Brief Idea: I am developing a small social networking kinda site.
Now there's a user "A" who has 100 followers...now what i want to do is whenever user "A" submits an article in the website all his followers should get an email with the article link...that is okay i can do it.
Problem: Now, there's a submit button on the page which stores the article in the DB and sends email to the followers...as there are many followers it takes a lot of time sending the emails...so the page keeps showing loading msg till all the emails are sent..how can i send all the emails asynchronously ??
i mean after the article has been submitted ...the emails should go automatically to the followers without putting the email sending function in the click event of the button....hope am not confusing you folks.
can i do something like store the article in the DB , redirect to the article page , start sending emails in a batch of 10 per 10 mins automatically...this process should start as soon as an article has been submitted by an user.
I had a similar issue with batch emails, and various other long-running tasks.
I developed a window service which contained a job manager. When a job needs to run from the main MVC application, the web application communicates with the service over HTTP (actually, using JSON), and the service performs the meat of actually sending emails, or performing other long-running tasks.
This means the web application request returns immediately.
The web application can also poll the service to determine the status of any particular job that is running (each job is given a unique identifier).
I would create a database table containing information about all pending email notifications.
When hitting submit, you can quickly add rows to this table.
Then, a background thread can check the table and send the mails (and of course remove the successfully sent ones from the table).
Have you thought to implement it using AJAX ?
When the user press on the submit button, instead of posting back to the server, create 2 ajax calls:
The first one is to save the article to the repository (database ?).
After receiving succesfull answer from the server (which can include the article id), invoke 2nd ajax call to send the mails. The server can start a thread to send the mails so the answer to the client will be immediate.
My preferred way of invoking ajax calls is using JQuery:
$.ajax({
type: "POST",
url: "services.aspx/SubmitArticle",
data: "{articlecontent: '[put here the content you want to send]'}",
contentType: "application/json; charset=utf-8",
dataType: "json",
error: function(response) {
// Handle Error here. The response object contains the error details
},
success: function(response) {
// Check here if the article has been saved:
// response.d property contains the server answer. It can be boolean,
// integer, string or any other complex object
// If article saved, invoke here the send mail ajax call. assuming the response.d contains
// the article id:
sendMails(response.d);
// sendMails invokes another ajax similiar to this code snippest
}
});
In the server side the async email send method can looks like:
[WebMethod]
public static bool SendMails(int articleId)
{
// Add the actual method that send mail to the thread pool
ThreadPool.QueueUserWorkItem(new WaitCallback(DoSendMail), articleId);
return true;
}
private void DoSendMail(object a)
{
int articleId = (int)a;
// Your code that sends mails goes here
}
You could use a queueing system like MassTransit, ZMQ or MSMQ.
Or... If you really wanted to create a cool app, you could pass the emailing task to a node.js app!?
Related
As per myunderstanding on masstransit
Publish: Sends a message to subscribers .
Send: Used to send messages in fire and forget fashion
Requests: uses request/reply pattern to just send a message and get a response
In my requirement i need to validate my request before calling the Send method. Here the validation should occur at DB level to check for say duplicate records.
I tried to use publish before my send method , but send method doesnt wait for the publish consumer to execute.
My scenario is if (validation is success) proceed with saving data ie the send request job to save data.
So should i use request response pattern here for doing the validation. I am a newbie to masstransit and microservice.
MyTestController{
if(validation success) // how to validate here
Send request to save data.
}
It sounds like you want to validate the data before it is sent out. Something conceptually like this.
class MyTestController
{
// ..
public async Task<IActionResult> Post(SomeData data)
{
if(DataIsValid(data))
_publishEndpoint.Publish(new Message())
}
}
You can validate the data (like null checking) like any other code before you publish. Nothing special here, so I'm guessing its something else.
You want to validate the data using some other data in a database. If its the same database that the website/api is using - that is also not a special thing, so I'm guessing that is not it either.
You want to, some how, validate the data is correct before sending the message. But that you need to use the data of the application that the message is going to. That is typically where I see people get tripped up.
Assuming its something like number three. Let's call the sending service "Service A" and the receiving service "Service B". Today it sounds like you are trying to put the validation in "Service A" but it really has to be in "Service B". What I would do is implement a Saga in "Service B". The first step would be to take request (creating an instance of a saga), then validate the data, then if it passes validation, the saga can take the next step that you want in the process. That should give you what you want in terms of validation before action (we just need to move it to "Service B").
