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  • How you would you describe the Observer pattern in beginner language?

    - by Sheldon
    Currently, my level of understanding is below all the coding examples on the web about the Observer Pattern. I understand it simply as being almost a subscription that updates all other events when a change is made that the delegate registers. However, I'm very unstable in my true comprehension of the benefits and uses. I've done some googling, but most are above my level of understanding. I'm trying to implement this pattern with my current homework assignment, and to truly make sense on my project need a better understanding of the pattern itself and perhaps an example to see what its use. I don't want to force this pattern into something just to submit, I need to understand the purpose and develop my methods accordingly so that it actually serves a good purpose. My text doesn't really go into it, just mentions it in one sentence. MSDN was hard for me to understand, as I'm a beginner on this, and it seems more of an advanced topic. How would you describe this Observer pattern and its uses in C# to a beginner? For an example, please keep code very simple so I can understand the purpose more than complex code snippets. I'm trying to use it effectively with some simple textbox string manipulations and using delegates for my assignment, so a pointer would help!

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  • Automatically create tag based on the string

    - by Gautam
    Hello, I am new to ruby on rails. Lets say i have this text.. Ashley Cole and Cheryl Cole Split. Is there a way to automatically tag this above text to Ashley Cole, Cheryl Code, ChelseaFC ( Ashley Cole plays football (Soccer) for that club. Please help.. Also which is the best tagging gem available? Looking forward for your help Thanks Gautam

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  • A format for storing personal contacts in a database

    - by Gart
    I'm thinking of the best way to store personal contacts in a database for a business application. The traditional and straightforward approach would be to create a table with columns for each element, i.e. Name, Telephone Number, Job title, Address, etc... However, there are known industry standards for this kind of data, like for example vCard, or hCard, or vCard-RDF/XML or even Windows Contacts XML Schema. Utilizing an standard format would offer some benefits, like inter-operablilty with other systems. But how can I decide which method to use? The requirements are mainly to store the data. Search and ordering queries are highly unlikely but possible. The volume of the data is 100,000 records at maximum. My database engine supports native XML columns. I have been thinking to use some XML-based format to store the personal contacts. Then it will be possible to utilize XML indexes on this data, if searching and ordering is needed. Is this a good approach? Which contacts format and schema would you recommend for this? Edited after first answers Here is why I think the straightforward approach is bad. This is due to the nature of this kind of data - it is not that simple. The personal contacts it is not well-structured data, it may be called semi-structured. Each contact may have different data fields, maybe even such fields which I cannot anticipate. In my opinion, each piece of this data should be treated as important information, i.e. no piece of data could be discarded just because there was no relevant column in the database. If we took it further, assuming that no data may be lost, then we could create a big text column named Comment or Description or Other and put there everything which cannot be fitted well into table columns. But then again - the data would lose structure - this might be bad. If we wanted structured data then - according to the database design principles - the data should be decomposed into entities, and relations should be established between the entities. But this adds complexity - there are just too many entities, and lots of design desicions should be made, like "How do we store Address? Personal Name? Phone number? How do we encode home phone numbers and mobile phone numbers? How about other contact info?.." The relations between entities are complex and multiple, and each relation is a table in the database. Each relation needs to be documented in the design papers. That is a lot of work to do. But it is possible to avoid the complexity entirely - just document that the data is stored according to such and such standard schema, period. Then anybody who would be reading that document should easily understand what it was all about. Finally, this is all about using an industry standard. The standard is, hopefully, designed by some clever people who anticipated and described the structure of personal contacts information much better than I ever could. Why should we all reinvent the wheel?? It's much easier to use a standard schema. The problem is, there are just too many standards - it's not easy to decide which one to use!

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  • C++, throw exception from initializer list

    - by aaa
    hello. what is the best way to throw exception from initializer list? for example: class C { T0 t0; // can be either valid or invalid, but does not throw directly T1 t1; // heavy object, do not construct if t0 is invalid, by throwing before C(int n) : t0(n), // throw exception if t0(n) is not valid t1() {} }; I thought maybe making wrapper, e.g. t0(throw_if_invalid(n)). What is the practice to handle such cases? Thanks

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  • Best practice in this situation?

    - by Steve
    My Delphi program relies heavily on Outlook automation. Outlook versions prior to 2007-SP2 tend to get stuck in memory due to badly written addins and badly written Outlook code. If Outlook is stuck, calling CreateOleObject('Outlook.Application') or GetActiveObject ... doesn't return and keeps my application hanging till Outlook.exe is closed in the task manager. I've thought of a solution, but I'm unsure whether it's good practice or not. I'd start Outlook with CreateOleObject in a separate thread, wait 10 seconds in my main thread and if Outlook hangs (CreateOleObject doesn't return), offer the user to kill the Outlook.exe process from my program. But since I don't want to force the user to kill the Outlook.exe proccess, as an alternative I also need a way to kill the new thread in my program which keeps hanging now. My questions are: a, Is this good practice b, How can I terminate a hanging thread in Delphi without leaking memory? Is there a way?

