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• How to handle this type of model validation in Ruby on Rails

  - by randombits

  I have a controller/model hypothetically named Pets. Pets has the following declarations: :belongs_to owner :has_many dogs :has_many cats Not the best example, but again, it demonstrates what I'm trying to solve. Now when a request comes in as an HTTP POST to http://127.0.0.1/pets, I want to create an instance of Pets. The restriction here is, if the user doesn't submit at least one dog or one cat, it should fail validation. It can have both, but it can't be missing both. How does one handle this in Ruby on Rails? Dogs don't care if cats exists and the inverse is also true. Can anyone show some example code of what the Pets model would look like to ensure that one or the other exists, or fail otherwise? errors.add also takes an attribute, in this case, there is no particular attribute that's failing. It's almost a 'virtual' combination that's missing.

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• Using ActiveRecord::Base.transaction in a rake task?

  - by Brian Jordan

  I am writing a rake task which, at one point, uses a custom YAML file import method to seed the database. At one point in the import code, I have: ActiveRecord::Base.transaction do Trying to run the rake task throws: You have a nil object when you didn't expect it! You might have expected an instance of ActiveRecord::Base. The error occurred while evaluating nil.[] The stack trace points to the aforementioned line in the code. Is there a way to instantiate ActiveRecord::Base during a rake task? Thanks!

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• Best method for Binding ComboBox

  - by LnDCobra

  I am going to be developing a large project which will include a large number of ComboBoxes. Most of these combo boxes will be bound to a database field which is a related to another daataset/table. For instance. I have the following 2 tables: Company {CompanyID, CompanyName, MainContact} Contacts {ContactID, ContactName} And when the user clicks to edit a company, A TextBox will be there to edit a company name, but also a ComboBox will be there. The way I am currently doing it is binding the ComboBox to the Contacts dataset, and manually updating the Company MainContact field in code behind. Is there anyway for me to bind the selected item to the Company MainContact field in XAML and the items to the ContactName and eliminate the code behind? Reason for this is when you start making 100's combo boxes all over the application it gets long winded each time creating code behind to do the update.

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• How to Initialise a static Map in Java

  - by fahdshariff

  How would you initialise a static Map in Java? Method one: Static initialiser Method two: instance initialiser (anonymous subclass) or some other method? What are the pros and cons of each? Here is an example illustrating two methods: import java.util.HashMap; import java.util.Map; public class Test { private static final Map<Integer, String> myMap = new HashMap<Integer, String>(); static { myMap.put(1, "one"); myMap.put(2, "two"); } private static final Map<Integer, String> myMap2 = new HashMap<Integer, String>(){ { put(1, "one"); put(2, "two"); } }; }

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• sed: search and replace string with line number

  - by tigerstyle

  Hi volks, I have a XML file with a lot of empty tag attributes. For instance: <mytag id=""> <ontent>aaa</content> </mytag> <mytag id=""> <ontent>bbb</content> </mytag> <mytag id=""> <ontent>ccc</content> </mytag> Now I want to replace id="" with e.g. id="2443" (id="[linenumber]") I tried to do this with sed, but I did not get a successful result. I hope someone here can help me :-)

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• Empty Structures compile in VB 10+

  - by Mark Hurd

  This is at least a documentation error, if not a bug. In VB.NET prior to .NET 4.0 (i.e. VB.NET 7 through 9) an empty Structure declaration fails at compile-time with error BC30281: Structure 'MySimpleEmpty' must contain at least one instance member variable or Event declaration. E.g. The following two structures compile successfully in VB10, and not prior: Structure MySimpleEmpty End Structure Public Structure AnotherEmpty Public Const StillEmpty As Boolean = True End Structure I note the documentation for the Error BC30281 stops at VB9, but the documentation for the Structure statement still has the datamemberdeclarations as required even as of VB11 (.NET 4.5 VS2012). These two Structures compile in VB11 (VS2012) as well. (Thanks John Woo.) Is there some blog entry or documentation confirming this is an intended change or a bug in VB10 and later?

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• Passing dependent objects to a parent constructor in Scala

  - by Nick Johnson

  Suppose I have the following class heirarchy: class A() class B(a:A) class C(b:B) class BaseClass(b:B, c:C) Now I want to implement a subclass of BaseClass, which is given an instance of A, and constructs instances of B and C, which it passes to its superclass constructor. If I could use arbitrary expressions, I'd do something like this: b = new B(a) c = new C(b) super(b, c) Because the second argument to the parent constructor depends on the value of the first argument, though, I can't see any way to do this, without using a factory function, or a gratuitous hack, such as : class IntermediateSubclass(b:B) extends BaseClass(b, new C(b)) class RealSubclass(a:A) extends IntermediateSubclass(new B(a)) Is there clean way to do this?