Now "Service B" can expose the state of the Saga at an endpoint like /saga-instance/42 where the controller takes the 42, digs into the database, grabs the saga data and converts it into an API response. Service A can poll that endpoint to get updated status details.
Ultimately, I hope you see that there are a lot of variables at play, but that there is a path forward. You may have to simply adjust where certain actions are taken.
I am using the following libraries to connect a bot to a Google Pub/Sub endpoint to perform a simple reply to a card click event.
Google.Apis.HangoutsChat.v1 1.34.0.1233
Google.Cloud.PubSub.V1 1.0.0-beta18
When I construct my card, everything looks normal in the UI, including the button that is supposed to raise the event.
The topic and subscription contain the default settings, following the guide here
I found the following information from the Google documentation about retries here
Responding synchronously
A bot can respond to an event synchronously by returning a
JSON-formatted message payload in the HTTP response. The deadline for
a synchronous response is 30 seconds.
A synchronous response from a bot is always posted in the thread that
generated the event to the bot.
After clicking the button, my subscriber receives 3 duplicate events. The events have the correct response with all of the right metadata, but are exact duplicates of each other, including the id of the message itself.
I don't feel there is a necessarily large delay in the response of the bot (it should happen in <1 second for this test), so I am not sure why these messages are being duplicated.
I've also tried setting the thread id for the card when responding (via the Thread property itself, or the ThreadKey property), but I always seem to get a new thread id when I post a message.
var cardMessage = MessageSender.Spaces.Messages.Create(new Message()
{
Space = new Space()
{
Name = inReplyToThisMessage.Space.Name
},
Thread = new Thread()
{
Name = inReplyToThisMessage.Thread.Name
},
Cards = new List<Card>()
{
card
},
}, inReplyToThisMessage.Space.Name);
var sendCardResult = await cardMessage.ExecuteAsync().ConfigureAwait(false);
//Thread id of sendCardResult does not match inReplyToThisMessage.Thread.Name no matter what
Interestingly enough, trying to create a new message in response to the click event causes the bot to display a "Unable to connect to bot. Try again later", but displays 3 new messages. Also, when specifying an arbitrary thread key, this key is never echoed back in the bot's response.
Make sure you are returning the main event method properly. What looks to be happening is that you are making an asynchronous call to the chat, but then the chat is looking for a response from the actual event method itself. Google will traditionally try three times before giving up (even if it doesn't take thirty seconds)
If you are indeed returning the event call correctly after you made your api request, then there is something in your code that is causing the Google Bot to think it is not getting a response, so it tries three times. Since the issue could be multi-faceted I would need to look at how you are accepting and returning the click response.
This bug has finally been fixed by Google.
I have website used by hundred of viewers every day. One of the pages has a timer that ticks every 10 seconds, when it does so it gets the latest data from the database and updates the screen.
The problem i have is that a high number of users and a high number of database connections takes its toll on the server.
Is there a better way of doing this? Updating server side and all users would benefit from the latest data but only the server is carrying out the calls every 10 seconds and not by every user?
SignalR is the way you'll want to go. Right now, your application is probably loading a page. Then you got some jQuery that probably sets a timer for 10 seconds. Then your timer is kicking off and you're probably doing an ajax call to get refreshed data, then putting that refreshed data into a <div> or something.
So essentially, every 10 seconds, your back end is calling your SQL server, doing some kind of SELECT statement, then the data from the SQL Server is being transmitted to your application server, where you are taking that data, transforming into displayable data.
SignalR, on the other hand works differently. It uses push technology. Push technology works like this. Lets say you have 5 people visiting your page right now. One person (person A) is doing something that saves something to the database. No one else is seeing this data though yet. But SignalR will send a signal out to everyone else (or just the people in which this database save affects) that says "Hey! There is newer data available. You should update now". The other people connected do an ajax call and get the refreshed data. And viola! The other 4 people now have updated data on their screen!
I hope I explained this clearly enough for you to understand! Scott Hanselman wrote a good introduction to SignalR.
