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  • "Collection was modified..." Issue

    - by Tyler Murry
    Hey guys, I've got a function that checks a list of objects to see if they've been clicked and fires the OnClick events accordingly. I believe the function is working correctly, however I'm having an issue: When I hook onto one of the OnClick events and remove and insert the element into a different position in the list (typical functionality for this program), I get the "Collection was modified..." error. I believe I understand what is going on: The function cycles through each object firing OnClick events where necessary An event is fired and the object changes places in the list per the hooked function An exception is thrown for modifying the collection while iterating through it My question is, how to do I allow the function to iterate through all the objects, fire the necessary events at the proper time and still give the user the option of manipulating the object's position in the list? Thanks, Tyler

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  • C# Design Questions

    - by guazz
    How to approach unit testing of private methods? I have a class that loads Employee data into a database. Here is a sample: public class EmployeeFacade { public Employees EmployeeRepository = new Employees(); public TaxDatas TaxRepository = new TaxDatas(); public Accounts AccountRepository = new Accounts(); //and so on for about 20 more repositories etc. public bool LoadAllEmployeeData(Employee employee) { if (employee == null) throw new Exception("..."); EmployeeRepository emps = new EmployeeRepository(); bool exists = emps.FetchExisting(emps.Id); if (!exists) { emps.AddNew(); } try { emps.Id = employee.Id; emps.Name = employee.EmployeeDetails.PersonalDetails.Active.Names.FirstName; emps.SomeOtherAttribute; } catch() {} try { emps.Save(); } catch(){} try { LoadorUpdateTaxData(employee.TaxData); } catch() {} try { LoadorUpdateAccountData(employee.AccountData); } catch() {} ... etc. for about 20 more other employee objects } private bool LoadorUpdateTaxData(employeeId, TaxData taxData) { if (taxData == null) throw new Exception("..."); ...same format as above but using AccountRepository } private bool LoadorUpdateAccountData(employee.TaxData) { ...same format as above but using TaxRepository } } I am writing an application to take serialised objects(e.g. Employee above) and load the data to the database. I have a few design question that I would like opinions on: A - I am calling this class "EmployeeFacade" because I am (attempting?) to use the facade pattern. Is it good practace to name the pattern on the class name? B - Is it good to call the concrete entities of my DAL layer classes "Repositories" e.g. "EmployeeRepository" ? C - Is using the repositories in this way sensible or should I create a method on the repository itself to take, say, the Employee and then load the data from there e.g. EmployeeRepository.LoadAllEmployeeData(Employee employee)? I am aim for cohesive class and but this will requrie the repository to have knowledge of the Employee object which may not be good? D - Is there any nice way around of not having to check if an object is null at the begining of each method? E - I have a EmployeeRepository, TaxRepository, AccountRepository declared as public for unit testing purpose. These are really private enities but I need to be able to substitute these with stubs so that the won't write to my database(I overload the save() method to do nothing). Is there anyway around this or do I have to expose them? F - How can I test the private methods - or is this done (something tells me it's not)? G- "emps.Name = employee.EmployeeDetails.PersonalDetails.Active.Names.FirstName;" this breaks the Law of Demeter but how do I adjust my objects to abide by the law?

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  • Using ThreadPool.QueueUserWorkItem in ASP.NET in a high traffic scenario

    - by Michael Hart
    I've always been under the impression that using the ThreadPool for (let's say non-critical) short-lived background tasks was considered best practice, even in ASP.NET, but then I came across this article that seems to suggest otherwise - the argument being that you should leave the ThreadPool to deal with ASP.NET related requests. So here's how I've been doing small asynchronous tasks so far: ThreadPool.QueueUserWorkItem(s => PostLog(logEvent)) And the article is suggesting instead to create a thread explicitly, similar to: new Thread(() => PostLog(logEvent)){ IsBackground = true }.Start() The first method has the advantage of being managed and bounded, but there's the potential (if the article is correct) that the background tasks are then vying for threads with ASP.NET request-handlers. The second method frees up the ThreadPool, but at the cost of being unbounded and thus potentially using up too many resources. So my question is, is the advice in the article correct? If your site was getting so much traffic that your ThreadPool was getting full, then is it better to go out-of-band, or would a full ThreadPool imply that you're getting to the limit of your resources anyway, in which case you shouldn't be trying to start your own threads? Clarification: I'm just asking in the scope of small non-critical asynchronous tasks (eg, remote logging), not expensive work items that would require a separate process (in these cases I agree you'll need a more robust solution).

