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• How to generate a Program template by generating an abstract class

  - by Byron-Lim Timothy Steffan

  i have the following problem. The 1st step is to implement a program, which follows a specific protocol on startup. Therefore, functions as onInit, onConfigRequest, etc. will be necessary. (These are triggered e.g. by incoming message on a TCP Port) My goal is to generate a class for example abstract one, which has abstract functions as onInit(), etc. A programmer should just inherit from this base class and should merely override these abstract functions of the base class. The rest as of the protocol e.g. should be simply handled in the background (using the code of the base class) and should not need to appear in the programmers code. What is the correct design strategy for such tasks? and how do I deal with, that the static main method is not inheritable? What are the key-tags for this problem? (I have problem searching for a solution since I lack clear statements on this problem) Goal is to create some sort of library/class, which - included in ones code - results in executables following the protocol. EDIT (new explanation): Okay let me try to explain more detailled: In this case programs should be clients within a client server architecture. We have a client server connection via TCP/IP. Each program needs to follow a specific protocol upon program start: As soon as my program starts and gets connected to the server it will receive an Init Message (TcpClient), when this happens it should trigger the function onInit(). (Should this be implemented by an event system?) After onInit() a acknowledgement message should be sent to the server. Afterwards there are some other steps as e.g. a config message from the server which triggers an onConfig and so on. Let's concentrate on the onInit function. The idea is, that onInit (and onConfig and so on) should be the only functions the programmer should edit while the overall protocol messaging is hidden for him. Therefore, I thought using an abstract class with the abstract methods onInit(), onConfig() in it should be the right thing. The static Main class I would like to hide, since within it e.g. there will be some part which connects to the tcp port, which reacts on the Init Message and which will call the onInit function. 2 problems here: 1. the static main class cant be inherited, isn it? 2. I cannot call abstract functions from the main class in the abstract master class. Let me give an Pseudo-example for my ideas: public abstract class MasterClass { static void Main(string[] args){ 1. open TCP connection 2. waiting for Init Message from server 3. onInit(); 4. Send Acknowledgement, that Init Routine has ended successfully 5. waiting for Config message from server 6..... } public abstract void onInit(); public abstract void onConfig(); } I hope you get the idea now! The programmer should afterwards inherit from this masterclass and merely need to edit the functions onInit and so on. Is this way possible? How? What else do you recommend for solving this? EDIT: The strategy ideo provided below is a good one! Check out my comment on that.

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• Saving data to server with user accounts.

  - by AKRamkumar

  Ok, so for an app I am making, I want the user to be able to save data online. On my website, I will provide a web server with tables of UserName/Password/SaveData. How can I do this without crashing the server load? How can I guarantee security ? Is there a Design Pattern for this?Is there a better way of doing this? This is going to be a free application, available to the public and I would like for their settings to be available, no matter the computer they are using. Is there a better way of doing this? I am using MEF for plugins so is there a way I can save plugin data as well?

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• MVVM pattern: ViewModel updates after Model server roundtrip

  - by Pavel Savara

  I have stateless services and anemic domain objects on server side. Model between server and client is POCO DTO. The client should become MVVM. The model could be graph of about 100 instances of 20 different classes. The client editor contains diverse tab-pages all of them live-connected to model/viewmodel. My problem is how to propagate changes after server round-trip nice way. It's quite easy to propagate changes from ViewModel to DTO. For way back it would be possible to throw away old DTO and replace it whole with new one, but it will cause lot of redrawing for lists/DataTemplates. I could gather the server side changes and transmit them to client side. But the names of fields changed would be domain/DTO specific, not ViewModel specific. And the mapping seems nontrivial to me. If I should do it imperative way after round-trip, it would break SOC/modularity of viewModels. I'm thinking about some kind of mapping rule engine, something like automappper or emit mapper. But it solves just very plain use-cases. I don't see how it would map/propagate/convert adding items to list or removal. How to identify instances in collections so it could merge values to existing instances. As well it should propagate validation/error info. Maybe I should implement INotifyPropertyChanged on DTO and try to replay server side events on it ? And then bind ViewModel to it ? Would binding solve the problems with collection merges nice way ? Is EventAgregator from PRISM useful for that ? Is there any event record-replay component ? Is there better client side pattern for architecture with server side logic ?

