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  • Which layer should create DataContext?

    - by Kevin
    I have a problem to decide which layer in my system should create DataContext. I have read a book, saying that if do not pass the same DataContext object for all the database updates, it will sometimes get an exception thrown from the DataContext. That's why i initially create new instance of DataContext in business layer, and pass it into data access layer. So that the same datacontext is used for all the updates. But this lead to one design problem, if i wanna change my DAL to Non-LinqToSQL in future, i need to re-write the code in business layer as well. Please give me some advice on this. Thanks. Example code 'Business Layer Public Sub SaveData(name As String) Using ts AS New TransactionScope() Using db As New MyDataContext() DAL.Insert(db,name) DAL.Insert(db,name) End Using ts.Complete() End Using End Sub 'Data Access Layer Public Sub Insert(db as MyDataContext,name As string) db.TableAInsert(name) End Sub

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  • Empty data problem - data layer or DAL?

    - by luckyluke
    I designing the new App now and giving the following question a lot of thought. I consume a lot of data from the warehouse, and the entities have a lot of dictionary based values (currency, country, tax-whatever data) - dimensions. I cannot be assured though that there won't be nulls. So I am thinking: create an empty value in each of teh dictionaries with special keyID - ie. -1 do the ETL (ssis) do the correct stuff and insert -1 where it needs to let the DAL know that -1 is special (Static const whatever thing) don't care in the code to check for nullness of dictionary entries because THEY will always have a value But maybe I should be thinking: import data AS IS let the DAL do the thinking using empty record Pattern still don't care in the code because business layer will have what it needs from DAL. I think is more of a approach thing but maybe i am missing something important here... What do You think? Am i clear? Please don't confuse it with empty record problem. I do use emptyCustomer think all the time and other defaults too.

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  • Machine Learning Algorithm for Peer-to-Peer Nodes

    - by FreshCode
    I want to apply machine learning to a classification problem in a parallel environment. Several independent nodes, each with multiple on/off sensors, can communicate their sensor data with the goal of classifying an event as defined by a heuristic, training data or both. Each peer will be measuring the same data from their unique perspective and will attempt to classify the result while taking into account that any neighbouring node (or its sensors or just the connection to the node) could be faulty. Nodes should function as equal peers and determine the most likely classification by communicating their results. Ultimately each node should make a decision based on their own sensor data and their peers' data. If it matters, false positives are OK for certain classifications (albeit undesirable) but false negatives would be totally unacceptable. Given that each final classification will receive good or bad feedback, what would be an appropriate machine learning algorithm to approach this problem with if the nodes could communicate with each other to determine the most likely classification?

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  • C# Process flow - Datastream, XML and datagrid

    - by Farstucker
    Im looking for some advice/suggestions on how I should setup the work flow of a small application Im building. When the application is launched the datagrid will be populated via the XML file. Once running the application will receive a datastream that I hope to update the file and datagrid. So Im curious what you would suggest on how I setup the workflow (ie, split the data from the data stream and simultaneously populate the file and grid or would you suggest populating the XML file first and setting up a timer to have the grid read the file?) Im really looking for optimal performance.

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  • What is the relationship between Turing Machine & Modern Computer ?

    - by smwikipedia
    I heard a lot that modern computers are based on Turing machine. I just cannot build a bridge from a conceptual Turing Machine to a real modern computer. Could someone help me build this bridge? Below is my current understanding. I think the computer is a big general-purpose Turing machine. Each program we write is a small specific-purpose Turing machine. The classical Turing machine do its job based on the input and its current state inside and so do our programs. Let's take a running program (a process) as an example. We know that in the process's address space, there's areas for stack, heap, and code. A classical Turing machine doesn't have the ability to remember many things, so we borrow the concept of stack from the push-down automaton. The heap and stack areas contains the state of our specific-purpose Turing machine (our program). The code area represents the logic of this small Turing machine. And various I/O devices supply input to this Turing machine.