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  • Strategy pattern and "action" classes explosion

    - by devoured elysium
    Is it bad policy to have lots of "work" classes(such as Strategy classes), that only do one thing? Let's assume I want to make a Monster class. Instead of just defining everything I want about the monster in one class, I will try to identify what are its main features, so I can define them in interfaces. That will allow to: Seal the class if I want. Later, other users can just create a new class and still have polymorphism by means of the interfaces I've defined. I don't have to worry how people (or myself) might want to change/add features to the base class in the future. All classes inherit from Object and they implement inheritance through interfaces, not from mother classes. Reuse the strategies I'm using with this monster for other members of my game world. Con: This model is rigid. Sometimes we would like to define something that is not easily achieved by just trying to put together this "building blocks". public class AlienMonster : IWalk, IRun, ISwim, IGrowl { IWalkStrategy _walkStrategy; IRunStrategy _runStrategy; ISwimStrategy _swimStrategy; IGrowlStrategy _growlStrategy; public Monster() { _walkStrategy = new FourFootWalkStrategy(); ...etc } public void Walk() { _walkStrategy.Walk(); } ...etc } My idea would be next to make a series of different Strategies that could be used by different monsters. On the other side, some of them could also be used for totally different purposes (i.e., I could have a tank that also "swims"). The only problem I see with this approach is that it could lead to a explosion of pure "method" classes, i.e., Strategy classes that have as only purpose make this or that other action. In the other hand, this kind of "modularity" would allow for high reuse of stratagies, sometimes even in totally different contexts. What is your opinion on this matter? Is this a valid reasoning? Is this over-engineering? Also, assuming we'd make the proper adjustments to the example I gave above, would it be better to define IWalk as: interface IWalk { void Walk(); } or interface IWalk { IWalkStrategy WalkStrategy { get; set; } //or something that ressembles this } being that doing this I wouldn't need to define the methods on Monster itself, I'd just have public getters for IWalkStrategy (this seems to go against the idea that you should encapsulate everything as much as you can!) Why? Thanks

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  • Factory pattern vs ease-of-use?

    - by Curtis White
    Background, I am extending the ASP.NET Membership with custom classes and extra tables. The ASP.NET MembershipUser has a protected constructor and a public method to read the data from the database. I have extended the database structure with custom tables and associated classes. Instead of using a static method to create a new member, as in the original API: I allow the code to instantiate a simple object and fill the data because there are several entities. Original Pattern #1 Protected constructor > static CreateUser(string mydata, string, mydata, ...) > User.Data = mydata; > User.Update() My Preferred Pattern #2 Public constructor > newUser = new MembershipUser(); > newUser.data = ... > newUser.ComplextObject.Data = ... > newUser.Insert() > newUser.Load(string key) I find pattern #2 to be easier and more natural to use. But method #1 is more atomic and ensured to contain proper data. I'd like to hear any opinions on pros/cons. The problem in my mind is that I prefer a simple CRUD/object but I am, also, trying to utilize the underlying API. These methods do not match completely. For example, the API has methods, like UnlockUser() and a readonly property for the IsLockedOut

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  • How to show validation messages in MVC?