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• Why would it be a bad idea to have database connection open between client requests?

  - by AspOnMyNet

  1) Book I’m reading argues that connections shouldn’t be opened between client requests, since they are a finite resource. I realize that max pool size can quickly be reached and thus any further attempts to open a connection will be queued until connection becomes available and for that reason it would be imperative that we release connection as soon as possible. But assuming all request will open connection to the same DB, then I’m not sure how having a connection open between two client requests would be any less efficient than having each request first acquiring a connection from connection pool and later returning that object to connection pool? 2) Book also recommends that when database code is encapsulated in a dedicated data access class, then method M opening a database connection should also close that connection. a) I assume one reason why M should also close it, is because if method M opening the connection doesn’t also close it, but instead this connection object is used inside several methods, then it’s more likely that a programmer will forget to close it. b) Are there any other reasons why a method opening the connection should also close it? thanx

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• When to use Factory method pattern?

  - by Jaswant Agarwal

  When to use Factory method pattern? Please provide me some specific idea when to use it in project? and how it is a better way over new keyword?

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• Is It Incorrect to Make Domain Objects Aware of The Data Access Layer?

  - by Noah Goodrich

  I am currently working on rewriting an application to use Data Mappers that completely abstract the database from the Domain layer. However, I am now wondering which is the better approach to handling relationships between Domain objects: Call the necessary find() method from the related data mapper directly within the domain object Write the relationship logic into the native data mapper (which is what the examples tend to do in PoEAA) and then call the native data mapper function within the domain object. Either it seems to me that in order to preserve the 'Fat Model, Skinny Controller' mantra, the domain objects have to be aware of the data mappers (whether it be their own or that they have access to the other mappers in the system). Additionally it seems that Option 2 unnecessarily complicates the data access layer as it creates table access logic across multiple data mappers instead of confining it to a single data mapper. So, is it incorrect to make the domain objects aware of the related data mappers and to call data mapper functions directly from the domain objects? Update: These are the only two solutions that I can envision to handle the issue of relations between domain objects. Any example showing a better method would be welcome.

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• Why doesn't DomainContext from WCF RIA Services implement the IDisposable pattern ?

  - by Scott Davies

  Hi, Just doing some work with RIA services and I see in the MSDN documentation that neither it or any parents up its' hierarchy implement IDisposable. I'm wondering what the design decision was for this...as DomainContext is a stateful resource, wouldn't it be nice to have a Dispose() to release it when done ? Thanks, Scott

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• Is testability alone justification for dependency injection?

  - by fearofawhackplanet

  The advantages of DI, as far as I am aware, are: Reduced Dependencies More Reusable Code More Testable Code More Readable Code Say I have a repository, OrderRepository, which acts as a repository for an Order object generated through a Linq to Sql dbml. I can't make my orders repository generic as it performs mapping between the Linq Order entity and my own Order POCO domain class. Since the OrderRepository by necessity is dependent on a specific Linq to Sql DataContext, parameter passing of the DataContext can't really be said to make the code reuseable or reduce dependencies in any meaningful way. It also makes the code harder to read, as to instantiate the repository I now need to write new OrdersRepository(new MyLinqDataContext()) which additionally is contrary to the main purpose of the repository, that being to abstract/hide the existence of the DataContext from consuming code. So in general I think this would be a pretty horrible design, but it would give the benefit of facilitating unit testing. Is this enough justification? Or is there a third way? I'd be very interested in hearing opinions.

