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• Singletons and other design issues

  - by Ahmed Saleh

  I have worked using different languages like C++/Java and currently AS3. Most applications were computer vision, and small 2D computer games. Most companies that I have worked for, they use Singletons in a language like AS3, to retrieve elements or classes in an easy way. Their problem is basically they needs some variables or to call other functions from other classes. In a language like AS3, there is no private constructor, and they write a hacky code to prevent new instances. In Java and C++ I also faced the situation that I need to use other classe's members or to call their functions in different classes. The question is, is there a better or another design, to let other classes interact with each others without using singletons? I feel that composition is the answer, but I need more detailed solutions or design suggestions.

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• Ecommerce database design looking for good book

  - by meyosef

  Hi I looking for good book about E-commerce database design. Thanks

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• design pattern tools to use?

  - by ajsie

  i have noticed that every area has some tools you can use to make things easier. eg. css = dreamweaver doctrine/propel = orm designer // you dont have to hardcore code schemas manually and remembering all the syntax/variables mysql = mysql workbench // the same etc. in this way you get aided and dont have to type things the hard way, and can learn the structure, but then use GUI tools to help you develop faster. now i'm learning design patterns (singleton, factory, command, memento etc) and im wondering if there are some kind of tools you can use that will help you develop faster. i dont know exactly what tools i'm trying to find, just helping me when coding with design patterns (schema drawings? references?) are there any?

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• Java: design problem with private-final-int-value and empty constructor

  - by HH

  $ javac InitInt.java InitInt.java:7: variable right might not have been initialized InitInt(){} ^ 1 error $ cat InitInt.java import java.util.*; import java.io.*; public class InitInt { private final int right; //DUE to new Klowledge: Design Problem //I think having an empty constructor like this // is an design problem, shall I remove it? What do you think? // When to use an empty constructor? InitInt(){} public static void main(String[] args) { InitInt test = new InitInt(); System.out.println(test.getRight()); } public int getRight(){return right;} } Initialization problem with Constructor InitInt{ // Still the error, "may not be initialized" // How to initialise it? if(snippetBuilder.length()>(charwisePos+25)){ right=charwisePos+25; }else{ right=snippetBuilder.length()-1; } }

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• Looking for some Feedback on a DB Design

  - by zSysop

  I'm currently working on a ticketing system which allows our users to submit tickets based on their own needs. i.e. if Department "A" is submitting a ticket they can have certain types of problem categories (such as "Supplies" or "Printer") along with details pertaining to the chosen category. I have laid out a partial db design and i was looking for some feedback on it. I've never built a system from the ground up by myself so i'm a little bit nervous. here's my a draft version of my db design Issues Table Id | CreatedBy | CreateDate | Status | Owner | AssignedTo | AssignmentDate | ----------------------------------------------------------------------------- EquipmentIssueDetails Table Id | IssueId | Serial # | Make | Model | .... --------------------------------------------- SupplyIssueDetails Table Id | IssueId | SupplyId | ItemId | QTY | UnitOfMeasurement ------------------------------------------------------------- NetworkIssueDetails Table Id | IssueId | Supervisor | Details | ------------------------------------------------------------- Notes Table Id | IssueId | Note | CreatedBy | CreateDate ------------------------------------------------------------- Thanks in advance

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• ready to use design pattern APIs for PHP?

  - by ajsie

  i know that in Java you can use their built-in APIs for design pattern. eg. if you want to use the observer pattern, you just have to extend your Subject class with the Observable class. is this possible for PHP? are there any libraries for the design patterns ready to use. in this way you don't have to reinvent the wheel and you also let many developers follow a standard. does Zend library have these API:s?

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• Looking for design patterns to isolate framework layers from each other

  - by T Reddy

  Hi, I'm wondering if anyone has any experience in "isolating" framework objects from each other (Spring, Hibernate, Struts). I'm beginning to see design "problems" where an object from one framework gets used in another object from a different framework. My fear is we're creating tightly coupled objects. For instance, I have an application where we have a DynaActionForm with several attributes...one of which is a POJO generated by the Hibernate Tools. This POJO gets used everywhere...the JSP populates data to it, the Struts Action sends it down to a Service Layer, the DAO will persist it...ack! Now, imagine that someone decides to do a little refactoring on that POJO...so that means the JSP, Action, Service, DAO all needs to be updated...which is kind of painful...There has got to be a better way?! There's a book called Core J2EE Patterns: Best Practices and Design Strategies (2nd Edition)...is this worth a look? I don't believe it touches on any specific frameworks, but it looks like it might give some insight on how to properly layer the application... Thanks!