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  • realtime diagnostics

    - by Ion Todirel
    I have an application which has a loop, part of a "Scheduler", which runs at all time and is the heart of the application. Pretty much like a game loop, just that my application is a WPF application and it's not a game. Naturally the application does logging at many points, but the Scheduler does some sensitive monitoring, and sometimes it's impossible just from the logs to tell what may have gotten wrong (and by wrong I don't mean exceptions) or the current status. Because Scheduler's inner loop runs at short intervals, you can't do file I/O-based logging (or using the Event Viewer) in there. First, you need to watch it in real-time, and secondly the log file would grow in size very fast. So I was thinking of ways to show this data to the user in the realtime, some things I considered: Display the data in realtime in the UI Use AllocConsole/WriteConsole to display this information in a console Use a different console application which would display this information, communicate between the Scheduler and the console app using pipes or other IPC techniques Use Windows' Performance Monitor and somehow feed it with this information ETW Displaying in the UI would have its issues. First it doesn't integrate with the UI I had in mind for my application, and I don't want to complicate the UI just for this. This diagnostics would only happen rarely. Secondly, there is going to be some non-trivial data protection, as the Scheduler has it's own thread. A separate console window would work probably, but I'm still worried if it's not too much threshold. Allocating my own console, as this is a windows app, would probably be better than a different console application (3), as I don't need to worry about IPC communication, and non-blocking communication. However a user could close the console I allocated, and it would be problematic in that case. With a separate process you don't have to worry about it. Assuming there is an API for Performance Monitor, it wouldn't be integrated too well with my app or apparent to the users. Using ETW also doesn't solve anything, just a random idea, I still need to display this information somehow. What others think, would there be other ways I missed?

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  • How much business logic belongs in RIA services layer?

    - by jkohlhepp
    I have been experimenting recently with Silverlight, RIA Services, and Entity Framework using .NET 4.0. I'm trying to figure out if that stack makes sense for use in any of my upcoming projects. It certainly seems like these technologies can be very productive for developing applications, but I'm struggling to decide how an application on top of this stack should be architected. The main issue I have is that in most of the demos I've seen most of the business logic ends up as DataAnnotations and custom validations in the RIA Services domain service class. This seems inappropriate to me. I view the domain service as basically a glorified web service that happens to make it easy to push information to the client. But most of what I've seen seems to orient the domain service as the main source of business logic in the application. So, my questions: What is the best location for business logic (rules, validations, behaviors, authorization) in an application using this stack? Are there any guidelines published at an architectural level for using this stack? My questions pertain to large, complex, and long-lived applications. Obviously for an application of only a few screens this is less of a concern. Edit: Another thing I meant to mention is that obviously you can make the domain service class stupid, but then you lose a lot of the automagic entity information (e.g. validations) being pushed to the client. And then if you lose that is there any point to using RIA services?

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  • Providing multi-version databases for backward compatibility for production applications/databases.

    - by JavaRocky
    How can I manage multiple versions of a database easily? I have some data (as views as selects for data originating in tables from other schemas), which other database may reference using various means including database synonyms & links. I wish to provide a sort of interface/guarantee in-case future for applications/databases which use this data. All of this is for in the event i need to update the views for correctness or applicability inside my database. How can i achieve this in a maintained, controlled and easy way? I am using Oracle 10g if that matters.

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  • Basic questions about SNMP

    - by David Hodgson
    Hi, I'm learning about SNMP, and writing some applications using it. I have some basic questions about the protocol: Do the agents store its state on the device itself? If there is a trap set on an agent, can you do a poll on the same OID to get the same information? Without using a mib file, is there a way to query a device for all of its information at once? If not, and you're writing your own customized manager, do you have to know the structure of what it reports up front? If you're setting up an agent to report, is there usually a way to control the frequency of how often it sends a trap? Or does it usually send a trap as often as some condition is satisfied?

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  • How do I send an XML document to an ASP.NET MVC page for manipuation

    - by Decker
    I have some hierarchical data stored as an multiple XML files on the server according to a vendor's schema. In my ASP.NET MVC (2!) application, I'd like the user to choose one of these hierarchies (i.e. file -- I provide a list in my controller's Index action). When the user selects one to "edit" my edit action should return a page that presents the XML hierarchy (it's a representation of a folder tree). So my thoughts are that the view would return HTML that contained a JQuery on load ajax call back to the server for the XML data -- at which point I would present the tree using one of the many JQuery tree controls. On the client side I'd like the user to manipulate the tree and when done, I'd like to post back the new hierarchy where I would replace the original XML file that represents that hierarchy. So my questions are: What form should I use to send the data down? XML or JSON?. If I send down XML then I would have to not only read the XML -- which JQuery can do -- but I would also have to be able to modify that XML and then send it back. Can I use JQuery to modify this XML DOM? And will all the namespace declarations be preserved? What form should I send the data back? If I originally sent the client the hierarchy as JSON (using JsonResult), then presumably I would have a hierarchy of javascript objects. What options would I have to post that back? Would I have to recreate the XML reprentation on the client and post that back? Or should I serialize back to JSON, post that to the server, and then have the server do the work of recreating the XML according to the schema. Thanks for any advice.

