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  • Can a binary tree or tree be always represented in a Database table as 1 table and self-referencing?

    - by Jian Lin
    I didn't feel this rule before, but it seems that a binary tree or any tree (each node can have many children but children cannot point back to any parent), then this data structure can be represented as 1 table in a database, with each row having an ID for itself and a parentID that points back to the parent node. That is in fact the classical Employee - Manager diagram: one boss can have many people under him... and each person under him can have n people under him, etc. This is a tree structure and is represented in database books as a common example as a single table Employee.

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  • how to share a variable between two threads

    - by prmatta
    I just inherited some code, two threads within this code need to perform a system task. One thread should do the system task before the other thread. They should not be performing the system task together. The two threads do not have references to each other. Now, I know I can use some sort of a semaphore to achieve this. But my question is what is the right way to get both threads to access this semaphore. I could create a static variable/method a new class : public class SharedSemaphore { private static Semaphore s = new Semaphore (1, true); public static void performSystemTask () { s.acquire(); } public static void donePerformingSystemTask() { s.release(); } } This would work (right?) but this doesn't seem like the right thing to do. Because, the threads now have access to a semaphore, without ever having a reference to it. This sort of thing doesn't seem like a good programming practice. Am I wrong?

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  • Where are the readonly/const in .NET?

    - by acidzombie24
    In C++ you'll see void func(const T& t) everywhere. However, i havent seen anything similar in .NET. Why? I have notice a nice amount of parameters using struct. But i see no functions with readonly/const. In fact now that i tried it i couldnt use those keywords to make a function that promises to not modify a list being passed in. Is there no way to promise the caller that this function will never modify the contents of list? Is there no way to say to call code and say this list should never be modified? (I know i can clone the list or look at documentation but i like compile errors sometime)

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  • designing multi module J2EE application

    - by user728947
    Might be my question is abstract or out of context, but i am asking here since i have little idea how this happens. I am wondering how big application/ platform break down there application in to multiple module and how they able to manage modules dependencies. For example in some E-commerce application they tend to break down it in various modules like pricing,promotions,shipping.import/export and many more. when we develop those application we hardly think about the underlying modules and how they have been designed to provides functionalists. Most of those module are not web-applications but are standalone module and not deployed in the web-app as jar files. can any one help me to understand how they break up things or is there any standard way to do this.any help/resources to get insight will really be helpful

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  • How can I sync three classes?

    - by TheMachineCharmer
    class Foo { Bar b; List<Foo> Neighbours; } class Bar { Spam s; List<Bar> Neighbours; } class Spam { List<string> Neighbours; } Each of these classes have AddNeighbour,RemoveNeighbour methods. User can add/remove Neighbours from any of the class at random. I want these three objects to be in sync. How can I do this?

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  • user interface pattern for associating single or many objects to an entity

    - by Samuel
    Need suggestions on implementing associating single or many objects to an entity. All soccer team players are registered individually (e.g. they are part of 'players' table) A soccer team has many players. The click sequence is like this:- a] Soccer team owner provides a name and brief description of the soccer team. b] Now it wants to add players to this team. c] You have the following button 'Add players to team' which lets you navigate to the 'View Players' page and lets you multi select users from there. Assuming this is a paginated list of players, how do you handle the following:- Do you provide a check box against each player and let the manager do a multi selection. If you need to add more players, it doesn't make sense to show the players who have been already added to the team. Do you mark those entries as not selectable or you would adding showing these entries. If you need to filter, do you provide search filters at the top of this page. Am looking for ideas on how to implement this or sites which have already done something similar.

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  • How to implement Administrator rights in Java Application?

    - by Yatendra Goel
    I am developing a Data Modeling Software that is implemented in Java. This application converts the textual data (stored in a database) to graphical form so that users can interpret the data in a more efficient form. Now, this application will be accessed by 3 kinds of persons: 1. Managers (who can fill the database with data and they can also view the visual form of the data after entering the data into the database) 2. Viewers (who can only view the visual form of data that has been filled by managers) 3. Administrators (who can create and manage other administrators, managers and viewers) Now, how to implement 3 diff. views of the same application. Note: Managers, Viewers and Administrators can be located in any part of the world and should access the application through internet. One idea that came in my mind is as follows: Step1: Code all the business logic in EJBs so that it can be used in distributed environment (means which can be accessed by several users through internet) Step2: Code 3 Swing GUI Clients: One for administrators, one for managers and one for viewers. These 3 GUI clients can access business logic written in EJBs. Step3: Distribute the clients corresponding to their users. For instance, manager client to managers. =================================QUESTIONS======================================= Q1. Is the above approach is correct? Q2. This is very common functionality that various softwares have. So, Do they implement this kind of functionality through this way or any other way? Q3. If any other approach would be more better, then what is that approach?

