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• AntFarm anti-pattern -- strategies to avoid, antidotes to help heal from

  - by alchemical

  I'm working on a 10 page web site with a database back-end. There are 500+ objects in use, trying to implement the MVP pattern in ASP.Net. I'm tracing the code-execution from a single-page, my finger has been on F-11 in Visual Studio for about 40 minutes, there seems to be no end, possibly 1000+ method calls for one web page! If it was just 50 objects that would be one thing, however, code execution snakes through all these objects just like millions of ants frantically woring in their giant dirt mound house, riddled with object tunnels. Hence, a new anti-pattern is born : AntFarm. AntFarm is also known as "OO-Madnes", "OO-Fever", OO-ADD, or simply design-pattern junkie. This is not the first time I've seen this, nor my associates at other companies. It seems that this style is being actively propogated, or in any case is a misunderstanding of the numerous OO/DP gospels going around... I'd like to introduce an anti-pattern to the anti-pattern: GST or "Get Stuff Done" AKA "Get Sh** done" AKA GRD (GetRDone). This pattern focused on just what it says, getting stuff done, in a simple way. I may try to outline it more in a later post, or please share your ideas on this antidote pattern. Anyway, I'm in the midst of a great example of AntFarm anti-pattern as I write (as a bonus, there is no documentation or comments). Please share you thoughts on how this anti-pattern has become so prevelant, how we can avoid it, and how can one undo or deal with this pattern in a live system one must work with!

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• relational data from xml

  - by Beta033

  Our problem is this, we have a relational database to store objects in tables. As any relational database could, several of these tables have multiple foreign keys pointing to other tables (all pretty normal stuff) We've been trying to identify a solution to allow export of this relational data, ideally, only 1 of the objects in the model, to some sort of file (xml, text, ??). So it wouldn't be simple enough to just export 1 table as data stored in other tables would contribute to the complete model of the object. Something like the following picture: Toward this, i've written a routine to export the structure by following the foreign key paths which exports something similar to the following. <Tables> <TableA PK="1", val1, val2, val3> <TableC PK="1", FK_A="1", Val1, val2, val3> <TableC PK="2", FK_A="1", val1, val2, val3> <TableB PK="1", FK_A="1", FK_C="1", val1, val2, val3> <TableB PK="2", FK_A="1", FK_C="2", val1, val2, val3> <TableD PK="1", FK_B="1", FK_C="1", val1> <TableD PK="2", FK_B="2", FK_C="1", val1> </Tables> However, given this structure, it cannot be placed into a heirarchial format (ie D2 is a child of C1 and B2; and B2 is a child of C2) Which in turn, makes my life very difficult when trying to identify a methodology to reimport (and reKey) these objects. Has anybody done anything like this? how do you do it? are there tools or documentation on how this is best accomplished? Thanks for your help.

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• Manditory read-only fields in django

  - by jamida

  I'm writing a test "grade book" application. The models.py file is shown below. class Student(models.Model): name = models.CharField(max_length=50) parent = models.CharField(max_length=50) def __unicode__(self): return self.name class Grade(models.Model): studentId = models.ForeignKey(Student) finalGrade = models.CharField(max_length=3) I'd like to be able to change the final grade for several students in a modelformset but for now I'm just trying one student at a time. I'm also trying to create a form for it that shows the student name as a field that can not be changed, the only thing that can be changed here is the finalGrade. So I used this trick to make the studentId read-only. class GradeROForm(ModelForm): studentId = forms.ModelChoiceField(queryset=Student.objects.all()) def __init__(self, *args, **kwargs): super(GradeROForm,self).__init__(*args, **kwargs) instance = getattr(self, 'instance', None) if instance and instance.id: self.fields['studentId'].widget.attrs['disabled']='disabled' def clean_studentId(self): instance = getattr(self,'instance',None) if instance: return instance.studentId else: return self.cleaned_data.get('studentId',None) class Meta: model=Grade And here is my view: def modifyGrade(request,student): student = Student.objects.get(name=student) mygrade = Grade.objects.get(studentId=student) if request.method == "POST": myform = GradeROForm(data=request.POST, instance=mygrade) if myform.is_valid(): grade = myform.save() info = "successfully updated %s" % grade.studentId else: myform=GradeROForm(instance=mygrade) return render_to_response('grades/modifyGrade.html',locals()) This displays the form like I expect, but when I hit "submit" I get a form validation error for the student field telling me this field is required. I'm guessing that, since the field is "disabled", the value is not being reported in the POST and for reasons unknown to me the instance isn't being used in its place. I'm a new Django/Python programmer, but quite experienced in other languages. I can't believe I've stumbled upon such a difficult to solve problem in my first significant django app. I figure I must be missing something. Any ideas?

