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• What are the most interesting equivalences arising from the Curry-Howard Isomorphism?

  - by Tom

  I came upon the Curry-Howard Isomorphism relatively late in my programming life, and perhaps this contributes to my being utterly fascinated by it. It implies that for every programming concept there exists a precise analogue in formal logic, and vice versa. Here's an "obvious" list of such analogies, off the top of my head: program/definition | proof type/declaration | proposition inhabited type | theorem function | implication function argument | hypothesis/antecedent function result | conclusion/consequent function application | modus ponens recursion | induction identity function | tautology non-terminating function | absurdity tuple | conjunction (and) disjoint union | exclusive disjunction (xor) parametric polymorphism | universal quantification So, to my question: what are some of the more interesting/obscure implications of this isomorphism? I'm no logician so I'm sure I've only scratched the surface with this list. For example, here are some programming notions for which I'm unaware of pithy names in logic: currying | "((a & b) => c) iff (a => (b => c))" scope | "known theory + hypotheses" And here are some logical concepts which I haven't quite pinned down in programming terms: primitive type? | axiom set of valid programs? | theory ? | disjunction (or)

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• TDD test data loading methods

  - by Dave Hanson

  I am a TDD newb and I would like to figure out how to test the following code. I am trying to write my tests first, but I am having trouble for creating a test that touches my DataAccessor. I can't figure out how to fake it. I've done the extend the shipment class and override the Load() method; to continue testing the object. I feel as though I end up unit testing my Mock objects/stubs and not my real objects. I thought in TDD the unit tests were supposed to hit ALL of the methods on the object; however I can never seem to test that Load() code only the overriden Mock Load My tests were write an object that contains a list of orders based off of shipment number. I have an object that loads itself from the database. public class Shipment { //member variables protected List<string> _listOfOrders = new List<string>(); protected string _id = "" //public properties public List<string> ListOrders { get{ return _listOfOrders; } } public Shipment(string id) { _id = id; Load(); } //PROBLEM METHOD // whenever I write code that needs this Shipment object, this method tries // to hit the DB and fubars my tests // the only way to get around is to have all my tests run on a fake Shipment object. protected void Load() { _listOfOrders = DataAccessor.GetOrders(_id); } } I create my fake shipment class to test the rest of the classes methods .I can't ever test the Real load method without having an actual DB connection public class FakeShipment : Shipment { protected new void Load() { _listOfOrders = new List<string>(); } } Any thoughts? Please advise. Dave

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• How to implement properly plugins in C#?

  - by MartyIX

  I'm trying to add plugins to my game and what I'm trying to implement is this: Plugins will be either mine or 3rd party's so I would like a solution where crashing of the plugin would not mean crashing of the main application. Methods of plugins are called very often (for example because of drawing of game objects). What I've found so far: 1) http://www.codeproject.com/KB/cs/pluginsincsharp.aspx - simple concept that seems like it should work nicely. Since plugins are used in my game for every round I would suffice to add the Restart() method and if a plugin is no longer needed Unload() method + GC should take care of that. 2) http://mef.codeplex.com/Wikipage - Managed Extensibility Framework - my program should work on .NET 3.5 and I don't want to add any other framework separately I want to write my plugin system myself. Therefore this solution is out of question. 3) Microsoft provides: http://msdn.microsoft.com/en-us/library/system.addin.aspx but according to a few articles I've read it is very complex. 4) Different AppDomains for plugins. According to Marc Gravell ( http://stackoverflow.com/questions/665668/usage-of-appdomain-in-c ) different AppDomains allow isolation. Unloading of plugins would be easy. What would the performance load be? I need to call methods of plugins very often (to draw objects for example). Using Application Domains - http://msdn.microsoft.com/en-us/library/yb506139.aspx A few tutorials on java2s.com Could you please comment on my findings? New approaches are also welcomed! Thanks!

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• Delphi 2009 dbExpress and Interbase: Unicode migration steps and risks?