I would use the setInterval() to fire an ajax function every 10 seconds.
window.setInterval("javascript function", milliseconds);
the javascript function would be similar to
function GetLatest(){
$.ajax({
type: 'POST',
url: '../Services/UpdateService.asmx/GetLatest',
data: '',
contentType: "application/json; charset=utf-8",
success: function (data) {
//use the data.d to get the info passed back from webservice. then
add your logic to update your html
},
error: function () {
//catch any bad data
}
});
}
your backend method should look like this. Object is whatever your objcet is
[WebMethod]
[ScriptMethod(ResponseFormat = ResponseFormat.Json)]
public Object GetLatest()
{
Object obj= new Object ();
obj.FirstName = "Dave";
obj.LastName = "Ward";
return obj;
}
Have you considered having your server side code cache the data for that 10 seconds. Cache it and set it's expiration for 10 seconds. That way, everyone gets the same information for 10 seconds and then the first after that 10 retrieves a new data set and then caches it. That way, only the first person to refresh causes a DB query, the rest get data up to 10 seconds old. Something like this:
Cache.Insert(key, data, Nothing, DateTime.Now.AddSeconds(10), TimeSpan.Zero)
I guess this is assuming that the users are all getting the same data at each poll. If they are all getting unique datasets, this won't cut it for you.
I'm newbie with SignalR and want to learn so much. i already read beginner documents. But in this case i've stucked. what i want to do is when a user got new message i want to fire a script, like alert or showing div like "you have new mail" for notify the recieved user. And my question is how can i do that ? is there anyone know how to achieve this ? or good "step-by-step" document? i really want to work with SignalR.
ps: i'm using Visual Studio 2012 and MsSQL server
edit: i forgot to write, notification must be fired when message created to DB
Thank you
In your Scripts use the following, naturally this is not all the code, but enough based off tutorials to get you going. Your userId will be generated server side, and somehow your script can get it off an element of the page, or whatever method you want. It runs when the connection is started and then every 10 seconds. Pinging our server side method of CheckMessage() .
This js would need refactoring but should give you the general idea.
...
var messageHub = $.connection.messageHub;
var userId = 4;
$.connection.hub.start().done(function () {
StartCheck();
}
//Runs every 10 seconds..
function StartCheck()
{
setInterval(messageHub.server.checkMessage(userId,$.connection.hub.id), 10000);
}
This method takes in a userId, assuming your db is set up that way, and grabs them all from your database; naturally the method used is probably not appropriate for your system, however change it as you need to. It also checks if the user has any messages, and if so sends down another message to our SignalR scripts.
public void CheckMessage(int userId,int connectionId)
{
var user = userRepo.RetrieveAllUsers.FirstOrDefault(u=>u.id == userId);
if(user.HasMessages)
{
Clients.Group(connectionId).DisplayMailPopUp();
}
}
Finally this message, upon being called would run your code to do the 'You have Mail alert' - be it a popup, a div being faded in or whatever.
...
messageHub.client.displayMailPopUp = function () {
alert("You have Mail!");
};
...
Hopefully this helps - I recommend the following links for reading up and building your first SignalR app:
http://www.asp.net/signalr/overview/signalr-20/getting-started-with-signalr-20/tutorial-getting-started-with-signalr-20-and-mvc-5
And a smaller sample: http://code.msdn.microsoft.com/SignalR-Getting-Started-b9d18aa9
When the user clicks on a link to generate report I make an AJAX call which generates a pdf file in the background.Now the files are huge running upto 10mb or more.So it takes some time.In the mean time the user should be able to navigate other links as if nothing has happened.So I need to implement in such a way that the pdf generation process gets started & user doesn't have to wait for the process to finish.Is this possible?I am using AJAX Pro with c# with dot net framework 2.0
The problem here is that as soon as the AJAX activity begins the browser enters into a hung stage & the user has to wait although he clicks on a different link.
I would probably create a 'queue' or an 'inbox' for the user ...
start your pdf generation routine with a ThreadPool.QueueUserWorkItem (you would also need to modify your generation method to output to their inbox)
then on each http request check that inbox and notify the user of the item ... you can always poll the server on an interval or somthing
Sure, but once the user navigates to another page, the Javascript that is waiting for the Ajax response is no longer running, so that request is lost. You'd have to either find a way to keep that page open (using frames or exclusively Ajaxified navigiation), or find a way to store the response and notify the user of its completion on the next page view. For instance, storing a session variable that indicates that the operation is completed, or storing it in a database with (perhaps) an "unread" boolean value.
You can have asynchronous Ajax call with which you can do other tasks while response objects returns from the Ajax page.
Here is some example, testAjax.aspx is the Ajax page here :
http_request.onreadystatechange = function() { alertContents(http_request); };
http_request.open('GET', 'testAjax.aspx?', true);
http_request.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
http_request.send(null);
function alertContents(http_request)
{//debugger;
if (http_request.readyState == 4)
{
if (http_request.status == 200)
{
var vResult;
vResult=http_request.responseText;
//Write your logic after successful Ajax call here.
}
else
{
alert('There was a problem with the request.');
}
}
}