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• How to access attributes using Nokogiri

  - by Liz

  I have a simple task of accessing the values of some attributes. Below is a simple script that uses Nokogiri::XML::Builder to create a simple xml doc. require 'nokogiri' builder = Nokogiri::XML::Builder.new(:encoding => 'UTF-8') do |xml| xml.Placement(:messageId => "392847-039820-938777", :system => "MOD", :version => "2.0") { xml.objects { xml.object(:myattribute => "99", :anotherattrib => "333") xml.nextobject_ '9387toot' xml.Entertainment "Last Man Standing" } } end puts builder.to_xml puts builder.root.attributes["messageId"] The results are below: <?xml version="1.0" encoding="UTF-8"?> <Placement messageId="392847-039820-938777" version="2.0" system="MOD"> <objects> <object anotherattrib="333" myattribute="99"/> <nextobject>9387toot</nextobject> <Entertainment>Last Man Standing</Entertainment> </objects> </Placement> C:/Ruby/lib/ruby/gems/1.8/gems/nokogiri-1.4.2-x86-mingw32/lib/nokogiri/xml/document.rb:178:in `add_child': Document already has a root node (RuntimeError) from C:/Ruby/lib/ruby/gems/1.8/gems/nokogiri-1.4.2-x86-mingw32/lib/nokogiri/xml/node.rb:455:in `parent=' from C:/Ruby/lib/ruby/gems/1.8/gems/nokogiri-1.4.2-x86-mingw32/lib/nokogiri/xml/builder.rb:358:in `insert' from C:/Ruby/lib/ruby/gems/1.8/gems/nokogiri-1.4.2-x86-mingw32/lib/nokogiri/xml/builder.rb:350:in `method_missing' from C:/Documents and Settings/etrojan/workspace/Lads/tryXPATH2.rb:15 The xml that is generated looks fine. However, my attempts to access attributes cause an error to be generated, "Document already has a root node". I don't understand why a puts statement would cause this error. Any suggestions would be greatly appreciated.

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• Login URL using authentication information in Django

  - by fuSi0N

  I'm working on a platform for online labs registration for my university. Login View [project views.py] from django.http import HttpResponse, HttpResponseRedirect, Http404 from django.shortcuts import render_to_response from django.template import RequestContext from django.contrib import auth def index(request): return render_to_response('index.html', {}, context_instance = RequestContext(request)) def login(request): if request.method == "POST": post = request.POST.copy() if post.has_key('username') and post.has_key('password'): usr = post['username'] pwd = post['password'] user = auth.authenticate(username=usr, password=pwd) if user is not None and user.is_active: auth.login(request, user) if user.get_profile().is_teacher: return HttpResponseRedirect('/teachers/'+user.username+'/') else: return HttpResponseRedirect('/students/'+user.username+'/') else: return render_to_response('index.html', {'msg': 'You don\'t belong here.'}, context_instance = RequestContext(request) return render_to_response('login.html', {}, context_instance = RequestContext(request)) def logout(request): auth.logout(request) return render_to_response('index.html', {}, context_instance = RequestContext(request)) URLS #========== PROJECT URLS ==========# urlpatterns = patterns('', (r'^media/(?P<path>.*)$', 'django.views.static.serve', {'document_root': settings.MEDIA_ROOT }), (r'^admin/', include(admin.site.urls)), (r'^teachers/', include('diogenis.teachers.urls')), (r'^students/', include('diogenis.students.urls')), (r'^login/', login), (r'^logout/', logout), (r'^$', index), ) #========== TEACHERS APP URLS ==========# urlpatterns = patterns('', (r'^(?P<username>\w{0,50})/', labs), ) The login view basically checks whether the logged in user is_teacher [UserProfile attribute via get_profile()] and redirects the user to his profile. Labs View [teachers app views.py] from django.http import HttpResponse, HttpResponseRedirect, Http404 from django.shortcuts import render_to_response from django.template import RequestContext from django.contrib.auth.decorators import user_passes_test from django.contrib.auth.models import User from accounts.models import * from labs.models import * def user_is_teacher(user): return user.is_authenticated() and user.get_profile().is_teacher @user_passes_test(user_is_teacher, login_url="/login/") def labs(request, username): q1 = User.objects.get(username=username) q2 = u'%s %s' % (q1.last_name, q1.first_name) q2 = Teacher.objects.get(name=q2) results = TeacherToLab.objects.filter(teacher=q2) return render_to_response('teachers/labs.html', {'results': results}, context_instance = RequestContext(request)) I'm using @user_passes_test decorator for checking whether the authenticated user has the permission to use this view [labs view]. The problem I'm having with the current logic is that once Django authenticates a teacher user he has access to all teachers profiles basically by typing the teachers username in the url. Once a teacher finds a co-worker's username he has direct access to his data. Any suggestions would be much appreciated.