  - by mjustin

  Currently, our database uses Win1252 as the only character encoding. We will have to support Unicode in the database tables soon, which means we have to perform this migration for four databases and around 80 Delphi applications which run in-house in a 24/7 environment. Are there recommendations for database migrations to UTF-8 (or UNICODE_FSS) for Delphi applications? Some questions listed below. Many thanks in advance for your answers! are there tools which help with the migration of the existing databases (sizes between 250 MB and 2 GB, no Blob fields), by dumping the data, recreating the database with UNICODE_FSS or UTF-8, and loading the data back? are there known problems with Delphi 2009, dbExpress and Interbase 7.5 related to Unicode character sets? would you recommend to upgrade the databases to Interbase 2009 first? (This upgrade is planned but does not have a high priority) can we simply migrate the database and Delphi will handle the Unicode character sets automatically, or will we have to change all character field types in every Datamodule (dfm and source code) too? which strategy would you recommend to work on the migration in parallel with the normal development and maintenance of the existing application? The application runs in-house so development and database administration is done internally. Update: one problem I found now is that there are two different persistent field types for Unicode and non Unicode character fields. For the existing database, dbExpress creates TStringField objects. For the Unicode database fields, dbExpress creates (or expects!) TWideStringField objects. This looks like a lot of work lies ahead. While we could try to avoid persistent fields (and add calculated fields at run time), Of course we would prefer a solution which does not require so many changes in existing units and DFM files.

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• WPF - Setting ComboBox.SelectedItem in XAML based on matching object

  - by Andy T

  Hi, so, I have templated combobox that is basically acting as a simple colour palette. It is populated with a list of SolidColorBrush objects. Fine. Now, I have some data that holds the hex value of the current colour. I have a converter that converts the hex into a SolidColorBrush. Also fine. Now, I want to set the SelectedItem property of the combobox based on the colour from my datasource. Since my combo is populated with objects of type SolidColourBrush, and my binding converter is returning a SolidColorBrush, I assumed it would be as simple as saying: SelectedItem="{Binding Color, Converter={StaticResource StringToBrush}}" However... it doesn't work :( I've tested that the binding is working behind the scenes by using the exact same value for the Background property of the combobox. It works fine. So, clearly I can't just say SelectedItem = [something] where that [something] is basically an object equal to the item I want to be selected. What is the right way to do this? Surely it's possible in a XAML-only styley using binding, and I don't have to do some nasty C# iterating through all items in the combobox trying to find a match (that seems awfully old-school)...? Any help appreciated. Many thanks! AT

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• Add data to Django form class using modelformset_factory

  - by dean

  I have a problem where I need to display a lot of forms for detail data for a hierarchical data set. I want to display some relational fields as labels for the forms and I'm struggling with a way to do this in a more robust way. Here is the code... class Category(models.Model): name = models.CharField(max_length=160) class Item(models.Model): category = models.ForeignKey('Category') name = models.CharField(max_length=160) weight = models.IntegerField(default=0) class Meta: ordering = ('category','weight','name') class BudgetValue(models.Model): value = models.IntegerField() plan = models.ForeignKey('Plan') item = models.ForeignKey('Item') I use the modelformset_factory to create a formset of budgetvalue forms for a particular plan. What I'd like is item name and category name for each BudgetValue. When I iterate through the forms each one will be labeled properly. class BudgetValueForm(forms.ModelForm): item = forms.ModelChoiceField(queryset=Item.objects.all(),widget=forms.HiddenInput()) plan = forms.ModelChoiceField(queryset=Plan.objects.all(),widget=forms.HiddenInput()) category = "" < assign dynamically on form creation > item = "" < assign dynamically on form creation > class Meta: model = BudgetValue fields = ('item','plan','value') What I started out with is just creating a dictionary of budgetvalue.item.category.name, budgetvalue.item.name, and the form for each budget value. This gets passed to the template and I render it as I intended. I'm assuming that the ordering of the forms in the formset and the querset used to genererate the formset keep the budgetvalues in the same order and the dictionary is created correctly. That is the budgetvalue.item.name is associated with the correct form. This scares me and I'm thinking there has to be a better way. Any help would be greatly appreciated.

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• "select * from table" vs "select colA,colB,etc from table" interesting behaviour in SqlServer2005