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• quantity of measurable units design pattern

  - by Berryl

  Hello I am thinking through a nice pattern to be useful across domains of measurable units (ie, Length, Time) and came up with the following use case and initial classes, and of course, questions! 1) Does a Composite pattern help or complicate? 2) Should the Convert method(s) in the ComposityNode be a separate converter class? All comments appreciated. Cheers, Berryl Example Use Case: var inch = new ConvertableUnit("inch", 1) var foot = new ConvertableUnit("foot", 12) var imperialUnits = new CompositeConvertableUnit("imperial units", .024) imperialUnits.AddChild(inch) imperialUnits.AddChild(foot) var meter = new ConvertableUnit("meter", 1) var millimeter = new ConvertableUnit("millimeter ", .001) var imperialUnits = new CompositeConvertableUnit("metric units", 1) imperialUnits.AddChild(meter) imperialUnits.AddChild(millimeter) var oneInch = new Quantity(1, inch); var oneFoot = new Quantity(1, foot); oneFoot.ToBase() // "12 inches" var oneMeter = new Quantity(1, meter); oneInch.ToBase() // .024 meters Possible Solution ConvertableUnit : Node double Rate string Name Quantity ConvertableUnit Unit double Amount CompositeConvertableUnit : Node ISet<ConvertableUnit> _children ConvertableUnit BaseUnit {get{ return _children.Where(c=>c.Rate == 1).First() } } Quantity ConvertTo(Quantity from, Quantity to) Quantity ToBase(Quantity from);

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• logic of button to be disabled or not in mvc

  - by rod

  Hi All, Here's an excerpt from a book I'm reading about application design with MVC: Ideally, the view is so simple and logic-free as to need virtually no testing. Users (and developers before users) can reasonably test the view by simply looking at the pixels on the screen. Anything else beyond pure graphical rendering should ideally be taken out of the view and placed in the controller and model. This includes, for example, the logic that determines whether a certain button should be enabled or grayed out at some point. what does the bold statement mean to you? what would this look like? thanks, rod.

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• Shouldn't ObjectInputStream extend FilterInputStream?

  - by Vaibhav Bajpai

  The block quotes are from the Java Docs - A FilterInputStream contains some other input stream, which it uses as its basic source of data, possibly transforming the data along the way or providing additional functionality. A DataInputStream lets an application read primitive Java data types from an underlying input stream in a machine-independent way. The DataInputStream therefore extends FilterInputStream An ObjectInputStream deserializes primitive data and objects previously written using an ObjectOutputStream. However, for some reason the ObjectInputStream does NOT extend FilterInputStream even though it is also reading objects (this time and not primitive types) from the underlying input stream. Here is the branching of the concerned classes. Is there is a design reasoning for the same?

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• Bi-directional view model syncing with "live" collections and properties (MVVM)

  - by Schneider

  I am getting my knickers in a twist recently about View Models (VM). Just like this guy I have come to the conclusion that the collections I need to expose on my VM typically contain a different type to the collections exposed on my business objects. Hence there must be a bi-directional mapping or transformation between these two types. (Just to complicate things, on my project this data is "Live" such that as soon as you change a property it gets transmitted to other computers) I can just about cope with that concept, using a framework like Truss, although I suspect there will be a nasty surprise somewhere within. Not only must objects be transformed but a synchronization between these two collections is required. (Just to complicate things I can think of cases where the VM collection might be a subset or union of business object collections, not simply a 1:1 synchronization). I can see how to do a one-way "live" sync, using a replicating ObservableCollection or something like CLINQ. The problem then becomes: What is the best way to create/delete items? Bi-directinal sync does not seem to be on the cards - I have found no such examples, and the only class that supports anything remotely like that is the ListCollectionView. Would bi-directional sync even be a sensible way to add back into the business object collection? All the samples I have seen never seem to tackle anything this "complex". So my question is: How do you solve this? Is there some technique to update the model collections from the VM? What is the best general approach to this?

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• What is the most stupid coded solution you have read/improved/witnessed?

