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• Learning about the low level

  - by Anoners

  I'm interested in learning more about the PC from a lower (machine) level. I graduated from a school which taught us concepts using the Java language which abstracted out that level almost completely. As a result I only learned a bit from the one required assembly language course. In order to cram in ASM and quite a few details about architecture, it was hard to get a very deep picture of what is going on there. At work I focus on unix socket programming in C, so i'm much closer to the hardware now, but I feel I should learn a bit more about what streams really are, how memory management and paging works, what goes on when you call "paint()" on a graphics buffer, etc. I missed out on a lot of this and i'm looking for a good resource to get me started. I've heard a lot about the "Pink Book" by Peter Norton (Programmer's Guide to the IBM PC, Programmer's Guide to inside the PC, etc). It seems like this is on the right track, however the original is quite out dated and the newer ones have had conflicting reviews, with many people saying to stay away from it. I'm not sure what the SO crowd thinks about this book or if they have some suggestions for similar books, online resources, etc that may be good primers for this sort of thing. Any suggestions would be appreciated.

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• Entity Framework Multiple associations to a table causes error 3033

  - by taylonr

  I'm using EF 3.5 SP1. I have 3 tables: Pendants PendantAccessories PartsData Basically #1 and 2 are used for product selection, so #1 has a "Number of Buttons" property and other options. #2 has fields like "Cable Type" etc. The third table contains property information for all of our parts, such as what plant it's manufactured in, it's weight etc. What I'm trying to do is set up an association between #1 and #3 and also between #2 and #3. The PK in all 3 tables is the PartNumber. I set it up between #2 and 3 by going into Mapping Details and adding a Maps to PartsData and mapping the columns. Everything worked good. I then tried the same thing between #1 and 3. However, now when I compile I get "Error 3033: Problem in Mapping Fragment starting at line 713: EntitySets 'pendants' and 'pendantAccessories' are both mapped to the table 'PartsData'. Their Primary Keys may collide." Does anyone know what I'm doing wrong here?

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• How to detect hidden field tampering?

  - by Myron

  On a form of my web app, I've got a hidden field that I need to protect from tampering for security reasons. I'm trying to come up with a solution whereby I can detect if the value of the hidden field has been changed, and react appropriately (i.e. with a generic "Something went wrong, please try again" error message). The solution should be secure enough that brute force attacks are infeasible. I've got a basic solution that I think will work, but I'm not security expert and I may be totally missing something here. My idea is to render two hidden inputs: one named "important_value", containing the value I need to protect, and one named "important_value_hash" containing the SHA hash of the important value concatenated with a constant long random string (i.e. the same string will be used every time). When the form is submitted, the server will re-compute the SHA hash, and compare against the submitted value of important_value_hash. If they are not the same, the important_value has been tampered with. I could also concatenate additional values with the SHA's input string (maybe the user's IP address?), but I don't know if that really gains me anything. Will this be secure? Anyone have any insight into how it might be broken, and what could/should be done to improve it? Thanks!

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• Beginning 3.2+ iPhone development

  - by Dinah

  I'm interested in learning Objective C for iPhone development. This is a topic which I realize has been covered to death. The qualifying difference is: I'd like to start learning beginning with the latest version (the most recent iPhone OS as of May, 2010 is ver. 3.2 and 4 beta is also out). I'd like to not have to wade through or unlearn legacy information. Using the links I've found throughout related topics on Stack Overflow, I'll read a blog post or tutorial which will say one thing, but then the comments will say, "this is different now in version xyz." For example, I've found this a few times regarding memory management/garbage collection. I assume that Apple's "getting started" doc.s will have the most recent info but many SO posts have said that those are not the most clear. The Stanford iPhone course looks great, but how do I know if it still applies to the most recent versions? Where should one start learning Objective C for iPhone development starting with version 3.2 or later without having as much exposure to legacy information?

