are going to be.
I've also tried passing the `prodId` as a parameter to `GetChanges()` method but I'm not sure what to pass in the `sendNotification()` method that calls the `GetChanges()` method.
public class MyHub : Hub
{
public BidDetailViewModel GetChanges(int pid)
{
............
string query = @"select Id,
BidDate,
BidAmount,
BidStatusId,
BidderId,
ProductId
from [dbo].[Bids]
where ProductId = " + pid +
" order by BidDate desc ";
...............
}
private void dependency_OnChange(object sender, SqlNotificationEventArgs e)
{
if (e.Type == SqlNotificationType.Change) SendNotifications();
}
private void SendNotifications()
{
//What do I pass here?
BidDetailViewModel vm = GetChanges();
..............
}
}
I'm not sure how to proceed from here on, any pointers would be appreciated! Also, thanks for reading this long post.
