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• Avoiding Duplicate Data in DB (for use with Rails)

  - by ants

  I have five tables that I am trying to get to work nicely together but may need some help. I have three main tables: accounts members and roles. With two join tables account_members and account_member_roles. The accounts and members table are joined by account_members (fk account_id and member_id) table. The other 2 tables are the problem (roles and account_member_roles). A member of an account can have more than one role and I have the account_member_roles (fk account_member_id and role_id) table joining the account_members join table and the roles table. That seems logical but can you have a relationship with a join table? What I'd like to be able to do is when creaeting an account, for instance, I would like @account.save to include the roles and update the account_member_roles table neatly ..... but through the account_members join table. I've tried ..... accept_nested_attributes_for :members, :account_member_roles in the account.rb but I get ..... ActiveRecord::HasManyThroughCantAssociateThroughHasManyReflection (Cannot modify association 'Account#account_member_roles' because the source reflection class 'AccountMemberRole' is associated to 'AccountMember' via :has_many.) upon trying to save a record. Any advice on how I should approach this? CIA -ants

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• Saving complex aggregates using Repository Pattern

  - by Kevin Lawrence

  We have a complex aggregate (sensitive names obfuscated for confidentiality reasons). The root, R, is composed of collections of Ms, As, Cs, Ss. Ms have collections of other low-level details. etc etc R really is an aggregate (no fair suggesting we split it!) We use lazy loading to retrieve the details. No problem there. But we are struggling a little with how to save such a complex aggregate. From the caller's point of view: r = repository.find(id); r.Ps.add(factory.createP()); r.Cs[5].updateX(123); r.Ms.removeAt(5); repository.save(r); Our competing solutions are: Dirty flags Each entity in the aggregate in the aggregate has a dirty flag. The save() method in the repository walks the tree looking for dirty objects and saves them. Deletes and adds are a little trickier - especially with lazy-loading - but doable. Event listener accumulates changes. Repository subscribes a listener to changes and accumulates events. When save is called, the repository grabs all the change events and writes them to the DB. Give up on repository pattern. Implement overloaded save methods to save the parts of the aggregate separately. The original example would become: r = repository.find(id); r.Ps.add(factory.createP()); r.Cs[5].updateX(123); r.Ms.removeAt(5); repository.save(r.Ps); repository.save(r.Cs); repository.save(r.Ms); (or worse) Advice please! What should we do?

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• ER Data Model - confused by diagram.

  - by Khou

  Hi im a little confused by this diagram http://www.b-eye-network.com/images/content/i030ht0104.gif (Last diagram in the article) 1 - In the "ACCOUNTING ENTRY" table it shows "DebitEntry" and "CreditEntry" i) is this two column or ii) is this two rows of data? or iii) is it two separate tables on its own, Acounting_entry_credit and Accounting_entry_debit? Same question with the "ACCOUNT" table, it shows asset account, livabilities account, equaity account? are they 3 columns or are they 3 rows? Source: http://www.tdan.com/view-articles/5227/

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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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• Python: Recursively access dict via attributes as well as index access?

  - by Luke Stanley

  I'd like to be able to do something like this: from dotDict import dotdictify life = {'bigBang': {'stars': {'planets': [] } } } dotdictify(life) #this would be the regular way: life['bigBang']['stars']['planets'] = {'earth': {'singleCellLife': {} }} #But how can we make this work? life.bigBang.stars.planets.earth = {'singleCellLife': {} } #Also creating new child objects if none exist, using the following syntax life.bigBang.stars.planets.earth.multiCellLife = {'reptiles':{},'mammals':{}} My motivations are to improve the succinctness of the code, and if possible use similar syntax to Javascript for accessing JSON objects for efficient cross platform development.(I also use Py2JS and similar.)

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• A web framework where AJAX was not an after thought

  - by Pirate for Profit

  AJAX is a pain in the ass because it essentially means you'll have to write two sets of similarish code: one for browsers with JavaScript enabled and those without. Not only this, but you have to connect JavaScript events to hook into your models and display the results. And if all that weren't bad enough, you need to send an address change with the request, otherwise the user won't be able to "click back" correctly (if confused look at what happens to the address bar when you click links in GMail). We're searching for something that had the foresight and design goals with all these concerns in mind. Performance and security are also obvious major concerns. We love config-based systems as well, where you don't have to write a lot of code you just drop it into an easily read config format. It's like asking for the holy grail right?