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• .NET 2.0: Invoking Methods Using Reflection And Generics Causes Exception

  - by David Derringer

  Hi all, I'm new to Stack Overflow, so forgive me. I've just started transititoning over to C# and I am stuck on a problem. I am wanting to pass a generic class in and call a method from that class. So, my code looks as such: public void UpdateRecords<T>(T sender) where T : new() //where T: new() came from Resharper { Type foo = Type.GetType(sender.GetType().ToString()); object[] userParameters = new object[2]; userParameters[0] = x; userParameters[1] = y; sender = new T(); //This was to see if I could solve my exception problem MethodInfo populateRecord = foo.GetMethod("MethodInOtherClass"); populateMethod.Invoke(sender, userParameters); } Exception thrown: "Object reference not set to an instance of an object." Again, I really apologize, as I am nearly brand new to C# and this is the first time I've ever handled reflection and generics. Thank you!

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• Alternative to NOT EXISTS

  - by Dave Colwell

  Hi all, I have two tables linked by an ID column, lets call them Table A and table B. My goal is to find all the records in table A that have no record in table B. For instance: Table A: ID----Value 1-----value1 2-----value2 3-----value3 4-----value4 Table B ID----Value 1-----x 2-----y 4-----z 4-----l As you can see, record with ID = 3 does not exist in table B, so i want a query that will give me record 3 from table A. the way i am currently doing this is by saying AND NOT EXISTS (SELECT ID FROM TableB) but since the tables are huge, the performance on this is terrible. Also, when i tried using a Left Join where TableB.ID is null, it didnt work. Can anyone suggest an alternative?

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• Lucene .NET IndexWriter lock

  - by Pini Salim

  My question related to the next code snippet: static void Main(string[] args) { Lucene.Net.Store.Directory d = FSDirectory.Open(new DirectoryInfo(/*my index path*/)); IndexWriter writer = new IndexWriter(d, new WhitespaceAnalyzer()); //Exiting without closing the indexd writer... } In this test, I opened an IndexWriter without closing it - so even after the test exits, the write.lock file still exists in the index directory, so I expected that the next time I open an instance of IndexWriter to that index, a LockObatinFailedException will be thrown. Can someone please explain to me why am I wrong? I mean, does the meaning of the write.lock file is to protect creation of two IndexWriters in the same process only? that doesnt seems the right answer to me...

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• What Use are Threads Outside of Parallel Problems on MultiCore Systesm?

  - by Robert S. Barnes

  Threads make the design, implementation and debugging of a program significantly more difficult. Yet many people seem to think that every task in a program that can be threaded should be threaded, even on a single core system. I can understand threading something like an MPEG2 decoder that's going to run on a multicore cpu ( which I've done ), but what can justify the significant development costs threading entails when you're talking about a single core system or even a multicore system if your task doesn't gain significant performance from a parallel implementation? Or more succinctly, what kinds of non-performance related problems justify threading? Edit Well I just ran across one instance that's not CPU limited but threads make a big difference: TCP, HTTP and the Multi-Threading Sweet Spot Multiple threads are pretty useful when trying to max out your bandwidth to another peer over a high latency network connection. Non-blocking I/O would use significantly less local CPU resources, but would be much more difficult to design and implement.

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• Windows Azure local development environment speed

  - by Paperjam

  I've started porting an existing ASP.NET web app to Windows Azure and have noticed that the development process is really slow. Each time I make a change to my code and want to view it, I have to effectively redeploy it to the local dev cloud (using Start debugging (F5) or Start without debugging (Ctrl-F5). The process itself takes over a minute, during which time Visual Studio is completely unresponsive. Am I doing something wrong or is that simply how things are developing for Azure? My specs: Visual Studio 2008 9.0.30729.1 SP 5 projects running on .NET 3.5 SP1 Azure SDK 1.1 (February 2010) Single instance of a single web role Dual-core AMD 64 machine with 8GB RAM, 64-bit Windows 7, fully patched The main project itself is quite large (3k files, ~200k lines) but compiles normally in 10-15 seconds

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• How to use the vtable to determine class type

  - by Alex Silverman

  I was recently on an interview for a position where C/C++ is the primary language and during one question I was told that it's possible to use the vtable to determine which class in a hierarchy a base pointer actually stores. So if, for example you have class A { public: A() {} virtual ~A() {} virtual void method1() {} }; class B : public A { public: B() {} virtual ~B() {} virtual void method1() {} }; and you instantiate A * pFoo = new B(), is it indeed possible to use the vtable to determine whether pFoo contains a pointer to an instance of A or B?