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• Backend raising (INotify)PropertyChanged events to all connected clients?

  - by Jörg Battermann

  One of our 'frontend' developers keeps requesting from us backend developers that the backend notifies all connected clients (it's a client/server environment) of changes to objects. As in: whenever one user makes a change, all other connected clients must be notified immediately of the change. At the moment our architecture does not have a notification system of that kind and we don't have a sort of pub/sub model for explicitly chosen objects (e.g. the one the frontend is currently implementing).. which would make sense in such a usecase imho, but obviously requires extra implementation. However, I thought frontends typically check for locks for concurrently existing user changes on the same object and rather pull for changes / load on demand and in the background rather than the backend pushing all changes to all clients for all objects constantly.. which seems rather excessive to me. However, it's being argumented that e.g. the MS Entity Framework does in fact publish (INotify)PropertyChanged not only for local changes, but for all such changes including other client connections, but I have found no proof or details regarding this. Can anyone shed some light into this? Do other e.g. ORMs etc provide broadcasted (INotify)PropertyChanged events on entities?

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• What does this svn2git error mean?

  - by Hisham

  I am trying to import my repository from svn to git using svn2git, but it seems like it's failing when it hits a branch. What's the problem? Found possible branch point: https://s.aaa.com/repo/trunk/project => https://s.aaa.com/repo/branches/project-beta1.0, 128 Use of uninitialized value in substitution (s///) at /opt/local/libexec/git-core/git-svn line 1728. Use of uninitialized value in concatenation (.) or string at /opt/local/libexec/git-core/git-svn line 1728. refs/remotes/trunk: 'https://s.aaa.com/repo' not found in '' Running command: git branch -l --no-color * master Running command: git branch -r --no-color trunk Running command: git checkout trunk Note: checking out 'trunk'. You are in 'detached HEAD' state. You can look around, make experimental changes and commit them, and you can discard any commits you make in this state without impacting any branches by performing another checkout. If you want to create a new branch to retain commits you create, you may do so (now or later) by using -b with the checkout command again. Example: git checkout -b new_branch_name HEAD is now at f4e6268... Changing svn repository in cap files Running command: git branch -D master Deleted branch master (was f4e6268). Running command: git checkout -f -b master Switched to a new branch 'master' Running command: git gc Counting objects: 450, done. Delta compression using up to 2 threads. Compressing objects: 100% (368/368), done. Writing objects: 100% (450/450), done. Total 450 (delta 63), reused 450 (delta 63)

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• Core data and @unionOfSets

  - by KevinD

  Im having trouble using the @unionOfSets on my core-data objects. NSLog(@"%@", [NSApp valueForKeyPath:@"delegate.mainWindowController.sidebarViewController.arrayController.selection.list.listElement"]); Prints the set of listElements as expected 2010-03-24 18:11:15.844 Pirouette[7459:80f] Relationship objects for {( (entity: PRPlaylistElement; id: 0x10a71b0 ; data: ), (entity: PRPlaylistElement; id: 0x10ac7d0 ; data: ), (entity: PRPlaylistElement; id: 0x10acf60 ; data: ), (entity: PRPlaylistElement; id: 0x10a6850 ; data: ) However when I try to get the set of file objects for each of the list elements. NSLog(@"%@", [NSApp valueForKeyPath:@"delegate.mainWindowController.sidebarViewController.arrayController.selection.list.listElement.@unionOfArrays.file"]); I get the following error 2010-03-24 18:16:45.843 Pirouette[7505:80f] An uncaught exception was raised 2010-03-24 18:16:45.844 Pirouette[7505:80f] [<NSCFSet 0x10415e0> valueForKeyPath:]: this class does not implement the unionOfArrays operation. 2010-03-24 18:16:45.847 Pirouette[7505:80f] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '[<NSCFSet 0x10415e0> valueForKeyPath:]: this class does not implement the unionOfArrays operation.' Confused because I thought calling to-many relationships in core-data were NSSets.