    - by Ian Boyd
    When a user tries to click:        Save and they have entered in some invalid data, i want to notify them. This can be with methods such as: directing their attention to the thing that needs their attention with a balloon hint automatically dropping down a combo-box triggering an animation showing a modal dialog box etc What is the mechanism where a controller tells the view to show a validation message for some controls, given that different views have different notification methods? p.s. the controller doesn't know the order that controls are physically arranged in the view (e.g. LTR locale wants to notify the user in a top-down-left-to-right visual order, while RTL locale wants to notify the user in a bottom-up-right-to-left order)

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  • Best way to define an immutable class in Objective C

    - by Patrick Marty
    Hi, I am a newbie in Objective C and I was wondering what is the best way to define an immutable class in Objective-C (like NSString for example). I want to know what are the basic rules one has to follow to make a class immutable. I think that : setters shouldn't be provided if properties are used, they should be readonly accessInstanceVariablesDirectly must be override and return NO Did I forget something ? Thanks

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  • Working with jTempalte and objects

    - by Dejan.S
    EDITSolved the one object question I had at first Hi I'm using jTemplate for the first time. I been reading and it's not that hard to use it BUT I just found a examaple on one object use. <script type="text/html" id="TemplateREsultTable"> <div style="background-color: #ccc">{$T.Email}</div> <div style="background-color: #ddd">{$T.Password}</div> </script> One question about jTempaltes I got is what is better to do them in htm file or script? Another thought I got, is jTemplate the way to go?

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  • Worse is better. Is there an example?

    - by J.F. Sebastian
    Is there a widely-used algorithm that has time complexity worse than that of another known algorithm but it is a better choice in all practical situations (worse complexity but better otherwise)? An acceptable answer might be in a form: There are algorithms A and B that have O(N**2) and O(N) time complexity correspondingly, but B has such a big constant that it has no advantages over A for inputs less then a number of atoms in the Universe. Examples highlights from the answers: Simplex algorithm -- worst-case is exponential time -- vs. known polynomial-time algorithms for convex optimization problems. A naive median of medians algorithm -- worst-case O(N**2) vs. known O(N) algorithm. Backtracking regex engines -- worst-case exponential vs. O(N) Thompson NFA -based engines. All these examples exploit worst-case vs. average scenarios. Are there examples that do not rely on the difference between the worst case vs. average case scenario? Related: The Rise of ``Worse is Better''. (For the purpose of this question the "Worse is Better" phrase is used in a narrower (namely -- algorithmic time-complexity) sense than in the article) Python's Design Philosophy: The ABC group strived for perfection. For example, they used tree-based data structure algorithms that were proven to be optimal for asymptotically large collections (but were not so great for small collections). This example would be the answer if there were no computers capable of storing these large collections (in other words large is not large enough in this case). Coppersmith–Winograd algorithm for square matrix multiplication is a good example (it is the fastest (2008) but it is inferior to worse algorithms). Any others? From the wikipedia article: "It is not used in practice because it only provides an advantage for matrices so large that they cannot be processed by modern hardware (Robinson 2005)."

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  • I'm going to write 'Unit of Work', please help me find out all gimmicks

    - by o..o
    Hi everybody, I'm going to write my own DAL in C#. I decided to use 'Unit of Work' pattern (next mentioned as uow) with request as a scope and Identity map stored in HttpContext.Items. I have right now question about implementing of CRUD methods. How/where are they implemented? Are they implemented in every single business class (as in active records pattern) or are implemented somehow in uow class (if so, how)? I also suppose that I need to use as the scope not just the request, but also the db connection. But how? Should I open the connection a the start of the request and close it on uow disposing? Every advice is strongly appreciated, especially Your "real world" experiences. Thank you all :)

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  • I've Heard Global Variables Are Bad, What Alternative Solution Should I Use?

    - by Jay
    I've read all over the place that global variables are bad and alternatives should be used. In Javascript specifically, what solution should I choose. I'm thinking of a function, that when fed two arguments (function globalVariables(Variable,Value)) looks if Variable exists in a local array and if it does set it's value to Value, else, Variable and Value are appended. If the function is called without arguments (function globalVariables()) it returns the array. Perhaps if the function is fired with just one argument (function globalVariables(Variable)) it returns the value of Variable in the array. What do you think? I'd like to hear your alternative solutions and arguments for using global variables.