  - by kristof

  Apology for a lengthy post but I needed to post some code to illustrate the problem. Inspired by the question What is the reason not to use select * ? posted a few minutes ago, I decided to point out some observations of the select * behaviour that I noticed some time ago. So let's the code speak for itself: IF EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[starTest]') AND type in (N'U')) DROP TABLE [dbo].[starTest] CREATE TABLE [dbo].[starTest]( [id] [int] IDENTITY(1,1) NOT NULL, [A] [varchar](50) NULL, [B] [varchar](50) NULL, [C] [varchar](50) NULL ) ON [PRIMARY] GO insert into dbo.starTest(a,b,c) select 'a1','b1','c1' union all select 'a2','b2','c2' union all select 'a3','b3','c3' go IF EXISTS (SELECT * FROM sys.views WHERE object_id = OBJECT_ID(N'[dbo].[vStartest]')) DROP VIEW [dbo].[vStartest] go create view dbo.vStartest as select * from dbo.starTest go go IF EXISTS (SELECT * FROM sys.views WHERE object_id = OBJECT_ID(N'[dbo].[vExplicittest]')) DROP VIEW [dbo].[vExplicittest] go create view dbo.[vExplicittest] as select a,b,c from dbo.starTest go select a,b,c from dbo.vStartest select a,b,c from dbo.vExplicitTest IF EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[starTest]') AND type in (N'U')) DROP TABLE [dbo].[starTest] CREATE TABLE [dbo].[starTest]( [id] [int] IDENTITY(1,1) NOT NULL, [A] [varchar](50) NULL, [B] [varchar](50) NULL, [D] [varchar](50) NULL, [C] [varchar](50) NULL ) ON [PRIMARY] GO insert into dbo.starTest(a,b,d,c) select 'a1','b1','d1','c1' union all select 'a2','b2','d2','c2' union all select 'a3','b3','d3','c3' select a,b,c from dbo.vExplicittest select a,b,c from dbo.vStartest If you execute the following query and look at the results of last 2 select statements, the results that you will see will be as follows: select a,b,c from dbo.vExplicittest a1 b1 c1 a2 b2 c2 a3 b3 c3 select a,b,c from dbo.vStartest a1 b1 d1 a2 b2 d2 a3 b3 d3 As you can see in the results of select a,b,c from dbo.vStartest the data of column c has been replaced with the data from colum d. I believe that is related to the way the views are compiled, my understanding is that the columns are mapped by column indexes (1,2,3,4) as apposed to names. I though I would post it as a warning for people using select * in their sql and experiencing unexpected behaviour. Note: If you rebuild the view that uses select * each time after you modify the table it will work as expected

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• Django Cannot set values on a ManyToManyField which specifies an intermediary model

  - by dana

  i am using a m2m and a through table, and when i was trying to save, my error was: Cannot set values on a ManyToManyField which specifies an intermediary model so, i've modified my code, so that when i save the form, to insert data into the 'through' table too.But now, i'm having another error. (i've bolded the lines where i think i am wrong) i have in models.py: class Classroom(models.Model): user = models.ForeignKey(User, related_name = 'classroom_creator') classname = models.CharField(max_length=140, unique = True) date = models.DateTimeField(auto_now=True) open_class = models.BooleanField(default=True) members = models.ManyToManyField(User,related_name="list of invited members", through = 'Membership') class Membership(models.Model): accept = models.BooleanField(User) date = models.DateTimeField(auto_now = True) classroom = models.ForeignKey(Classroom, related_name = 'classroom_membership') member = models.ForeignKey(User, related_name = 'user_membership') and in def save_classroom(request): if request.method == 'POST': form = ClassroomForm(request.POST, request.FILES, user = request.user) **classroom_instance = Classroom member_instance = Membership** if form.is_valid(): new_obj = form.save(commit=False) new_obj.user = request.user r = Relations.objects.filter(initiated_by = request.user) membership = Membership.objects.create(**classroom = classroom_instance, member = member_instance,date=datetime.datetime.now())** new_obj.save() form.save_m2m() return HttpResponseRedirect('/classroom/classroom_view/{{user}}/') else: form = ClassroomForm(user = request.user) return render_to_response('classroom/classroom_form.html', { 'form': form, }, context_instance=RequestContext(request)) but i don't seem to initialise okay the classroom_instance and menber_instance.My error os: Cannot assign "": "Membership.classroom" must be a "Classroom" instance. Thanks!

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• Mingling C++ classes with Objective C classes

  - by Joey

  I am using the iphone SDK and coding primarily in C++ while using parts of the SDK in obj-c. Is it possible to designate a C++ class in situations where an obj-c class is needed? For instance: 1) when setting delegates to obj-c objects. I cannot make a C++ class derive from a Delegate protocol so this and possibly other reasons prevent me from making my C++ class a delegate for various obj-c objects. What I do as a solution is create an obj-c adapter class that contains a ptr to the C++ class and is used as the delegate (notifying the C++ class when it is called). It feels cumbersome to write these every time I need to get delegate notifications to a C++ class. 2) when setting selectors This goes hand in hand with item 1. Say I want to set a callback to fire when something is done, like a button press or a setAnimationDidStopSelector in the UIView animation functionality. It would be nice to be able to designate a C++ function along with the relevant delegate for setAnimationDelegate. Well, I suspect this isn't readily possible, but if anyone has any suggestions on how to do it if it is, or on how to write such things more easily, I would love to hear them. Thanks.