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• How to do fixed price quote for design sessions?

  - by Shaul

  Normally when I do a system for a customer, I do design sessions on an hourly rate and then come out with a fixed price quotation for the full system development. Now this customer has thrown me a curveball: he doesn't want an hourly rate for design, either - he wants me to quote a fixed price to do all the design, too! Not that he's trying to cheap out, but he doesn't want to be in a situation where the longer design stretches out, the more he has to pay - and I can understand that. For the business layer it was actually not too difficult to work with this, because from his original functional spec I got a good idea of what the core business objects were, and in our design agreement I defined several objects which would be covered by a fixed design price; if any new non-trivial objects were discovered, they would be considered variances, and those would be billed on an hourly rate. So far so good. But when it comes to the UI, things start getting a lot more woolly. How many screens will there be? Don't know yet. What's going to be on each screen? Don't know yet. All we know is that it's a "dashboard" type of system, and there will be a lot of visual reporting involved e.g. gauges, graphs, etc. So maybe make it fixed price per screen design? Not a great definition; he might say that everything is going to be on one screen. Maybe a price per "visual report" design, including ability to slice & dice? Again not so easy - it might be that the entire system is just one report, and all the intelligence is going to go into how to present that segmentation. Anyone have any ideas how to do a fixed price quotation for a UI design like this?

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• The cost of passing by shared_ptr

  - by Artem

  I use std::tr1::shared_ptr extensively throughout my application. This includes passing objects in as function arguments. Consider the following: class Dataset {...} void f( shared_ptr< Dataset const > pds ) {...} void g( shared_ptr< Dataset const > pds ) {...} ... While passing a dataset object around via shared_ptr guarantees its existence inside f and g, the functions may be called millions of times, which causes a lot of shared_ptr objects being created and destroyed. Here's a snippet of the flat gprof profile from a recent run: Each sample counts as 0.01 seconds. % cumulative self self total time seconds seconds calls s/call s/call name 9.74 295.39 35.12 2451177304 0.00 0.00 std::tr1::__shared_count::__shared_count(std::tr1::__shared_count const&) 8.03 324.34 28.95 2451252116 0.00 0.00 std::tr1::__shared_count::~__shared_count() So, ~17% of the runtime was spent on reference counting with shared_ptr objects. Is this normal? A large portion of my application is single-threaded and I was thinking about re-writing some of the functions as void f( const Dataset& ds ) {...} and replacing the calls shared_ptr< Dataset > pds( new Dataset(...) ); f( pds ); with f( *pds ); in places where I know for sure the object will not get destroyed while the flow of the program is inside f(). But before I run off to change a bunch of function signatures / calls, I wanted to know what the typical performance hit of passing by shared_ptr was. Seems like shared_ptr should not be used for functions that get called very often. Any input would be appreciated. Thanks for reading. -Artem

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• Need advice on OOP philosophy

  - by David Jenings

  I'm trying to get the wheels turning on a large project in C#. My previous experience is in Delphi, where by default every form was created at applicaton startup and form references where held in (gasp) global variables. So I'm trying to adapt my thinking to a 100% object oriented environment, and my head is spinning just a little. My app will have a large collection of classes Most of these classes will only really need one instance. So I was thinking: static classes. I'm not really sure why, but much of what I've read here says that if my class is going to hold a state, which I take to mean any property values at all, I should use a singleton structure instead. Okay. But there are people out there who for reasons that escape me, think that singletons are evil too. None of these classes is in danger of being used anywhere except in this program. So they could certainly work fine as regular objects (vs singletons or static classes) Then there's the issue of interaction between objects. I'm tempted to create a Global class full of public static properties referencing the single instances of many of these classes. I've also considered just making them properties (static or instance, not sure which) of the MainForm. Then I'd have each of my classes be aware of the MainForm as Owner. Then the various objects could refer to each other as Owner.Object1, Owner.Object2, etc. I fear I'm running out of electronic ink, or at least taxing the patience of anyone kind enough to have stuck with me this long. I hope I have clearly explained my state of utter confusion. I'm just looking for some advice on best practices in my situation. All input is welcome and appreciated. Thanks in advance, David Jennings

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• How can I write reusable Javascript?