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• AES Encryption Java Invalid Key length

  - by wuntee

  I am trying to create an AES encryption method, but for some reason I keep getting a 'java.security.InvalidKeyException: Key length not 128/192/256 bits'. Here is the code: public static SecretKey getSecretKey(char[] password, byte[] salt) throws NoSuchAlgorithmException, InvalidKeySpecException{ SecretKeyFactory factory = SecretKeyFactory.getInstance("PBEWithMD5AndDES"); // NOTE: last argument is the key length, and it is 256 KeySpec spec = new PBEKeySpec(password, salt, 1024, 256); SecretKey tmp = factory.generateSecret(spec); SecretKey secret = new SecretKeySpec(tmp.getEncoded(), "AES"); return(secret); } public static byte[] encrypt(char[] password, byte[] salt, String text) throws NoSuchAlgorithmException, InvalidKeySpecException, NoSuchPaddingException, InvalidKeyException, InvalidParameterSpecException, IllegalBlockSizeException, BadPaddingException, UnsupportedEncodingException{ SecretKey secret = getSecretKey(password, salt); Cipher cipher = Cipher.getInstance("AES"); // NOTE: This is where the Exception is being thrown cipher.init(Cipher.ENCRYPT_MODE, secret); byte[] ciphertext = cipher.doFinal(text.getBytes("UTF-8")); return(ciphertext); } Can anyone see what I am doing wrong? I am thinking it may have something to do with the SecretKeyFactory algorithm, but that is the only one I can find that is supported on the end system I am developing against. Any help would be appreciated. Thanks.

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• Code Golf: Quickly Build List of Keywords from Text, Including # of Instances

  - by Jonathan Sampson

  I've already worked out this solution for myself with PHP, but I'm curious how it could be done differently - better even. The two languages I'm primarily interested in are PHP and Javascript, but I'd be interested in seeing how quickly this could be done in any other major language today as well (mostly C#, Java, etc). Return only words with an occurrence greater than X Return only words with a length greater than Y Ignore common terms like "and, is, the, etc" Feel free to strip punctuation prior to processing (ie. "John's" becomes "John") Return results in a collection/array Extra Credit Keep Quoted Statements together, (ie. "They were 'too good to be true' apparently")Where 'too good to be true' would be the actual statement Extra-Extra Credit Can your script determine words that should be kept together based upon their frequency of being found together? This being done without knowing the words beforehand. Example: "The fruit fly is a great thing when it comes to medical research. Much study has been done on the fruit fly in the past, and has lead to many breakthroughs. In the future, the fruit fly will continue to be studied, but our methods may change." Clearly the word here is "fruit fly," which is easy for us to find. Can your search'n'scrape script determine this too? Source text: http://sampsonresume.com/labs/c.txt Answer Format It would be great to see the results of your code, output, in addition to how long the operation lasted.

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• Interface Casting vs. Class Casting

  - by Legatou

  I've been led to believe that casting can, in certain circumstances, become a measurable hindrance on performance. This may be moreso the case when we start dealing with incoherent webs of nasty exception throwing\catching. Given that I wish to create more correct heuristics when it comes to programming, I've been prompted to ask this question to the .NET gurus out there: Is interface casting faster than class casting? To give a code example, let's say this exists: public interface IEntity { IParent DaddyMommy { get; } } public interface IParent : IEntity { } public class Parent : Entity, IParent { } public class Entity : IEntity { public IParent DaddyMommy { get; protected set; } public IParent AdamEve_Interfaces { get { IEntity e = this; while (this.DaddyMommy != null) e = e.DaddyMommy as IEntity; return e as IParent; } } public Parent AdamEve_Classes { get { Entity e = this; while (this.DaddyMommy != null) e = e.DaddyMommy as Entity; return e as Parent; } } } So, is AdamEve_Interfaces faster than AdamEve_Classes? If so, by how much? And, if you know the answer, why?

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• Automation Error upon running VBA script in Excel

  - by brohjoe

  Hi guys, I'm getting an Automation error upon running VBA code in Excel 2007. I'm attempting to connect to a remote SQL Server DB and load data to from Excel to SQL Server. The error I get is, "Run-time error '-2147217843(80040e4d)': Automation error". I checked out the MSDN site and it suggested that this may be due to a bug associated with the sqloledb provider and one way to mitigate this is to use ODBC. Well I changed the connection string to reflect ODBC provider and associated parameters and I'm still getting the same error. Here is the code with ODBC as the provider: Dim cnt As ADODB.Connection Dim rst As ADODB.Recordset Dim stSQL As String Dim wbBook As Workbook Dim wsSheet As Worksheet Dim rnStart As Range Public Sub loadData() 'This was set up using Microsoft ActiveX Data Components version 6.0. 'Create ADODB connection object, open connection and construct the connection string object. Set cnt = New ADODB.Connection cnt.ConnectionString = _ "Driver={SQL Server}; Server=onlineSQLServer2010.foo.com; Database=fooDB Uid=logonalready;Pwd='helpmeOB1';" cnt.Open On Error GoTo ErrorHandler 'Open Excel and run query to export data to SQL Server. strSQL = "SELECT * INTO SalesOrders FROM OPENDATASOURCE('Microsoft.ACE.OLEDB.12.0', & _ "'Data Source=C:\Database.xlsx; Extended Properties=Excel 12.0')...[SalesOrders$]" cnt.Execute (strSQL) 'Error handling. ErrorExit: 'Reclaim memory from the connection objects Set rst = Nothing Set cnt = Nothing Exit Sub ErrorHandler: MsgBox Err.Description, vbCritical Resume ErrorExit 'clean up and reclaim memory resources. cnt.Close If CBool(cnt.State And adStateOpen) Then Set rst = Nothing Set cnt = Nothing End If End Sub

