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  • Help with iphone dev - beyond bounds error

    - by dusk
    I'm just learning iphone development, so please forgive me for what is probably a beginner error. I've searched around and haven't found anything specific to my problem, so hopefully it is an easy fix. The book has examples of building a table from data hard coded via an array. Unfortunately it never really tells you how to get data from a URL, so I've had to look that up and that is where my problems show up. When I debug in xcode, it seems like the count is correct, so I don't understand why it is going out of bounds? This is the error message: 2010-05-03 12:50:42.705 Simple Table[3310:20b] *** Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[NSCFArray objectAtIndex:]: index (1) beyond bounds (0)' My URL returns the following string: first,second,third,fourth And here is the iphone code with the book's working example commented out #import "Simple_TableViewController.h" @implementation Simple_TableViewController @synthesize listData; - (void)viewDidLoad { /* //working code from book NSArray *array = [[NSArray alloc] initWithObjects:@"Sleepy", @"Sneezy", @"Bashful", @"Bashful", @"Happy", @"Doc", @"Grumpy", @"Thorin", @"Dorin", @"Norin", @"Ori", @"Balin", @"Dwalin", @"Fili", @"Kili", @"Oin", @"Gloin", @"Bifur", @"Bofur", @"Bombur", nil]; self.listData = array; [array release]; */ //code from interwebz that crashes NSString *urlstr = [[NSString alloc] initWithFormat:@"http://www.mysite.com/folder/iphone-test.php"]; NSURL *url = [[NSURL alloc] initWithString:urlstr]; NSString *ans = [NSString stringWithContentsOfURL:url]; NSArray *listItems = [ans componentsSeparatedByString:@","]; self.listData = listItems; [urlstr release]; [url release]; [ans release]; [listItems release]; [super viewDidLoad]; } - (void)didReceiveMemoryWarning { // Releases the view if it doesn't have a superview. [super didReceiveMemoryWarning]; // Release any cached data, images, etc that aren't in use. } - (void)viewDidUnload { // Release any retained subviews of the main view. // e.g. self.myOutlet = nil; self.listData = nil; [super viewDidUnload]; } - (void)dealloc { [listData release]; [super dealloc]; } #pragma mark - #pragma mark Table View Data Source Methods - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section { return [self.listData count]; } - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { static NSString *SimpleTableIdentifier = @"SimpleTableIdentifier"; UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:SimpleTableIdentifier]; if (cell == nil) { cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:SimpleTableIdentifier] autorelease]; } NSUInteger row = [indexPath row]; cell.textLabel.text = [listData objectAtIndex:row]; return cell; } @end

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  • What's the correct way to use Cakephp urls?

    - by Pichan
    Hello all, it's my first post here :) I'm having some difficulties with dealing with urls and parameters. I've gone through the router class api documentation over and over again and found nothing useful. First of all, I'd like to know if there is any 'universal' format in CakePHP(1.3) for handling urls. I'm currently handling all my urls as simple arrays(in the format that Router::url and $html-link accepts) and it's easy as long as I only need to pass them as arguments to cake's own methods. It usually gets tricky if I need something else. Mainly I'm having problems with converting string urls to the basic array format. Let's say I want to convert $arrayUrl to string and than again into url: $arrayUrl=array('controller'=>'SomeController','action'=>'someAction','someValue'); $url=Router::url($arrayUrl); //$url is now '/path/to/site/someController/someAction/someValue' $url=Router::normalize($url); //remove '/path/to/site' $parsed=Router::parse($url); /*$parsed is now Array( [controller] => someController [action] => someAction [named] => Array() [pass] => Array([0] => someValue) [plugin] => ) */ That seems an awful lot of code to do something as simple as to convert between 2 core formats. Also, note that $parsed is still not in the same as $arrayUrl. Of course I could tweak $parsed manually and actually I've done that a few times as a quick patch but I'd like to get to the bottom of this. I also noticed that when using prefix routing, $this-params in controller has the prefix embedded in the action(i.e. [action] = 'admin_edit') and the result of Router::parse() does not. Both of course have the prefix in it's own key. To summarize, how do I convert an url between any of these 3(or 4, if you include the prefix thing) mentioned formats the right way? Of course it would be easy to hack my way through this, but I'd still like to believe that cake is being developed by a bunch of people who have a lot more experience and insight than me, so I'm guessing there's a good reason for this "perceived misbehavior". I've tried to present my problem as good as I can, but due to my rusty english skills, I had to take a few detours :) I'll explain more if needed.

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  • Adding a valuetype to IDL, compile and it fails with "No factory found"

    - by jim
    I can't figure out why the client keeps complaining about the not finding the factory method. I've tried the IDL with and without the "factory" keyword and that didn't change the behavior. The SDMGeoVT IDL matches other objects used (which run successfully). The SDMGeoVT classes generated match other generated classes in regards to inheritance and methods. The IDL is as follows; The idlj compiler runs w/o error. I implement the function on the server and I see the server code run and serialize the object over the wire (the server code runs fine). The client bombs with the following stack trace (the first couple of lines is from the jacORB library). I've created a small app just to compile and test the code (ArrayClient & ArrayServer). The base app (from the jacORB demo) works fine. I've tried using the base class OFBaseVT and a single object (SDMGeoVT vs the list return) and have the same issue. 2010-05-27 15:37:11.813 FINE read GIOP message of size 100 from ClientGIOPConnection to 127.0.0.1:47030 (1e4853f) 2010-05-27 15:37:11.813 FINE read GIOP message of size 100 from ClientGIOPConnection to 127.0.0.1:47030 (1e4853f) org.omg.CORBA.MARSHAL: No factory found for: IDL:pl/SDMGeoVT:1.0 at org.jacorb.orb.CDRInputStream.read_untyped_value(CDRInputStream.java:2906) at org.jacorb.orb.CDRInputStream.read_typed_value(CDRInputStream.java:3082) at org.jacorb.orb.CDRInputStream.read_value(CDRInputStream.java:2679) at com.helloworld.pl.SDMGeoVTHelper.read(SDMGeoVTHelper.java:106) at com.helloworld.pl.SDMGeoVTListHelper.read(SDMGeoVTListHelper.java:51) at com.helloworld.pl._PLManagerIFStub.getSDMGeos(_PLManagerIFStub.java:28) at com.helloworld.ArrayClient.<init>(ArrayClient.java:40) at com.helloworld.ArrayClient.main(ArrayClient.java:125) valuetype SDMGeoVT : common::OFBaseVT{ private string sdmName; private string zip; private string atz; private long long primaryDeptId; private string deptName; factory instance(in string name,in string ZIP,in string ATZ,in long long primaryDeptId,in string deptName,in string name); string getZIP(); void setZIP(in string ZIP); string getATZ(); void setATZ(in string ATZ); long long getPrimaryDeptId(); void setPrimaryDeptId(in long long primaryDeptId); string getDeptName(); void setDeptName(in string deptName); }; typedef sequence<SDMGeoVT> SDMGeoVTList; interface PLManagerIF : PublicManagerIF { pl::SDMGeoVTList getSDMGeos(in framework::ITransactionHandle tHandle, in long long productionLocationId); };

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  • Java: repetition, overuse -- ?

