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• General advice and guidelines on how to properly override object.GetHashCode()

  - by Svish

  According to MSDN, a hash function must have the following properties: If two objects compare as equal, the GetHashCode method for each object must return the same value. However, if two objects do not compare as equal, the GetHashCode methods for the two object do not have to return different values. The GetHashCode method for an object must consistently return the same hash code as long as there is no modification to the object state that determines the return value of the object's Equals method. Note that this is true only for the current execution of an application, and that a different hash code can be returned if the application is run again. For the best performance, a hash function must generate a random distribution for all input. I keep finding myself in the following scenario: I have created a class, implemented IEquatable<T> and overridden object.Equals(object). MSDN states that: Types that override Equals must also override GetHashCode ; otherwise, Hashtable might not work correctly. And then it usually stops up a bit for me. Because, how do you properly override object.GetHashCode()? Never really know where to start, and it seems to be a lot of pitfalls. Here at StackOverflow, there are quite a few questions related to GetHashCode overriding, but most of them seems to be on quite particular cases and specific issues. So, therefore I would like to get a good compilation here. An overview with general advice and guidelines. What to do, what not to do, common pitfalls, where to start, etc. I would like it to be especially directed at C#, but I would think it will work kind of the same way for other .NET languages as well(?). I think maybe the best way is to create one answer per topic with a quick and short answer first (close to one-liner if at all possible), then maybe some more information and end with related questions, discussions, blog posts, etc., if there are any. I can then create one post as the accepted answer (to get it on top) with just a "table of contents". Try to keep it short and concise. And don't just link to other questions and blog posts. Try to take the essence of them and then rather link to source (especially since the source could disappear. Also, please try to edit and improve answers instead of created lots of very similar ones. I am not a very good technical writer, but I will at least try to format answers so they look alike, create the table of contents, etc. I will also try to search up some of the related questions here at SO that answers parts of these and maybe pull out the essence of the ones I can manage. But since I am not very stable on this topic, I will try to stay away for the most part :p

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• display MultiPolygonField data on Geodjango/OpenLayers

  - by Markos Gogoulos

  Hi all, I'm a Geodjango novice and would like to get some help on the following: I have a MultiPolygonField field, for a GeoDjango application, and would like to display it on my view as cool as it gets displayed on django admin Say for example I have def index(request): "Index,main view" border = WorldBorders.objects.get(name='Italy') return render_to_response('world/index.html', {'user': request.user, 'border': border}, context_instance=RequestContext(request)) then on world/index.html, what is the way to display the border, as it would be on django admin? Thanks in advance for all replies!

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• Convert to list after Cast<T>

  - by Timmie Sarjanen

  Hi, I need to convert an IQueryable to List(is it possible to convert to IList?). There had not been an problem if it was not that i need to Cast because I have interfaces to my objects. I've tried most things but for some reason I must run Cast first and then ToList() which generates System.NullReferenceException. How do I solve this? public IQueryable GetPhrases() { return (from r in _repository.All<Phrase>() select r).Cast<IPhrase() }

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• How can I reliably check client identity whilst making DCOM calls to a C# .Net 3.5 Server?