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• c# (wcf) architecture file and directory structure (and instantiation)

  - by stevenrosscampbell

  Hello and thanks for any assistance. I have a wcf service that I'm trying to properly modularize. I'm interested in finding out if there is a better way or implementing the file and directory structure along with instanciatation, is there a more appropriate way of abstraction that I may be missing? Is this the best approach? especially if performance and the ability to handle thousands of simultanious request? Currently I have this following structure: -Root\Service.cs public class Service : IService { public void CreateCustomer(Customer customer) { CustomerService customerService = new CustomerService(); customerService.Create(customer); } public void UpdateCustomer(Customer customer) { CustomerService customerService = new CustomerService(); customerService.Update(customer); } } -Root\Customer\CustomerService.cs pulbic class CustomerService { public void Create(Customer customer) { //DO SOMETHING } public void Update(Customer customer) { //DO SOMETHING } public void Delete(int customerId) { //DO SOMETHING } public Customer Retrieve(int customerId) { //DO SOMETHING } } Note: I do not include the Customer Object or the DataAccess libraries in this example as I am only concerned about the service. If you could either let me know what you think, if you know a better way, or a resource that could help out. Thanks Kindly. Steven

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• Sysdeo Tomcat DevLoader - Hot deploy of java class causes whole application to restart

  - by Gala101

  Hi, I am using sysdeo tomcat plugin 3.2.1 with eclipse 3.5.1 (Galileo) and tomcat 5.5.23 on windows XP. I can get tomcat plugin working in eclipse, and have extracted devloader.zip into [tomcat]\server\classes. I have also updated the context and now it has this entry: <Context path="/myapp1" reloadable="true" docBase="F:\Work\eclipse_workspace\myapp1" workDir="F:\Work\eclipse_workspace\myapp1\work" > <Logger className="org.apache.catalina.logger.SystemOutLogger" verbosity="4" timestamp="true"/> <Loader className="org.apache.catalina.loader.DevLoader" reloadable="true" debug="1" useSystemClassLoaderAsParent="false" /> </Context> I have activated devloader (in Project Properties Tomcat Devloader Classpath) and have 'checked' all my classes and jars, I haven't 'checked' commons-loggin.jar jsp-api.jar, servlet-api.jar. So on launching tomcat via the plugin, I can get it running with devloader as shown in eclipse console view [DevLoader] Starting DevLoader [DevLoader] projectdir=F:\Work\eclipse_workspace\myapp1 [DevLoader] added file:/F:/Work/eclipse_workspace/myapp1/WEB-INF/classes/ [DevLoader] added file:/F:/Work/eclipse_workspace/myapp1/WEB-INF/lib/activation.jar However, if I even add a single System.out.println into any java file and save it, the whole application gets reloaded (takes ~80 sec) which is as good as stopping/starting tomcat itself. I've tried adding -Xdebug in JAVA_OPTS in the catalina.bat but no luck :( Can you please guide where I may be doing it wrong.. Please note that I can 'redeploy' the whole application on tomcat but that's not what I need, I am looking to be able to make small changes in java classes 'on-the-fly' while coding/debugging without having to wait for complete app restart. Another annoyance is that restarting tomcat/application causes the session/debug progress to be lost.. Can you please guide me how to go about it. PS: I am not using any ant/maven scripts explicitly, just relying on eclipse to do the build for me (which it does).