    - by HH
    I try to be as minimalist as possible. Repetition is a problem. I hate it. When is it really a problem? what is static-overuse? what is field-method overuse? what is class-overuse? are there more types of overuse? Problem A: when it is too much to use of static? private static class Data { private static String fileContent; private static SizeSequence lineMap; private static File fileThing; private static char type; private static boolean binary; private static String name; private static String path; } private static class Print { //<1st LINE, LEFT_SIDE, 2nd LINE, RIGHT_SIDE> private Integer[] printPositions=new Integer[4]; private static String fingerPrint; private static String formatPrint; } Problem B: when it is too much to get field data with private methods? public Stack<Integer> getPositions(){return positions;} public Integer[] getPrintPositions(){return printPositions;} private Stack<String> getPrintViews(){return printViews;} private Stack<String> getPrintViewsPerFile(){return printViewsPerFile;} public String getPrintView(){return printView;} public String getFingerPrint(){return fingerPrint;} public String getFormatPrint(){return formatPrint;} public String getFileContent(){return fileContent;} public SizeSequence getLineMap(){return lineMap;} public File getFile(){return fileThing;} public boolean getBinary(){return binary;} public char getType(){return type;} public String getPath(){return path;} public FileObject getData(){return fObj;} public String getSearchTerm(){return searchTerm;} Related interface overuse

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  • NHibernate (3.1.0.4000) NullReferenceException using Query<> and NHibernate Facility

    - by TigerShark
    I have a problem with NHibernate, I can't seem to find any solution for. In my project I have a simple entity (Batch), but whenever I try and run the following test, I get an exception. I've triede a couple of different ways to perform a similar query, but almost identical exception for all (it differs in which LINQ method being executed). The first test: [Test] public void QueryLatestBatch() { using (var session = SessionManager.OpenSession()) { var batch = session.Query<Batch>() .FirstOrDefault(); Assert.That(batch, Is.Not.Null); } } The exception: System.NullReferenceException : Object reference not set to an instance of an object. at NHibernate.Linq.NhQueryProvider.PrepareQuery(Expression expression, ref IQuery query, ref NhLinqExpression nhQuery) at NHibernate.Linq.NhQueryProvider.Execute(Expression expression) at System.Linq.Queryable.FirstOrDefault(IQueryable`1 source) The second test: [Test] public void QueryLatestBatch2() { using (var session = SessionManager.OpenSession()) { var batch = session.Query<Batch>() .OrderBy(x => x.Executed) .Take(1) .SingleOrDefault(); Assert.That(batch, Is.Not.Null); } } The exception: System.NullReferenceException : Object reference not set to an instance of an object. at NHibernate.Linq.NhQueryProvider.PrepareQuery(Expression expression, ref IQuery query, ref NhLinqExpression nhQuery) at NHibernate.Linq.NhQueryProvider.Execute(Expression expression) at System.Linq.Queryable.SingleOrDefault(IQueryable`1 source) However, this one is passing (using QueryOver<): [Test] public void QueryOverLatestBatch() { using (var session = SessionManager.OpenSession()) { var batch = session.QueryOver<Batch>() .OrderBy(x => x.Executed).Asc .Take(1) .SingleOrDefault(); Assert.That(batch, Is.Not.Null); Assert.That(batch.Executed, Is.LessThan(DateTime.Now)); } } Using the QueryOver< API is not bad at all, but I'm just kind of baffled that the Query< API isn't working, which is kind of sad, since the First() operation is very concise, and our developers really enjoy LINQ. I really hope there is a solution to this, as it seems strange if these methods are failing such a simple test. EDIT I'm using Oracle 11g, my mappings are done with FluentNHibernate registered through Castle Windsor with the NHibernate Facility. As I wrote, the odd thing is that the query works perfectly with the QueryOver< API, but not through LINQ.

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  • HttpClient response handler always returns closed stream

    - by Alex Ciminian
    I'm new to Java development so please bear with me. Also, I hope I'm not the champion of tl;dr :). I'm using HttpClient to make requests over Http (duh!) and I'd gotten it to work for a simple servlet that receives an URL as a query string parameter. I realized that my code could use some refactoring, so I decided to make my own HttpResponseHandler, to clean up the code, make it reusable and improve exception handling. I currently have something like this: public class HttpResponseHandler implements ResponseHandler<InputStream>{ public InputStream handleResponse(HttpResponse response) throws ClientProtocolException, IOException { int statusCode = response.getStatusLine().getStatusCode(); InputStream in = null; if (statusCode != HttpStatus.SC_OK) { throw new HttpResponseException(statusCode, null); } else { HttpEntity entity = response.getEntity(); if (entity != null) { in = entity.getContent(); // This works // for (int i;(i = in.read()) >= 0;) System.out.print((char)i); } } return in; } } And in the method where I make the actual request: HttpClient httpclient = new DefaultHttpClient(); HttpGet httpget = new HttpGet(target); ResponseHandler<InputStream> httpResponseHandler = new HttpResponseHandler(); try { InputStream in = httpclient.execute(httpget, httpResponseHandler); // This doesn't work // for (int i;(i = in.read()) >= 0;) System.out.print((char)i); return in; } catch (HttpResponseException e) { throw new HttpResponseException(e.getStatusCode(), null); } The problem is that the input stream returned from the handler is closed. I don't have any idea why, but I've checked it with the prints in my code (and no, I haven't used them both at the same time :). While the first print works, the other one gives a closed stream error. I need InputStreams, because all my other methods expect an InputStream and not a String. Also, I want to be able to retrieve images (or maybe other types of files), not just text files. I can work around this pretty easily by giving up on the response handler (I have a working implementation that doesn't use it), but I'm pretty curious about the following: Why does it do what it does? How do I open the stream, if something closes it? What's the right way to do this, anyway :)? I've checked the docs and I couldn't find anything useful regarding this issue. To save you a bit of Googling, here's the Javadoc and here's the HttpClient tutorial (Section 1.1.8 - Response handlers). Thanks, Alex

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  • What are the benefits of using ORM over XML Serialization/Deserialization?