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  • What's the best way to explain parsing to a new programmer?

    - by Daisetsu
    I am a college student getting my Computer Science degree. A lot of my fellow students really haven't done a lot of programming. They've done their class assignments, but let's be honest here those questions don't really teach you how to program. I have had several other students ask me questions about how to parse things, and I'm never quite sure how to explain it to them. Is it best to start just going line by line looking for substrings, or just give them the more complicated lecture about using proper lexical analysis, etc. to create tokens, use BNF, and all of that other stuff? They never quite understand it when I try to explain it. What's the best approach to explain this without confusing them or discouraging them from actually trying.

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  • Databinding in WinForms performing async data import

    - by burnside
    I have a scenario where I have a collection of objects bound to a datagrid in winforms. If a user drags and drops an item on to the grid, I need to add a placeholder row into the grid and kick off a lengthy async import process. I need to communicate the status of the async import process back to the UI, updating the row in the grid and have the UI remain responsive to allow the user to edit the other rows. What's the best practice for doing this? My current solution is: binding a thread safe implementation of BindingList to the grid, filled with the objects that are displayed as rows in the grid. When a user drags and drops an item on to the grid, I create a new object containing the sparse info obtained from the dropped item and add that to the BindingList, disabling the editing of that row. I then fire off a separate thread to do the import, passing it the newly bound object I have just created to fill with data. The import process, periodically sets the status of the object and fires an event which is subscribed to by the UI telling it to refresh the grid to see the new properties on the object. Should I be passing the same object that is bound to the grid to the import process thread to operate on, or should I be creating a copy and merging back the changes to the object on the UI thread using BeginInvoke? Any problems or advice with this implementation? Thanks

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  • linq2sql - where to enlist transaction (repository or bll)?

    - by Caroline Showden
    My app uses a business layer which calls a repository which uses linq to sql. I have an Item class that has an enum type property and an ItemDetail property. I need to implement a delete method that: (1) always delete the Item (2) if the item.type is XYZ and the ItemDetail is not null, delete the ItemDetail as well. My question is where should this logic be housed? If I have it in my business logic which I would prefer, this involves two separate repository calls, each of which uses a separate datacontext. I would have to wrap both calls is a System.Transaction which (in sql 2005) get promoted to a distributed transaction which is not ideal. I can move it all to a single repository call and the transaction will be handled implicitly by the datacontext but feel that this is really business logic so does not belong in the repository. Thoughts? Carrie

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  • Using nullable types in C#

    - by Martin Brown
    I'm just interested in people's opinions. When using nullable types in C# what is the best practice way to test for null: bool isNull = (i == null); or bool isNull = !i.HasValue; Also when assigning to a non-null type is this: long? i = 1; long j = (long)i; better than: long? i = 1; long j = i.Value;

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  • Dynamic find methods Vs conditional statements

    - by piemesons
    Student.find(:all, :conditions => [‘name = ? and status = ?’ ‘mohit’, 1]) Vs Student.find_all_by_name_and_status(‘mohit’, 1) Both the queries will result the same set of row but first one is preferable cause in the second way there will be exception generated method_missing and then rails will try to relate it as dynamic method. if fine then result set to returned. Can any body explain me this in a good manner. What exactly is happening behind the screen. Please correct me if i am wrong.

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  • Empty constructor or no constructor

    - by Ram
    Hi, I think it is not mandatory to have a default constructor in a class (C#). So in that situation shall I have a empty constructor in the class or I can skip it? Is it a best practice to have a default empty constructor? Class test { test() { } ...... } or Class test { ...... }

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  • To Ajax or Not to Ajax a listing page