  - by pionium

  Hi, I have an old Win32 C++ DCOM Server that I am rewriting to use C# .Net 3.5. The client applications sit on remote XP machines and are also written in C++. These clients must remain unchanged, hence I must implement the interfaces on new .Net objects. This has been done, and is working successfully regarding the implementation of the interfaces, and all of the calls are correctly being made from the old clients to the new .Net objects. However, I'm having problems obtaining the identity of the calling user from the DCOM Client. In order to try to identify the user who instigated the DCOM call, I have the following code on the server... [DllImport("ole32.dll")] static extern int CoImpersonateClient(); [DllImport("ole32.dll")] static extern int CoRevertToSelf(); private string CallingUser { get { string sCallingUser = null; if (CoImpersonateClient() == 0) { WindowsPrincipal wp = System.Threading.Thread.CurrentPrincipal as WindowsPrincipal; if (wp != null) { WindowsIdentity wi = wp.Identity as WindowsIdentity; if (wi != null && !string.IsNullOrEmpty(wi.Name)) sCallingUser = wi.Name; } if (CoRevertToSelf() != 0) ReportWin32Error("CoRevertToSelf"); } else ReportWin32Error("CoImpersonateClient"); return sCallingUser; } } private static void ReportWin32Error(string sFailingCall) { Win32Exception ex = new Win32Exception(); Logger.Write("Call to " + sFailingCall + " FAILED: " + ex.Message); } When I get the CallingUser property, the value returned the first few times is correct and the correct user name is identified, however, after 3 or 4 different users have successfully made calls (and it varies, so I can't be more specific), further users seem to be identified as users who had made earlier calls. What I have noticed is that the first few users have their DCOM calls handled on their own thread (ie all calls from a particular client are handled by a single unique thread), and then subsequent users are being handled by the same threads as the earlier users, and after the call to CoImpersonateClient(), the CurrentPrincipal matches that of the initial user of that thread. To Illustrate: User Tom makes DCOM calls which are handled by thread 1 (CurrentPrincipal correctly identifies Tom) User Dick makes DCOM calls which are handled by thread 2 (CurrentPrincipal correctly identifies Dick) User Harry makes DCOM calls which are handled by thread 3 (CurrentPrincipal correctly identifies Harry) User Bob makes DCOM calls which are handled by thread 3 (CurrentPrincipal incorrectly identifies him as Harry) As you can see in this illustration, calls from clients Harry and Bob are being handled on thread 3, and the server is identifying the calling client as Harry. Is there something that I am doing wrong? Are there any caveats or restrictions on using Impersonations in this way? Is there a better or different way that I can RELIABLY achieve what I am trying to do? All help would be greatly appreciated. Regards Andrew

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• singleton vs factory?

  - by fayer

  i've got 3 Log classes that all implements iLog interface: DatabaseLog FileLog ScreenLog there can only be one instance of them. initially i though of using single pattern for each class but then i thought why not use a factory for instantiation instead, cause then i wont have to create single pattern for each one of them and for all future Log classes. and maybe someone would want them as multiple objects in the future. so my questions is: should i use factory or singleton pattern here?

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• Using EHCache with ASP.NET?

  - by frankadelic

  I have heard of .NET APIs for memcached. Is there any equivalent for EHCache? I am envisioning a cluster of linux machines running EHCache, serving cached objects for a farm of ASP.NET webservers. Is this practical? Can this be done without installing Java on the ASP.NET servers?

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• WPF Timeline Control

  - by Sam Tr

  Hi, I am looking for a WPF Timeline User Control. I have checked out Blendables Timeline and Animated Timeline control from IdentityMine, but it is rather basic and buggy. I am looking for a timeline control that is similar to the MIT Similie timeline. http://www.simile-widgets.org/timeline/ What i need to be able to do is add interactive objects to the timeline, for example video, images, etc. Any ideas? Cheers

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• Is String.toLowerCase() preserving original string length?

  - by MicSim

  Assume two Java String objects String str = "<my string>"; String strLower = str.toLowerCase(); Is it then true that for every value of <my string> (str.length() == strLower.length()) evaluates to true? So, does String.toLowerCase() preserve original string length for any value of String?

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• Copying contents of a model

  - by Hulk

  If there exists an old data of a model say , query=Emp.objects.filter(pk=profile.id) Is there a easier way to copy the same values into the same model again.. Now that the id will be different so.. I have this requirement. Thanks..

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• Django disable editing (but allow adding) in TabularInline view

  - by VoteyDisciple

  I want to disable editing ALL objects within a particular TabularInline instance, while still allowing additions and while still allowing editing of the parent model. I have this trivial setup: class SuperviseeAdmin(admin.TabularInline): model = Supervisee class SupervisorAdmin(admin.ModelAdmin): inlines = [SuperviseeAdmin] admin.site.register(Supervisor, SupervisorAdmin) I have tried adding a has_change_permission function to SuperviseeAdmin that returns False unconditionally, but it had no effect. I have tried setting actions = None in SuperviseeAdmin but it had no effect. What might I be overlooking that could get this to work?

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• Reflection - SetValue of array within class?