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• User control attributes at design-time

  - by ciscoheat

  I'm testing a simple User Control in Visual Studio 2008: A Panel named Wrapper with some controls inside. Can Visual Studio handle this at design time? public partial class TestControl : System.Web.UI.UserControl { [Description("Css class of the div around the control.")] [CssClassProperty] public string CssClass { get { return Wrapper.CssClass; } set { Wrapper.CssClass = value; } } } When setting the CssClass property, it doesn't update the css of the Panel at design time. Am I hoping for too much?

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• Use a custom value object or a Guid as an entity identifier in a distributed system?

  - by Kazark

  tl;dr I've been told that in domain-driven design, an identifier for an entity could be a custom value object, i.e. something other than Guid, string, int, etc. Can this really be advisable in a distributed system? Long version I will invent an situation analogous to the one I am currently facing. Say I have a distributed system in which a central concept is an egg. The system allows you to order eggs and see spending reports and inventory-centric data such as quantity on hand, usage, valuation and what have you. There area variety of services backing these behaviors. And say there is also another app which allows you to compose recipes that link to a particular egg type. Now egg type is broken down by the species—ostrich, goose, duck, chicken, quail. This is fine and dandy because it means that users don't end up with ostrich eggs when they wanted quail eggs and whatnot. However, we've been getting complaints because jumbo chicken eggs are not even close to equivalent to small ones. The price is different, and they really aren't substitutable in recipes. And here we thought we were doing users a favor by not overwhelming them with too many options. Currently each of the services (say, OrderSubmitter, EggTypeDefiner, SpendingReportsGenerator, InventoryTracker, RecipeCreator, RecipeTracker, or whatever) are identifying egg types with an industry-standard integer representation the species (let's call it speciesCode). We realize we've goofed up because this change could effect every service. There are two basic proposed solutions: Use a predefined identifier type like Guid as the eggTypeID throughout all the services, but make EggTypeDefiner the only service that knows that this maps to a speciesCode and eggSizeCode (and potentially to an isOrganic flag in the future, or whatever). Use an EggTypeID value object which is a combination of speciesCode and eggSizeCode in every service. I've proposed the first solution because I'm hoping it better encapsulates the definition of what an egg type is in the EggTypeDefiner and will be more resilient to changes, say if some people now want to differentiate eggs by whether or not they are "organic". The second solution is being suggested by some people who understand DDD better than I do in the hopes that less enrichment and lookup will be necessary that way, with the justification that in DDD using a value object as an ID is fine. Also, they are saying that EggTypeDefiner is not a domain and EggType is not an entity and as such should not have a Guid for an ID. However, I'm not sure the second solution is viable. This "value object" is going to have to be serialized into JSON and URLs for GET requests and used with a variety of technologies (C#, JavaScript...) which breaks encapsulation and thus removes any behavior of the identifier value object (is either of the fields optional? etc.) Is this a case where we want to avoid something that would normally be fine in DDD because we are trying to do DDD in a distributed fashion? Summary Can it be a good idea to use a custom value object as an identifier in a distributed system (solution #2)?

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• High level programming logic, design, pattern

  - by Muhammad Shahzad

  I have been doing programming from last 7 years, getting better and better, but still i think that am lacking something. I have been doing work in JOOMLA, MAGENTO, WP, Custom PHP, Opencart, laravel, codeignitor. Sometimes i need to design logic for a huge database application, in the applications we need nesting loops and queries, although i follow OOPS standards, ORM etc, still i feel i need more robust coding designs. I need to know how can i improve these things, so that code remain neat, efficient and faster. Also how big webapps like facebook twitter tests there code speed? How high level programmers choose design patterns. If you can help me find something useful with examples?

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• Database design efficiency with 1 to many relationships limited 1 to 3

  - by Joe

  This is in mysql, but its a database design issue. If you have a one to many relationship, like a bank customer to bank-accounts, typically you would have the table that records the bank-account information have a foreign key that keeps track of the relationship between account and customer. Now this follows the 3rd normal form thing and is a widely accepted way of doing it. Now lets say that you are going to limit a user to only having 3 accounts. The current database implementation will support this and nothing would need to change. But another way to do this would have 3 coloms in the account table that have the id of the 3 respective accounts in them. By the way this violates 1st normal form of db design. The question is what would be the advantage and disadvantages of having the user account relationship recored in this way over the traditional?