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  • How to "wrap" implementation in C#

    - by igor
    Hello, I have these classes in C# (.NET Framework 3.5) described below: public class Base { public int State {get; set;} public virtual int Method1(){} public virtual string Method2(){} ... public virtual void Method10(){} } public class B: Base { // some implementation } public class Proxy: Base { private B _b; public class Proxy(B b) { _b = b; } public override int Method1() { if (State == Running) return _b.Method1(); else return base.Method1(); } public override string Method2() { if (State == Running) return _b.Method2(); else return base.Method2(); } public override void Method10() { if (State == Running) _b.Method10(); else base.Method10(); } } I want to get something this: public Base GetStateDependentImplementation() { if (State == Running) // may be some other rule return _b; else return base; // compile error } and my Proxy's implementation will be: public class Proxy: Base { ... public override int Method1() { return GetStateDependentImplementation().Method1(); } public override string Method2() { return GetStateDependentImplementation().Method2(); } ... } Of course, I can do this (aggregation of base implementation): public RepeaterOfBase: Base // no any overrides, just inheritance { } public class Proxy: Base { private B _b; private RepeaterOfBase _Base; public class Proxy(B b, RepeaterOfBase aBase) { _b = b; _base = aBase; } } ... public Base GetStateDependentImplementation() { if (State == Running) return _b; else return _Base; } ... But instance of Base class is very huge and I have to avoid to have other additional copy in memory. So I have to simplify my code have to "wrap" implementation have to avoid a code duplication have to avoid aggregation of any additional instance of Base class (duplication) Is it possible to reach these goals?

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  • How to make notification to group users with read/unread flag?

    - by user2335065
    I am making a notification system so that when users in a group perform an action, it will notify all the other users in the group. I want the notification to be marked "read" or "unread" for each user of the group. With that, I can easily retreive any unread notification for a user and display it. I am think about creating a notification table that have the following fields. +----------------------+ | notification | +----------------------+ | id | | userid | | content | | status (read/unread) | | time | +----------------------+ My question is: Whether it is the correct way of making the system? As it means that when there is 1,000 users in a group, then I have to insert 1,000 rows to the table. If not, what is the better way of doing this? If it is the way to do this, how can I write the php/mysql codes to do the looping of inserting the rows? Thanks!

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  • Inheritance in tables - structure problem

    - by Naor
    I have 3 types of users in my system. each type has different information I created the following tables: BaseUser(base_user_id, username, password, additional common data) base_user_id is PK and Identity UserType1(user_id, data related to type1 only) user_id is PK and FK to base_user_id UserType2(user_id, data related to type2 only) user_id is PK and FK to base_user_id UserType3(user_id, data related to type3 only) user_id is PK and FK to base_user_id Now I have relation from each type of user to warehouses table. Users from type1 and type2 should have only warehouse_id and users from type3 should have warehouse_id and customer_id. I thought about this structure: WarehouseOfUser(base_user_id,warehouse_id) base_user_id is FK to base_user_id in BaseUser WarehouseOfTyp3User(base_user_id,warehouse_id, customer_id) base_user_id is FK to base_user_id in BaseUser The problem is that such structure allows 2 things I want to prevent: 1. add to WarehouseOfTyp3User data of user from type2 or type1. 2. add to WarehouseOfUser data of user from type3. what is the best structure for such case?

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  • Have you ever derived a programming solution from nature?

    - by Ryu
    When you step back and look at ... the nature of animals, insects, plants and the problems they have organically solved perhaps even the nature and balance of the universe Have you ever been able to solve a problem by deriving an approach from nature? I've heard of Ant Colony Algorithms being able to optimize supply chain amongst other things. Also Fractal's being the "geometry of nature" have been applied to a wide range of problems. Now that spring is here again and the world is coming back to life I'm wondering if anybody has some experiences they can share. Thanks PS I would recommend watching the "Hunting the Hidden Dimension" Nova episode on fractals.