    - by Tequila Jinx
    I've been reading about NHibernate and Microsoft's Entity Framework to perform Object Relational Mapping against my data access layer. I'm interested in the benefits of having an established framework to perform ORM, but I'm curious as to the performance costs of using it against standard XML Serialization and Deserialization. Right now, I develop stored procedures in Oracle and SQL Server that use XML Types for either input or output parameters and return or shred XML depending on need. I use a custom database command object that uses generics to deserialize the XML results into a specified serializable class. By using a combination of generics, xml (de)serialization and Microsoft's DAAB, I've got a process that's fairly simple to develop against regardless of the data source. Moreover, since I exclusively use Stored Procedures to perform database operations, I'm mostly protected from changes in the data structure. Here's an over-simplified example of what I've been doing. static void main() { testXmlClass test = new test(1); test.Name = "Foo"; test.Save(); } // Example Serializable Class ------------------------------------------------ [XmlRootAttribute("test")] class testXmlClass() { [XmlElement(Name="id")] public int ID {set; get;} [XmlElement(Name="name")] public string Name {set; get;} //create an instance of the class loaded with data. public testXmlClass(int id) { GenericDBProvider db = new GenericDBProvider(); this = db.ExecuteSerializable("myGetByIDProcedure"); } //save the class to the database... public Save() { GenericDBProvider db = new GenericDBProvider(); db.AddInParameter("myInputParameter", DbType.XML, this); db.ExecuteSerializableNonQuery("mySaveProcedure"); } } // Database Handler ---------------------------------------------------------- class GenericDBProvider { public T ExecuteSerializable<T>(string commandText) where T : class { XmlSerializer xml = new XmlSerializer(typeof(T)); // connection and command code is assumed for the purposes of this example. // the final results basically just come down to... return xml.Deserialize(commandResults) as T; } public void ExecuteSerializableNonQuery(string commandText) { // once again, connection and command code is assumed... // basically, just execute the command along with the specified // parameters which have been serialized. } public void AddInParameter(string name, DbType type, object value) { StringWriter w = new StringWriter(); XmlSerializer x = new XmlSerializer(value.GetType()); //handle serialization for serializable classes. if (type == DbType.Xml && (value.GetType() != typeof(System.String))) { x.Serialize(w, value); w.Close(); // store serialized object in a DbParameterCollection accessible // to my other methods. } else { //handle all other parameter types } } } I'm starting a new project which will rely heavily on database operations. I'm very curious to know whether my current practices will be sustainable in a high-traffic situation and whether or not I should consider switching to NHibernate or Microsoft's Entity Framework to perform what essentially seems to boil down to the same thing I'm currently doing. I appreciate any advice you may have.

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  • Variable sized packet structs with vectors

    - by Rev316
    Lately I've been diving into network programming, and I'm having some difficulty constructing a packet with a variable "data" property. Several prior questions have helped tremendously, but I'm still lacking some implementation details. I'm trying to avoid using variable sized arrays, and just use a vector. But I can't get it to be transmitted correctly, and I believe it's somewhere during serialization. Now for some code. Packet Header class Packet { public: void* Serialize(); bool Deserialize(void *message); unsigned int sender_id; unsigned int sequence_number; std::vector<char> data; }; Packet ImpL typedef struct { unsigned int sender_id; unsigned int sequence_number; std::vector<char> data; } Packet; void* Packet::Serialize(int size) { Packet* p = (Packet *) malloc(8 + 30); p->sender_id = htonl(this->sender_id); p->sequence_number = htonl(this->sequence_number); p->data.assign(size,'&'); //just for testing purposes } bool Packet::Deserialize(void *message) { Packet *s = (Packet*)message; this->sender_id = ntohl(s->sender_id); this->sequence_number = ntohl(s->sequence_number); this->data = s->data; } During execution, I simply create a packet, assign it's members, and send/receive accordingly. The above methods are only responsible for serialization. Unfortunately, the data never gets transferred. Couple of things to point out here. I'm guessing the malloc is wrong, but I'm not sure how else to compute it (i.e. what other value it would be). Other than that, I'm unsure of the proper way to use a vector in this fashion, and would love for someone to show me how (code examples please!) :) Edit: I've awarded the question to the most comprehensive answer regarding the implementation with a vector data property. Appreciate all the responses!

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  • Advantage of creating a generic repository vs. specific repository for each object?

    - by LuckyLindy
    We are developing an ASP.NET MVC application, and are now building the repository/service classes. I'm wondering if there are any major advantages to creating a generic IRepository interface that all repositories implement, vs. each Repository having its own unique interface and set of methods. For example: a generic IRepository interface might look like (taken from this answer): public interface IRepository : IDisposable { T[] GetAll<T>(); T[] GetAll<T>(Expression<Func<T, bool>> filter); T GetSingle<T>(Expression<Func<T, bool>> filter); T GetSingle<T>(Expression<Func<T, bool>> filter, List<Expression<Func<T, object>>> subSelectors); void Delete<T>(T entity); void Add<T>(T entity); int SaveChanges(); DbTransaction BeginTransaction(); } Each Repository would implement this interface (e.g. CustomerRepository:IRepository, ProductRepository:IRepository, etc). The alternate that we've followed in prior projects would be: public interface IInvoiceRepository : IDisposable { EntityCollection<InvoiceEntity> GetAllInvoices(int accountId); EntityCollection<InvoiceEntity> GetAllInvoices(DateTime theDate); InvoiceEntity GetSingleInvoice(int id, bool doFetchRelated); InvoiceEntity GetSingleInvoice(DateTime invoiceDate, int accountId); //unique InvoiceEntity CreateInvoice(); InvoiceLineEntity CreateInvoiceLine(); void SaveChanges(InvoiceEntity); //handles inserts or updates void DeleteInvoice(InvoiceEntity); void DeleteInvoiceLine(InvoiceLineEntity); } In the second case, the expressions (LINQ or otherwise) would be entirely contained in the Repository implementation, whoever is implementing the service just needs to know which repository function to call. I guess I don't see the advantage of writing all the expression syntax in the service class and passing to the repository. Wouldn't this mean easy-to-messup LINQ code is being duplicated in many cases? For example, in our old invoicing system, we call InvoiceRepository.GetSingleInvoice(DateTime invoiceDate, int accountId) from a few different services (Customer, Invoice, Account, etc). That seems much cleaner than writing the following in multiple places: rep.GetSingle(x => x.AccountId = someId && x.InvoiceDate = someDate.Date); The only disadvantage I see to using the specific approach is that we could end up with many permutations of Get* functions, but this still seems preferable to pushing the expression logic up into the Service classes. What am I missing?

