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  • IN statement performance in PostgreSQL (and in general)

    - by Vasil
    I know this has probably been asked before, but I can't find it with SO's search. Lets say i've TABLE1 and TABLE2, who should I expect the performance of a query such as this: SELECT * FROM TABLE1 WHERE id IN SUBQUERY_ON_TABLE2; as the number of rows in TABLE1 and TABLE2 grow and id is a primary key on TABLE1. Yes, I know using IN is such a n00b mistake, but TABLE2 has a generic relation (django generic relation) to multiple other tables so I can't think of another way to filter the data. At what (aproximate) ammount of rows in TABLE1 and TABLE2 should I expect to notice performance issues because of this? Will performance degrade linearly, exponentially etc. depending on the number of rows?

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  • Java generics: Illegal forward reference

    - by Arian
    Given a generic interface interface Foo<A, B> { } I want to write an implementation that requires A to be a subclass of B. So I want to do class Bar<A, B super A> implements Foo<A, B> { } // --> Syntax error or class Bar<A extends B, B> implements Foo<A, B> { } // --> illegal forward reference But the only solution that seems to work is this: class Bar<B, A extends B> implements Foo<A, B> { } which is kind of ugly, because it reverses the order of the generic parameters. Are there any solutions or workarounds to this problem?

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  • 'Why' and 'Where' Generics is actually used?

    - by NLV
    Hi all I know that generics are used to achieve type safety and i frequently read that they are largely used in custom collections. But why actually do we need to have it generic? For example, Why cant i use string[] instead of List<string> Lets consider i declare generic class and it has a property X T x; If i provide a method for the class which does x = x + 1; what does it mean actually? I dono what T is actually going to be and i dono what x = x + 1 going to perform actually? If i'm not able to do my own manipulations in my methods how the generics are going to be help me anyway? I've already studied lot of bookish answers. It would be much appreciated if any one can provide some clear insights in this. Regards NLV

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  • Websphere exception handling

    - by Benjamin
    Hi all, From a security standpoint, what is the best solution to handle application errors with Websphere? I've been thinking of creating a class that is called every time an application error is generated, log the error and display a generic error message to the users. In PHP this can be achieved using the set_exception_handler() function. Is there something similar for websphere that could be configured in the web.xml? I've found codes like this on the internet: <error-page> <error-code>500</error-code> <location>/servlet/ExceptionHandlerServlet</location> </error-page> But that would only work with "500" HTTP error codes. I really want something generic that catches everything. Something like a class that implements a certain interface which can have access to all information about the error. Thanks for your time.

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  • PHP Type Hinting: array supported, object NOT?

    - by Marius Burz
    Am I missing something or there really is no support for generic object type hinting in PHP 5.x? I find it really strange that hinting arrays is supported while hinting objects is not, at least not out of the box. I'd like to have something like this: function foo(object $o) Just as we have: function foo(array $o) Example of possible use: methods of an objects collection class. Workaround: using an interface "Object" implemented by all classes or extending all classes from a generic class "Object" and writing something like this: function foo(Object $o) Well, that just ain't cute. Edit: somebody suggested in a deleted post using stdClass. It doesn't work: Catchable fatal error: Argument 1 passed to c::add() must be an instance of stdClass, instance of b given

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  • How does one avoid "Value restriction" errors with F#'s Seq.cast?

    - by gatoatigrado
    I see that Seq has a cast function from IEnumerable to Seq, but how do I get it to work? open System.Text.RegularExpressions;; let v = Regex.Match("abcd", "(ab)");; Seq.cast (v.Captures);; This produces, error FS0030: Value restriction. The value 'it' has been inferred to have generic type val it : seq<'_a Either define 'it' as a simple data term, make it a function with explicit arguments or, if you do not intend for it to be generic, add a type annotation.

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  • How to avoid Eclipse warnings when using legacy code without generics?

    - by Paul Crowley
    I'm using JSON.simple to generate JSON output from Java. But every time I call jsonobj.put("this", "that"), I see a warning in Eclipse: Type safety: The method put(Object, Object) belongs to the raw type HashMap. References to generic type HashMap should be parameterized The clean fix would be if JSONObject were genericized, but since it isn't, I can't add any generic type parameters to fix this. I'd like to switch off as few warnings as possible, so adding "@SuppressWarnings("unchecked")" to lots of methods is unappealing, but do I have any other option besides putting up with the warnings?