  - by Rigo Vides

  And for stupid I mean Illogical, non-effective, complex(the bad way), ugly code style. I will start: We had a requirement there when we needed to hide certain objects given the press of a button. So this framework we were using at the time provided a way to tag objects and retrieve all the objects with a certain tag in a complete iterable collection. So I presented the most logically solution given these conditions to my partner: Me: you know, tag all the objects we needed to hide with the same tag, then call the function to get them all, iterate trough them and make them hidden. Partner: I don't know, that is hardcoding for me... Me: So what do you suggest? 20 mins later... Partner: I don't know... let's put a tag to all the objects to be hidden like this, 1, 2, 3, 4, 5, 6, 7 (and so for each object to be hidden), Then we make a for from 1 to n (where n was the number of objects to hide) and we hide them all there!

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• How to restrict access to a class's data based on state?

  - by Marcus Swope

  In an ETL application I am working on, we have three basic processes: Validate and parse an XML file of customer information from a third party Match values received in the file to values in our system Load customer data in our system The issue here is that we may need to display the customer information from any or all of the above states to an internal user and there is data in our customer class that will never be populated before the values have been matched in our system (step 2). For this reason, I would like to have the values not even be available to be accessed when the customer is in this state, and I would like to have to avoid some repeated logic everywhere like: if (customer.IsMatched) DisplayTextOnWeb(customer.SomeMatchedValue); My first thought for this was to add a couple interfaces on top of Customer that would only expose the properties and behaviors of the current state, and then only deal with those interfaces. The problem with this approach is that there seems to be no good way to move from an ICustomerWithNoMatchedValues to an ICustomerWithMatchedValues without doing direct casts, etc... (or at least I can't find one). I can't be the first to have come across this, how do you normally approach this? As a last caveat, I would like for this solution to play nice with FluentNHibernate :) Thanks in advance...

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• How can i return abstract class from any factory?

  - by programmerist

  using System; using System.Collections.Generic; using System.Linq; using System.Web; namespace EfTestFactory { public abstract class _Company { public abstract List<Personel> GetPersonel(); public abstract List<Prim> GetPrim(); public abstract List<Finans> GetFinans(); } public abstract class _Radyoloji { public abstract List<string> GetRadyoloji(); } public abstract class _Satis { public abstract List<string> GetSatis(); } public abstract class _Muayene { public abstract List<string> GetMuayene(); } public class Company : _Company { public override List<Personel> GetPersonel() { throw new NotImplementedException(); } public override List<Prim> GetPrim() { throw new NotImplementedException(); } public override List<Finans> GetFinans() { throw new NotImplementedException(); } } public class Radyoloji : _Radyoloji { public override List<string> GetRadyoloji() { throw new NotImplementedException(); } } public class Satis : _Satis { public override List<string> GetSatis() { throw new NotImplementedException(); } } public class Muayene : _Muayene { public override List<string> GetMuayene() { throw new NotImplementedException(); } } public class GenoTipController { public object CreateByEnum(DataModelType modeltype) { string enumText = modeltype.ToString(); // will return for example "Company" Type classType = Type.GetType(enumText); // the Type for Company class object t = Activator.CreateInstance(classType); // create an instance of Company class return t; } } public class AntsController { static Dictionary<DataModelType, Func<object>> s_creators = new Dictionary<DataModelType, Func<object>>() { { DataModelType.Radyoloji, () => new _Radyoloji() }, { DataModelType.Company, () => new _Company() }, { DataModelType.Muayene, () => new _Muayene() }, { DataModelType.Satis, () => new _Satis() }, }; public object CreateByEnum(DataModelType modeltype) { return s_creators[modeltype](); } } public class CompanyView { public static List<Personel> GetPersonel() { GenoTipController controller = new GenoTipController(); _Company company = controller.CreateByEnum(DataModelType.Company) as _Company; return company.GetPersonel(); } } public enum DataModelType { Radyoloji, Satis, Muayene, Company } } if i write above codes i see some error: Cannot create an instance of abstract class or interface 'EfTestFactory_Company'How can i solve it? Look please below pic.