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  • Silverlight with MVVM Inheritance: ModelView and View matching the Model

    - by moonground.de
    Hello Stackoverflowers! :) Today I have a special question on Silverlight (4 RC) MVVM and inheritance concepts and looking for a best practice solution... I think that i understand the basic idea and concepts behind MVVM. My Model doesn't know anything about the ViewModel as the ViewModel itself doesn't know about the View. The ViewModel knows the Model and the Views know the ViewModels. Imagine the following basic (example) scenario (I'm trying to keep anything short and simple): My Model contains a ProductBase class with a few basic properties, a SimpleProduct : ProductBase adding a few more Properties and ExtendedProduct : ProductBase adding another properties. According to this Model I have several ViewModels, most essential SimpleProductViewModel : ViewModelBase and ExtendedProductViewModel : ViewModelBase. Last but not least, according Views SimpleProductView and ExtendedProductView. In future, I might add many product types (and matching Views + VMs). 1. How do i know which ViewModel to create when receiving a Model collection? After calling my data provider method, it will finally end up having a List<ProductBase>. It containts, for example, one SimpleProduct and two ExtendedProducts. How can I transform the results to an ObservableCollection<ViewModelBase> having the proper ViewModel types (one SimpleProductViewModel and two ExtendedProductViewModels) in it? I might check for Model type and construct the ViewModel accordingly, i.e. foreach(ProductBase currentProductBase in resultList) if (currentProductBase is SimpleProduct) viewModels.Add( new SimpleProductViewModel((SimpleProduct)currentProductBase)); else if (currentProductBase is ExtendedProduct) viewModels.Add( new ExtendedProductViewModels((ExtendedProduct)currentProductBase)); ... } ...but I consider this very bad practice as this code doesn't follow the object oriented design. The other way round, providing abstract Factory methods would reduce the code to: foreach(ProductBase currentProductBase in resultList) viewModels.Add(currentProductBase.CreateViewModel()) and would be perfectly extensible but since the Model doesn't know the ViewModels, that's not possible. I might bring interfaces into game here, but I haven't seen such approach proven yet. 2. How do i know which View to display when selecting a ViewModel? This is pretty the same problem, but on a higher level. Ended up finally having the desired ObservableCollection<ViewModelBase> collection would require the main view to choose a matching View for the ViewModel. In WPF, there is a DataTemplate concept which can supply a View upon a defined DataType. Unfortunately, this doesn't work in Silverlight and the only replacement I've found was the ResourceSelector of the SLExtensions toolkit which is buggy and not satisfying. Beside that, all problems from Question 1 apply as well. Do you have some hints or even a solution for the problems I describe, which you hopefully can understand from my explanation? Thank you in advance! Thomas

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  • Advice for Architecture Design Logic for software application

    - by Prasad
    Hi, I have a framework of basic to complex set of objects/classes (C++) running into around 500. With some rules and regulations - all these objects can communicate with each other and hence can cover most of the common queries in the domain. My Dream: I want to provide these objects as icons/glyphs (as I learnt recently) on a workspace. All these objects can be dragged/dropped into the workspace. They have to communicate only through their methods(interface) and in addition to few iterative and conditional statements. All these objects are arranged finally to execute a protocol/workflow/dataflow/process. After drawing the flow, the user clicks the Execute/run button. All the user interaction should be multi-touch enabled. The best way to show my dream is : Jeff Han's Multitouch Video. consider Jeff is playing with my objects instead of the google maps. :-) it should be like playing a jigsaw puzzle. Objective: how can I achieve the following while working on this final product: a) the development should be flexible to enable provision for web services b) the development should enable easy web application development c) The development should enable client-server architecture - d) further it should also enable mouse based drag/drop desktop application like Adobe programs etc. I mean to say: I want to economize on investments. Now I list my efforts till now in design : a) Created an Editor (VB) where the user writes (manually) the object / class code b) On Run/Execute, the code is copied into a main() function and passed to interpreter. c) Catch the output and show it in the console. The interpreter can be separated to become a server and the Editor can become the client. This needs lot of standard client-server architecture work. But some how I am not comfortable in the tightness of this system. Without interpreter is there much faster and better embeddable solution to this? - other than writing a special compiler for these objects. Recently learned about AXIS-C++ can help me - looks like - a friend suggested. Is that the way to go ? Here are my questions: (pl. consider me a self taught programmer and NOT my domain) a) From the stage of C++ objects to multi-touch product, how can I make sure I will develop the parallel product/service models as well.? What should be architecture aspects I should consider ? b) What technologies are best suited for this? c) If I am thinking of moving to Cloud Computing, how difficult/ how redundant / how unnecessary my efforts will be ? d) How much time in months would it take to get the first beta ? I take the liberty to ask if any of the experts here are interested in this project, please email me: [email protected] Thank you for any help. Looking forward.

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  • PHP MVC Principles

    - by George
    I'm not using an off-the-shelf framework and don't particularly want to (nor d I want to go into the reasons why...). Anyway, onto my question(s), I hope it make sense.... I'm trying to get my head around what should go in the model and what should go in the controller. Originally I had the impression that a model class should represent an actual object (eg - a car from the cars table of a database) and model properties should mirror the database fields. However I'm now getting the feeling that I've got the wrong idea - should an instance of a model class represent an actual item, or should it contain a number of methods for doing stuff - sometimes to one car or sometimes to multiple cars based on my example earlier. For example I want to get all the cars from a the database and show them in the view. Am I right in think it should be along the lines of this? Controller File function list() { $cars = $this->model->get_all(); $this->view->add($cars); $this->view->render('cars-list'); } Model File function get_all() { // Use a database interaction class that I've written $cars = Database::select(); return $cars; } Now, if the car had a "status" field that was stored as an integer in the database and I wanted to change that to a string, where should that be done? By looping the SQL results array in the get_all() method in the model? Also, where should form validation live? I have written a validation class that works a little like this: $validator = new Validator(); $validator->check('field_name', 'required'); If the check fails, it adds an error message to the array in the Validator. This array of error messages would then get passed to the view. Should the use of my validator class go in model or the controller? Thanks in advance for for any help anyone can offer. If you know of any links to a simple MVC example / open source application that deals with basic CRUD, they would be much appreciated.