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  • Dynamic Array Java program converted to C#

    - by Sef
    Hello, The folowing program was orignally in java. But i still get 1 error with the program in C#. (the eror is listed in comment in the 2nd block of code). using System; using System.Collections.Generic; using System.Linq; using System.Text; using System; using System.Collections.Generic; using System.Linq; using System.Text; namespace DynArray { public class DynArrayTester { static void Main(string[] args) { DynArray da = new DynArray(5); for (int i = 1; i <= 7; i++) { da.setData(i, i); //da.put(0, 0); //da.put(6, 6); } Console.WriteLine(da); } }/*DynArrayTester*/ } using System; using System.Collections.Generic; using System.Linq; using System.Text; namespace DynArray { public class DynArray { //toestand private int[] data; //gedrag public DynArray(int size) { data = new int[size]; } public int getData(int index) { return data[index - 1]; } private void expand(int size) { int[] tmp = data; data = new int[size]; for (int i = 0; i < tmp.Length; i++) { data[i] = tmp[i]; } }/*expand*/ public void setData(int index, int data) { if (0 < index) { if (index > this.data.length) // ***error, does not contain definition for "lenght" and no exetension method "lenght"*** expand(index); this.data[index - 1] = data; } } public override string ToString() { StringBuilder buf = new StringBuilder(); for (int i = 0; i < data.Length; i++) { buf.Append("[" + i + "]"); buf.Append(data[i]); buf.Append('\n'); } return buf.ToString(); } }/*DynArray*/ }

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  • Please help, now I have a matrix, I want use Combination algorithm to generate a array for length 6

    - by user313429
    The first thanks a lot for your help , the following is my matrix, I want to implement combination algorithm between multiple arrays in LINQ for this matrix. int[,] cj = { { 10, 23, 16, 20 }, { 22, 13, 1, 33 }, { 7, 19, 31, 12 }, { 30, 14, 21, 4 }, { 2, 29, 32, 6 }, { 18, 26, 17, 8 }, { 25, 11, 5, 28 }, { 24, 3, 15, 27 } }; other: public static IEnumerable<IEnumerable<T>> Combinations<T>(this IEnumerable<T> elements, int k) { return k == 0 ? new[] { new T[0] } : elements.SelectMany((e, i) => elements.Skip(i + 1).**Combinations**(k - 1).Select(c => (new[] { e }).Concat(c))); } The above method has a error in my project, System.Collections.Generic.IEnumerable' does not contain a definition for 'Combinations' and no extension method 'Combinations' accepting a first argument of type 'System.Collections.Generic.IEnumerable' could be found (are you missing a using directive or an assembly reference? I use .Net Framework3.5, what is the reason it?

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  • How to combine 2 or more querysets in a Django view?

    - by Espen Christensen
    Hi, I am trying to build the search for a Django site I am building, and in the search I am searching in 3 different models. And to get pagination on the search result list I would like to use a generic object_list view to display the results. But to do that i have to merge 3 querysets into one. How can i do that? Ive tried this: result_list = [] page_list = Page.objects.filter(Q(title__icontains=cleaned_search_term) | Q(body__icontains=cleaned_search_term)) article_list = Article.objects.filter(Q(title__icontains=cleaned_search_term) | Q(body__icontains=cleaned_search_term) | Q(tags__icontains=cleaned_search_term)) post_list = Post.objects.filter(Q(title__icontains=cleaned_search_term) | Q(body__icontains=cleaned_search_term) | Q(tags__icontains=cleaned_search_term)) for x in page_list: result_list.append(x) for x in article_list: result_list.append(x) for x in post_list: result_list.append(x) return object_list(request, queryset=result_list, template_object_name='result', paginate_by=10, extra_context={'search_term': search_term}, template_name="search/result_list.html") But this doesnt work I get an error when i try to use that list in the generic view. The list is missing the clone attribute. Anybody know how i can merge the three lists, page_list, article_list and post_list?

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  • Logical Matrix .... Solution

    - by Sanju
    Suppose you have an NxN matrix and you have to check whether it's a upper diagonal matrix or not. Is there any generic method to solve this problem? I am elaborating my question: Some thing is like this: Suppose you have NXN matrix having the value of N=4 then matrix will look like this: |5 6 9 2| |1 8 4 9| |5 8 1 6| |7 6 3 2| Its a 4X4 square matrix and again if it's upper triangle matrix it will look something like this: |5 6 9 2| |1 8 4 0| |5 8 0 0| |7 0 0 0| I need to generate a generic program in any language to check wether a square matrix is upper trailgle or not.

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  • What alternative is there to writing a TCP/IP data relay?

    - by LoudNPossiblyRight
    I am about to write a tcp/ip data relay - application that passes a one way stream of data from one host/port to another host/port. Initially it will be generic, but later on i will customize it to the need of a specific business request. I am guessing that something generic already exists out there so my question is: Has anyone used a third party (preferably open source) data relay in a production environment, if so what is, and do you recommend it? Any platform is fine. Thanks.