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• nHibernate Domain Model and Mapping Files in Separate Projects

  - by Blake Blackwell

  Is there a way to separate out the domain objects and mapping files into two separate projects? I would like to create one project called MyCompany.MyProduct.Core that contains my domain model, and another project that is called MyCompany.MYProduct.Data.Oracle that contains my Oracle data mappings. However, when I try to unit test this I get the following error message: Named query 'GetClients' not found. Here is my mapping file: <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="MyCompany.MyProduct.Core" namespace="MyCompany.MyProduct.Core" > <class name="MyCompany.MyProduct.Core.Client" table="MY_CLIENT" lazy="false"> <id name="ClientId" column="ClientId"></id> <property name="ClientName" column="ClientName" /> <loader query-ref="GetClients"/> </class> <sql-query name="GetClients" callable="true"> <return class="Client" /> call procedure MyPackage.GetClients(:int_SummitGroupId) </sql-query> </hibernate-mapping> Here is my unit test: try { var cfg = new Configuration(); cfg.Configure(); cfg.AddAssembly( typeof( Client ).Assembly ); ISessionFactory sessionFactory = cfg.BuildSessionFactory(); IStatelessSession session = sessionFactory.OpenStatelessSession(); IQuery query = session.GetNamedQuery( "GetClients" ); query.SetParameter( "int_SummitGroupId", 3173 ); IList<Client> clients = query.List<Client>(); Assert.AreNotEqual( 0, clients.Count ); } catch( Exception ex ) { throw ex; } I think I may be improperly referencing the assembly, because if I do put the domain model object in the MyComapny.MyProduct.Data.Oracle class it works. Only when I separate out in to two projects do I run into this problem.

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• Anyone got a nifty credit expiry algorithm?

  - by garethkeenan

  Our website uses a credit system to allow users to purchase inexpensive digital goods (eg. photos). We use credits, rather than asking the user to pay for items individually, because the items are cheap and we are trying to keep our credit-card/PayPal overhead low. Because we aren't a bank, we have to expire credits after a certain amount of time. We expire deposit credits after a year, but other types of credits (bonuses, prizes, refunds) may have a different shelf-life. When a buyer buys an item, we spend the credit that is going to expire first. Our current system keeps track of every deposit by storing the original value and the remainder to be spent. We keep a list of all purchases as well, of course. I am currently moving to a system which is much more like a traditional double-entry accounting system. A deposit will create a ledger item, increasing the user's 'spending' account balance. Every purchase will also create a ledger item, decreasing the user's 'spending' account balance. The new system has running balances, while the old system does not, which greatly improves our ability to find problems and do reconciliations. We do not want to use the old system of keeping a 'remainder' value attached to each deposit record because it is inefficient to replay a user's activities to calculate what the remainder of each deposit is over time (for the user's statement). So, after all of this verbose introduction, my question is "Does anyone else out there have a similar system of expiring credits?" If you could describe how you calculate expired credits it would be a great help. If all expired credits had the exact same shelf life, we would be able to calculate the expired amount using: Total Deposits - Total Spending - Deposits Not Due To Expire = Amount to Expire However, because deposits can have different shelf lives, this formula does not work because more than one deposit can be partially spent at any given time.

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• Classic ASP to WCF using the Service Moniker

  - by Jab

  I am trying to consume a WCF logging service from classic ASP without deploy a Com wrapper. I found a method of doing so here. Here is the vb script, simplified. Dim addr addr = "service:mexAddress=""net.pipe://localhost/Services/Logging/LoggingManager/Mex""," _ & "address=""net.pipe://localhost/Services/Logging/LoggingManager/classic/""," _ & "contract=""ILoggingManagerClassic"", contractNamespace=""http://Services.Logging.Classic/""," _ & "binding=""NetNamedPipeBinding_ILoggingManagerClassic"", bindingNamespace=""http://Services.Logging.Classic/""" set objErrorLogger = GetObject(addr) Dim strError : strError = objErrorLogger.LogError("blahblah") This works on Server 2008, but fails with this error on Server 2003. Failed to do mex retrieval:Metadata contains a reference that cannot be resolved: net.pipe://localhost/Services/Logging/LoggingManager/Mex.. Only when running through ASP does it fail, a sample VBS file on the same machine using the same code works fine. I think it may be permission related, but don't know where to begin. Anyone have any ideas? EDIT - let me clarify that the WCF host is a windows service running as NETWORK SERVICE. If this belongs on server fault, a moderator can move it. I have an account there as well.