  - by Jaymz87

  OK, I've been working on something for a while now, using reflection to accomplish a lot of what I need to do, but I've hit a bit of a stumbling block... I'm trying to use reflection to populate the properties of an array of a child property... not sure that's clear, so it's probably best explained in code: Parent Class: Public Class parent Private _child As childObject() Public Property child As childObject() Get Return _child End Get Set(ByVal value As child()) _child = value End Set End Property End Class Child Class: Public Class childObject Private _name As String Public Property name As String Get Return _name End Get Set(ByVal value As String) _name = value End Set End Property Private _descr As String Public Property descr As String Get Return _descr End Get Set(ByVal value As String) _descr = value End Set End Property End Class So, using reflection, I'm trying to set the values of the array of child objects through the parent object... I've tried several methods... the following is pretty much what I've got at the moment (I've added sample data just to keep things simple): Dim Results(1) As String Results(0) = "1,2" Results(1) = "2,3" Dim parent As New parent Dim child As childObject() = New childObject() {} Dim PropInfo As PropertyInfo() = child.GetType().GetProperties() Dim i As Integer = 0 For Each res As String In Results Dim ResultSet As String() = res.Split(",") ReDim child(i) Dim j As Integer = 0 For Each PropItem As PropertyInfo In PropInfo PropItem.SetValue(child, ResultSet(j), Nothing) j += 1 Next i += 1 Next parent.child = child This fails miserably on PropItem.SetValue with ArgumentException: Property set method not found. Anyone have any ideas? @Jon :- Thanks, I think I've gotten a little further, by creating individual child objects, and then assigning them to an array... The issue is now trying to get that array assigned to the parent object (using reflection). It shouldn't be difficult, but I think the problem comes because I don't necessarily know the parent/child types. I'm using reflection to determine which parent/child is being passed in. The parent always has only one property, which is an array of the child object. When I try assigning the child array to the parent object, I get a invalid cast exception saying it can't convert Object[] to . EDIT: Basically, what I have now is: Dim PropChildInfo As PropertyInfo() = ResponseObject.GetType().GetProperties() For Each PropItem As PropertyInfo In PropChildInfo PropItem.SetValue(ResponseObject, ResponseChildren, Nothing) Next ResponseObject is an instance of the parent Class, and ResponseChildren is an array of the childObject Class. This fails with: Object of type 'System.Object[]' cannot be converted to type 'childObject[]'.

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• Using Android SAXParser, one my my XML Elements is mysteriously breaking in half.

  - by Drennen

  And its not '&' Im using the SAXParser object do parse the actual XML. This is normally done by passing a URL to the XMLReader.Parse method. Because my XML is coming from a POST request to a webservice, I am saving that result as a String and then employing StringReader / InputSource to feed this string back to the XMLReader.Parse method. However, something strange is happening at the 2001st character of the XMLstring. The 'characters' method of the document handler is being called TWICE in between the startElement and endElement methods, effectively breaking my string (in this case a project title) into two pieces. Because I am instantiating objects in my characters method, I am getting two objects instead of one. This line, about 2000 chars into the string fires 'characters' two times, breaking between "Lower" and "Level" <title>SUMC-BOOKSTORE, LOWER LEVEL RENOVATIONS</title> When I bypass the StringReader / InputSource workaround and feed a flat XML file to XMLReader.Parse, it works absolutely fine. Something about StringReader and or InputSource is somehow screwing this up. Here is my method that takes and XML string and parses is through the SAXParser. public void parseXML(String XMLstring) { try { SAXParserFactory spf = SAXParserFactory.newInstance(); SAXParser sp = spf.newSAXParser(); XMLReader xr = sp.getXMLReader(); xr.setContentHandler(this); // Something is happening in the StringReader or InputSource // That cuts the XML element in half at the 2001 character mark. StringReader sr = new StringReader(XMLstring); InputSource is = new InputSource(sr); xr.parse(is); } catch (IOException e) { Log.e("CMS1", e.toString()); } catch (SAXException e) { Log.e("CMS2", e.toString()); } catch (ParserConfigurationException e) { Log.e("CMS3", e.toString()); } } I would greatly appreciate any ideas on how to not have 'characters' firing off twice when I get to this point in the XML String. Or, show me how to use a POST request and still pass off the URL to the Parse function. THANK YOU.