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• XCTest.framework build error

  - by user2703123

  I am using the DropBox Core API in my app and therefore, I must include the XCTest framework, because, when I haven't added the XCTest framework, my app can't connect to dropbox, however when I do add the framework, I get an error while building for the simulator. There is nothing wrong with my code! Here is the error: Ld /Users/Zach/Library/Developer/Xcode/DerivedData/SnapDrop!-fchnxyvnqyeefscfhmohrzxtiqeb/Build/Products/Debug-iphonesimulator/SnapDrop!.app/SnapDrop! normal i386 cd "/Users/Zach/Desktop/SnapDrop!" setenv IPHONEOS_DEPLOYMENT_TARGET 6.1 setenv PATH "/Applications/Xcode5-DP6.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/usr/bin:/Applications/Xcode5-DP6.app/Contents/Developer/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin" /Applications/Xcode5-DP6.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang -arch i386 -isysroot /Applications/Xcode5-DP6.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator7.0.sdk -L/Users/Zach/Library/Developer/Xcode/DerivedData/SnapDrop!-fchnxyvnqyeefscfhmohrzxtiqeb/Build/Products/Debug-iphonesimulator -F/Users/Zach/Library/Developer/Xcode/DerivedData/SnapDrop!-fchnxyvnqyeefscfhmohrzxtiqeb/Build/Products/Debug-iphonesimulator -F/Users/Zach/Downloads/dropbox-ios-sdk-1.3.5 -F/Users/Zach/Downloads/dropbox-ios-sync-sdk-1-1.1.0 -F/Applications/Xcode5-DP6.app/Contents/Developer/Library/Frameworks -F/Users/Zach/Desktop -filelist /Users/Zach/Library/Developer/Xcode/DerivedData/SnapDrop!-fchnxyvnqyeefscfhmohrzxtiqeb/Build/Intermediates/SnapDrop!.build/Debug-iphonesimulator/SnapDrop!.build/Objects-normal/i386/SnapDrop!.LinkFileList -Xlinker -objc_abi_version -Xlinker 2 -fobjc-arc -fobjc-link-runtime -Xlinker -no_implicit_dylibs -mios-simulator-version-min=6.1 -framework iAd -framework AssetsLibrary -framework QuartzCore -framework SystemConfiguration -framework Security -framework CFNetwork -framework XCTest -framework Dropbox -framework DropboxSDK -framework CoreGraphics -framework UIKit -framework Foundation -Xlinker -dependency_info -Xlinker /Users/Zach/Library/Developer/Xcode/DerivedData/SnapDrop!-fchnxyvnqyeefscfhmohrzxtiqeb/Build/Intermediates/SnapDrop!.build/Debug-iphonesimulator/SnapDrop!.build/Objects-normal/i386/SnapDrop!_dependency_info.dat -o /Users/Zach/Library/Developer/Xcode/DerivedData/SnapDrop!-fchnxyvnqyeefscfhmohrzxtiqeb/Build/Products/Debug-iphonesimulator/SnapDrop!.app/SnapDrop! ld: building for iOS Simulator, but linking against dylib built for MacOSX file '/Applications/Xcode5-DP6.app/Contents/Developer/Library/Frameworks/XCTest.framework/XCTest' for architecture i386 clang: error: linker command failed with exit code 1 (use -v to see invocation) What should I do? If my framework is corrupt, can you tell me how to reinstall it? I have tried deleting and reinstalling Xcode with no luck.

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• Frameworks to manage dates (effective date and expiry dates)

  - by user214626

  Hello, We have an object that can has an effective date and expiry date.(Ex. i want to maintain the price of a commodity for a time period) Business Rules - Effective date is always a valid date (a datestamp) but, expiry date can be null to indicate that the object is active throughout. Also, both effective and expiry date can be set to some valid dates. Are there any frameworks that manage objects such that the objects are consistent,i.e there are no overlaps of the validity periods ? Ex. class XBOX { double price; Date effectiveDate; Date expiryDate; } XBOX x1 = new XBOX(400$, '2007-01-01','2008-12-31' ); XBOX x2 = new XBOX(200$, '2009-01-01',null ); Assume that we get a new rate from '2010-01-01' and a new XBOX object has to be created (to persist). Is there a framework/pattern that can do the following, so that the XBOX is consistent. x2.setExpiryDate('2009-12-31') XBOX x3 = new XBOX(150$, '2010-01-01',null ); Thanks in advance.