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• How to change input button image using CSS?

  - by Baltimark

  So, I can create an input button with an image using <INPUT type="image" src="/images/Btn.PNG" value=""> But, I can't get the same behavior using CSS. for instance, i've tried <INPUT type="image" class="myButton" value=""> where "myButton" is defined in the css file as .myButton{ background:url(/images/Btn.PNG) no-repeat; cursor:pointer; width: 200px; height: 100px; border: none; } If that's all I wanted to do, I could use the original style, but I want to change the button's appearance on hover (using a myButton:hover class). I know the links are good because I've been able to load them for a background image for other parts of the page (just as a check). I found examples on the web of how to do it using javascript, but I'm looking for a css solution. I'm using Firefox 3.0.3 if that makes a difference. Thanks

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• Combing a symlink to an external folder with a Rewrite Rule?

  - by Tristan

  I've created a symlink in an account to an folder external to that user account (although with the same ownership). The symlink works but I'd like to combine it with a RewriteRule, and I'm having problems with that. For instance I create the symlink with: ln -s /home/target shortcut And I add the following RewriteRule to .htaccess: RewriteRule ^shortcut/([a-zA-Z0-9_-]+) shortcut/index.php?var=$1 This however fails. Yet if instead of being located in an external folder, the target folder is in the same folder as the shortcut address, then the RewriteRule will work. i.e. it works if the symlink is: ln -s ./target shortcut How might I get the RewriteRule working for the case where the target folder is an external folder?

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• How can I tell Visual Studio to NOT BREAK on a particular exception?

  - by Noel Kennedy

  I have a particular type of exception that I would like Visual Studio to not catch with the Exception Assistant. Essentially I would like it just to let my normal exception handling infrastructure deal with it. The exception is an inheritor of System.Exception which I wrote and have the source code for. Any where this is thrown I want VS to not catch it, ie it is not useful to just supress a single throw new BlahException(); in code. This is because the exception is thrown a lot, and I don't want to have to supress every single instance individually. In case it makes a difference I am on Visual Studio 2010 Ultimate, Framework 3.5 SP1.

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• Overriding setter on domain class in grails 1.1.2

  - by Pavel P

  I have following two domain classes in Grails 1.1.2: class A implements Serializable { MyEnumType myField Date fieldChanged void setMyField(MyEnumType val) { if (myField != null && myField != val) { myField = val fieldChanged = new Date() } } } class B extends A { List children void setMyField(MyEnumType val) { if (myField != null && myField != val) { myField = val fieldChanged = new Date() children.each { child -> child.myField = val } } } When I set B instance's myField, I get the setter into the cycle... myField = val line calls setter again instead of assiging the new value. Any hint how to override the setter correctly? Thanks

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• DDEX Firebird editing queries duplicates columns in Visual Studio 2008

  - by A Bothe

  Hello everybody! I don't know if some of you also has experienced it but when I edit a query in Visual Studio (it uses DDEX 2.0.5 for accessing the Firebird 2.5 database), it duplicates some of the columns. What's really interesting is the fact that only System.Boolean columns are duplicated: Originally, there was only ,for instance, a 'PRO_DELETED' field... Now I wanted to sort my results by this field - I had to change the select statement in the so-called QueryBuilder by adding "ORDER BY PRO_DELETED" ...After clicking OK it somehow created a new column (!?) called 'PRO_DELETED1' My question is: Why does DDEX add such a new row to the column view and why can't I access the original PRO_DELETED field anymore? Thanks in advance!

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• Terminating app due to uncaught exception / / SIGABRT // C++ please help!