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  • Cannot implicitly convert type ... to ... problem

    - by Younes
    I have this code: public static IEnumerable<dcCustomer> searchCustomer(string Companyname) { TestdbDataContext db = new TestdbDataContext(); IEnumerable<dcCustomer> myCustomerList = (from Customer res in db.Customers where res.CompanyName == Companyname select res); return myCustomerList; } And whatever i try i keep getting the convert error. Error 1 Cannot implicitly convert type 'System.Collections.Generic.IEnumerable<ConnectionWeb.Customer>' to 'System.Collections.Generic.IEnumerable<ConnectionWeb.DAL.dcCustomer>'. An explicit conversion exists (are you missing a cast?) \\srv01\home$\Z****\Visual Studio 2008\Projects\ConnectionWeb\ConnectionWeb\DAL\dcCustomer.cs 63 20 ConnectionWeb I want to try get myCustomerList to keep the values in an enumerator and return it.

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  • Flex 3 multiple upload progress monitoring

    - by Darko Z
    I have a Flex3 application which has to be capable of uploading multiple files and monitoring each files individual progress using a label NOT a progress bar. My problem is that a generic progress handler for the uploads has no way (that I know of) of indicating WHICH upload it is that is progressing. I know that a file name is available to check but in the case of this app the file name might be the same for multiple uploads. My question: With a generic progress handler how does one differentiate between 2 multiple uploads with the same file name? EDIT: answerers may assume that I am a total newb to Flex... because I am.

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  • Java 7 API design best practice - return Array or return Collection

    - by Shengjie
    I know this question has be asked before generic comes out. Array does win out a bit given Array enforces the return type, it's more type-safe. But now, with latest JDK 7, every time when I design this type of APIs: public String[] getElements(String type) vs public List<String> getElements(String type) I am always struggling to think of some good reasons to return A Collection over An Array or another way around. What's the best practice when it comes to the case of choosing String[] or List as the API's return type? Or it's courses for horses. I don't have a special case in my mind, I am more looking for a generic pros/cons comparison.

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  • Type or namespace name could not be found

    - by Pandiya Chendur
    I use this: public IQueryable<MaterialsView> FindAllMaterials() { var materials = from m in db.Materials join Mt in db.MeasurementTypes on m.MeasurementTypeId equals Mt.Id select new MaterialsView { MatId = m.Mat_Name, MesName = Mt.Name, MesType = m.Mat_Type }; return materials; } It gives me the following errors: The type or namespace name MaterialsView could not be found (are you missing a using directive or an assembly reference?) Cannot implicitly convert type System.Collections.Generic.IEnumerable<MaterialsView> to System.Linq.IQueryable<MaterialsView>. An explicit conversion exists (are you missing a cast?) The type arguments for method System.Linq.Enumerable.ToList<TSource>(System.Collections.Generic.IEnumerable<TSource>) cannot be inferred from the usage. Try specifying the type arguments explicitly. I have googled it and found this SO question but it doesn't help. What's wrong?

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  • 2 sites each in a different country with 1 set of content (cloaking)

    - by Greg
    Hi, I have a question re: cloaking. I have a friend who has a business in Canada and the UK. Currently the .ca site is hosted on Godaddy. The co.uk domain is registered (with uk ip address) with domainmonster and is using a cloaked/framed redirect to the .ca site. As a result (my assumption) the .ca site is indexed fine by google, the .co.uk is not. The content is generic for both sites. How do I point the .co.uk site directly to the content independently (preferably without duplicating the content hosting in the UK), so that for instance if the .ca domain was taken away altogether the .co.uk domain would remain an entity in itself from Google's point of view? Does Google index a generic set of content and then associate different country domains with that content? I hope I have explained this ok. Thanks, Greg

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  • LINQ-to-SQL: Searching against a CSV

    - by Peter Bridger
    I'm using LINQtoSQL and I want to return a list of matching records for a CSV contains a list of IDs to match. The following code is my starting point, having turned a CSV string in a string array, then into a generic list (which I thought LINQ would like) - but it doesn't: Error Error 22 Operator '==' cannot be applied to operands of type 'int' and 'System.Collections.Generic.List<int>' C:\Documents and Settings\....\Search.cs 41 42 C:\...\ Code DataContext db = new DataContext(); List<int> geographyList = new List<int>( Convert.ToInt32(geography.Split(',')) ); var geographyMatches = from cg in db.ContactGeographies where cg.GeographyId == geographyList select new { cg.ContactId }; Where do I go from here?

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  • Dictionary.ContainsKey return False, but a want True

    - by SkyN
    namespace Dic { public class Key { string name; public Key(string n) { name = n; } } class Program { static string Test() { Key a = new Key("A"); Key b = new Key("A"); System.Collections.Generic.Dictionary<Key, int> d = new System.Collections.Generic.Dictionary<Key, int>(); d.Add(a, 1); return d.ContainsKey(b).ToString(); } static void Main(string[] args) { System.Console.WriteLine(Test()); } } } I want TRUE!!!