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• Proper way to validate model in ASP.NET MVC 2 and ViewModel apporach

  - by adrin

  I am writing an ASP.NET MVC 2 application using NHibernate and repository pattern. I have an assembly that contains my model (business entities), moreover in my web project I want to use flattened objects (possibly with additional properties/logic) as ViewModels. These VMs contain UI-specific metadata (eg. DisplayAttribute used by Html.LabelFor() method). The problem is that I don't know how to implement validation so that I don't repeat myself throughout various tiers (specifically validation rules are written once in Model and propagated to ViewModel). I am using DataAnnotations on my ViewModel but this means no validation rules are imposed on the Model itself. One approach I am considering is deriving ViewModel objects from business entities adding new properties/overriding old ones, thus preserving validation metadata between the two however this is an ugly workaround. I have seen Automapper project which helps to map properties, but I am not sure if it can handle ASP.NET MVC 2 validation metadata properly. Is it difficult to use custom validation framework in asp.net mvc 2? Do you have any patterns that help to preserve DRY in regard to validation?

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• How do I implement repository pattern and unit of work when dealing with multiple data stores?

  - by Jason

  I have a unique situation where I am building a DDD based system that needs to access both Active Directory and a SQL database as persistence. Initially this wasnt a problem because our design was setup where we had a unit of work that looked like this: public interface IUnitOfWork { void BeginTransaction() void Commit() } and our repositories looked like this: public interface IRepository<T> { T GetByID() void Save(T entity) void Delete(T entity) } In this setup our load and save would handle the mapping between both data stores because we wrote it ourselves. The unit of work would handle transactions and would contain the Linq To SQL data context that the repositories would use for persistence. The active directory part was handled by a domain service implemented in infrastructure and consumed by the repositories in each Save() method. Save() was responsible with interacting with the data context to do all the database operations. Now we are trying to adapt it to entity framework and take advantage of POCO. Ideally we would not need the Save() method because the domain objects are being tracked by the object context and we would just need to add a Save() method on the unit of work to have the object context save the changes, and a way to register new objects with the context. The new proposed design looks more like this: public interface IUnitOfWork { void BeginTransaction() void Save() void Commit() } public interface IRepository<T> { T GetByID() void Add(T entity) void Delete(T entity) } This solves the data access problem with entity framework, but does not solve the problem with our active directory integration. Before, it was in the Save() method on the repository, but now it has no home. The unit of work knows nothing other than the entity framework data context. Where should this logic go? I argue this design only works if you only have one data store using entity framework. Any ideas how to best approach this issue? Where should I put this logic?

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• Android: Change the source of ImageView present in ListView

  - by Vivek

  Hi All, I have a ListView specified by list_item.xml Now I need to change the Image in my list inside onListItemClick. How to achieve this? //list_item.xml <?xml version="1.0" encoding="UTF-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="wrap_content"> <ImageView android:layout_width="wrap_content" android:layout_height="wrap_content" android:src="@drawable/play" android:id="@+id/img" /> <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:gravity="center_vertical" android:id="@+id/txt" /> </LinearLayout> I have a Custom Adapter to populate my list. Code below is the adapter. public class MyCustomAdapter extends ArrayAdapter<String> { public MyCustomAdapter(Context context, int textViewResourceId, String[] objects) { super(context, textViewResourceId, objects); // TODO Auto-generated constructor stub } @Override public View getView(int position, View convertView, ViewGroup parent) { // TODO Auto-generated method stub LayoutInflater inflater=getLayoutInflater(); View row=inflater.inflate(R.layout.list_item, parent, false); TextView label=(TextView)row.findViewById(R.id.txt); label.setText(Sounds[position]); ImageView icon=(ImageView)row.findViewById(R.id.img); icon.setMaxHeight(32); icon.setMaxWidth(32); icon.setPadding(2, 1, 5, 1); icon.setImageResource(R.drawable.play); return row; } } And in onCreate I do the following @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); try { setListAdapter(new MyCustomAdapter(this, R.layout.list_item, Sounds)); //Sounds --> String array } catch(Exception e) { e.printStackTrace(); } } Now when any row is selected, I need to change the image associated with the selected view. Your help is appreciated. Thanks.