  - by user282076

  I have just finished one of my apps when I got this message. I cannot for the life of me work out what is wrong. (gdb) continue 2010-02-26 14:05:51.443 BrainTester[2638:207] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[UIViewController _loadViewFromNibNamed:bundle:] was unable to load a nib named "SplitSecondViewController"' 2010-02-26 14:05:51.452 BrainTester[2638:207] Stack: ( 861696817, 860329709, 861252493, 861252395, 835170725, 835170141, 835074651, 13515, 834774231, 834773467, 835014237, 835012689, 835011495, 861063661, 861449261, 861447005, 834770767, 834765939, 11025, 10920 ) terminate called after throwing an instance of 'NSException' Program r eceived signal: “SIGABRT”. (gdb) If someone can help, any help is appreciated.

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• Rails: getting logic to run at end of request, regardless of filter chain aborts?

  - by JSW

  Is there a reliable mechanism discussed in rails documentation for calling a function at the end of the request, regardless of filter chain aborts? It's not after filters, because after filters don't get called if any prior filter redirected or rendered. For context, I'm trying to put some structured profiling/reporting information into the app log at the end of every request. This information is collected throughought the request lifetime via instance variables wrapped in custom controller accessors, and dumped at the end in a JSON blob for use by a post-processing script. My end goal is to generate reports about my application's logical query distribution (things that depend on controller logic, not just request URIs and parameters), performance profile (time spent in specific DB queries or blocked on webservices), failure rates (including invalid incoming requests that get rejected by before_filter validation rules), and a slew of other things that cannot really be parsed from the basic information in the application and apache logs. At a higher level, is there a different "rails way" that solves my app profiling goal?

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• iPhone YouTube Channel App

  - by pki

  What would the steps be to creating an app that connected to YouTube's XML API. Here is my setup currently but it is not working. App Delegate creates object "YTXMLParser" App Delegate calls [parser prepAndPrase]; In Prep and Parse the app initiates a NSURLConnection The app downloads the XML Data using the NSURLConnection well appeneding to NSMutableData The app parses the data with NSXMLParser At the end of each "entry" the app adds the current dictionary to the class. At the beginning of each "entry" the app creates an instance of a dictionary. Here's where i'm stuck. How do I get this data back to my app delegate?

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• WCF net.tcp server disconnects - how to handle properly on client side?

  - by RoastedBattleSquirrel

  I'm stuck with a bit of an annoying problem right now. I've got a Silverlight 4 application (which runs OOB by default). It uses WCF with net.tcp as means of communicating with the server. The client uses a central instance of the wcf client proxy. As long as everything keeps running on the server side, everything's fine. If i kill the server in the middle of everything, i drown in an avalanche of exceptions on the client side (connection lost, channel faulted etc etc). Now i'm looking for a way to handle this in a clean and centralized way (if centralized is possible). The SL app has one central client object sitting in App.cs (public static MyClient Client { get;set;}), which gets initialized on application start. Any idea how to properly handle any connectivity problems on the client object?

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• How does Windows' 'Open with' work?

  - by Frederick

  I was under the impression that when you double click a file (or choose 'Open With' from the right click menu), Windows simply calls the application with the filename as the parameter. Something like this: C: App.exe file.abc However, I just double clicked an .xls file and then checked the PEB of the Excel instance that sprang up. To my surprise the commandline did not contain the filename as a parameter. So that set me wondering. What exactly is mechanism Windows uses to have a file opened by a relevant application? Is there a special API that each application that supports such facility must expose?

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• Is a function kind of like a static method?

  - by lkm

  I'm a java programmer and am trying to understand the difference between a method (java methods) and a function (such as in c++). I used to think that they are the same, just different naming conventions for different programming languages. But now that I know they are not, I am having trouble understanding the difference. I know that a method relates to an instance of a class and has access to class data (member variables), while a function does not (?). So is a function kind of like a static method? See here for explanations I read which led me to think this.

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• Django. default=datetime.now() problem

  - by Shamanu4

  Hello. I've such db model: from datetime import datetime class TermPayment(models.Model): dev_session = models.ForeignKey(DeviceSession, related_name='payments') user_session = models.ForeignKey(UserSession, related_name='payment') date = models.DateTimeField(default=datetime.now(),blank=True) sum = models.FloatField(default=0) cnt = models.IntegerField(default=0) class Meta: db_table = 'term_payments' ordering = ['-date'] and here new instance is added: # ... tp = TermPayment() tp.dev_session = self.conn.session # device session hash tp.user_session = self.session # user session hash tp.sum = sum tp.cnt = cnt tp.save() But i've a problem: all records in database have the same value in date field - the date of the first payment. After server restart - one record have new date and others have the same as first after restart. It's look like some data cache is using but I can't found where. database: mysql 5.1.25 django v1.1.1

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