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  • The question about the basics of LINQ to SQL

    - by Alex
    I just started learning LINQ to SQL, and so far I'm impressed with the easy of use and good performance. I used to think that when doing LINQ queries like from Customer in DB.Customers where Customer.Age > 30 select Customer LINQ gets all customers from the database ("SELECT * FROM Customers"), moves them to the Customers array and then makes a search in that Array using .NET methods. This is very inefficient, what if there are hundreds of thousands of customers in the database? Making such big SELECT queries would kill the web application. Now after experiencing how actually fast LINQ to SQL is, I start to suspect that when doing that query I just wrote, LINQ somehow converts it to a SQL Query string SELECT * FROM Customers WHERE Age > 30 And only when necessary it will run the query. So my question is: am I right? And when is the query actually run? The reason why I'm asking is not only because I want to understand how it works in order to build good optimized applications, but because I came across the following problem. I have 2 tables, one of them is Books, the other has information on how many books were sold on certain days. My goal is to select books that had at least 50 sales/day in past 10 days. It's done with this simple query: from Book in DB.Books where (from Sale in DB.Sales where Sale.SalesAmount >= 50 && Sale.DateOfSale >= DateTime.Now.AddDays(-10) select Sale.BookID).Contains(Book.ID) select Book The point is, I have to use the checking part in several queries and I decided to create an array with IDs of all popular books: var popularBooksIDs = from Sale in DB.Sales where Sale.SalesAmount >= 50 && Sale.DateOfSale >= DateTime.Now.AddDays(-10) select Sale.BookID; BUT when I try to do the query now: from Book in DB.Books where popularBooksIDs.Contains(Book.ID) select Book It doesn't work! That's why I think that we can't use thins kinds of shortcuts in LINQ to SQL queries, like we can't use them in real SQL. We have to create straightforward queries, am I right?

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  • How to convert a 32bpp image to an indexed format?

    - by Ed Swangren
    So here are the details (I am using C# BTW): I receive a 32bpp image (JPEG compressed) from a server. At some point, I would like to use the Palette property of a bitmap to color over-saturated pixels (brightness 240) red. To do so, I need to get the image into an indexed format. I have tried converting the image to a GIF, but I get quality loss. I have tried creating a new bitmap in an index format by these methods: // causes a "Parameter not valid" error Bitmap indexed = new Bitmap(orig.Width, orig.Height, PixelFormat.Indexed) // no error, but the resulting image is black due to information loss I assume Bitmap indexed = new Bitmap(orig.Width, orig.Height, PixelFormat.Format8bppIndexed) I am at a loss now. The data in this image is changed constantly by the user, so I don't want to manually set pixels that have a brightness 240 if I can avoid it. If I can set the palette once when the image is created, my work is done. If I am going about this the wrong way to begin with please let me know. EDIT: Thanks guys, here is some more detail on what I am attempting to accomplish. We are scanning a tissue slide at high resolution (pathology application). I write the interface to the actual scanner. We use a line-scan camera. To test the line rate of the camera, the user scans a very small portion and looks at the image. The image is displayed next to a track bar. When the user moves the track bar (adjusting line rate), I change the overall intensity of the image in an attempt to model what it would look like at the new line rate. I do this using an ImageAttributes and ColorMatrix object currently. When the user adjusts the track bar, I adjust the matrix. This does not give me per pixel information, but the performance is very nice. I could use LockBits and some unsafe code here, but I would rather not rewrite it if possible. When the new image is created, I would like for all pixels with a brightness value of 240 to be colored red. I was thinking that defining a palette for the bitmap up front would be a clean way of doing this.

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  • Avoiding stack overflows in wrapper DLLs

    - by peachykeen
    I have a program to which I'm adding fullscreen post-processing effects. I do not have the source for the program (it's proprietary, although a developer did send me a copy of the debug symbols, .map format). I have the code for the effects written and working, no problems. My issue now is linking the two. I've tried two methods so far: Use Detours to modify the original program's import table. This works great and is guaranteed to be stable, but the user's I've talked to aren't comfortable with it, it requires installation (beyond extracting an archive), and there's some question if patching the program with Detours is valid under the terms of the EULA. So, that option is out. The other option is the traditional DLL-replacement. I've wrapped OpenGL (opengl32.dll), and I need the program to load my DLL instead of the system copy (just drop it in the program folder with the right name, that's easy). I then need my DLL to load the Cg framework and runtime (which relies on OpenGL) and a few other things. When Cg loads, it calls some of my functions, which call Cg functions, and I tend to get stack overflows and infinite loops. I need to be able to either include the Cg DLLs in a subdirectory and still use their functions (not sure if it's possible to have my DLLs import table point to a DLL in a subdirectory) or I need to dynamically link them (which I'd rather not do, just to simplify the build process), something to force them to refer to the system's file (not my custom replacement). The entire chain is: Program loads DLL A (named opengl32.dll). DLL A loads Cg.dll and dynamically links (GetProcAddress) to sysdir/opengl32.dll. I now need Cg.dll to also refer to sysdir/opengl32.dll, not DLL A. How would this be done? Edit: How would this be done easily without using GetProcAddress? If nothing else works, I'm willing to fall back to that, but I'd rather not if at all possible. Edit2: I just stumbled across the function SetDllDirectory in the MSDN docs (on a totally unrelated search). At first glance, that looks like what I need. Is that right, or am I misjudging? (off to test it now) Edit3: I've solved this problem by doing thing a bit differently. Instead of dropping an OpenGL32.dll, I've renamed my DLL to DInput.dll. Not only does it have the advantage of having to export one function instead of well over 120 (for the program, Cg, and GLEW), I don't have to worry about functions running back in (I can link to OpenGL as usual). To get into the calls I need to intercept, I'm using Detours. All in all, it works much better. This question, though, is still an interesting problem (and hopefully will be useful for anyone else trying to do crazy things in the future). Both the answers are good, so I'm not sure yet which to pick...

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  • iPhone noob - setting NSMutableDictionary entry inside Singleton?