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  • COM: How to handle a specific exception?

    - by Ian Boyd
    i'm talking to a COM object (Microsoft ADO Recordset object). In a certain case the recordset will return a failed (i.e. negative) HRESULT, with the message: Item cannot be found in the collection corresponding to the requested name or ordinal i know what this error message means, know why it happened, and i how to fix it. But i know these things because i read the message, which fortunately was in a language i understand. Now i would like to handle this exception specially. The COM object threw an HRESULT of 0x800A0CC1 In an ideal world Microsoft would have documented what errors can be returned when i try to access: records.Fields.Items( index ) with an invalid index. But they do not; they most they say is that an error can occur, i.e.: If Item cannot find an object in the collection corresponding to the Index argument, an error occurs. Given that the returned error code is not documented, is it correct to handle a specific return code of `0x800A0CC1' when i'm trying to trap the exception: Item cannot be found in the collection corresponding to the requested name or ordinal ? Since Microsoft didn't document the error code, they technically change it in the future.

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  • Reordering arguments using recursion (pro, cons, alternatives)

    - by polygenelubricants
    I find that I often make a recursive call just to reorder arguments. For example, here's my solution for endOther from codingbat.com: Given two strings, return true if either of the strings appears at the very end of the other string, ignoring upper/lower case differences (in other words, the computation should not be "case sensitive"). Note: str.toLowerCase() returns the lowercase version of a string. public boolean endOther(String a, String b) { return a.length() < b.length() ? endOther(b, a) : a.toLowerCase().endsWith(b.toLowerCase()); } I'm very comfortable with recursions, but I can certainly understand why some perhaps would object to it. There are two obvious alternatives to this recursion technique: Swap a and b traditionally public boolean endOther(String a, String b) { if (a.length() < b.length()) { String t = a; a = b; b = t; } return a.toLowerCase().endsWith(b.toLowerCase()); } Not convenient in a language like Java that doesn't pass by reference Lots of code just to do a simple operation An extra if statement breaks the "flow" Repeat code public boolean endOther(String a, String b) { return (a.length() < b.length()) ? b.toLowerCase().endsWith(a.toLowerCase()) : a.toLowerCase().endsWith(b.toLowerCase()); } Explicit symmetry may be a nice thing (or not?) Bad idea unless the repeated code is very simple ...though in this case you can get rid of the ternary and just || the two expressions So my questions are: Is there a name for these 3 techniques? (Are there more?) Is there a name for what they achieve? (e.g. "parameter normalization", perhaps?) Are there official recommendations on which technique to use (when)? What are other pros/cons that I may have missed?

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  • GAE modeling relationship options

    - by Sway
    Hi there, I need to model the following situation and I can't seem to find a consistent example on how to do it "correctly" for the google app engine. Suppose I've got a simple situation like the following: [Company] 1 ----- M [Stare] A company has one to many stores. Each store has an address made up of a address line 1, city, state, country, postcode etc. Ok. Lets say we need to create say an "Audit". An Audit is for a company and can be across one to many stares. So something like: [Audit] 1 ------ 1 [Company] 1 ------ M [Store] Now we need to query all of the "audits" based on the Store "addresses" in order to send the "Auditors" to the right locations. There seem to be numerous articles like this one: http://code.google.com/appengine/articles/modeling.html Which give examples of creating a "ContactCompany" model class. However they also say that you should use this kind of relationship only when you "really need to" and with "care" for performance. I've also read - frequently - that you should denormalize as much as possible thereby moving all of the "query-able" data into the Audit class. So what would you suggest as the best way to solve this? I've seen that there is an Expando class but I'm not sure if that is the "best" option for this. Any help or thoughts on this would be totally appreciated. Thanks in advance, Matt

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  • Is JavaScript 's "new" Keyword Considered Harmful?

    - by Pablo Fernandez
    In another question, a user pointed out that the new keyword was dangerous to use and proposed a solution to object creation that did not use new... I didn't believe that was true, mostly because I've used Prototype, Scriptaculous and other excellent JavaScript libraries, and everyone of them used the new keyword... In spite of that, yesterday I was watching Douglas Crockford's talk at YUI theater and he said the exactly same thing, that he didn't use the new keyword anymore in his code. Is it 'bad' to use the new keyword? what are the advantages and disadvantages of using it?