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• unable to find a MessageBodyReader

  - by Cristian Boariu

  Hi guys, I have this interface: @Path("inbox") public interface InboxQueryResourceTest { @POST @Path("{membershipExternalId}/query") @Consumes(MediaType.APPLICATION_XML) @Produces("multipart/mixed") public MultipartOutput query(@PathParam("membershipExternalId") final String membershipExternalId, @QueryParam("page") @DefaultValue("0") final int page, @QueryParam("pageSize") @DefaultValue("10") final int pageSize, @QueryParam("sortProperty") final List<String> sortPropertyList, @QueryParam("sortReversed") final List<Boolean> sortReversed, @QueryParam("sortType") final List<String> sortTypeString, final InstanceQuery instanceQuery) throws IOException; } I have implemented the method to return a MultipartOutput. I am posting an xml query from Fiddler and i receive the result without any problem. BUT i have done an integration test for the same interface, i send the same objects and i put the response like: final MultipartOutput multiPartOutput = getClient().query(getUserRestAuth(), 0, 25, null, null, null, instanceQuery); But here, so from integration tests, i receive a strange error: Unable to find a MessageBodyReader of content-type multipart/mixed;boundary="74c5b6b4-e820-452d-abea-4c56ffb514bb" and type class org.jboss.resteasy.plugins.providers.multipart.MultipartOutput Anyone has any ideea why only in integration tests i receive this error? PS: Some of you will say that i do not send application/xml as ContentType but multipart, which of course is false because the objects are annotated with the required @XmlRootElement etc, otherways neither the POST from Fiddler would work.

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• In ParallelPython, a method of an object ( object.func() ) fails to manipulate a variable of an object ( object.value )

  - by mehmet.ali.anil

  With parallelpython, I am trying to convert my old serial code to parallel, which heavily relies on objects that have methods that change that object's variables. A stripped example in which I omit the syntax in favor of simplicity: class Network: self.adjacency_matrix = [ ... ] self.state = [ ... ] self.equilibria = [ ... ] ... def populate_equilibria(self): # this function takes every possible value that self.state can be in # runs the boolean dynamical system # and writes an integer within self.equilibria for each self.state # doesn't return anything I call this method as: Code: j1 = jobserver.submit(net2.populate_equilibria,(),(),("numpy as num")) The job is sumbitted, and I know that a long computation takes place, so I speculate that my code is ran. The problem is, i am new to parallelpython , I was expecting that, when the method is called, the variable net2.equilibria would be written accordingly, and I would get a revised object (net2) . That is how my code works, independent objects with methods that act upon the object's variables. Rather, though the computation is apparent, and reasonably timed, the variable net2.equilibria remains unchanged. As if PP only takes the function and the object, computes it elsewhere, but never returns the object, so I am left with the old one. What do I miss? Thanks in advance.

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• Getter and Setter vs. Builder strategy

  - by Extrakun

  I was reading a JavaWorld's article on Getter and Setter where the basic premise is that getters expose internal content of an object, hence tightening coupling, and go on to provide examples using builder objects. I was rather leery of abolishing getter/setter but on second reading of the article, see to quite like the idea. However, sometimes I just need one cruical element of an entity class, such as the user's id and writing one whole class just to extract that cruical element seems like overkill. It also implies that for different view, a different type of importer/exporter must be implemented (or the whole data of the class to be exported out, thus resulting in waste). Usually I tend towards filtering the result of a getter - for example, if I need to output the price of a product in different currency, I would code it as: return CurrencyOutput::convertTo($product->price(), 'USD'); This is with the understanding that the raw output of a getter is not necessary the final result to be pushed onto a screen or a database. Is getter/setter really as bad as it is protrayed to be? When should one adopt a builder strategy, or a 'get the result and filter it' approach? How do you avoid having a class needing to know about every other objects if you are not using getter/setter?

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• Sorting an XML in Java

  - by Java Guy

  Hello I have an XML similiar to below, which needed to be sorted using the date field. <root> <Node1><date></date></Node1> <Node1><date></date></Node1> <Node1> <date></date></Node1> <Node1> <date></date></Node1> <Node2> <date></date></Node2> <Node2> <date></date></Node2> <Node2> <date></date></Node2> <Node2> <date></date> </Node2> </root> I would like to sort the XML based on the date(say asc order), irrespective of whether the date is under Node1 or Node2. Actually in Java code I have two seperate lists, one with Node1 objects and other with Node2 obects. I can sort the list in any order sperately inside java. But I need to have the dates sorted irrespective of the nodes it is apperaing on the XML. What is the best approach to sort this way in Java? Actaully I am using Castor for marshalling the java objects to XML. If you know this can be done with Castor, that will be great!