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• What is the best design to this class?

  - by HPT

  assume this class: public class Logger { static TextWriter fs = null; public Logger(string path) { fs = File.CreateText(path); } public static void Log(Exception ex) { ///do logging } public static void Log(string text) { ///do logging } } and I have to use this like: Logger log = new Logger(path); and then use Logger.Log() to log what I want. the question is: is this a good design? to instantiate a class and then always call it's static method? any suggestion yield in better design is appreciated.

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• Resources for dashboard app backend design

  - by Nix

  I am looking for examples of code/data/infrastructure design for a dashboard-style webapp. I am designing an interface for staff and faculty at a university to access departmental resources and be alerted of cyclical processes, events, deadlines, etc. Technologies I am working with: apache tomcat 6 and a mySQL database, JSP (including JSTL), bootstrap 3, and javascript/jquery. I have basic experience most of these technologies building smaller web apps but was hoping someone could direct me towards a book or other resource that discusses how to design the db architecture (and maybe how to template) for a dashboard, esp. for something like a notification systems. Any suggestions?

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• Design Documents for Python/Django?

  - by british_trader

  After working on a Django project for a while, I now have to do some design documents for it (UML type stuff). However the code doesn't have classes, but instead uses views.py with modules in it... What would be the best way to show the design of my application from the initial __init__.py, to the urls.py where the HTML requests are then filtered to the specific urls.py in each of the packages and then handled by the views.py? i.e. django-app urls.py views.py settings.py manager.py __init__.py django-package urls.py views.py

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• design-pattern libraries ready-to-use?

  - by fayer

  symfony has released some of their components free to use outside the framework. i have used the event dispatcher and dependency injection...they are awesome! i wonder if there are other components/libraries (from other frameworks etc) that in the same way help you manage various design patterns? eg. decorator, facade, singleton, chain of commands etc. i think symfony is on the right path, abstracting away the design patterns. are there any other components out there doing the same? thanks

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• More swing design & actions

  - by takoi

  Im pretty new to gui programming so i've been reading through every post on this site about swing and design. Whats been answered over and over again is that one should have a class which handles all the action. Like this: (GUI being some JFrame) Now, this works great for one-way actions, like OpenDialog. But the actions for buttons in DialogA and B will have to have access to all the components (there will be many) in its dialog, and the controller. This is where im stuck. The only sane way i can see is to put it in DialogA/B but i would then need to pass the controller all the way down, through classes that dont even need it, and it'll get all spaghetti. Really dont want that. Someone must have encountered this problem before. So where should i put this Action? Or should i just drop the whole design?

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• Inventory Management OOP design

  - by rgamber

  This was an OOP design and implementation interview question, which I came across on glassdoor.com. Design and implement a inventory management system to minimize the number of missed delivery dates while keeping costs to the company low. Of course there is no right answer to this, but I am not sure I understand the question correctly and am wondering what would be a good answer. Is this as simple as creating an undirected graph with nodes as the delivery points, and edges having weights as the cost of the delivery, and then use a single-source-shortest-path algorithm (like Dijkstras, or Bellman-Ford) on the graph? Not sure if this type of question should be asked here,so let me know and I will delete it.

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• System State Backups using NTbackup fail with error 0x800423f4 (relating to volume shadow copy)

  - by Paul Zimmerman

  We have a Windows Server 2003 R2 running Service Pack 2. It is a domain controller (Global Catalog) and our main internal DNS server. We run a System State backup of the machine to back up Active Directory information and save the backup to a different server. This server has a single drive (C:), and we do have Shadow Copies enabled for the volume (which are completing successfully). The System State Backup is now failing with the following listed in the backup logs: Volume shadow copy creation: Attempt 1. "Event Log Writer" has reported an error 0x800423f4. This is part of System State. The backup cannot continue. Error returned while creating the volume shadow copy:800423f4 Aborting Backup. The operation did not successfully complete. When doing a vssadmin list writers, we sometimes get the following reported for the Event Log Writer (other times it says that it is in the state of "[1] Stable" with "No error"): Writer name: 'Event Log Writer' Writer Id: {eee8c692-67ed-4250-8d86-390603070d00} Writer Instance Id: {c7194e96-868a-49e5-ba99-89b61977753c} State: [8] Failed Last error: Retryable error We have tried disabling the event log service via the registry, rebooting, deleting the event log files from the drive, then re-enabling the service via the registry and rebooting, but this didn't seem to solve the issue. We also get an error message when in the event viewer when trying to open the log for the "File Replication Service" of "Unable to complete the operation on 'File Replication Service'. The security descriptor structure is invalid." I have searched the error via Google and tried a number of different things, but nothing has seemed to help. Any suggestions on what we might try to get the Event Log Writer to behave would be greatly appreciated!