  - by RenderIn

  I've started to wrap my functions inside of Objects, e.g.: var Search = { carSearch: function(color) { }, peopleSearch: function(name) { }, ... } This helps a lot with readability, but I continue to have issues with reusabilty. To be more specific, the difficulty is in two areas: Receiving parameters. A lot of times I will have a search screen with multiple input fields and a button that calls the javascript search function. I have to either put a bunch of code in the onclick of the button to retrieve and then martial the values from the input fields into the function call, or I have to hardcode the HTML input field names/IDs so that I can subsequently retrieve them with Javascript. The solution I've settled on for this is to pass the field names/IDs into the function, which it then uses to retrieve the values from the input fields. This is simple but really seems improper. Returning values. The effect of most Javascript calls tends to be one in which some visual on the screen changes directly, or as a result of another action performed in the call. Reusability is toast when I put these screen-altering effects at the end of a function. For example, after a search is completed I need to display the results on the screen. How do others handle these issues? Putting my thinking cap on leads me to believe that I need to have an page-specific layer of Javascript between each use in my application and the generic methods I create which are to be used application-wide. Using the previous example, I would have a search button whose onclick calls a myPageSpecificSearchFunction, in which the search field IDs/names are hardcoded, which marshals the parameters and calls the generic search function. The generic function would return data/objects/variables only, and would not directly read from or make any changes to the DOM. The page-specific search function would then receive this data back and alter the DOM appropriately. Am I on the right path or is there a better pattern to handle the reuse of Javascript objects/methods?

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• GeoDjango: Exceptions for basic geographic queries

  - by omat

  I am having problems with geographic queries with GeoDjango running on SpatiaLite on my development environment. from django.contrib.gis.db import models class Test(models.Model): poly = models.PolygonField() point = models.PointField() geom = models.GeometryField() objects = models.GeoManager() Testing via shell: >>> from geotest.models import Test >>> from django.contrib.gis.geos import GEOSGeometry >>> >>> point = GEOSGeometry("POINT(0 0)") >>> point <Point object at 0x105743490> >>> poly = GEOSGeometry("POLYGON((0 0, 0 1, 1 1, 1 0, 0 0))") >>> poly <Polygon object at 0x105743370> >>> With these definitions, lets try some basic geographic queries. First contains: >>> Test.objects.filter(point__within=poly) Assertion failed: (0), function appendGeometryTaggedText, file WKTWriter.cpp, line 228. Abort trap And the django shell dies. And with within: >>> Test.objects.filter(poly__contains=point) GEOS_ERROR: Geometry must be a Point or LineString Traceback (most recent call last): ... GEOSException: Error encountered checking Coordinate Sequence returned from GEOS C function "GEOSGeom_getCoordSeq_r". >>> Other combinations also cause a variety of exceptions. I must be missing something obvious as these are very basic. Any ideas?

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• Variant datatype library for C

  - by Joey Adams

  Is there a decent open-source C library for storing and manipulating dynamically-typed variables (a.k.a. variants)? I'm primarily interested in atomic values (int8, int16, int32, uint, strings, blobs, etc.), while JSON-style arrays and objects as well as custom objects would also be nice. A major case where such a library would be useful is in working with SQL databases. The most obvious feature of such a library would be a single type for all supported values, e.g.: struct Variant { enum Type type; union { int8_t int8_; int16_t int16_; // ... }; }; Other features might include converting Variant objects to/from C structures (using a binding table), converting values to/from strings, and integration with an existing database library such as SQLite. Note: I do not believe this is question is a duplicate of http://stackoverflow.com/questions/649649/any-library-for-generic-datatypes-in-c , which refers to "queues, trees, maps, lists". What I'm talking about focuses more on making working with SQL databases roughly as smooth as working with them in interpreted languages.

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• JAXB - Beans to XSD or XSD to beans?

  - by bajafresh4life

  I have an existing data model. I would like to express this data model in terms of XML. It looks like I have two options if I'm to use JAXB: Create an XSD that mirrors my data model, and use xjc to create binding objects. Marshalling and unmarshalling will involve creating a "mapping" class that would take my existing data objects and map them to the objects that xjc created. For example, in my data model I have a Doc class, and JAXB would create another Doc class with basically the same exact fields, and I would have to map from my Doc class to xjc's Doc class. Annotate my existing data model with JAXB annotations, and use schemagen to generate an XSD from my annotated classes. I can see advantanges and disadvantages of both approaches. It seems that most people using JAXB start with the XSD file. It makes sense that the XSD should be the gold standard truth, since it expresses the data model in a truly cross-platform way. I'm inclined to start with the XSD first, but it seems icky that I have to write and maintain a separate mapping class that shuttles data in between my world and JAXB world. Any recommendations?

