In Silverlight I got the following problem. If you fire multiple requests to the web service, the responses might not return in an ordered sequence. Meaning if the first request takes longer than the following ones, its response will return at last:
1. Sending request A.. (takes longer for some reason)
2. Sending request B..
3. Sending request C..
4. ...
5. Receiving response B
6. Receiving response C
7. Receiving response A
Now in my scenario, I am only interested in the most recent request being made. So A and B should be discareded and C should be kept as only accepted response.
What is the best approach to manage this? I came up with this solution so far:
Pass a generated GUID as user object when sending the request and store that value somewhere. As all responses will contain their respective GUID, you can now filter out the stale responses. A request-counter instead of a GUID would work as well.
Now I wonder if there are any better approaches to this. Maybe there are any out of the box features to make this possible? Any ideas are welcome..
I take a similar approach in my non-WCF ASP.NET web services, though I use the DateTime of the request instead and then just store the DateTime of the most recent request. This way I can do a direct less than comparison to determine if the returning service is the most recent or not.
I did look into canceling old service calls before making new ones, but there is no CancelAsync call for web services in Silverlight and I have been unable to find an equivalent way of doing this.
Both of these approaches are what I took when I worked on a real time system with a lot of service calls. Basically just have some way to keep track of order ( incrementing variable, timestamp, etc. ) then keep track of highest received response. If the current response is lower than the highest, drop it.
Related
I know that GET is used to retrieve data from the server without modifying anything. Whereas POST is used to add data. I won't get into PUT/PATCH, and assume that POST is always used to update and replace data.
The theory is nice, but in practice I have encountered many situations where my GET calls need to be replaced with POST calls. This is because the response often gets incorrectly cached. Where I work there are proxy servers for security, caching, load balancing, etc., and often times the response for GET calls is directly cached to speed up the call, whereas POST calls never get fully cached.
So for my question, if I have an API call /api/get_orders/month. Theoretically, this should be a GET call, however, the number of orders might update any second. So if I call this API at any moment it may return for example 1000, and calling it just two seconds later should return 1001. However, because of the cache, and although adding a version flag such as ?v=<date_as_int> should ensure that the updated value is returned, there seems to be some caches in the proxy servers that might ignore this.
Basically, I don't feel safe enough using GET unless I know for certain that the data will not be modified or if I know for a fact that the response is always the updated data.
So, would you recommend using POST/GET in the case of retrieving daily/monthly number of orders. And if GET, with all the different and complex layers and server set-ups, how can one be certain that the data is always updated?
If you're doing multiple GET request and something is caching the data in between, you have no idea what it is or how to change it's behavior then POST is a valid workaround.
In any normal situation you would take the time what sits in between your browser and your server, and if there's something that's behaving in a way that doesn't make sense, I would try to investigate and fix that.
So you work at a place where some of that infrastructure exists. Maybe talk to the people that maintain it? But if that's not an option and you just want to find the 'ignore every convention and make my request work'-workaround, then you can use POST.
I have to create a table, such that it sends Http Request with a parameter (first column value) for each row in the table and shows processing status for that request.
There is same backend process for each row with a column value passed as a parameter.
On completion of the request for the first row, the status column in the table should show 'Success' and then the request for the second record should be sent.
The request should be sent synchronously as there is moderately heavy backend process attached i.e. on completion of the previous request only next request has to be sent.
I have to achieve this using Angular 5 and DotNet Core 2.0.
Please let me know if there is a feature already available for doing such a thing in Angular 5 and .net Core in an optimized way. I have heard of ReactiveX but I am not able to figure out the best way to achieve this as Reactivex is for asynchronous programming.
Any suggestions or similar examples on this would be helpful.
Thanks
For a RESTful API that I'm creating, I need to have some functionality that get's a resource, but if it doesn't exist, creates it and then returns it. I don't think this should be the default behaviour of a GET request. I could enable this functionality on a certain parameter I give to the GET request, but it seems a little bit dirty.
The main point is that I want to do only one request for this, as these requests are gonna be done from mobile devices that potentially have a slow internet connection, so I want to limit the requests that need to be done as much as possible.