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• Looking for a help desk ticketing system..

  - by Dan

  Hi guys Im looking for a good help desk ticket solution. It must perform the following actions for it to be useful. It needs to have a single point of contact via email..e.g [email protected] If we recieve a telephone(or an email outside of the system) we need to be able to create a ticket as if had been added via the single point of contact, this needs to be done with ease in order to save time. Certain people within our organisation deal with certain customers, so if the email/ custom input support call as mentioned in bullet 2 is picked up as having a relationship with that certain person in our organisation it needs to be sent to them/put in their queue for them to work on. If a person is out of office or sick any tickets sent to them must be forwarded to somebody else or put into a seperate pool of tickets that anybody can access. Perhaps have an agent that sorts through tickets in the pool and assigns them to anybody who is available, preferably the person with fewest tickets in their queue/list. Once a customer emails and the system logs it they immediately get a response with a ticket number and maybe details of who is dealing with the problem. Any correspondance in relation to a particular ticket is automatically grouped into some sort of message, and not made into a load of separate tickets. I.e system scans incoming email subjects for ticket numbers and assosciates it with exisiting tickets if that number exists. Any help is much appreciated Thanks P.S I have taken a look at OTRS but i'm not feeling it so unless someone can convince me I guess i'm after an alternative.

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• how to remove an entry from system tray?

  - by altvali

  I've searched for an answer to this one and I haven't found one yet. How do i remove a single item from Windows' System tray? I'm targeting Windows XP. Edit: This is not about preventing items from starting up. I want the program to keep running, I just need another script/program to remove the first one's entry from system tray. Second Edit: One approach that I can think of is to try to hide the intended app by modifying registry keys. On several test machines I've found some registry entries that match the System tray information at HKEY_USERS\something-that-looks-like S-1-5-21-682003330-1563985344-725345543-1003\Software\Microsoft\Windows\CurrentVersion\Explorer\TrayNotify with BalloonTip, IconStream and PastIconsStream containing systray information. The important one is IconStream. On other machines, these are found at hkey_classes_root/local/setting/software/microsoft/windows/currentversion/TrayNotify I'm quite sure there's no danger in changing those specific registries, but I don't know how to write code for that. Can anyone help me with the code and with confirming if this has the desired effect of hiding the systray icon for an active program?

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• Hourly SQL Server 2005 Slowness (Possibly caused by SYSTEM)

  - by Zorlack

  We're trying to diagnose the cause of slowness on our Database server. We're running the latest rev SQL Server 2005 on Windows 2008x64. The behavior that we're seeing is this: We see the SYSTEM process spike one of the CPUs for about 2 minutes, during this time SQL server slows down by a factor of 10. The slowness lasts until SYSTEM is done, then in an hour everything starts again. During these slowdowns disk writes don't spike, paging doesn't spike, the only noticeable precursor we see is that SYSTEM maxes out one of the sixteen (HT)CPUs. Note that this doesn't happen at the top of the hour, it just happens once an hour, and it shifts a bit depending on the length of the incident. At the moment this is causing intermittent slowdowns, but when the server is really busy it can cause Worker Thread starvation. The server is a Dual Quad Dell R710 with 96GB of RAM and RAID10 data/log disks. Has anyone experienced this kind of problem? Does anyone know where we should look?