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• Linq to sql DataContext cannot set load options after results been returned

  - by David Liddle

  I have two tables A and B with a one-to-many relationship respectively. On some pages I would like to get a list of A objects only. On other pages I would like to load A with objects in B attached. This can be handled by setting the load options DataLoadOptions options = new DataLoadOptions(); options.LoadWith<A>(a => a.B); dataContext.LoadOptions = options; The trouble occurs when I first of all view all A's with load options, then go to edit a single A (do not use load options), and after edit return to the previous page. I understand why the error is occurring but not sure how to best get round this problem. I would like the DataContext to be loaded up per request. I thought I was achieving this by using StructureMap to load up my DataContext on a per request basis. This is all part of an n-tier application where my Controllers call Services which in turn call Repositories. ForRequestedType<MyDataContext>() .CacheBy(InstanceScope.PerRequest) .TheDefault.Is.Object(new MyDataContext()); ForRequestedType<IAService>() .TheDefault.Is.OfConcreteType<AService>(); ForRequestedType<IARepository>() .TheDefault.Is.OfConcreteType<ARepository>(); Here is a brief outline of my Repository public class ARepository : IARepository { private MyDataContext db; public ARepository(MyDataContext context) { db = context; } public void SetLoadOptions(DataLoadOptions options) { db.LoadOptions = options; } public IQueryable<A> Get() { return from a in db.A select a; } So my ServiceLayer, on View All, sets the load options and then gets all A's. On editing A my ServiceLayer should spin up a new DataContext and just fetch a list of A's. When sql profiling, I can see that when I go to the Edit page it is requesting A with B objects.

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• Django Forms - change the render multiple select widget

  - by John

  Hi, In my model I have a manytomany field mentors = models.ManyToManyField(MentorArea, verbose_name='Areas', blank=True) In my form I want to render this as: drop down box with list of all MentorArea objects which has not been associated with the object. Next to that an add button which will call a javascript function which will add it to the object. Then under that a ul list which has each selected MentorArea object with a x next to it which again calls a javascript function which will remove the MentorArea from the object. I know that to change how an field element is rendered you create a custom widget and override the render function and I have done that to create the add button. class AreaWidget(widgets.Select): def render(self, name, value, attrs=None, choices=()): jquery = u''' <input class="button def" type="button" value="Add" id="Add Area" />''' output = super(AreaWidget, self).render(name, value, attrs, choices) return output + mark_safe(jquery) However I don't know how to list the currently selected ones underneath as a list. Can anyone help me? Also what is the best way to filter down the list so that it only shows MentorArea objects which have not been added? I currently have the field as mentors = forms.ModelMultipleChoiceField(queryset=MentorArea.objects.all(), widget = AreaWidget, required=False) but this shows all mentors no matter if they have been added or not. Thanks

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• How to deal with recursive dependencies between static libraries using the binutils linker?

  - by Jack Lloyd

  I'm porting an existing system from Windows to Linux. The build is structured with multiple static libraries. I ran into a linking error where a symbol (defined in libA) could not be found in an object from libB. The linker line looked like g++ test_obj.o -lA -lB -o test The problem of course being that by the time the linker finds it needs the symbol from libA, it has already passed it by, and does not rescan, so it simply errors out even though the symbol is there for the taking. My initial idea was of course to simply swap the link (to -lB -lA) so that libA is scanned afterwards, and any symbols missing from libB that are in libA are picked up. But then I find there is actually a recursive dependency between libA and libB! I'm assuming the Visual C++ linker handles this in some way (does it rescan by default?). Ways of dealing with this I've considered: Use shared objects. Unfortunately this is undesirable from the perspective of requiring PIC compliation (this is performance sensitive code and losing %ebx to hold the GOT would really hurt), and shared objects aren't needed. Build one mega ar of all of the objects, avoiding the problem. Restructure the code to avoid the recursive dependency (which is obviously the Right Thing to do, but I'm trying to do this port with minimal changes). Do you have other ideas to deal with this? Is there some way I can convince the binutils linker to perform rescans of libraries it has already looked at when it is missing a symbol?

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• Implementing the ‘defer’ statement from Go in Objective-C?