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• Subview Doesnt AutoSize When Added to Root View Controller

  - by Per

  Hello, I have a root view controller that will have up to 10 or so subviews. I am implementing autorotation/autosize accross the entire app. My problem is this: - When I allocate all the view controllers and add each as a subview to the root controller during startup, everything works as it should. The only problem is that each view controller needs time to initialize. This causes my application to load very slowly. Instead I am trying to allocate the view controllers as they are required. Now I find that if the application goes into Landscape, and I allocate a view controller that is designed in portrait, it will autorotate but the autosize doesnt happen. In other words as soon as the subview is added to the root controller in portrait mode it rotates and sizes correctly (and stays that way). If the subview is added when the root controller is in landscape it rotates but doesnt autosize (and view sizes remain messed up rotating back to portrait) I have tried to force an autosize by calling SetNeedsLayout, SetNeedsDisplay, and LayoutIfNeeded but nothing works. I know i could probably do this manually by determining the root controllers orientation and resizing the subviews appropriately, but this is a lot of work for something that should work automatically. Am I missing something? Any help would be appreciated. My project is an iPad port from an iPhone app, the iPhone app doesnt rotate so Im not sure if this may be something wrong with the 3.2 beta.

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• Error when running rake db:create

  - by Amy

  Hi, I am trying to setup an ror app but I keep getting this error. Any ideas as to what may be causing the problem? /usr/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:31:in `gem_original_require' /usr/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:31:in `require' /usr/lib/ruby/gems/1.8/gems/activesupport-2.3.5/lib/active_support/dependencies.rb:156:in `require' /usr/lib/ruby/gems/1.8/gems/activesupport-2.3.5/lib/active_support/dependencies.rb:521:in `new_constants_in' /usr/lib/ruby/gems/1.8/gems/activesupport-2.3.5/lib/active_support/dependencies.rb:156:in `require' /home/projects/testproject/lib/tasks/more_tasks.rake:3 /usr/lib/ruby/gems/1.8/gems/activesupport-2.3.5/lib/active_support/dependencies.rb:145:in `load_without_new_constant_marking' /usr/lib/ruby/gems/1.8/gems/activesupport-2.3.5/lib/active_support/dependencies.rb:145:in `load' /usr/lib/ruby/gems/1.8/gems/activesupport-2.3.5/lib/active_support/dependencies.rb:521:in `new_constants_in' /usr/lib/ruby/gems/1.8/gems/activesupport-2.3.5/lib/active_support/dependencies.rb:145:in `load' /usr/lib/ruby/gems/1.8/gems/rails-2.3.5/lib/tasks/rails.rb:9 /usr/lib/ruby/gems/1.8/gems/rails-2.3.5/lib/tasks/rails.rb:9:in `each' /usr/lib/ruby/gems/1.8/gems/rails-2.3.5/lib/tasks/rails.rb:9 /usr/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:31:in `gem_original_require' /usr/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:31:in `require' /home/projects/testproject/Rakefile:10 /usr/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2383:in `load' /usr/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2383:in `raw_load_rakefile' /usr/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2017:in `load_rakefile' /usr/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2068:in `standard_exception_handling' /usr/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2016:in `load_rakefile' /usr/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2000:in `run' /usr/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2068:in `standard_exception_handling' /usr/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:1998:in `run' /usr/lib/ruby/gems/1.8/gems/rake-0.8.7/bin/rake:31 /usr/bin/rake:19:in `load' /usr/bin/rake:19

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• Find first item inside angular brackets after occurrence of other item, using RegEx, in C#

  - by Mihaela

  I have an xml-like text, in which I would like to find the item that occurs in the first occurrence of a certain pattern: typically: ... <PropertyGroup><name>true</name></PropertyGroup><PropertyGroup>.... .... Could also be ... <PropertyGroup> <name> true</name> </PropertyGroup> ... <PropertyGroup> ... In the above, I need to extract the "name". My initial assumption was that all occurrences were to be in one line, and I wrote my code using string properties, but it is very difficult o take in consideration every possibility, and only RegEx can save me. I just don't know how to write it... I Have started with something like this: Regex regex = new Regex("(?<=<PropertyGroup>#)<+"); Match matches = regex.Matches(Text)[0]; MessageBox.Show(matches.ToString()); I think this finds the first item after a <PropertyGroup>, but I don't know how to make it get the item within the angular brackets... (which may be after one or more newlines, and/or spaces). I know that there are utilities for parsing xml, but I am looking for something simple to insert in a c# program Can someone please help me ? Thank you very much.