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• System Center 2012 VMM UI is very slow

  - by Grant

  I've recently setup system center 2012 a new server 2008 r2 server which I'm using for virtual machines. Everything seems to be working fine, and the virtual machines are nice and fast. But the Virtual Machine Manager interface is always excruciatingly slow. Sometimes taking up to 15 seconds moving between screens. It's very frustrating trying to use it when a task that just involves a couple clicks ends up taking several minutes. Pages that have a lot of form fields seem to take the longest to load - such as the page to change hardware settings of a virtual machine. Is this just normal performance for VMM? If not, where can I look to find what is slowing it down. Nothing else on the system seems to suffer. I can load and use Hyper-V manager with no noticable slowness. Even programs like event viewer that are usually rather slow seem to load fairly fast. Only the system center programs seem slow. Server is a Dell R710, 2x16 core opteron 6274 processors, 96GB RAM. OS drive is 2x500GB 7.2k RPM SAS drives in RAID1 (opted for the less expensive 7.2k drives since pretty much everything is stored on the SAN). Am I just being impatient? Does anyone else use VMM 2012 and find it slow?

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• What do I need to know to design a language and write a interpreter for it?

  - by alFReD NSH

  I know this question has been asked and even there are thousands of books and articles about it. But the problem is that there are too many, and I don't know are they good enough, I have to design a language and write a interpreter for it. The base language is javascript (using nodejs) but it's ok if the compiler was written in another language that I can use from node. I had done a research about compiler compilers in JS, there is jison (Bison implementaion in JS), waxeye, peg.js. I decided to give jison a try, due to the popularity and its being used by coffee script, so it should be able to cover my language too. The grammar definition syntax is similar to bison. But when I tried read the bison manual it seemed very hard to understand for me. And I think it's because I don't know a lot of things about what I'm doing. Like I don't what is formal language theory. I am experienced in Javascript (I'm more talented in JS than most average programmers). And also know basic C and C++ (not much experience but can write a working code for basic things). I haven't had any formal education, so I may not be familiar with some software engineering and computer science principles. Though everyday I try to grasp a lot of articles and improve. So I'm asking if you know any good book or article that can help me. Please also write why the resource you're suggesting is good. --update-- The language I'm trying to create, is not really complicated. All it has is expressions (with or without units), comparisons and logical operators. There are no functions, loops, ... The goal is to create a language that non-programmers can easily learn. And to write customized validations and calculations.

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• Do cross reference database tables have a place in domain driven design?

  - by Mike Cellini

  First some background. Let's say we have a system where a customer is placing an order in a web interface. The items that customer is ordering can priced in various ways. Sometimes including the cost of delivery and sometimes not at all. That pricing effectively depends on a variety of factors including the vendor's own pricing model, that vendor's individual contracts with customers as well as that vendor's contracts with its own suppliers. Let's assume that once a customer places an order for a particular item and chooses a contract if any, the method of delivery can be determined by variables on those contracts. Those delivery methods also live in their own table in the database and have various properties consumed downstream. It makes sense that a cross reference or lookup table would store that information. That table would be loaded into the domain and could then be used to apply the appropriate delivery method while processing the order. Does this make sense in the context of domain driven design? Or is my thinking too relational? Is this logic that should be built into it's own class/method (I mean beyond apply the cross reference table data)?

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• What are some good tips for a developer trying to design a scalable MySQL database?

  - by CFL_Jeff

  As the question states, I am a developer, not a DBA. I have experience with designing good ER schemas and am fairly knowledgeable about normalization and good schema design. I have also worked with data warehouses that use dimensional modeling with fact tables and dim tables. However, all of the database-driven applications I've developed at previous jobs have been internal applications on the company's intranet, never receiving "real-world traffic". Furthermore, at previous jobs, I have always had a DBA or someone who knew much more than me about these things. At this new job I just started, I've been asked to develop a public-facing application with a MySQL backend and the data stored by this application is expected to grow very rapidly. Oh, and we don't have a DBA. Well, I guess I am the DBA. ;) As far as designing a database to be scalable, I don't even know where to start. Does anyone have any good tips or know of any good educational materials for a developer who has been sort of shoved into a DBA/database designer role and has been tasked with designing a scalable database to support an application like this? Have any other developers been through this sort of thing? What did you do to quickly become good at this role? I've found some good slides on the subject here but it's hard to glean details from slides. Wish I could've attended that guy's talk. I also found a good blog entry called 5 Ways to Boost MySQL Scalability which had some good information, though some of it was over my head. tl;dr I just want to make sure the database doesn't have to be completely redesigned when it scales up, and I'm looking for tips to get it right the first time. The answer I'm looking for is a "list of things every developer should know about making a scalable MySQL database so your application doesn't perform like crap when the data gets huge".

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