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  • postgresql duplicate table names best practice

    - by veilig
    My company has a handful of apps that we deploy in the websites we build. Recently a very old app needed to be included along side a newer app and there was a conflict w/ a duplicate table name needed to be used by both apps. We are now in the process of updating an old app and there will be some DB updates. I'm curious what people consider best practice (or how do you do it) to help ensure these name collisions don't happen. I've looked at schema's but not sure if thats the right path we want to take. As the documentation prescribes, I don't want to "wire" a particular schema name into an application and if I add schema's to the user search path how would it know which table I was referring to if two schema's have the same table name. although, maybe I'm reading to much into this. Any insights or words of wisdom would be greatly appreciated!

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  • Find recipes that can be cooked from provided ingridients

    - by skaurus
    Sorry for bad English :( Suppose i can preliminary organize recipes and ingredients data in any way. How can i effectively conduct search of recipes by user-provided ingredients, preferably sorted by max match - so, first going recipes that use maximum of provided ingridients and do not contain any other ingrs, after them recipes that uses less of provided set and still not any other ingrs, after them recipes with minimum additional requirements and so on? All i can think about is represent recipe ingridients like bitmasks, and compare required bitmask with all recipes, but it is obviously a bad way to go. And related things like Levenstein distance i don't see how to use here. I believe it should be quite common task...

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  • What's the proper approach for writing multi-path "story" flows?

    - by Basiclife
    Hi, I wonder if you can help me. I'm writing a game (2d) which allows players to take multiple routes, some of which branch/merge - perhaps even loop. Each section of the game will decide which section is loaded next. I'm calling each section an IStoryElement - And I'm wondering how best to link these elements up in a way that is easily changed/configured and at the same time, graphable I'm going to have an engine/factory assembly which will load the appropriate StoryElement(s) based on various config options. I initially planned to give each StoryElement a NextElement() As IStoryElement property and a Completed() event. When the vent fires, the engine reads the NextElement property to find the next StoryElement. The downside to this is that if I ever wanted to graph all the routes through the game, I would be unable to - I couldn't determine all possible targets for each StoryElement. I considered a couple of other solutions but they all feel a little clunky - eg Do I need an additional layer of abstraction? ie StoryElementPlayers or similar - Each one would be responsible for stringing together multiple StoryElement perhaps a Series and a ChoicePlayer with each responsible for graphing its own StoryElement - But this will just move the problem up a layer. In short, I need some way of emulating a simple but dynamic workflow (but I'd rather not actually use WWF). Is there a pattern for something this simple? All the ones I've managed to find relate to more advanced control flow (parallel processing, etc.)

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  • Pattern or recommneded refactoring for method

    - by iKode
    I've written a method that looks like this: public TimeSlotList processTimeSlots (DateTime startDT, DateTime endDT, string bookingType, IList<Booking> normalBookings, GCalBookings GCalBookings, List<DateTime> otherApiBookings) { { ..... common process code ...... while (utcTimeSlotStart < endDT) { if (bookingType == "x") { //process normal bookings using IList<Booking> normalBookings } else if (bookingType == "y") { //process google call bookings using GCalBookings GCalBookings } else if (bookingType == "z" { //process other apibookings using List<DateTime> otherApiBookings } } } So I'm calling this from 3 different places, each time passing a different booking type, and each case passing the bookings I'm interested in processing, as well as 2 empty objects that aren't used for this booking type. I'm not able to get bookings all into the same datatype, which would make this easier and each booking type needs to be processed differently, so I'm not sure how I can improve this. Any ideas?

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  • Protocol specification in XML

    - by Mathijs
    Is there a way to specify a packet-based protocol in XML, so (de)serialization can happen automatically? The context is as follows. I have a device that communicates through a serial port. It sends and receives a byte stream consisting of 'packets'. A packet is a collection of elementary data types and (sometimes) other packets. Some elements of packets are conditional; their inclusion depends on earlier elements. I have a C# application that communicates with this device. Naturally, I don't want to work on a byte-level throughout my application; I want to separate the protocol from my application code. Therefore I need to translate the byte stream to structures (classes). Currently I have implemented the protocol in C# by defining a class for each packet. These classes define the order and type of elements for each packet. Making class members conditional is difficult, so protocol information ends up in functions. I imagine XML that looks like this (note that my experience designing XML is limited): <packet> <field name="Author" type="int32" /> <field name="Nickname" type="bytes" size="4"> <condition type="range"> <field>Author</field> <min>3</min> <max>6</min> </condition> </field> </packet> .NET has something called a 'binary serializer', but I don't think that's what I'm looking for. Is there a way to separate protocol and code, even if packets 'include' other packets and have conditional elements?