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• Error mounting CloudDrive snapshot in Azure

  - by Dave

  Hi, I've been running a cloud drive snapshot in dev for a while now with no probs. I'm now trying to get this working in Azure. I can't for the life of me get it to work. This is my latest error: Microsoft.WindowsAzure.Storage.CloudDriveException: Unknown Error HRESULT=D000000D ---> Microsoft.Window.CloudDrive.Interop.InteropCloudDriveException: Exception of type 'Microsoft.WindowsAzure.CloudDrive.Interop.InteropCloudDriveException' was thrown. at ThrowIfFailed(UInt32 hr) at Microsoft.WindowsAzure.CloudDrive.Interop.InteropCloudDrive.Mount(String url, SignatureCallBack sign, String mount, Int32 cacheSize, UInt32 flags) at Microsoft.WindowsAzure.StorageClient.CloudDrive.Mount(Int32 cacheSize, DriveMountOptions options) Any idea what is causing this? I'm running both the WorkerRole and Storage in Azure so it's nothing to do with the dev simulation environment disconnect. This is my code to mount the snapshot: CloudDrive.InitializeCache(localPath.TrimEnd('\\'), size); var container = _blobStorage.GetContainerReference(containerName); var blob = container.GetPageBlobReference(driveName); CloudDrive cloudDrive = _cloudStorageAccount.CreateCloudDrive(blob.Uri.AbsoluteUri); string snapshotUri; try { snapshotUri = cloudDrive.Snapshot().AbsoluteUri; Log.Info("CloudDrive Snapshot = '{0}'", snapshotUri); } catch (Exception ex) { throw new InvalidCloudDriveException(string.Format( "An exception has been thrown trying to create the CloudDrive '{0}'. This may be because it doesn't exist.", cloudDrive.Uri.AbsoluteUri), ex); } cloudDrive = _cloudStorageAccount.CreateCloudDrive(snapshotUri); Log.Info("CloudDrive created: {0}", snapshotUri, cloudDrive); string driveLetter = cloudDrive.Mount(size, DriveMountOptions.None); The .Mount() method at the end is what's now failing. Please help as this has me royally stumped! Thanks in advance. Dave

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• Merge replication server side foreign key violation from unpublished table

  - by Reiste

  We are using SQL Server 2005 Merge Replication with SQL CE 3.5 clients. We are using partitions with filtering for the separate subscriptions, and nHibernate for the ORM mapping. There is automatic ID range management from SQL Server for the subscriptions. We have a table, Item, and a table with a foreign key to Item - ItemHistory. Both of these are replicated down, filtered according to the subscription. Item has a column called UserId, and is filtered per subscription with this filter: WHERE UserId IN (SELECT... [complicated subselect]...) ItemHistory hangs off Item in the publication filter articles. On the server, we have a table ItemHistoryExport, which has a foreign key to ItemHistory. ItemHistoryExport is not published. Entries in the Item and ItemHistory tables are never deleted, on the server or the client. However, the "ownership" of items (and hence their ItemHistories) MAY change, which causes them to be moved from one client subscription/partition to another from time to time. When we sync, we occasionally get the following error: A row delete at '48269404 - 4108383dbb11' could not be propagated to 'MyServer\MyInstance.MyDatabase'. This failure can be caused by a constraint violation. The DELETE statement conflicted with the REFERENCE constraint "FK_ItemHistoryExport_ItemHistory". The conflict occurred in database "MyDatabase", table "dbo.ItemHistoryExport", column 'ItemHistoryId'. Can anyone help us understand why this happens? There shouldn't ever be a delete happening on the server side.

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• Idiomatic Scala way to deal with base vs derived class field names?

  - by Gregor Scheidt

  Consider the following base and derived classes in Scala: abstract class Base( val x : String ) final class Derived( x : String ) extends Base( "Base's " + x ) { override def toString = x } Here, the identifier 'x' of the Derived class parameter overrides the field of the Base class, so invoking toString like this: println( new Derived( "string" ).toString ) returns the Derived value and gives the result "string". So a reference to the 'x' parameter prompts the compiler to automatically generate a field on Derived, which is served up in the call to toString. This is very convenient usually, but leads to a replication of the field (I'm now storing the field on both Base and Derived), which may be undesirable. To avoid this replication, I can rename the Derived class parameter from 'x' to something else, like '_x': abstract class Base( val x : String ) final class Derived( _x : String ) extends Base( "Base's " + _x ) { override def toString = x } Now a call to toString returns "Base's string", which is what I want. Unfortunately, the code now looks somewhat ugly, and using named parameters to initialize the class also becomes less elegant: new Derived( _x = "string" ) There is also a risk of forgetting to give the derived classes' initialization parameters different names and inadvertently referring to the wrong field (undesirable since the Base class might actually hold a different value). Is there a better way? Edit: To clarify, I really only want the Base values; the Derived ones just seem necessary for initializing the Base ones. The example only references them to illustrate the ensuing issues. It might be nice to have a way to suppress automatic field generation if the derived class would otherwise end up hiding a base class field.