    - by kaivalya
    Here i am talking about product listing pages where there are multiple filters that filter the list of products appearing on the page like product types, categories price range etc. I have done such pages using both ajax and no ajax way in the past. What I like about using ajax in such page is that, when filters are selected I only update the section that contains the product list. There is no need to refresh the whole page which could end up re-loading the images on top bar, banners etc and slow down the user performance. Ajax way in my opinion becomes more compact and responsive from user experience. Down side for ajax route for me is; since filter states are not maintained in the URL I end up maintaining them on the server. This becomes complicated if I want to handle multi window scenarios and it is also costly to maintain such state on server memory for each session. Not using ajax and simply keeping all filter values on url and refreshing the page is quite simple but the luxury of refreshing only the pane that really needs to be refreshed is lost. Lately I am seeing a lot of large scale e-commerce sites that are using non-ajax approach on their listing pages and this is making me question one more time if it might be more efficient to build non-ajax listing make due to the long term maintenance ease and sacrifice a little bit from user experience. I am about to start implementing a new listing page for a product which I have the flexibility to go either way and I would appreciate your inputs.

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  • How to organize a large number of objects

    - by shane
    We have a large number of documents and metadata (xml files) associated with these documents. What is the best way to organize them? Currently we put them into a series of nested folders: /repository/category/date(when they were loaded into our db)/document_number.pdf and .xml We use the path as a unique identifier for the document in our system. This is more versatile than putting them all in a single flat folder. also it is independent from our database/application, so we can reload them in case of failure. Yet, it introduces some limitations. for example we can't move the files once they've been placed in this structure, also it takes work to put them this way. What is the best practice? How websites such as Scribd deal with this problem?

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  • DDD principlers and ASP.NET MVC project design

    - by kaivalya
    Two part questions I have a product aggregate that has; Prices PackagingOptions ProductDescriptions ProductImages etc I have modeled one product repository and did not create individual repositories for any of the child classes. All db operations are handled through product repository. Am I understanding the DDD concept correctly so far? Sometimes the question comes to my mind that having a repository for lets say packaging options could make my life easier by directly fetching a the packaging option from the DB by using its ID instead of asking the product repository to find it in its PackagingOptions collection and give it to me.. Second part is managing the edit create operations using ASP.MVC frame work I am currently trying to manage all add edit remove of these child collections of product through product controller(sound right?). One challenge I am now facing is; If I edit a specific packaging option of product through mydomain/product/editpackagingoption/10 I have access to the id of the packaging option But I don't have the ID of the product it self and this forces me to write a query to first find the product that has this specific packaging option then edit that product and the revelant packaging option. I can do this as all packaging option have their unique ID but this would fail if I have collections that don't have unique ID. That feels very wrong.. The next option I thought of is sending both the product and packaging option IDs on the url like; mydomain/product/editpackagingoption/3/10 But I am not sure if that is a good design either. So I am at a point that I am a bit confused. might be having fundamental misunderstandings around all of this... I would appreciate if you bear with the long question and help me put this together. thanks!

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  • EJB3 Business Delegates

    - by mykola
    Is there any reason for making delegate when using EJB3? Because the only real benefit i see from delegate is that it allows to hide lookup and access details of EJB architecture. Well it also provides some decoupling but it's mostly unused, imho. With EJB3 we have injection so now i can just create a variable with @EJB annotation and use it as is. Do i still need delegates? Is this injection resource consuming? I mean if i use it in JSF's request managed beans may be it's still better to use delegates just to lessen these injection calls? Thank you!

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  • What should be the responsibility of a presenter here?

    - by Achu
    I have a 3 layer design. (UI / BLL / DAL) UI = ASP.NET MVC In my view I have collection of products for a category. Example: Product 1, Product 2 etc.. A user able to select or remove (by selecting check box) product’s from the view, finally save as a collection when user submit these changes. With this 3 layer design how this product collection will be saved? How the filtering of products (removal and addition) to the category object? Here are my options. (A) It is the responsibility of the controller then the pseudo Code would be Find products that the user selected or removed and compare with existing records. Add or delete that collection to category object. Call SaveCategory(category); // BLL CALL Here the first 2 process steps occurs in the controller. (B) It is the responsibility of BLL then pseudo Code would be Collect products what ever user selected SaveCategory(category, products); // BLL CALL Here it's up to the SaveCategory (BLL) to decide what products should be removed and added to the database. Thanks

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