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• do's and don'ts for writing mysql queries

  - by nik

  One thing I always wonder while writing query is that am I writing most optimized query or not? I know certain things like: 1) using SELECT field1, filed2 instead of SELECT * 2) Giving proper indexes to the tables but I am sure there are more things that should be kept in mind for writing queries, since most of the database can only grow more and optimal query will help gr8 in execution time, Can u share some tips and tricks on writing queries?

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• C# Memoization of functions with arbitrary number of arguments

  - by Lirik

  I'm trying to create a memoization interface for functions with arbitrary number of arguments, but I'm failing miserably. The first thing I tried is to define an interface for a function which gets memoized automatically upon execution: class EMAFunction:IFunction { Dictionary<List<object>, List<object>> map; class EMAComparer : IEqualityComparer<List<object>> { private int _multiplier = 97; public bool Equals(List<object> a, List<object> b) { List<object> aVals = (List<object>)a[0]; int aPeriod = (int)a[1]; List<object> bVals = (List<object>)b[0]; int bPeriod = (int)b[1]; return (aVals.Count == bVals.Count) && (aPeriod == bPeriod); } public int GetHashCode(List<object> obj) { // Don't compute hash code on null object. if (obj == null) { return 0; } // Get length. int length = obj.Count; List<object> vals = (List<object>) obj[0]; int period = (int) obj[1]; return (_multiplier * vals.GetHashCode() * period.GetHashCode()) + length;; } } public EMAFunction() { NumParams = 2; Name = "EMA"; map = new Dictionary<List<object>, List<object>>(new EMAComparer()); } #region IFunction Members public int NumParams { get; set; } public string Name { get; set; } public object Execute(List<object> parameters) { if (parameters.Count != NumParams) throw new ArgumentException("The num params doesn't match!"); if (!map.ContainsKey(parameters)) { //map.Add(parameters, List<double> values = new List<double>(); List<object> asObj = (List<object>)parameters[0]; foreach (object val in asObj) { values.Add((double)val); } int period = (int)parameters[1]; asObj.Clear(); List<double> ema = TechFunctions.ExponentialMovingAverage(values, period); foreach (double val in ema) { asObj.Add(val); } map.Add(parameters, asObj); } return map[parameters]; } public void ClearMap() { map.Clear(); } #endregion } Here are my tests of the function: private void MemoizeTest() { DataSet dataSet = DataLoader.LoadData(DataLoader.DataSource.FROM_WEB, 1024); List<String> labels = dataSet.DataLabels; Stopwatch sw = new Stopwatch(); IFunction emaFunc = new EMAFunction(); List<object> parameters = new List<object>(); int numRuns = 1000; long sumTicks = 0; parameters.Add(dataSet.GetValues("open")); parameters.Add(12); // First call for(int i = 0; i < numRuns; ++i) { emaFunc.ClearMap();// remove any memoization mappings sw.Start(); emaFunc.Execute(parameters); sw.Stop(); sumTicks += sw.ElapsedTicks; } Console.WriteLine("Average ticks not-memoized " + (sumTicks/numRuns)); sumTicks = 0; // Repeat call for (int i = 0; i < numRuns; ++i) { sw.Start(); emaFunc.Execute(parameters); sw.Stop(); sumTicks += sw.ElapsedTicks; } Console.WriteLine("Average ticks memoized " + (sumTicks/numRuns)); } The performance is confusing me... I expected the memoized function to be faster, but it didn't work out that way: Average ticks not-memoized 106,182 Average ticks memoized 198,854 I tried doubling the data instances to 2048, but the results were about the same: Average ticks not-memoized 232,579 Average ticks memoized 446,280 I did notice that it was correctly finding the parameters in the map and it going directly to the map, but the performance was still slow... I'm either open for troubleshooting help with this example, or if you have a better solution to the problem then please let me know what it is.

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• F#: Define an abstract class that inherits an infterface, but does not implement it

  - by akaphenom

  I owuld like to define an abstract class that inerhits from UserControl and my own Interface IUriProvider, but doesn't implement it. The goal is to be able to define pages (for silverlight) that implement UserControl but also provide their own Uri's (and then stick them in a list / array and deal with them as a set: type IUriProvider = interface abstract member uriString: String ; abstract member Uri : unit -> System.Uri ; end type UriUserControl() as this = inherit IUriProvider with abstract member uriString: String ; inherit UserControl() Also the Uri in the definition - I would like to implement as a property getter - and am having issues with that as well. this does not compile type IUriProvider = interface abstract member uriString: String with get; end Thank you...