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  • In .NET which loop runs faster for or foreach

    - by Binoj Antony
    In c#/VB.NET/.NET which loop runs faster for or foreach? Ever since I read that for loop works faster than foreach a long time ago I assumed it stood true for all collections, generic collection all arrays etc. I scoured google and found few articles but most of them are inconclusive (read comments on the articles) and open ended. What would be ideal is to have each scenarios listed and the best solution for the same e.g: (just example of how it should be) for iterating an array of 1000+ strings - for is better than foreach for iterating over IList (non generic) strings - foreach is better than for Few references found on the web for the same: Original grand old article by Emmanuel Schanzer CodeProject FOREACH Vs. FOR Blog - To foreach or not to foreach that is the question asp.net forum - NET 1.1 C# for vs foreach [Edit] Apart from the readability aspect of it I am really interested in facts and figures, there are applications where the last mile of performance optimization squeezed do matter.

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  • Generics vs Object performance

    - by Risho
    I'm doing practice problems from MCTS Exam 70-536 Microsft .Net Framework Application Dev Foundation, and one of the problems is to create two classes, one generic, one object type that both perform the same thing; in which a loop uses the class and iterated over thousand times. And using the timer, time the performance of both. There was another post at C# generics question that seeks the same questoion but nonone replied. Basically if in my code I run the generic class first it takes loger to process. If I run the object class first than the object class takes longer to process. The whole idea was to prove that generics perform faster. I used the original users code to save me some time. I didn't particularly see anything wrong with the code and was puzzled by the outcome. Can some one explain why the unusual results? Thanks, Risho Here is the code: class Program { class Object_Sample { public Object_Sample() { Console.WriteLine("Object_Sample Class"); } public long getTicks() { return DateTime.Now.Ticks; } public void display(Object a) { Console.WriteLine("{0}", a); } } class Generics_Samle<T> { public Generics_Samle() { Console.WriteLine("Generics_Sample Class"); } public long getTicks() { return DateTime.Now.Ticks; } public void display(T a) { Console.WriteLine("{0}", a); } } static void Main(string[] args) { long ticks_initial, ticks_final, diff_generics, diff_object; Object_Sample OS = new Object_Sample(); Generics_Samle<int> GS = new Generics_Samle<int>(); //Generic Sample ticks_initial = 0; ticks_final = 0; ticks_initial = GS.getTicks(); for (int i = 0; i < 50000; i++) { GS.display(i); } ticks_final = GS.getTicks(); diff_generics = ticks_final - ticks_initial; //Object Sample ticks_initial = 0; ticks_final = 0; ticks_initial = OS.getTicks(); for (int j = 0; j < 50000; j++) { OS.display(j); } ticks_final = OS.getTicks(); diff_object = ticks_final - ticks_initial; Console.WriteLine("\nPerformance of Generics {0}", diff_generics); Console.WriteLine("Performance of Object {0}", diff_object); Console.ReadKey(); } }

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  • No-argument method on window.external is invoked when checking with typeof

    - by janko
    Hi, I am trying to display an HTML page with embedded JavaScript code inside a System.Windows.Forms.WebBrowser control. The JavaScript code is expected to interact with the embedding environment through the window.external object. Before invoking a method on window.external, JavaScript is supposed to check for the existance of the method. If it is not there, the code should invoke a generic fallback method. // basic idea if (typeof(window.external.MyMethod) != 'undefined') { window.external.MyMethod(args); } else { window.external.Generic("MyMethod", args); } However, checking for a no-argument method with typeof seems to invoke the method already. That is, if MyMethod accepts any positive number of arguments, the code above will work perfectly; but, if MyMethod is a no-argument method, then the expression typeof(window.external.MyMethod) will not check for its type but invoke it, too. Is there any work-around to this behavior? Can I somehow escape the expression window.external.MyMethod to prevent the method call from occurring?

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  • Linq Query Giving Error

    - by user275561
    I am getting this error when I use the Linq expression of var emp = _testModel.Where(m => m.Date == DateTime.Now).Select(m=>m); 'System.Collections.Generic.IEnumerable' does not contain a definition for 'System' and no extension method 'System' accepting a first argument of type 'System.Collections.Generic.IEnumerable' could be found (are you missing a using directive or an assembly reference?). I have google'd and looked everywhere by I have no idea what it is talking about? It doesn't throw an exception. The only way I found out about this was stepping through the expression.

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  • Django: request object to template context transparancy

    - by anars
    Hi! I want to include an initialized data structure in my request object, making it accessible in the context object from my templates. What I'm doing right now is passing it manually and tiresome within all my views: render_to_response(...., ( {'menu': RequestContext(request)})) The request object contains the key,value pair which is injected using a custom context processor. While this works, I had hoped there was a more generic way of passing selected parts of the request object to the template context. I've tried passing it by generic views, but as it turns out the request object isn't instantiated when parsing the urlpatterns list.

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