    - by codemonkey
    Yet another iPhone/Objective-C noob question. I'm using a singleton to store app state information. I'm including the singleton in a Utilities class that holds it (and eventually other stuff). This utilities class is in turn included and used from various view controllers, etc. The utilities class is set up like this: // Utilities.h #import <Foundation/Foundation.h> @interface Utilities : NSObject { } + (id)GetAppState; - (id)GetAppDelegate; @end // Utilities.m #import "Utilities.h" #import "CHAPPAppDelegate.h" #import "AppState.h" @implementation Utilities CHAPPAppDelegate* GetAppDelegate() { return (CHAPPAppDelegate *)[UIApplication sharedApplication].delegate; } AppState* GetAppState() { return [GetAppDelegate() appState]; } @end ... and the AppState singleton looks like this: // AppState.h #import <Foundation/Foundation.h> @interface AppState : NSObject { NSMutableDictionary *challenge; NSString *challengeID; } @property (nonatomic, retain) NSMutableDictionary *challenge; @property (nonatomic, retain) NSString *challengeID; + (id)appState; @end // AppState.m #import "AppState.h" static AppState *neoAppState = nil; @implementation AppState @synthesize challengeID; @synthesize challenge; # pragma mark Singleton methods + (id)appState { @synchronized(self) { if (neoAppState == nil) [[self alloc] init]; } return neoAppState; } + (id)allocWithZone:(NSZone *)zone { @synchronized(self) { if (neoAppState == nil) { neoAppState = [super allocWithZone:zone]; return neoAppState; } } return nil; } - (id)copyWithZone:(NSZone *)zone { return self; } - (id)retain { return self; } - (unsigned)retainCount { return UINT_MAX; //denotes an object that cannot be released } - (void)release { // never release } - (id)init { if (self = [super init]) { challengeID = [[NSString alloc] initWithString:@"0"]; challenge = [NSMutableDictionary dictionary]; } return self; } - (void)dealloc { // should never be called, but just here for clarity [super dealloc]; } @end ... then, from a view controller I'm able to set the singleton's "challengeID" property like this: [GetAppState() setValue:@"wassup" forKey:@"challengeID"]; ... but when I try to set one of the "challenge" dictionary entry values like this: [[GetAppState() challenge] setObject:@"wassup" forKey:@"wassup"]; ... it fails giving me an "unrecognized selector sent..." error. I'm probably doing something really obviously dumb? Any insights/suggestions will be appreciated.

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  • How to add an XML parameter to a stored procedure in C#?

    - by salvationishere
    I am developing a C# web application in VS 2008 which interacts with my Adventureworks database in my SQL Server 2008. Now I am trying to add new records to one of the tables which has an XML column in it. How do I do this? This is the error I'm getting: System.Data.SqlClient.SqlException was caught Message="XML Validation: Text node is not allowed at this location, the type was defined with element only content or with simple content. Location: /" Source=".Net SqlClient Data Provider" ErrorCode=-2146232060 Class=16 LineNumber=22 Number=6909 Procedure="AppendDataC" Server="." State=1 StackTrace: at System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection) at System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection) at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj) at System.Data.SqlClient.TdsParser.Run(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj) at System.Data.SqlClient.SqlCommand.FinishExecuteReader(SqlDataReader ds, RunBehavior runBehavior, String resetOptionsString) at System.Data.SqlClient.SqlCommand.RunExecuteReaderTds(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, Boolean async) at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, DbAsyncResult result) at System.Data.SqlClient.SqlCommand.InternalExecuteNonQuery(DbAsyncResult result, String methodName, Boolean sendToPipe) at System.Data.SqlClient.SqlCommand.ExecuteNonQuery() at ADONET_namespace.ADONET_methods.AppendDataC(DataRow d, Hashtable ht) in C:\Documents and Settings\Admin\My Documents\Visual Studio 2008\Projects\AddFileToSQL\AddFileToSQL\ADONET methods.cs:line 212 InnerException: And this is a portion of my code in C#: try { SqlConnection conn2 = new SqlConnection(connString); SqlCommand cmd = conn2.CreateCommand(); cmd.CommandText = "dbo.AppendDataC"; cmd.CommandType = CommandType.StoredProcedure; cmd.Connection = conn2; ... sqlParam10.SqlDbType = SqlDbType.VarChar; SqlParameter sqlParam11 = cmd.Parameters.AddWithValue("@" + ht["@col11"], d[10]); sqlParam11.SqlDbType = SqlDbType.VarChar; SqlParameter sqlParam12 = cmd.Parameters.AddWithValue("@" + ht["@col12"], d[11]); sqlParam12.SqlDbType = SqlDbType.Xml; ... conn2.Open(); cmd.ExecuteNonQuery(); //This is the line it fails on and then jumps //to the Catch statement conn2.Close(); errorMsg = "The Person.Contact table was successfully updated!"; } catch (Exception ex) { Right now in my text input MDF file I have the XML parameter as: '<Products><id>3</id><id>6</id><id>15</id></Products>' Is this valid format for XML?

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  • How are you using IronPython?

    - by Will Dean
    I'm keen to drink some modern dynamic language koolaid, so I've believed all the stuff on Michael Foord's blog and podcasts, I've bought his book (and read some of it), and I added an embedded IPy runtime to a large existing app a year or so ago (though that was for someone else and I didn't really use it myself). Now I need to do some fairly simple code generation stuff, where I'm going to call a few methods on a few .net objects (custom, C#-authored objects), create a few strings, write some files, etc. The experience of trying this leaves me feeling like the little boy who thinks he's the only one who can see that The Emperor has no clothes on. If you're using IronPython, I'd really appreciate knowing how you deal with the following aspects of it: Code editing - do you use the .NET framework without Intellisense? Refactoring - I know a load of 'refactoring' is about working around language-related busywork, so if Python is sufficiently lightweight then we won't need that, But things like renames seem to me to be essential to iteratively developing quality code regardless of language. Crippling startup time - One of the things which is supposed to be good about interpreted languages is the lack of compile time leading to fast interactive development. Unfortunately I can compile a C# application and launch it quicker than IPy can start up. Interactive hacking - the IPy console/repl is supposed to be good for this, but I haven't found a good way to take the code you've interactively arrived at and persist it into a file - cut and paste from the console is fairly miserable. And the console seems to hold references to .NET assemblies you've imported, so you have to quit it and restart it if you're working on the C# stuff as well. Hacking on C# in something like LinqPad seems a much faster and easier way to try things out (and has proper Intellisense). Do you use the console? Debugging - what's the story here? I know someone on the IPy team is working on a command-line hobby-project, but let's just say I'm not immediately attracted to a command line debugger. I don't really need a debugger from little Python scripts, but I would if I were to use IPy for scripting unit tests, for example. Unit testing - I can see that dynamic languages could be great for this, but is there any IDE test-runner integration (like for Resharper, etc). The Foord book has a chapter about this, which I'll admit I have not yet read properly, but it does seem to involve driving a console-mode test-runner from the command prompt, which feels to be an enormous step back from using an integrated test runner like TestDriven.net or Resharper. I really want to believe in this stuff, so I am still working on the assumption that I've missed something. I would really like to know how other people are dealing with IPy, particularly if they're doing it in a way which doesn't feel like we've just lost 15 years'-worth of tool development.