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• What is the basic pattern for using (N)Hibernate?

  - by Vilx-

  I'm creating a simple Windows Forms application with NHibernate and I'm a bit confused about how I'm supposed to use it. To quote the manual: ISession (NHibernate.ISession) A single-threaded, short-lived object representing a conversation between the application and the persistent store. Wraps an ADO.NET connection. Factory for ITransaction. Holds a mandatory (first-level) cache of persistent objects, used when navigating the object graph or looking up objects by identifier. Now, suppose I have the following scenario: I have a simple classifier which is a MSSQL table with two columns - ID (auto_increment) and Name (nvarchar). To edit this classifier I create a form which contains a single gridview and two buttons - OK and Cancel. The user can nearly directly edit the table in the gridview, and when he hits OK the changes he made are persisted to the DB (or if he hits cancel, nothing happens). Now, I have several questions about how to organize this: What should the lifetime of my ISession be? Should I create a single ISession for my whole application; an ISession for each of my forms (the application is single-threaded MDI); or an ISession for every DB operation/transaction? Does NHibernate offer some kind of built-in dirty tracking or must I do this myself? The manual mentions something like it here and there but does not go into details. How is this done? Is there not a huge overhead? Is it somehow tied with the cache(s) that NHibernate has? What are these caches for? Are they not specific to a single ISession? That is, if I use a seperate ISession for every transaction, won't it break the dirty tracking? How does the built-in dirty tracking detect deleted objects?

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• O(log n) algorithm to find the element having rank i in union of pre-sorted lists

  - by Eternal Learner

  Given two sorted lists, each containing n real numbers, is there a O(log?n) time algorithm to compute the element of rank i (where i coresponds to index in increasing order) in the union of the two lists, assuming the elements of the two lists are distinct? I can think of using a Merge procedure to merge the 2 lists and then find the A[i] element in constant time. But the Merge would take O(n) time. How do we solve it in O(log n) time?

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• Using DTOs and BOs

  - by ryanzec

  One area of question for me about DTOs/BOs is about when to pass/return the DTOs and when to pass/return the BOs. My gut reaction tells me to always map NHibernate to the DTOs, not BOs, and always pass/return the DTOs. Then whenever I needed to perform business logic, I would convert my DTO into a BO. The way I would do this is that my BO would have a have a constructor that takes a parameter that is the type of my interface (that defines the required fields/properties) that both my DTO and BO implement as the only argument. Then I would be able to create my BO by passing it the DTO in the constructor (since both with implement the same interface, they both with have the same properties) and then be able to perform my business logic with that BO. I would then also have a way to convert a BO to a DTO. However, I have also seen where people seem to only work with BOs and only work with DTOs in the background where to the user, it looks like there are no DTOs. What benefits/downfalls are there with this architecture vs always using BO's? Should I always being passing/returning either DTOs or BOs or mix and match (seems like mixing and matching could get confusing)?

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• What resources will help me understand the fundamentals of Relational Database Systems.

  - by Rachel

  This are few of the fundamental database questions which has always given me trouble. I have tried using google and wiki but I somehow I miss out on understanding the functionality rather than terminology. If possible would really appreciate if someone can share more insights on this questions using some visual representative examples. What is a key? A candidate key? A primary key? An alternate key? A foreign key? What is an index and how does it help your database? What are the data types available and when to use which ones?

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• Pattern/Matcher in Java?

  - by user1007059

  I have a certain text in Java, and I want to use pattern and matcher to extract something from it. This is my program: public String getItemsByType(String text, String start, String end) { String patternHolder; StringBuffer itemLines = new StringBuffer(); patternHolder = start + ".*" + end; Pattern pattern = Pattern.compile(patternHolder); Matcher matcher = pattern.matcher(text); while (matcher.find()) { itemLines.append(text.substring(matcher.start(), matcher.end()) + "\n"); } return itemLines.toString(); } This code works fully WHEN the searched text is on the same line, for instance: String text = "My name is John and I am 18 years Old"; getItemsByType(text, "My", "John"); immediately grabs the text "My name is John" out of the text. However, when my text looks like this: String text = "My name\nis John\nand I'm\n18 years\nold"; getItemsByType(text, "My", "John"); It doesn't grab anything, since "My" and "John" are on different lines. How do I solve this?