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  • How do you use Linq2Sql in your applications ?

    - by this. __curious_geek
    I'm recently migrating to Linq2Sql and all my future projects would be done in Linq2Sql. Having said that, I researched a lot on how to properly plug-in Linq2Sql in application design. what to put at what layer ? Should I use DTOs over Linq2Sql entities ? I did not find any rock-solid material that really talked about one single thing and everyone had their own opinions and I found all of them justified right from their arguments. I'm looking forward to your ideas on how to integrate/use Linq2Sql in projects. My priority is maintenance[it should be maintenable and when multiple people work on same project] and scalabilty [it should have scope of evolution]. Thanks.

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  • Mimic remote API or extend existing django model

    - by drozzy
    I am in a process of designing a client for a REST-ful web-service. What is the best way to go about representing the remote resource locally in my django application? For example if the API exposes resources such as: List of Cars Car Detail Car Search Dealership summary So far I have thought of two different approaches to take: Try to wrangle the django's models.Model to mimic the native feel of it. So I could try to get some class called Car to have methods like Car.objects.all() and such. This kind of breaks down on Car Search resources. Implement a Data Access Layer class, with custom methods like: Car.get_all() Car.get(id) CarSearch.search("blah") So I will be creating some custom looking classes. Has anyone encoutered a similar problem? Perhaps working with some external API's (i.e. twitter?) Any advice is welcome. PS: Please let me know if some part of question is confusing, as I had trouble putting it in precise terms.

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  • Broadcast-style Bluetooth using Sockets on the iPhone?

    - by Kyle
    Is there any way to open a broadcast bluetooth socket, take a listen and send replies? I want a proper peer to peer system where I broadcast and listen for broadcasts in an area. That way, variable clients can mingle. Is this possible? My theory is this: If GameKit can sit around wasting 25 seconds of the users time whilst having access to a broadcast socket, can't I? Or, must I be in kernel mode for such access? I'm not really sure where the proper bluetooth headers are as well. Thanks for reading!

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  • [Perl] Testing for EAGAIN / EWOULDBLOCK on a recv

    - by Robert S. Barnes
    I'm testing a socket to see if it's still open: my $dummy = ''; my $ret = recv($sock, $dummy, 1, MSG_DONTWAIT | MSG_PEEK); if (!defined $ret || (length($dummy) == 0 && $! != EAGAIN && $! != EWOULDBLOCK )) { logerr("Broken pipe? ".__LINE__." $!"); } else { # socket still connected, reuse logerr(__LINE__.": $!"); return $sock; } I'm passing this code a socket I know for certain is open and it's always going through the first branch and logging "Broken pipe? 149 Resource temporarily unavailable". I don't understand how this is happening since "Resource temporarily unavailable" is supposed to correspond to EAGAIN as far as I know. I'm sure there must be something simple I'm missing. And yes, I know this is not a full proof way to test and I account for that.

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  • Need some help/advice on WCF Per-Call Service and NServiceBus interop.

    - by Alexey
    I have WCF Per-Call service wich provides data for clients and at the same time is integrated with NServiceBus. All statefull objects are stored in UnityContainer wich is integrated into custom service host. NServiceBus is configured in service host and uses same container as service instances. Every client has its own instance context(described by Juval Lowy in his book in chapter about Durable Services). If i need to send request over bus I just use some kind of dispatcher and wait response using Thread.Sleep().Since services are per-call this is ok afaik. But I am confused a bit about messages from bus, that service must handle and provide them to clients. For some data like stock quotes I just update some kind of statefull object and and then, when clients invoke GetQuotesData() just provide data from this object. But there are numerous service messages like new quote added and etc. At this moment I have an idea to implement something like "Postman daemon" =)) and store this type of messages in instance context. Then client will invoke "GetMail()",recieve those messages and parse them. Problem is that NServiceBus messages are "Interface based" and I cant pass them over WCF, so I need to convert them to types derieved from some abstract class. Dunno what is best way to handle this situation. Will be very gratefull for any advice on this. Thanks in advance.

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  • What is the big deal with IQueryable?