I'm not sure if this fits in the RESTful world, but if it doesn't, it will disappoint me, because it will mean I have to make a little hack on the REST idea.
Does anyone know of a RESTful way of doing this, or otherwise, a beatiful way that doesn't conflict with the REST idea?
Does the client need to provide any information as part of the creation? If so then you really need to separate out GET and POSTas otherwise you need to send that information with each GET and that will be very ugly.
If instead you are sending a GET without any additional information then there's no reason why the backend can't create the resource if it doesn't already exist prior to returning it. Depending on the amount of time it takes to create the resource you might want to think about going asynchronous and using 202 as per other answers, but that then means that your client has to handle (yet) another response code so it might be better off just waiting for the resource to be finalised and returned.
very simple:
Request: HEAD, examine response code: either 404 or 200. If you need the body, use GET.
It not available, perform a PUT or POST, the server should respond with 204 and the Location header with the URL of the newly created resource.
We call wcf svcs (not ours) and we're using gets for searching a product database.
Example:
http://foo.com/SearchProducts.svc?$skip=0$take=10$includeTotalCount=true
We were passing the Odata parameters to page the results of the SearchProducts svc. The svc has been changed to a POST because one of our filters "skus" is sometimes huge (hundres of skus) which causes the GET to break because the uri is too large. The easiest solution we thought was to just change the call to a post but now the Odata params dont seem to be used.
Do these params need to be sent in a different manner when doing a POST?
Compliant OData service will not support POST verb for queries (unless you use POST tunneling, but then you're going to be hitting the URL limit anyway). So I wonder how it works for you at all.
The URL size limit can be overcome using several approaches:
Simplify the query expression. Obviously this can only go so far, but it's usually the best solution as it will likely speed up the query execution as well.
Use batch instead. You can send the GET request inside a batch. The length of the URL is not an issue in this case, since the query URL is sent in the payload of the batch.
Define a service operation for the complex query you're using (but since you don't own the service this is probably not a good solution for you).
I've got a real lemon on my hands. I hope someone who has the same problem or know how to fix it could point me in the right direction.
The Setup
I'm trying to create a WCF data service that uses an ADO Entity Framework model to retrieve data from the DB. I've added the WCF service reference and all seems fine. I have two sets of data service calls. The first one retrieves a list of all "users" and returns (this list does not include any dependent data (eg. address, contact, etc.). The second call is when a "user" is selected, the application request to include a few more dependent information such as address, contact details, messages, etc. given a user id. This also seems to work fine.
The Lemon
After some user selection change, ie. calling for more dependent data from the data service, the application stops to respond.
Crash error:
The request channel timed out while waiting for a reply after 00:00:59.9989999. Increase the timeout value passed to the call to Request or increase the SendTimeout value on the Binding. The time allotted to this operation may have been a portion of a longer timeout.
I restart the debugging process but the application will not make any data service calls until after about a minute or so, VS 08 displays a message box with error:
Unable to process request from service. 'http://localhost:61768/ConsoleService.svc'. Catastrophic failure.
I've Googled the hell out of this error and related issues but found nothing of use.
Possible Solutions
I've found some leads as to the source of the problem. In the client's app.config:
maxReceivedMessageSize > Set to a higher value, eg. 5242880.
receiveTimeout > Set to a higher value, eg. 00:30:00
I've tried these but all in vain. I suspect there is an underlying problem that cannot be fixed by simply changing some numbers. Any leads would be much appreciated.
I've solved it =P.
Cause
The WCF service works fine. It was the data service calls that was the culprit. Every time I made the call, I instantiated a new reference to the data service, but never closed/disposed the service reference. So after a couple of calls, the data service reaches its maximum connection and halts.
Solution
Make sure to close/dispose of any data service reference properly. Best practice would be to enclose in a using statement.
using(var dataService = new ServiceNS.ServiceClient() )
{
// Use service here
}
// The service will be disposed and connection freed.
Glad to see you fixed your problem.
However, you need to be carefull about using the using statement. Have a look at this article:
http://msdn.microsoft.com/en-us/library/aa355056.aspx