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  • Creating a spam list with a web crawler in python

    - by user313623
    Hey guys, I'm not trying to do anything malicious here, I just need to do some homework. I'm a fairly new programmer, I'm using python 3.0, and I having difficulty using recursion for problem-solving. I've been stuck on this question for quite a while. Here's the assignment: Write a recursive method spam(url, n) that takes a url of a web page as input and a non-negative integer n, collects all the email address contained in the web page and adds them to a global dictionary variable spam_dict, and then recursively calls itself on every http hyperlink contained in the web page. You will use a dictionary so only one copy of every email address is save; your dictionary will store (key,value) pairs (email, email). The recursive call should use the parameter n-1 instead of n. If n = 0, you should collect the email addresses but no recursive calls should be made. The parameter n is used to limit the recursion to at most depth n. You will need to use the solutions of the two above problems; you method spam() will call the methods links2() and emails() and possibly other functions as well. Notes: 1. running spam() directly will produce no output on the screen; to find your spam_dict, you will need to read the value of spam_dict, and you will also need to reset it to the empty dictionary before every run of spam. 2. Recall how global variables are used. Usage: spam_dict = {} spam('http://reed.cs.depaul.edu/lperkovic/csc242/test1.html',0) spam_dict.keys() dict_keys([]) spam_dict = {} spam('http://reed.cs.depaul.edu/lperkovic/csc242/test1.html',1) spam_dict.keys() dict_keys(['[email protected]', '[email protected]']) So far, I've written a function that traverses web pages and puts all the links in a nice little list, and what I wanted to do was call that functions. And why would I use recursion on a dictionary? And how? I don't understand how n ties into all of this. def links2(url): content = str(urlopen(url).read()) myparser = MyHTMLParser() myparser.feed(content) lst = myparser.get() mergelst = [] for link in lst: mergelst.append(urljoin(lst[0],link)) print(mergelst) Any input (except why spam is bad) would be greatly appreciated. Also, I realize that the above function could probably look better, if you have a way to do it, I'm all ears. However, all I need is the point is for the program to produce the proper output.

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  • In a DDD approach, is this example modelled correctly?

    - by Tag
    Just created an acc on SO to ask this :) Assuming this simplified example: building a web application to manage projects... The application has the following requirements/rules. 1) Users should be able to create projects inserting the project name. 2) Project names cannot be empty. 3) Two projects can't have the same name. I'm using a 4-layered architecture (User Interface, Application, Domain, Infrastructure). On my Application Layer i have the following ProjectService.cs class: public class ProjectService { private IProjectRepository ProjectRepo { get; set; } public ProjectService(IProjectRepository projectRepo) { ProjectRepo = projectRepo; } public void CreateNewProject(string name) { IList<Project> projects = ProjectRepo.GetProjectsByName(name); if (projects.Count > 0) throw new Exception("Project name already exists."); Project project = new Project(name); ProjectRepo.InsertProject(project); } } On my Domain Layer, i have the Project.cs class and the IProjectRepository.cs interface: public class Project { public int ProjectID { get; private set; } public string Name { get; private set; } public Project(string name) { ValidateName(name); Name = name; } private void ValidateName(string name) { if (name == null || name.Equals(string.Empty)) { throw new Exception("Project name cannot be empty or null."); } } } public interface IProjectRepository { void InsertProject(Project project); IList<Project> GetProjectsByName(string projectName); } On my Infrastructure layer, i have the implementation of IProjectRepository which does the actual querying (the code is irrelevant). I don't like two things about this design: 1) I've read that the repository interfaces should be a part of the domain but the implementations should not. That makes no sense to me since i think the domain shouldn't call the repository methods (persistence ignorance), that should be a responsability of the services in the application layer. (Something tells me i'm terribly wrong.) 2) The process of creating a new project involves two validations (not null and not duplicate). In my design above, those two validations are scattered in two different places making it harder (imho) to see whats going on. So, my question is, from a DDD perspective, is this modelled correctly or would you do it in a different way?

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  • Is it possible to reliably auto-decode user files to Unicode? [C#]

    - by NVRAM
    I have a web application that allows users to upload their content for processing. The processing engine expects UTF8 (and I'm composing XML from multiple users' files), so I need to ensure that I can properly decode the uploaded files. Since I'd be surprised if any of my users knew their files even were encoded, I have very little hope they'd be able to correctly specify the encoding (decoder) to use. And so, my application is left with task of detecting before decoding. This seems like such a universal problem, I'm surprised not to find either a framework capability or general recipe for the solution. Can it be I'm not searching with meaningful search terms? I've implemented BOM-aware detection (http://en.wikipedia.org/wiki/Byte_order_mark) but I'm not sure how often files will be uploaded w/o a BOM to indicate encoding, and this isn't useful for most non-UTF files. My questions boil down to: Is BOM-aware detection sufficient for the vast majority of files? In the case where BOM-detection fails, is it possible to try different decoders and determine if they are "valid"? (My attempts indicate the answer is "no.") Under what circumstances will a "valid" file fail with the C# encoder/decoder framework? Is there a repository anywhere that has a multitude of files with various encodings to use for testing? While I'm specifically asking about C#/.NET, I'd like to know the answer for Java, Python and other languages for the next time I have to do this. So far I've found: A "valid" UTF-16 file with Ctrl-S characters has caused encoding to UTF-8 to throw an exception (Illegal character?) (That was an XML encoding exception.) Decoding a valid UTF-16 file with UTF-8 succeeds but gives text with null characters. Huh? Currently, I only expect UTF-8, UTF-16 and probably ISO-8859-1 files, but I want the solution to be extensible if possible. My existing set of input files isn't nearly broad enough to uncover all the problems that will occur with live files. Although the files I'm trying to decode are "text" I think they are often created w/methods that leave garbage characters in the files. Hence "valid" files may not be "pure". Oh joy. Thanks.

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  • What's the standard algorithm for syncing two lists of objects?