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• PowerBuilder Plug-in Architecture

  - by Adam Hawkes

  PowerBuilder seems to have some support for plug-ins since version 10. However, I can't find any documentation nor tutorials about this. The only hints I can manage are by examining the COM objects inside the existing DLLs. It doesn't help much, but I'm a novice at COM development. A very cursory example of how to do something would be awesome.

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• django: CheckboxMultiSelect problem with db queries

  - by xiackok

  firstly sorry for my bad english there is a simple model Person. That contains just languages: LANGUAGE_LIS = ( (1, 'English'), (2, 'Turkish'), (3, 'Spanish') ) class Person(models.Model): languages = models.CharField(max_length=100, choices=LANGUAGE_LIST) #languages is multi value (CheckBoxSelectMultiple) and here person_save_form: class person_save_form(forms.ModelForm): languages = forms.CharField(widget=forms.CheckBoxSelectMultiple(choices=LANGUAGE_LIST)) class Meta: model = Person it is ok. but how can i search persons for languages like "get persons who knows turkish and english" in the database (MySQL) record "languages" column seen like "[u'1', u'2']". but i want search persons like this: persons = Person.objects.filter(languages__in=request.POST.getlist('languages'))

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• Django many to many queries

  - by Hulk

  In the following, How to get designation when querying Emp sc=Emp.objects.filter(pk=profile.emp.id)[0] sc.desg //this gives an error class Emp(models.Model): name = models.CharField(max_length=255, unique=True) address1 = models.CharField(max_length=255) city = models.CharField(max_length=48) state = models.CharField(max_length=48) country = models.CharField(max_length=48) desg = models.ManyToManyField(Designation) class Designation(models.Model): description = models.TextField() title = models.TextField() def __unicode__(self): return self.board

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• OpenGL ES 2.0 equivalent of glOrtho()?

  - by Zippo

  In my iphone app, I need to project 3d scene into the 2D coordinates of the screen for some calculations. My objects go through various rotations, translations and scaling. So I figured I need to multiply the vertices with ModelView matrix first, then I need to multiply it with the Orthogonal projection matrix. First of all am on the right track? I have the Model View Matrix, but need the projection matrix. Is there a glOrtho() equivalent in ES 2.0?

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• Does SQL Azure Support Relational Databases?

  - by Goober

  I keep reading that SQL Azure doesn't support relational databases; however, I just tapped into my SQL Azure Database and scripted a relational database. I even checked to see what was present using: select * from sys.objects Any thoughts?

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• Get entry by week number using Django ORM?

  - by e-satis

  I tried something like: MyModel.objects.filter(year__week=1) It doesn't work. For now, I calculate the first day and the last day of the week and then use gte and lte, but it's less than efficient given that SQL comes with a Week function.

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• Loop through array in JavaScript

  - by Mark Szymanski

  In Java you can use a for() loop to go through objects in an array like so: String[] myStringArray = {"Hello","World"}; for(String s : myStringArray) { //Do something } can you do the same in JavaScript?

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• java IO to copy one File to another

  - by Aly

  I have two Java.io.File objects file1 and file2. I want to copy the contents from file1 to file2. Is there an standard way to do this without me having to create a method that reads file1 and write to file2

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• VBScript Out of String space