    - by jjr2527
    I've seen a lot of people talking about IQueryable and I haven't quite picked up on what all the buzz is about. I always work with generic List's and find they are very rich in the way you can "query" them and work with them, even run LINQ queries against them. So I'm wondering if there is a good reason to start considering a different default collection in my projects.

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  • Verbose Listing of All Application Layers/Tiers?

    - by leeand00
    I've looked at a few sites now, and I'm still struggling to find a complete listing of all the possible layers/tiers you can have in an application. From back in college (1999) I remember the following: Presentation Layer (Views) Application Layer (Controllers) Business Logic Layer (API/Rules) Persistence Layer (Database/Object Persistence/Model) I'm not advocating that they all be used...especially when you consider that too many layers/tiers could lead to an increase in complexity...I just wondered what the complete list might look like... Based on a couple of blogs I've found several different answers...and Javascript and client side technologies seem to have leaked in adding more client-side layers according to one blog the client side tier might even consist of Behavior Layer (Javascript, Flash) Presentation Layer (CSS/Images) Note: I though the entire client side layer was the presentation layer Structure Layer (XHTML, HTML) I'm just trying to get an abstract idea of what all the possible layers might be, (even though some people call them different things)

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  • How to map different UI views in a RESTful web application?

    - by MicE
    Hello, I'm designing a web application, which will support both standard UIs (accessed via browsers) and a RESTful API (an XML/JSON-based web service). User agents will be able to differentiate between these by using different values in the Accept HTTP header. The RESTful API will use the following URI structure (example for an "article" resource): GET /article/ - gets a list of articles POST /article/ - adds a new article PUT /article/{id} - updates an existing article based on {id} DELETE /article/{id} - deletes an existing article based on {id} The UI part of the application will however need to support multiple views, for example: a standard resource view a view for submitting a new resource a view for editing an existing resource a view for deleting an existing resource (i.e. display delete confirmation) Note that the latter three views are still accessed via GET, even though they are processed via overloaded POST. Possible solution: Introduce additional parameters (keywords) into URIs which would identify individual views - i.e. on top of the above, the application would support the following URIs (but only for Content-Type: text/html): GET /article/add - displays a form for adding a new article (fetched via GET, processed via POST) GET /article/123 - displays article 123 in "view" mode (fetched via GET) GET /article/123/edit - displays article 123 in "edit" mode (fetched via GET, processed via PUT overloaded as POST) GET /article/123/delete - displays "delete" confirmation for article 123 (fetched via GET, processed via DELETE overloaded as POST) A better implementation of the above might be to put the add/edit/delete keywords into a GET parameter - since they do not change the resource we're working with, it might be better to keep the base URI same for all of them. My question is: How would you map the above URI structure to UIs served to the regular user, considering that there can be several views per each resource, please? Do you agree with the possible solution detailed above, or would you recommend a different approach based on your experience? NB: we've already implemented an application which consists of a standalone RESTful API and a standalone web application. I'm currently looking into options for future projects where these two would be merged together (i.e. in order to reduce overhead). Thank you, M.

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  • Alternatives to NServiceBus that doesn't use MSMQ

    - by G33kKahuna
    I think the title sums it all .... We have a .NET 2.0 system trying to implement a distributed pub/ sub model. I came across NServiceBus, RhinoBus and MassTransit. Unfortunately, these are MSMQ based. I am tasked to figure out pub/ sub alternatives that uses a different messaging alternatives ... the only reason for seeking MSMQ alternatives is to overcome the message size restriction. Since our enterprise app messages can potentially get truncated due to per message restriction... any guidance is much appreciated

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  • Machine Learning Algorithm for Parallel Nodes

    - by FreshCode
    I want to apply machine learning to a classification problem in a parallel environment. Several independent nodes, each with multiple on/off sensors, can communicate their sensor data with the goal of classifying an event defined by a heuristic, training data or both. Each peer will be measuring the same data from their unique perspective and will attempt to classify the result while taking into account that any neighbouring node (or its sensors or just the connection to the node) could be faulty. Nodes should function as equal peers and determine the most likely classification by communicating their results. Ultimately each node should make a decision based on their own sensor data and their peers' data. If it matters, false positives are OK (albeit undesirable) but false negatives are totally unacceptable. Given that each final classification will receive good or bad feedback, what would be an appropriate machine learning algorithm to approach this problem with if the nodes could communicate with each other to determine the most likely classification?

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