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• Extending Throwable in Java

  - by polygenelubricants

  Java lets you create an entirely new subtype of Throwable, e.g: public class FlyingPig extends Throwable { ... } Now, very rarely, I may do something like this: throw new FlyingPig("Oink!"); and of course elsewhere: try { ... } catch (FlyingPig porky) { ... } My questions are: Is this a bad idea? And if so, why? What could've been done to prevent this subtyping if it is a bad idea? Since it's not preventable (as far as I know), what catastrophies could result? If this isn't such a bad idea, why not? How can you make something useful out of the fact that you can extends Throwable?

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• C# reference collection for storing reference types

  - by ivo s

  I like to implement a collection (something like List<T>) which would hold all my objects that I have created in the entire life span of my application as if its an array of pointers in C++. The idea is that when my process starts I can use a central factory to create all objects and then periodically validate/invalidate their state. Basically I want to make sure that my process only deals with valid instances and I don't re-fetch information I already fetched from the database. So all my objects will basically be in one place - my collection. A cool thing I can do with this is avoid database calls to get data from the database if I already got it (even if I updated it after retrieval its still up-to-date if of course some other process didn't update it but that a different concern). I don't want to be calling new Customer("James Thomas"); again if I initted James Thomas already sometime in the past. Currently I will end up with multiple copies of the same object across the appdomain - some out of sync other in sync and even though I deal with this using timestamp field on the MSSQL server I'd like to keep only one copy per customer in my appdomain (if possible process would be better). I can't use regular collections like List or ArrayList for example because I cannot pass parameters by their real local reference to the their existing Add() methods where I'm creating them using ref so that's not to good I think. So how can this be implemented/can it be implemented at all ? A 'linked list' type of class with all methods working with ref & out params is what I'm thinking now but it may get ugly pretty quickly. Is there another way to implement such collection like RefList<T>.Add(ref T obj)? So bottom line is: I don't want re-create an object if I've already created it before during the entire application life unless I decide to re-create it explicitly (maybe its out-of-date or something so I have to fetch it again from the db). Is there alternatives maybe ?

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• C++ classes with members referencing each other

  - by Saad Imran.

  I'm trying to write 2 classes with members that reference each other. I'm not sure if I'm doing something wrong or it's just not possible. Can anyone help me out here... Source.cpp #include "Headers.h" using namespace std; void main() { Network* network = new Network(); system("pause"); return; } Headers.h #ifndef Headers_h #define Headers_h #include <iostream> #include <vector> #include "Network.h" #include "Router.h" #endif Network.h #include "Headers.h" class Network { protected: vector<Router> Routers; }; Router.h #include "Headers.h" class Router { protected: Network* network; public: }; The errors I'm getting are: error C2143: syntax error : missing ';' before '<' error C2238: unexpected token(s) preceding ';' error C4430: missing type specifier - int assumed. I'm pretty sure I'm not missing any semicolons or stuff like that. The program works find if I take out one of the members. I tried finding similar questions and the solution was to use pointers, but that's what I'm doing and it does't seem to be working!

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• Sharing a connection string

  - by coure06

  hi, I am developing a class library (C#) that i will use it for my different projects (later). My class library dll will use the connection string /data context of the project which will reference my new dll. How can i do it? Lets say i have a class Library Project named "CLP", and a website project "WP". I can add reference to CLP.dll file but how i will pass a connection string/data context object to that dll? as CLP.dll will access db based on the connection string of the "WP". Not sure my problem is clear or not!

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• Is a "factory" method the right pattern?

  - by jdt141

  Hey all - So I'm working to improve an existing implementation. I have a number of polymorphic classes that are all composed into a higher level container class. The problem I'm dealing with at the moment is that the higher level container class, well, sucks. It looks something like this, which I really don't have a problem with (as the polymorphic classes in the container should be public). My real issue is the constructor... /* * class1 and class 2 derive from the same superclass */ class Container { public: boost::shared_ptr<ComposedClass1> class1; boost::shared_ptr<ComposedClass2> class2; private: ... } /* * Constructor - builds the objects that we need in this container. */ Container::Container(some params) { class1.reset(new ComposedClass1(...)); class2.reset(new ComposedClass2(...)); } What I really need is to make this container class more re-usable. By hard-coding up the member objects and instantiating them, it basically isn't and can only be used once. A factory is one way to build what I need (potentially by supplying a list of objects and their specific types to be created?) Other ways to get around this problem? Seems like someone should have solved it before... Thanks!