  - by MalsiaPro

  I got the following code to capture information for files on a specified drive, I ran the script againts a 600 GB hard drive on one of our servers and after a while I get the error Out of String space; "Join". Line 34, Char 2 For this code, file script.vbs: Option Explicit Dim objFS, objFld Dim objArgs Dim strFolder, strDestFile, blnRecursiveSearch ''Dim strLines Dim strCsv ''Dim i '' i = 0 ' 'Get the commandline parameters ' Set objArgs = WScript.Arguments ' strFolder = objArgs(0) ' strDestFile = objArgs(1) ' blnRecursiveSearch = objArgs(2) '######################################## 'SPECIFY THE DRIVE YOU WANT TO SCAN BELOW '######################################## strFolder = "C:\" strDestFile = "C:\InformationOutput.csv" blnRecursiveSearch = True 'Create the FileSystemObject Set objFS=CreateObject("Scripting.FileSystemObject") 'Get the directory you are working in Set objFld = objFS.GetFolder(strFolder) 'Open the csv file Set strCsv = objFS.CreateTextFile(strDestFile, True) '' 'Write the csv file '' Set strCsv = objFS.CreateTextFile(strDestFile, True) strCsv.WriteLine "File Path,File Size,Date Created,Date Last Modified,Date Last Accessed" '' strCsv.Write Join(strLines, vbCrLf) 'Now get the file details GetFileDetails objFld, blnRecursiveSearch '' 'Close and cleanup objects '' strCsv.Close '' 'Write the csv file '' Set strCsv = objFS.CreateTextFile(strDestFile, True) '' For i = 0 to UBound(strLines) '' strCsv.WriteLine strLines(i) '' Next 'Close and cleanup objects strCsv.Close Set strCsv = Nothing Set objFld = Nothing Set strFolder = Nothing Set objArgs = Nothing '---------------------------SCAN SPECIFIED LOCATION------------------------------- Private Sub GetFileDetails(fold, blnRecursive) Dim fld, fil dim strLine(4) on error resume next If InStr(fold.Path, "System Volume Information") < 1 Then If blnRecursive Then 'Work through all the folders and subfolders For Each fld In fold.SubFolders GetFileDetails fld, True If err.number <> 0 then LogError err.Description & vbcrlf & "Folder - " & fold.Path err.Clear End If Next End If 'Now work on the files For Each fil in fold.Files strLine(0) = fil.Path strLine(1) = fil.Size strLine(2) = fil.DateCreated strLine(3) = fil.DateLastModified strLine(4) = fil.DateLastAccessed strCsv.WriteLine Join(strLine, ",") if err.number <> 0 then LogError err.Description & vbcrlf & "Folder - " & fold.Path & vbcrlf & "File - " & fil.Name err.Clear End If Next End If end sub Private sub LogError(strError) dim strErr 'Write the csv file Set strErr = objFS.CreateTextFile("C:\test\err.log", false) strErr.WriteLine strError strErr.Close Set strErr = nothing End Sub RunMe.cmd wscript.exe "C:\temp\script\script.vbs" How can I avoid getting this error? The server drives are quite a bit <???? and I would imagine that the CSV file would be at least 40 MB. Edit by Guffa: I commented out some lines in the code, using double ticks ('') so you can see where.

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• Salesforce: Fire a SOAP Outbound Message using Apex

  - by codeulike

  I have an existing Workflow Rule that fires of a (SOAP) Outbound Message when a certain type of object is created or updated. That works fine. I want to extend it so that a similar Outbound Message is also sent when the objects are deleted. According to this discussion, Workflow Rules cannot be made to fire based on object deletions, so I have to write an Apex Trigger instead. So the question is, how do I kick off a SOAP Outbound Message from within Apex?

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• Querying many to many fields in django

  - by Hulk

  In the models there is a many to many fields as, from emp.models import Name def info(request): name = models.ManyToManyField(Name) And in emp.models the schema is as class Name(models.Model): name = models.CharField(max_length=512) def __unicode__(self): return self.name Now when i want to query a particular id say for ex: info= info.objects.filter(id=a) for i in info: logging.debug(i.name) //gives an error how should the query be to get the name Thanks..

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• PHP Object as XML Document

  - by Sam McAfee

  What is the best way to take a given PHP object and serialize it as XML? I am looking at simple_xml and I have used it to parse XML into objects, but it isn't clear to me how it works the other way around.

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• Is it possible to Take object members directly from a queue of type object?

  - by Luke Mcneice

  Hi all, If I where to have a Queue holding a collection of objects (Custom object,bool,bool,bool,bool) and the custom object holds three doubles itself. Can I use the .Take(IntegerValue) command to only take one of the doubles (for the specified take length) from the custom entity contained in the queue and cast it to a double array, possibly with the .ToArray<double> function? Thanks, Luke

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