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• WPF DataGrid binding difficulties

  - by Jasmin Pvvlovic

  This is the class: public class TrainingData { public string Training { get; set; } } And this is the rest of the code in MainWindow: Excel.Workbook xlWorkbook = xlApp.Workbooks.Open("D:/excel.xlsx"); Excel._Worksheet xlWorksheet = xlWorkbook.Sheets[1]; Excel.Range xlRange = xlWorksheet.UsedRange; List <TrainingData> tData= new List <TrainingData>(); int rowCount = xlRange.Rows.Count; int colCount = xlRange.Columns.Count; //int k = 0; for (int i = 1; i <= rowCount; i++) { tData.Add(new TrainingData() { Training = xlRange.Cells[i, 1].Value2.ToString() }); //MessageBox.Show(tData[k].Training); //k++; } Prikaz.ItemsSource = tData; DataGrid: <DataGrid AutoGenerateColumns="False" Height="120" HorizontalAlignment="Left" Margin="12,12,0,0" Name="Prikaz" VerticalAlignment="Top" Width="105" ItemsSource="{Binding}"> <DataGrid.Columns> <DataGridTextColumn Header="Header" /> </DataGrid.Columns> </DataGrid>` So, Prikaz is my DataGrid. tData is List of TrainingData objects. If I uncomment these three lines I can test if I have imported information from excel file correctly, and yes, that works just fine. So why am I getting empty DataGrid? It has right number of rows and only one column, that's ok, but there are no data in it. I used this line: Prikaz.ItemsSource = tData; to bind my objects list and DataGrid. Training is declared public so it should be present in DataGrid. What could be causing the problem?

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• Django's post_save signal behaves weirdly with models using multi-table inheritance

  - by hekevintran

  Django's post_save signal behaves weirdly with models using multi-table inheritance I am noticing an odd behavior in the way Django's post_save signal works when using a model that has multi-table inheritance. I have these two models: class Animal(models.Model): category = models.CharField(max_length=20) class Dog(Animal): color = models.CharField(max_length=10) I have a post save callback called echo_category: def echo_category(sender, **kwargs): print "category: '%s'" % kwargs['instance'].category post_save.connect(echo_category, sender=Dog) I have this fixture: [ { "pk": 1, "model": "animal.animal", "fields": { "category": "omnivore" } }, { "pk": 1, "model": "animal.dog", "fields": { "color": "brown" } } ] In every part of the program except for in the post_save callback the following is true: from animal.models import Dog Dog.objects.get(pk=1).category == u'omnivore' # True When I run syncdb and the fixture is installed, the echo_category function is run. The output from syncdb is: $ python manage.py syncdb --noinput Installing json fixture 'initial_data' from '~/my_proj/animal/fixtures'. category: '' Installed 2 object(s) from 1 fixture(s) The weird thing here is that the dog object's category attribute is an empty string. Why is it not 'omnivore' like it is everywhere else? As a temporary (hopefully) workaround I reload the object from the database in the post_save callback: def echo_category(sender, **kwargs): instance = kwargs['instance'] instance = sender.objects.get(pk=instance.pk) print "category: '%s'" % instance.category post_save.connect(echo_category, sender=Dog) This works but it is not something I like because I must remember to do it when the model inherits from another model and it must hit the database again. The other weird thing is that I must do instance.pk to get the primary key. The normal 'id' attribute does not work (I cannot use instance.id). I do not know why this is. Maybe this is related to the reason why the category attribute is not doing the right thing?

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• Why use SQL database?

  - by martinthenext

  I'm not quite sure stackoverflow is a place for such a general question, but let's give it a try. Being exposed to the need of storing application data somewhere, I've always used MySQL or sqlite, just because it's always done like that. As it seems like the whole world is using these databases, most of all software products, frameworks, etc. It is rather hard for a beginning developer like me to ask a question - why? Ok, say we have some object-oriented logic in our application, and objects are related to each other somehow. We need to map this logic to the storage logic, so we need relations between database objects too. This leads us to using relational database and I'm ok with that - to put it simple, our database rows sometimes will need to have references to other tables' rows. But why do use SQL language for interaction with such a database? SQL query is a text message. I can understand this is cool for actually understanding what it does, but isn't it silly to use text table and column names for a part of application that no one ever seen after deploynment? If you had to write a data storage from scratch, you would have never used this kind of solution. Personally, I would have used some 'compiled db query' bytecode, that would be assembled once inside a client application and passed to the database. And it surely would name tables and colons by id numbers, not ascii-strings. In the case of changes in table structure those byte queries could be recompiled according to new db schema, stored in XML or something like that. What are the problems of my idea? Is there any reason for me not to write it myself and to use SQL database instead?