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  • effective retrieve for a voting system in PHP and MySQL

    - by Adnan
    Hello, I have a system where registered users can vote up/vote down comment for a picture. Something very similar to SO's voting system. I store the votes in a table with values as such; vote_id | vote_comment_id | vote_user_id | vote_date | vote_type Now I have few a question concerned the speed and efficiency for the following; PROB: Once a user opens the picture page with comments I need, if that user has already voted UP/DOWN a comment to show it like; "you voted up" or "you voted down" next to the comment (in SO it the vote image is highlighted) MY POSSIBLE SOL: Right now when I open a picture page for each comment I loop thru, I loop thru my table of votes as well and check if a user has voted and show the status (I compare the vote_user_id with the user's session). How efficient is this? Anyone have a better approach to tackle this kind of problem?

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  • Is there a way to avoid debugger?

    - by Gabriel Šcerbák
    I don't like debugging in a debugger, because I think it is often below the abstraction layer of the programming language and it is often not reproducible. I favor usign unit tests when possible and I think they are a good way, but it is not always that easy to implement them. Do you know about any other alternative approaches to avoid the use of debugger?

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  • What is considered a long execution time?

    - by stjowa
    I am trying to figure out just how "efficient" my server-side code is. Using start and end microtime(true) values, I am able to calculate the time it took my script to run. I am getting times from .3 - .5 seconds. These scripts do a number of database queries to return different values to the user. What is considered an efficient execution time for PHP scripts that will be run online for a website? Note: I know it depends on exactly what is being done, but just consider this a standard script that reads from a database and returns values to the user. Also, I look at Google and see them search the internet in .15 seconds and I feel like my script is crap. Thanks.

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  • Factory Pattern - when do you say you need a specialised factory

    - by dbones
    Hi, I am having a little design crisis, I am making a Plane class, which is made of an engine 2 wings and N seats The engine takes in a engine size, and the wings have a span. would this still be feasible to have a PlaneFactory, when the factory may have to take in multiple parameters to setup the plane (wings, engine, no of seats) thanks in advance bones

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  • What is the best practice for using lock within inherited classes

    - by JDMX
    I want to know if one class is inheriting from another, is it better to have the classes share a lock object that is defined at the base class or to have a lock object defined at each inheritance level. A very simple example of a lock object on each level of the class public class Foo { private object thisLock = new object(); private int ivalue; public int Value { get { lock( thisLock ) { return ivalue; } } set { lock( thisLock ) { ivalue= value; } } } } public class Foo2: Foo { private object thisLock2 = new object(); public int DoubleValue { get { lock( thisLock2 ) { return base.Value * 2; } } set { lock( thisLock2 ) { base.Value = value / 2; } } } } public class Foo6: Foo2 { private object thisLock6 = new object(); public int TripleDoubleValue { get { lock( thisLock6 ) { return base.DoubleValue * 3; } } set { lock( thisLock6 ) { base.DoubleValue = value / 3; } } } } A very simple example of a shared lock object public class Foo { protected object thisLock = new object(); private int ivalue; public int Value { get { lock( thisLock ) { return ivalue; } } set { lock( thisLock ) { ivalue= value; } } } } public class Foo2: Foo { public int DoubleValue { get { lock( thisLock ) { return base.Value * 2; } } set { lock( thisLock ) { base.Value = value / 2; } } } } public class Foo6: Foo2 { public int TripleDoubleValue { get { lock( thisLock ) { return base.DoubleValue * 3; } } set { lock( thisLock ) { base.DoubleValue = value / 3; } } } } Which example is the preferred way to manage locking within an inherited class?

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  • CQRS - The query side

    - by mattcodes
    A lot of the blogsphere articles related to CQRS (command query repsonsibility) seperation seem to imply that all screens/viewmodels are flat. e.g. Name, Age, Location Of Birth etc.. and thus the suggestion that implementation wise we stick them into fast read source etc.. single table per view mySQL etc.. and pull them out with something like primitive SqlDataReader, kick that nasty nhibernate ORM etc.. However, whilst I agree that domain models dont mapped well to most screens, many of the screens that I work with are more dimensional, and Im sure this is pretty common in LOB apps. So my question is how are people handling screen where by for example it displays a summary of customer details and then a list of their orders with a [more detail] link etc.... I thought about keeping with the straight forward SQL query to the Query Database breaking off the outer join so can build a suitable ViewModel to View but it seems like overkill? Alternatively (this is starting to feel yuck) in CustomerSummaryView table have a text/big (whatever the type is in your DB) column called Orders, and the columns for the Order summary screen grid are seperated by , and rows by |. Even with XML datatype it still feeel dirty. Any thoughts on an optimal practice?