  - by zoul

  Hello! Today I read about the defer statement in the Go language: A defer statement pushes a function call onto a list. The list of saved calls is executed after the surrounding function returns. Defer is commonly used to simplify functions that perform various clean-up actions. I thought it would be fun to implement something like this in Objective-C. Do you have some idea how to do it? I thought about dispatch finalizers, autoreleased objects and C++ destructors. Autoreleased objects: @interface Defer : NSObject {} + (id) withCode: (dispatch_block_t) block; @end @implementation Defer - (void) dealloc { block(); [super dealloc]; } @end #define defer(__x) [Defer withCode:^{__x}] - (void) function { defer(NSLog(@"Done")); … } Autoreleased objects seem like the only solution that would last at least to the end of the function, as the other solutions would trigger when the current scope ends. On the other hand they could stay in the memory much longer, which would be asking for trouble. Dispatch finalizers were my first thought, because blocks live on the stack and therefore I could easily make something execute when the stack unrolls. But after a peek in the documentation it doesn’t look like I can attach a simple “destructor” function to a block, can I? C++ destructors are about the same thing, I would create a stack-based object with a block to be executed when the destructor runs. This would have the ugly disadvantage of turning the plain .m files into Objective-C++? I don’t really think about using this stuff in production, I’m just interested in various solutions. Can you come up with something working, without obvious disadvantages? Both scope-based and function-based solutions would be interesting.

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• detecting double free object, release or not release ...

  - by mongeta

  Hello, If we have this code in our interface .h file: NSString *fieldNameToStoreModel; NSFetchedResultsController *fetchedResultsController; NSManagedObjectContext *managedObjectContext; DataEntered *dataEntered; In our implementation file .m we must have: - (void)dealloc { [fieldNameToStoreModel release]; [fetchedResultsController release]; [managedObjectContext release]; [dataEntered release]; [super dealloc]; } The 4 objects are assigned from a previous UIViewController, like this: UIViewController *detailViewController; detailViewController = [[CarModelSelectViewController alloc] initWithStyle:UITableViewStylePlain]; ((CarModelSelectViewController *)detailViewController).dataEntered = self.dataEntered; ((CarModelSelectViewController *)detailViewController).managedObjectContext = self.managedObjectContext; ((CarModelSelectViewController *)detailViewController).fieldNameToStoreModel = self.fieldNameToStoreModel; [self.navigationController pushViewController:detailViewController animated:YES]; [detailViewController release]; The objects that now live in the new UIViewController, are the same as the previous UIViewController, and I can't release them in the new UIViewController ? The problems is that sometimes, my app crashes when I leave the new UIViewController and go to the previous one, not always. Normally the error that I'm getting is a double free object. I've used the malloc_error_break but I'm still not sure wich object is. Sometimes I can go from the previous UIViewController to the next one and come back 4 or 5 times, and the double free object appears. If I don't release any object, all is working and Instruments says that there are no memory leaks ... So, the final question, should I release those objects here or not ? Thanks, m.

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• Django access data passed to form

  - by realshadow

  Hey, I have got a choiceField in my form, where I display filtered data. To filter the data I need two arguments. The first one is not a problem, because I can take it directly from an object, but the second one is dynamically generated. Here is some code: class GroupAdd(forms.Form): def __init__(self, *args, **kwargs): self.pid = kwargs.pop('parent_id', None) super(GroupAdd, self).__init__(*args, **kwargs) parent_id = forms.IntegerField(widget=forms.HiddenInput) choices = forms.ChoiceField( choices = [ [group.node_id, group.name] for group in Objtree.objects.filter( type_id = ObjtreeTypes.objects.values_list('type_id').filter(name = 'group'), parent_id = 50 ).distinct()] + [[0, 'Add a new one'] ], widget = forms.Select( attrs = { 'id': 'group_select' } ) ) I would like to change the parent_id that is passed into the Objtree.objects.filter. As you can see I tried in the init function, as well with kwargs['initial']['parent_id'] and then calling it with self, but that doesnt work, since its out of scope... it was pretty much my last effort. I need to acccess it either trough the initial parameter or directly trough parent_id field, since it already holds its value (passed trough initial). Any help is appreciated, as I am running out of ideas.

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• Is There a Time at which to ignore IDisposable.Dispose?

  - by Mystagogue

  Certainly we should call Dipose() on IDisposable objects as soon as we don't need them (which is often merely the scope of a "using" statement). If we don't take that precaution then bad things, from subtle to show-stopping, might happen. But what about "the last moment" before process termination? If your IDisposables have not been explicitly disposed by that point in time, isn't it true that it no longer matters? I ask because unmanaged resources, beneath the CLR, are represented by kernel objects - and the win32 process termination will free all unmanaged resources / kernel objects anyway. Said differently, no resources will remain "leaked" after the process terminates (regardless if Dispose() was called on lingering IDisposables). Can anyone think of a case where process termination would still leave a leaked resource, simply because Dispose() was not explicitly called on one or more IDisposables? Please do not misunderstand this question: I am not trying to justify ignoring IDisposables. The question is just technical-theoretical. EDIT: And what about mono running on Linux? Is process termination there just as "reliable" at cleaning up unmanaged "leaks?"