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• Database solutions for storing/searching EXIF data

  - by webdestroya

  I have thousands of photos on my site (each with a numeric PhotoID) and I have EXIF data (photos can have different EXIF tags as well). I want to be able to store the data effectively and search it. Some photos have more EXIF data than others, some have the same, so on.. Basically, I want to be able to query say 'Select all photos that have a GPS location' or 'All photos with a specific camera' I can't use MySQL (tried it, it doesn't work). I thought about Cassandra, but I don't think it lets me query on fields. I looked at SimpleDB, but I would rather: not pay for the system, and I want to be able to run more advanced queries on the data. Also, I use PHP and Linux, so it would be awesome if it could interface nicely to PHP. Any ideas?

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• Ways to clean up java applications.

  - by Begui

  How do java people handle clean up of their apps when the program receives a kill signal? For instance, there is an application i connect to which wants any third party app ( my app) to send a "finish" command. What is the best say to send that "finish" command if one does a kill -9 on me.

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• Why isn't JML implemented as Annotations in Java?

  - by devoured elysium

  Contrary to Code Contracts in C#, in JML Code Contracts are just text that's used in the form of comments in the header of a method. Wouldn't it be better to have them exposed as Annotations, then? That way even when compiling the information would persist on the .class's metadata, contrary to comments, that get erased. Am I missing something? Thanks

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• Best way to plan a task ?

  - by Indigo Praveen

  Hi All, As I am very new to programming, I am very curious about learning the best ways/practices of programming. Whenever I want to write any program , I strat directly with coding while some guys say that you should plan your program first before starting the code. But I don't understand the real value of creating the class diagrams and all that kind of stuff coz I think that ultimately I have to write the code. Can you guys please share your experiences about how you are doing your programming means what is your first step when you start an application.

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• Dynamically specify the type in C#

  - by Lirik

  I'm creating a custom DataSet and I'm under some constrains: I want the user to specify the type of the data which they want to store. I want to reduce type-casting because I think it will be VERY expensive. I will use the data VERY frequently in my application. I don't know what type of data will be stored in the DataSet, so my initial idea was to make it a List of objects, but I suspect that the frequent use of the data and the need to type-cast will be very expensive. The basic idea is this: class DataSet : IDataSet { private Dictionary<string, List<Object>> _data; /// <summary> /// Constructs the data set given the user-specified labels. /// </summary> /// <param name="labels"> /// The labels of each column in the data set. /// </param> public DataSet(List<string> labels) { _data = new Dictionary<string, List<object>>(); foreach (string label in labels) { _data.Add(label, new List<object>()); } } #region IDataSet Members public List<string> DataLabels { get { return _data.Keys.ToList(); } } public int Count { get { _data[_data.Keys[0]].Count; } } public List<object> GetValues(string label) { return _data[label]; } public object GetValue(string label, int index) { return _data[label][index]; } public void InsertValue(string label, object value) { _data[label].Insert(0, value); } public void AddValue(string label, object value) { _data[label].Add(value); } #endregion } A concrete example where the DataSet will be used is to store data obtained from a CSV file where the first column contains the labels. When the data is being loaded from the CSV file I'd like to specify the type rather than casting to object. The data could contain columns such as dates, numbers, strings, etc. Here is what it could look like: "Date","Song","Rating","AvgRating","User" "02/03/2010","Code Monkey",4.6,4.1,"joe" "05/27/2009","Code Monkey",1.2,4.5,"jill" The data will be used in a Machine Learning/Artificial Intelligence algorithm, so it is essential that I make the reading of data very fast. I want to eliminate type-casting as much as possible, since I can't afford to cast from 'object' to whatever data type is needed on every read. I've seen applications that allow the user to pick the specific data type for each item in the csv file, so I'm trying to make a similar solution where a different type can be specified for each column. I want to create a generic solution so I don't have to return a List<object> but a List<DateTime> (if it's a DateTime column) or List<double> (if it's a column of doubles). Is there any way that this can be achieved? Perhaps my approach is wrong, is there a better approach to this problem?

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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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