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  • Objective-C Simple Inheritance and OO Principles

    - by bleeckerj
    I have a subclass SubClass that inherits from baseclass BaseClass. BaseClass has an initializer, like so: -(id)init { self = [super init]; if(self) { [self commonInit]; } return self; } -(void)commonInit { self.goodStuff = [[NSMutableArray alloc]init]; } SubClass does its initializer, like so: -(id)init { self = [super init]; if(self) { [self commonInit]; } return self; } -(void)commonInit { self.extraGoodStuff = [[NSMutableArray alloc]init]; } Now, I've *never taken a proper Objective-C course, but I'm a programmer more from the Electrical Engineering side, so I make do. I've developed server-side applications mostly in Java though, so I may be seeing the OO world through Java principles. When SubClass is initialized, it calls the BaseClass init and my expectation would be — because inheritance to me implies that characteristics of a BaseClass pass through to SubClass — that the commonInit method in BaseClass would be called during BaseClass init. It is not. I can *sorta understand maybe-possibly-stretch-my-imagination why it wouldn't be. But, then — why wouldn't it be based on the principles of OOP? What does "self" represent if not the instance of the class of the running code? Okay, so — I'm not going to argue that what a well-developed edition of Objective-C is doing is wrong. So, then — what is the pattern I should be using in this case? I want SubClass to have two main bits — the goodStuff that BaseClass has as well as the extraGoodStuff that it deserves as well. Clearly, I've been using the wrong pattern in this type of situation. Am I meant to expose commonInit (which makes me wonder about encapsulation principles — why expose something that, in the Java world at least, would be considered "protected" and something that should only ever be called once for each instance)? I've run into a similar problem in the recent past and tried to muddle through it, but now — I'm really wondering if I've got my principles and concepts all straight in my head. Little help, please.

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  • Looking for exercises to learn SQL, using the Northwind database

    - by MedicineMan
    I am trying to become more familiar with SQL by writing queries against the Northwind database. I am looking for some exercises that would help me to learn SQL and features of SQL Server. It is important that the exercises have solutions, and in complicated cases, it would be great if there was an explanation for the query. Thanks for the answers so far but I still have not found what I am looking for: Is there any free resource, available online, without registration, that I can find a list of these exercises?

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  • Use of @keyword in C# -- bad idea?

    - by Robert Fraser
    In my naming convention, I use _name for private member variables. I noticed that if I auto-generate a constructor with ReSharper, if the member is a keyword, it will generate an escaped keyword. For example: class IntrinsicFunctionCall { private Parameter[] _params; public IntrinsicFunctionCall(Parameter[] @params) { _params = @params; } } Is this generally considered bad practice or is it OK? It happens quite frequently with @params and @interface.

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  • where to enlist transaction with parent child delete (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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  • How-to limit feature functionality

    - by ph0enix
    Are there any standard or "best practice" ways of limiting feature functionality for a particular application? Example: We have a product with a variety of features, and our customers can pick and choose which features they would like to use, and the cost of the product varies based on which features they are actually using. In the past, we have distributed along with our software installer an encrypted license file that contains information about the customer, as well as the collection of features that they have enabled. In code, we read from the license file and enable the functionality according to the license file. This seems to work fine, except there a few disadvantages: Upgrading users with new functionality can be sort of a pain If a particular feature shows up in multiple places throughout the application, a developer might not realize that this feature should be licensed, and forget to check the license file before granting functionality to the user If the license file becomes corrupted, deleted, moved, renamed, etc. the application will not run We're getting ready to roll out a new set of features, and I was just curious what others in the community have done to tackle this problem?

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  • Rails: find by day of week with timestamp

    - by Sleepycat
    I need to grab the records for same day of the week for the preceeding X days of the week. There must be a better way to do it than this: Transaction.find_by_sql "select * from transactions where EXTRACT(DOW from date) = 1 and organisation_id = 4 order by date desc limit 7" It gets me what I need but is Postgres specific and not very "Rails-y". Date is a timestamp. Anyone got suggestions?

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  • How do I remove a folder from Windows Distributed File System?

    - by digiguru
    We recently moved to a webfarm and setup dfs, only to find a beta application was creating files like there was no tomorrow. 1.2 million files were replicated across the farm, and since then we have prevented the application from creating new files, but every time we try to remove the files, it replaces them on each server because of replication. The process of replacing them actually causes to server to run slowly and in some cases stall. Is there any way we can stop replication at a folder level?

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