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• ASP.NET MVC Model Binding into a List

  - by Maxim Z.

  In my ASP.NET MVC site, part of a feature allows the user to enter the hours when a certain venue is open. I've decided to store these hours in a VenueHours table in my database, with a FK-to-PK relationship to a Venues table, as well as DayOfWeek, OpeningTime, and ClosingTime parameters. In my View, I want to allow the user to only input the times they know about; in other words, some days may not be filled in for a Venue. I'm thinking of creating checkboxes that the user can check to enable the OpeningTime and ClosingTime fields for the DayOfWeek that the checkbox belongs to. My question relates to how to pass this information to my HttpPost Controller Action. As I know the maximum amount of Days that can be passed in (7), I could of course just write 7 nullable VenueHour parameters into my Action, but I'm sure there's a better way. Can I somehow bind the View information into a List that is passed to my Action? This will also help me if I run into a scenario where there is no limit to how much information the user can fill in.

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• Database warehoue design: fact tables and dimension tables

  - by morpheous

  I am building a poor man's data warehouse using a RDBMS. I have identified the key 'attributes' to be recorded as: sex (true/false) demographic classification (A, B, C etc) place of birth date of birth weight (recorded daily): The fact that is being recorded My requirements are to be able to run 'OLAP' queries that allow me to: 'slice and dice' 'drill up/down' the data and generally, be able to view the data from different perspectives After reading up on this topic area, the general consensus seems to be that this is best implemented using dimension tables rather than normalized tables. Assuming that this assertion is true (i.e. the solution is best implemented using fact and dimension tables), I would like to see some help in the design of these tables. 'Natural' (or obvious) dimensions are: Date dimension Geographical location Which have hierarchical attributes. However, I am struggling with how to model the following fields: sex (true/false) demographic classification (A, B, C etc) The reason I am struggling with these fields is that: They have no obvious hierarchical attributes which will aid aggregation (AFAIA) - which suggest they should be in a fact table They are mostly static or very rarely change - which suggests they should be in a dimension table. Maybe the heuristic I am using above is too crude? I will give some examples on the type of analysis I would like to carryout on the data warehouse - hopefully that will clarify things further. I would like to aggregate and analyze the data by sex and demographic classification - e.g. answer questions like: How does male and female weights compare across different demographic classifications? Which demographic classification (male AND female), show the most increase in weight this quarter. etc. Can anyone clarify whether sex and demographic classification are part of the fact table, or whether they are (as I suspect) dimension tables.? Also assuming they are dimension tables, could someone elaborate on the table structures (i.e. the fields)? The 'obvious' schema: CREATE TABLE sex_type (is_male int); CREATE TABLE demographic_category (id int, name varchar(4)); may not be the correct one.

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• Low Latency Serial Communications In .Net

  - by bvillersjr

  I have been researching various third party libraries and approaches to low latency serial communications in .Net. I've read enough that I have now come full circle and know as little as I did when I started due to the variety of conflicting opinions. For example, the functionality in the Framework was ruled out due to some convincing articles stating: "that the Microsoft provided solution has not been stable across framework versions and is lacking in functionality." I have found articles bashing many of the older COM based libraries. I have found articles bashing the idea of a low latency .Net app as a whole due to garbage collection. I have also read articles demonstrating how P/Invoking Windows API functionality for the purpose of low latency communication is unacceptable. THIS RULES OUT JUST ABOUT ANY APPROACH I CAN THINK OF! I would really appreciate some words from those with been there / done that experience. Ideally, I could locate a solid library / partner and not have to build the communications library myself. I have the following simple objectives: Sustained low latency serial communication in C# / VB.Net 32/64 bit Well documented (if the solution is 3rd party) Relatively unimpacted (communication and latency wise) by garbage collection . Flexible (I have no idea what I will have to interface with in the future!) The only requirement that I have for certain is that I need to be able to interface with many different industrial devices such as RS485 based linear actuators, serial / microcontroller based gauges, and ModBus (also RS485) devices. Any comments, ideas, thoughts or links to articles that may iron out my confusion are much appreciated!