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• Aren't Information Expert / Tell Don't Ask at odds with Single Responsibility Principle?

  - by moffdub

  It is probably just me, which is why I'm asking the question. Information Expert, Tell Don't Ask, and SRP are often mentioned together as best practices. But I think they are at odds. Here is what I'm talking about: Code that favors SRP but violates Tell Don't Ask, Info Expert: Customer bob = ...; // TransferObjectFactory has to use Customer's accessors to do its work, // violates Tell Don't Ask CustomerDTO dto = TransferObjectFactory.createFrom(bob); Code that favors Tell Don't Ask / Info Expert but violates SRP: Customer bob = ...; // Now Customer is doing more than just representing the domain concept of Customer, // violates SRP CustomerDTO dto = bob.toDTO(); If they are indeed at odds, that's a vindication of my OCD. Otherwise, please fill me in on how these practices can co-exist peacefully. Thank you. Edit: someone wants a definition of the terms - Information Expert: objects that have the data needed for the operation should host the operation Tell Don't Ask: don't ask objects for data in order to do work; tell the objects to do the work Single Responsibility Principle: each object should have a narrowly defined responsibility

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• Silverlight Data Access - how to keep the gruntwork on the server

  - by akaphenom

  What technologies are used / recommended for HTTP Rpc Calls from Silverlight. My Server Side stack is JBoss (servlets / json_rpc [jabsorb]), and we have a ton of business logic (object creation, validation, persistence, server side events) in place that I still want to take advantage of. This is our first attempt at bringing an applet style ria to our product, and ideally we keep both HTML and Silverlight versions. For better or worse the powers that be have pushed us down the silverlight path, and while flex / java fx / silverlight is an interesting debate, that question is removed from the equation. We just have to find a way to get silverlight to behave with our classes. Should I be defining .NET Class representation of our JSON objects and the methodology to serialize / deserialize access to those objects? IE "blah.com/dispenseRpc?servlet=xxxx&p1=blah&p2=blahblah creating functions that invoke the web request and convert the incomming response string to objects? Another way would be to reverse engineer the .NET wcf(or whatever) communications and implement the handler on the Java side that invokes the correct server side code and returns what .NET expects back. But that sounds much trickier. T

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• Requested Service not found - .NET Remoting

  - by bharat

  I am Getting this exception System.Runtime.Remoting.RemotingException occurred Message="Object '/55337266_9751_4f58_8446_c54ff254222e/rkutlpt5hvsxipmzhb+jkqyl_98.rem' has been disconnected or does not exist at the server." Source="mscorlib" StackTrace: Server stack trace: at System.Runtime.Remoting.Channels.ChannelServices.CheckDisconnectedOrCreateWellKnownObject(IMessage msg) at System.Runtime.Remoting.Channels.ChannelServices.DispatchMessage(IServerChannelSinkStack sinkStack, IMessage msg, IMessage& replyMsg) Exception rethrown at [0]: at System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage reqMsg, IMessage retMsg) at System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(MessageData& msgData, Int32 type) at Common.Interface.Repository.NA.INRR.GetNRun(Int32 NetworkRunId) at Module.NA.ViewModel.NRDViewModel.get_AS() InnerException: Most of the times i am getting this exception this is my remotingDomain method string tcpURL; TcpChannel channel; channel = new TcpChannel(); ChannelServices.RegisterChannel(channel, false); //-- // Remote domain objects //-- tcpURL = string.Format("tcp://{0}:{1}/DomainComposition", ServerName, TcpPort); RemotingConfiguration.RegisterWellKnownClientType(typeof(DomainComposition), tcpURL); //-- // Remote repository objects //-- tcpURL = string.Format("tcp://{0}:{1}/RepositoryComposition", ServerName, TcpPort); RemotingConfiguration.RegisterWellKnownClientType(typeof(RepositoryComposition), tcpURL); //-- // Remote utility objects //-- tcpURL = string.Format("tcp://{0}:{1}/UtilityComposition", ServerName, TcpPort); RemotingConfiguration.RegisterWellKnownClientType(typeof(UtilityComposition), tcpURL); this.Domain = new DomainComposition(); this.Repository = new RepositoryComposition(); this.Utility = new UtilityComposition(); How to Check if the object is disconnect then re initiate the service

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