    - by Oliver Giesen
    I'm pretty sure this must be in some kind of text book (or more likely in all of them) but I seem to be using the wrong keywords to search for it... :( A common task I'm facing while programming is that I am dealing with lists of objects from different sources which I need to keep in sync somehow. Typically there's some sort of "master list" e.g. returned by some external API and then a list of objects I create myself each of which corresponds to an object in the master list. Sometimes the nature of the external API will not allow me to do a live sync: For instance the external list might not implement notifications about items being added or removed or it might notify me but not give me a reference to the actual item that was added or removed. Furthermore, refreshing the external list might return a completely new set of instances even though they still represent the same information so simply storing references to the external objects might also not always be feasible. Another characteristic of the problem is that both lists cannot be sorted in any meaningful way. You should also assume that initializing new objects in the "slave list" is expensive, i.e. simply clearing and rebuilding it from scratch is not an option. So how would I typically tackle this? What's the name of the algorithm I should google for? In the past I have implemented this in various ways (see below for an example) but it always felt like there should be a cleaner and more efficient way. Here's an example approach: Iterate over the master list Look up each item in the "slave list" Add items that do not yet exist Somehow keep track of items that already exist in both lists (e.g. by tagging them or keeping yet another list) When done iterate once more over the slave list Remove all objects that have not been tagged (see 4.) Update Thanks for all your responses so far! I will need some time to look at the links. Maybe one more thing worthy of note: In many of the situations where I needed this the implementation of the "master list" is completely hidden from me. In the most extreme cases the only access I might have to the master list might be a COM-interface that exposes nothing but GetFirst-, GetNext-style methods. I'm mentioning this because of the suggestions to either sort the list or to subclass it both of which is unfortunately not practical in these cases unless I copy the elements into a list of my own and I don't think that would be very efficient. I also might not have made it clear enough that the elements in the two lists are of different types, i.e. not assignment-compatible: Especially, the elements in the master list might be available as interface references only.

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  • Dependency Injection and Unit of Work pattern

    - by sunwukung
    I have a dilemma. I've used DI (read: factory) to provide core components for a homebrew ORM. The container provides database connections, DAO's,Mappers and their resultant Domain Objects on request. Here's a basic outline of the Mappers and Domain Object classes class Mapper{ public function __constructor($DAO){ $this->DAO = $DAO; } public function load($id){ if(isset(Monitor::members[$id]){ return Monitor::members[$id]; $values = $this->DAO->selectStmt($id); //field mapping process omitted for brevity $Object = new Object($values); return $Object; } } class User(){ public function setName($string){ $this->name = $string; //mark modified by means fair or foul } } The ORM also contains a class (Monitor) based on the Unit of Work pattern i.e. class Monitor(){ private static array modified; private static array dirty; public function markClean($class); public function markModified($class); } The ORM class itself simply co-ordinates resources extracted from the DI container. So, to instantiate a new User object: $Container = new DI_Container; $ORM = new ORM($Container); $User = $ORM->load('user',1); //at this point the container instantiates a mapper class //and passes a database connection to it via the constructor //the mapper then takes the second argument and loads the user with that id $User->setName('Rumpelstiltskin');//at this point, User must mark itself as "modified" My question is this. At the point when a user sets values on a Domain Object class, I need to mark the class as "dirty" in the Monitor class. I have one of three options as I can see it 1: Pass an instance of the Monitor class to the Domain Object. I noticed this gets marked as recursive in FirePHP - i.e. $this-Monitor-markModified($this) 2: Instantiate the Monitor directly in the Domain Object - does this break DI? 3: Make the Monitor methods static, and call them from inside the Domain Object - this breaks DI too doesn't it? What would be your recommended course of action (other than use an existing ORM, I'm doing this for fun...)

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  • Proper way to use Linq with WPF

    - by Ingó Vals
    I'm looking for a good guide into the right method of using Linq to Sql together with WPF. Most guides only go into the bare basics like how to show data from a database but noone I found goes into how to save back to the database. Can you answer or point out to me a guide that can answer these questions. I have a separate Data project because the same data will also be used in a web page so I have the repository method. That means I have a seperate class that uses the DataContext and there are methods like GetAllCompanies() and GetCompanyById ( int id ). 1) Where there are collections is it best to return as a IQueryable or should I return a list? Inside the WPF project I have seen reccomendations to wrap the collection in a ObservabgleCollection. 2) Why should I use ObservableCollection and should I use it even with Linq / IQueryable Some properties of the linq entities should be editable in the app so I set them to two-way mode. That would change the object in the observableCollection. 3) Is the object in the ObservableCollection still a instance of the original linq entity and so is the change reflected in the database ( when submitchanges is called ) I should have somekind of save method in the repository. But when should I call it? What happens if someone edits a field but decides not to save it, goes to another object and edits it and then press save. Doesn't the original change also save? When does it not remember the changes to a linq entity object anymore. Should I instance the Datacontext class in each method so it loses scope when done. 4) When and how to call the SubmitChanges method 5) Should I have the DataContext as a member variable of the repository class or a method variable To add a new row I should create a new object in a event ( "new" button push ) and then add it to the database using a repo method. 6) When I add the object to the database there will be no new object in the ObservableCollection. Do I refresh somehow. 7) I wan't to reuse the edit window when creating new but not sure how to dynamically changing from referencing selected item from a listview to this new object. Any examples you can point out.

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  • Wondering about a way to conserve memory in C# using List<> with structs

    - by Michael Ryan
    I'm not even sure how I should phrase this question. I'm passing some CustomStruct objects as parameters to a class method, and storing them in a List. What I'm wondering is if it's possible and more efficient to add multiple references to a particular instance of a CustomStruct if a equivalent instance it found. This is a dummy/example struct: public struct CustomStruct { readonly int _x; readonly int _y; readonly int _w; readonly int _h; readonly Enum _e; } Using the below method, you can pass one, two, or three CustomStruct objects as parameters. In the final method (that takes three parameters), it may be the case that the 3rd and possibly the 2nd will have the same value as the first. List<CustomStruct> _list; public void AddBackground(CustomStruct normal) { AddBackground(normal, normal, normal); } public void AddBackground(CustomStruct normal, CustomStruct hover) { AddBackground(normal, hover, hover); } public void AddBackground(CustomStruct normal, CustomStruct hover, CustomStruct active) { _list = new List<CustomStruct>(3); _list.Add(normal); _list.Add(hover); _list.Add(active); } As the method stands now, I believe it will create new instances of CustomStruct objects, and then adds a reference of each to the List. It is my understanding that if I instead check for equality between normal and hover and (if equal) insert normal again in place of hover, when the method completes, hover will lose all references and eventually be garbage collected, whereas normal will have two references in the List. The same could be done for active. That would be better, right? The CustomStruct is a ValueType, and therefore one instance would remain on the Stack, and the three List references would just point to it. The overall List size is determined not by the object Type is contains, but by its Capacity. By eliminating the "duplicate" CustomStuct objects, you allow them to be cleaned up. When the CustomStruct objects are passed to these methods, new instances are created each time. When the structs are added to the List, is another copy made? For example, if i pass just one CustomStruct, AddBackground(normal) creates a copy of the original variable, and then passes it three times to Addbackground(normal, hover, active). In this method, three copies are made of the original copy. When the three local variables are added to the List using Add(), are additional copies created inside Add(), and does that defeat the purpose of any equality checks as previously mentioned? Am I missing anything here?

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