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• desing pattern for related inputs

  - by curiousMo

  My question is a design question : let's say i have a data entry web page with 4 drop down lists, each depending on the previous one, and a bunch of text boxes. country (ddl), state (ddl), city (ddl), boro (ddl), address (txtBox), zipcode(txtbox). and an object that represents a datarow with a value for each. naturally the country, state, city and boro values will be values of primary keys of some lookup tables. when the user chooses to edits that record, i would load it from database and load it into the page. the issue that I have is how to streamline loading the ddls. i have some code that would grab the object, look thru its values and move them to their corresponding input controls in one shot. but in this case i will have to load possible values of country, then assign values, then load values of state, then assign value ans so on. I guess i am looking for an elegant solution. i am using asp.net, but i think it is irrelevant to the question. i am looking more into a design pattern. thanks

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• ASP.NET MVC Paging for a search form

  - by James Alexander

  I've read several different posts on paging w/ in MVC but none describe a scenario where I have something like a search form and then want to display the results of the search criteria (with paging) beneath the form once the user clicks submit. My problem is that, the paging solution I'm using will create <a href="..."> links that will pass the desired page like so: http://mysite.com/search/2/ and while that's all fine and dandy, I don't have the results of the query being sent to the db in memory or anything so I need to query the DB again. If the results are handled by the POST controller action for /Search and the first page of the data is rendered as such, how do I get the same results (based on the form criteria specified by the user) when the user clicks to move to page 2? Some javascript voodoo? Leverage Session State? Make my GET controller action have the same variables expected by the search criteria (but optional), when the GET action is called, instantiate a FormCollection instance, populate it and pass it to the POST action method (there-by satisfying DRY)? Can someone point me in the right direction for this scenario or provide examples that have been implemented in the past? Thanks!

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• State pattern: Why doesn't the context class implement or inherit the State abstract interface/class

  - by Ricket

  I'm reading about the State pattern. I have only just begun, so of course I begin by reading the entire Wikipedia article on it. I noticed that both of the examples in the article have some base abstract class or Java interface for a generic State's methods/functions. Then there are some states which inherit from the base and implement those methods/functions in different ways. Then there's a Context class which has a private member of type State and which, at any time, can be equal to an instance of one of the implementations. That context class also implements the same methods, and passes them onto the current state instance, and then has an additional method to change the state (or depending on design I understand the change of state could be a reaction to one of the implemented methods). Why doesn't this context class specifically "extend" or "implement" the generic State base class/interface?

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• Could any help me in resource of how to build framework with api like facebook ?

  - by Space Cracker

  we will develop a web site that will have some free services and we want to make it as a framework that can any build application over it or can use its api in their site .. Could any lead me in how to start it , what's the better architecture and design pattern help in that , is there any resources discuss or explain how to do like this ? FYI : we are dot net developers but we can learn any other if its urgently needed in such a solution

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• How to perform a literal match with regex using wildcard

  - by kashif4u

  I am trying to perform literal match with regular expression using wildcard. string utterance = "Show me customer id 19"; string pattern 1 = "*tom*"; string patter 2 = "*customer id [0-9]*"; Desired results: if (Regex.IsMatch(utterance, pattern 1 )) { MATCH NOT FOUND } if (Regex.IsMatch(utterance, pattern 2 )) { MATCH FOUND } I have tried looking for literal match solution/syntax in wildcard but having difficulty. Could you also enlighten me with with an example on possible Pattern Matching Strength algorithm i.e. if code match 90 select? Note: I have table with 100000 records to perform literal matches from user utterances. Thanks in advance.

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• Decorator pattern in C++

  - by AlgoMan

  Can someone give me an example of Decorator pattern in C++ ? I have come across the Java version of it. But C++ i have found it difficult to understand the examples that are given.

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• What is the best approach to binding commands in a ViewModel to elements in the View?

  - by Micah

  Anyone who has tried to implement RoutedCommands in WPF using M-V-VM has undoubtedly run into issues. Commands (non-UI commands that is) should be implemented in the ViewModel. For instance if I needed to save a CustomerViewModel then I would implement that as a command directly on my CustomerViewModel. However if I wanted to pop up a window to show the users addresses I would implement a ShowCustomerAddress command directly in the view since this a UI specific function. How do I define the command bindings in the viewmodel, and use them in the view?