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• Combine 3 select fields and validate as one in my User model in ruby on rails 3

  - by Psychonetics

  Ok I have 3 select boxes for selecting date of birth. I have constants setup in my User model to provide months, years etc.. Anyway I can successfully validate these select boxes separately. What I want to do is combine the :day, :month and :year and store in :birthday and validate the whole date as one so I can return 1 error rather than 3 separate ones. Also doing this will make it easier to store the validated date in my birthday field in my database. Part of my form <td> <%= f.input :day, :required => false, :label => "Birthday: " , :prompt => "Day", :collection => User::DAYS %></td> <td> <%= f.input :month, :label => false, :prompt => "Month", :collection => User::MONTHS %> </td> <td> <%= f.input :year, :label => false, :prompt => "Year", :collection => User::YEAR_RANGE %> </td> Part of User model MONTHS = ["January", 1], ["February", 2], ["March", 3], ["April", 4], ["May", 5], ["June", 6], ["July", 7], ["August", 8], ["September", 9], ["October", 10], ["November", 11], ["December", 12] # finish this DAYS = 1..31 # finish this START_YEAR = Time.now.year - 106 END_YEAR = Time.now.year YEAR_RANGE = START_YEAR..END_YEAR class User < ActiveRecord::Base attr_accessor :day, :month, :year validates_presence_of :day, :message = 'What day in a month was you born?' validates_presence_of :month, :message = 'What month was you born?' validates_presence_of :year, :message = 'What is your year of birth?' end

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• Limit foreign key choices in select in an inline form in admin

  - by mightyhal

  Edited :-) Hopefully a bit clearer now. The logic is of the model is: A Building has many Rooms A Room may be inside another Room (a closet, for instance--ForeignKey on 'self') A Room can only in inside of another Room in the same building (this is the tricky part) Here's the code I have: #spaces/models.py from django.db import models class Building(models.Model): name=models.CharField(max_length=32) def __unicode__(self): return self.name class Room(models.Model): number=models.CharField(max_length=8) building=models.ForeignKey(Building) inside_room=models.ForeignKey('self',blank=True,null=True) def __unicode__(self): return self.number and: #spaces/admin.py from ex.spaces.models import Building, Room from django.contrib import admin class RoomAdmin(admin.ModelAdmin): pass class RoomInline(admin.TabularInline): model = Room extra = 2 class BuildingAdmin(admin.ModelAdmin): inlines=[RoomInline] admin.site.register(Building, BuildingAdmin) admin.site.register(Room) The inline will display only rooms in the current building (which is what I want). The problem, though, is that for the inside_room drop down, it displays all of the rooms in the Rooms table (including those in other buildings). In the inline of rooms, I need to limit the inside_room choices to only rooms which are in the current building being displayed by the main form. I can't figure out a way to do it with either a limit_choices_to in the model, nor can I figure out how exactly to override the admin's inline formset properly (I feel like I should be somehow create a custom inline form, pass the building_id of the main form to the custom inline, then limit the queryset for the field's choices based on that--but I just can't wrap my head around how to do it). Maybe this is too complex for the admin site, but it seems like something that would be generally useful... Thanks again for your help!

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• sqlite is must for merb ?????

  - by mayank

  Hello All, I have a doubt regarding merb dependency with sqlite. I am going to install merb on my m/c and I don't have installed sqlite on my m/c . I tried this command "gem install merb" and faced following error. If is there any way to install merb with mysql please tell me. Thanks Mayank Building native extensions. This could take a while... ERROR: Error installing merb: ERROR: Failed to build gem native extension. /usr/bin/ruby1.8 extconf.rb checking for sqlite3.h... no * extconf.rb failed * Could not create Makefile due to some reason, probably lack of necessary libraries and/or headers. Check the mkmf.log file for more details. You may need configuration options. Provided configuration options: --with-opt-dir --without-opt-dir --with-opt-include --without-opt-include=${opt-dir}/include --with-opt-lib --without-opt-lib=${opt-dir}/lib --with-make-prog --without-make-prog --srcdir=. --curdir --ruby=/usr/bin/ruby1.8 --with-sqlite3-dir --without-sqlite3-dir --with-sqlite3-include --without-sqlite3-include=${sqlite3-dir}/include --with-sqlite3-lib --without-sqlite3-lib=${sqlite3-dir}/lib Gem files will remain installed in /usr/lib/ruby/gems/1.8/gems/do_sqlite3-0.10.2 for inspection. Results logged to /usr/lib/ruby/gems/1.8/gems/do_sqlite3-0.10.2/ext/do_sqlite3/gem_make.out

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