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• Binding a WPF ComboBox to a different ItemsSource within a ListBox DataTemplate

  - by tjans

  I have a ListBox that contains a textbox and a combobox in its datatemplate: <ListBox Height="147" Margin="158,29,170,0" Name="PitcherListBox" VerticalAlignment="Top" ItemsSource="{Binding SomeCollectionOfObjects}" Background="Black"> <ListBox.ItemTemplate> <DataTemplate> <StackPanel Orientation="Horizontal"> <TextBox Text="{Binding Path=Name}" /> <ComboBox ItemsSource="{Binding LocalArrayOfIntsProperty}" /> </StackPanel> </DataTemplate> </ListBox.ItemTemplate> </ListBox> I want to bind the listbox to a collection of objects (which I've done successfully), but I want the combobox in the above datatemplate to have its itemssource set to a local property on the window (array of ints). I still want the combobox to have a two-way bind between its selected item and a property on the collection of objects... I have the following in code: PitcherListBox.DataContext = this; Basically in the end, I want the combobox within the listbox to have a different itemssource than the listbox itself. I can't seem to figure out how to change the ComboBox's ItemsSource in XAML. Can someone provide me some feedback? Thanks!

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• Solving problems involving more complex data structures with CUDA

  - by Nils

  So I read a bit about CUDA and GPU programming. I noticed a few things such that access to global memory is slow (therefore shared memory should be used) and that the execution path of threads in a warp should not diverge. I also looked at the (dense) matrix multiplication example, described in the programmers manual and the nbody problem. And the trick with the implementation seems to be the same: Arrange the calculation in a grid (which it already is in case of the matrix mul); then subdivide the grid into smaller tiles; fetch the tiles into shared memory and let the threads calculate as long as possible, until it needs to reload data from the global memory into shared memory. In case of the nbody problem the calculation for each body-body interaction is exactly the same (page 682): bodyBodyInteraction(float4 bi, float4 bj, float3 ai) It takes two bodies and an acceleration vectors. The body vector has four components it's position and the weight. When reading the paper, the calculation is understood easily. But what is if we have a more complex object, with a dynamic data structure? For now just assume that we have an object (similar to the body object presented in the paper) which has a list of other objects attached and the number of objects attached is different in each thread. How could I implement that without having the execution paths of the threads to diverge? I'm also looking for literature which explains how different algorithms involving more complex data structures can be effectively implemented in CUDA.

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• How to invalidate the OutputCache in a webfarm?

  - by Pure.Krome

  Hi folks, i've got a website that uses OutputCache attribute to cache pages. Works great. Now, I'm in the middle of R&D'ing scaling up this site to be in a web farm. Along with the usual suspects for webfarm pain ... I've noticed (pretty quickly/obviously) that the OutputCache from Server_A doesn't invalidate the OutputCache from Server_B .. if a try and invalidate a single server's OutputCache. This makes total sense - how can S_A 'tell' S_B to invalidate when they are physically 2 seperate machines, etc? So - what are our options? Velocity? I understand this will move the caching to a different layer .. which means that the final result (output) will always be required to be determined .. as opposed to the OutputCache whic remembers the final output content (yes, varby gives different versions, etc.. which is totally fine). So even though the poco or business objects are all sync'd, there's still that last rendering effort required (even if it's tiny .. compared to the effort to generate/sync business objects). So yeah .. not sure of the options here and what other people do?

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• Does WPF break an Entity Framework ObjectContext?

  - by David Veeneman

  I am getting started with Entity Framework 4, and I am getting ready to write a WPF demo app to learn EF4 better. My LINQ queries return IQueryable<T>, and I know I can drop those into an ObservableCollection<T> with the following code: IQueryable<Foo> fooList = from f in Foo orderby f.Title select f; var observableFooList = new ObservableCollection<Foo>(fooList); At that point, I can set the appropriate property on my view model to the observable collection, and I will get WPF data binding between the view and the view model property. Here is my question: Do I break the ObjectContext when I move my foo list to the observable collection? Or put another way, assuming I am otherwise handling my ObjectContext properly, will EF4 properly update the model (and the database)? The reason why I ask is this: NHibernate tracks objects at the collection level. If I move an NHibernate IList<T> to an observable collection, it breaks NHibernate's change tracking mechanism. That means I have to do some very complicated object wrapping to get NHibernate to work with WPF. I am looking at EF4 as a way to dispense with all that. So, to get EF4 working with WPF, is it as simple as dropping my IQueryable<T> results into an ObservableCollection<T>. Does that preserve change-tracking on my EDM entity objects? Thanks for your help.

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