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• Can the Singleton be replaced by Factory?

  - by lostiniceland

  Hello Everyone There are already quite some posts about the Singleton-Pattern around, but I would like to start another one on this topic since I would like to know if the Factory-Pattern would be the right approach to remove this "anti-pattern". In the past I used the singleton quite a lot, also did my fellow collegues since it is so easy to use. For example, the Eclipse IDE or better its workbench-model makes heavy usage of singletons as well. It was due to some posts about E4 (the next big Eclipse version) that made me start to rethink the singleton. The bottom line was that due to this singletons the dependecies in Eclipse 3.x are tightly coupled. Lets assume I want to get rid of all singletons completely and instead use factories. My thoughts were as follows: hide complexity less coupling I have control over how many instances are created (just store the reference I a private field of the factory) mock the factory for testing (with Dependency Injection) when it is behind an interface In some cases the factories can make more than one singleton obsolete (depending on business logic/component composition) Does this make sense? If not, please give good reasons for why you think so. An alternative solution is also appreciated. Thanks Marc

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• Implement Exception Handling in ASP.NET C# Project

  - by Shrewd Demon

  hi, I have an application that has many tiers. as in, i have... Presentation Layer (PL) - contains all the html My Codes Layer (CL) - has all my code Entity Layer (EL) - has all the container entities Business Logic Layer (BLL) - has the necessary business logic Data Logic Layer (DLL) - any logic against data Data Access Layer (DAL) - one that accesses data from the database Now i want to provide error handling in my DLL since it is responsible for executing statement like ExecureScalar and all.... And i am confused as to how to go about it...i mean do i catch the error in the DLL and throw it back to the BLL and from there throw it back to my code or what.... can any one please help me how do i implement a clean and easy error handling techinque help you be really appreciated. Thank you.

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• How build my own Application Setting

  - by adisembiring

  I want to build a ApplicationSetting for my application. The ApplicationSetting can be stored in a properties file or in a database table. The settings are stored in key-value pairs. E.g. ftp.host = blade ftp.username = dummy ftp.pass = pass content.row_pagination = 20 content.title = How to train your dragon. I have designed it as follows: Application settings reader: interface IApplicationSettingReader { read(); } DatabaseApplicationSettingReader { dao appSettingDao; AppSettings read() { List<AppSettingEntity> listEntity = appSettingsDao.findAll(); Map<String, String> map = new HaspMap<String, String>(); foreach (AppSettingEntity entity : listEntity) { map.put(entity.getConfigName(), entity.getConfigValue()); } return new AppSettings(map); } } DatabaseApplicationSettingReader { dao appSettingDao; AppSettings read() { //read from some properties file return new AppSettings(map); } } Application settings class: AppSettings { private static AppSettings instance; private Map map; Public AppSettings(Map map) { this.map = map; } public static AppSettings getInstance() { if (instance == null) { throw new RuntimeException("Object not configure yet"); } return instance; } public static configure(IApplicationSettingReader reader) { instance = reader.read(); } public String getFtpSetting(String param) { return map.get("ftp." + param); } public String getContentSetting(String param) { return map.get("content." + param); } } Test class: AppSettingsTest { IApplicationSettingReader reader; @Before public void setUp() throws Exception { reader = new DatabaseApplicationSettingReader(); } @Test public void getContentSetting_should_get_content_title() { AppSettings.configure(reader); Instance settings = AppSettings.getInstance(); String title = settings.getContentSetting("title"); assertNotNull(title); Sysout(title); } } My questions are: Can you give your opinion about my code, is there something wrong? I configure my application setting once, while the application start, I configure the application setting with appropriate reader (DbReader or PropertiesReader), I make it singleton. The problem is, when some user edit the database or file directly to database or file, I can't get the changed values. Now, I want to implement something like ApplicationSettingChangeListener. So if the data changes, I will refresh my application settings. Do you have any suggestions how this can be implemented?

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