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  • Using an embedded DB (SQLite / SQL Compact) for Message Passing within an app?

    - by wk1989
    Hello, Just out of curiosity, for applications that have a fairly complicated module tree, would something like sqlite/sql compact edition work well for message passing? So if I have modules containing data such as: \SubsystemA\SubSubSysB\ModuleB\ModuleDataC, \SubSystemB\SubSubSystemC\ModuleA\ModuleDataX Using traditional message passing/routing, you have to go through intermediate modules in order to pass a message to ModuleB to request say ModuleDataC. Instead of doing that, if we we simply store "\SubsystemA\SubSubSysB\ModuleB\ModuleDataC" in a sqlite database, getting that data is as simple as a sql query and needs no routing and passing stuff around. Has anyone done this before? Even if you haven't, do you foresee any issues & performance impact? The only concern I have right now would be the passing of custom types, e.g. if ModuleDataC is a custom data structure or a pointer, I'll need some way of storing the data structure into the DB or storing the pointer into the DB. Thanks, JW EDIT One usage case I haven't thought about is when you want to send a message from ModuleA to ModuleB to get ModuleB to do something rather than just getting/setting data. Is it possible to do this using an embedded DB? I believe callback from the DB would be needed, how feasible is this?

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  • LINQ to SQL - Lightweight O/RM?

    - by CoffeeAddict
    I've heard from some that LINQ to SQL is good for lightweight apps. But then I see LINQ to SQL being used for Stackoverflow, and a bunch of other .coms I know (from interviewing with them). Ok, so is this true? for an e-commerce site that's bringing in millions and you're typically only doing basic CRUDs most the time with the exception of an occasional stored proc for something more complex, is LINQ to SQL complete enough and performance-wise good enough or able to be tweaked enough to run happily on an e-commerce site? I've heard that you just need to tweak performance on the DB side when using LINQ to SQL for a better approach. So there are really 2 questions here: 1) Meaning/scope/definition of a "Lightweight" O/RM solution: What the heck does "lightweight" mean when people say LINQ to SQL is a "lightweight O/RM" and is that true??? If this is so lightweight then why do I see a bunch of huge .coms using it? Is it good enough to run major .coms (obviously it looks like it is) and what determines what the context of "lightweight" is...it's such a generic statement. 2) Performance: I'm working on my own .com and researching different O/RMs. I'm not really looking at the Entity Framework (yet), just want to figure out the LINQ to SQL basics here and determine if it will be efficient enough for me. The problem I think is you can't tweak or control the SQL it generates...

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  • What is the best way to restore(rollback) data in an application to a specified state(date) ?

    - by panzerschreck
    Hello, An example would set the context right, the example below captures the various states of the entity, which needs to be reverted(rolled back) . State 1 - Recorded on 01-Mar-2010 Column1 Column2 Data1 0.56 State 2 - Recorded on 02-Mar-2010 Column1 Column2 Data1 0.57 State 3 - Recorded on 03-Mar-2010 Column1 Column2 Data1 0.58 User notices that state3 is not what he intended to be in, decides to revert back to state2. One approach that I can think of, without modifying the entity is via "auditing" all the inserts/updates, as below, the rollback information captures the data just before the updates/modifications on the entity, so that it can be applied in an order when you need to revert.Please note that changing the entity's schema, is not an option. Rollback - R1 recorded on 01-Mar-2010 Column1 Column2 Data1 0.56 Rollback - R2 Recorded on 02-Mar-2010 Column1 Column2 Data1 0.56 Rollback - R3 Recorded on 03-Mar-2010 Column1 Column2 Data1 0.57 So, to get to state2 , we would start with rollback information R1,apply R2 onto it. Is there a better approach to achieve this ? Thanks for your time.

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  • drawbacks of storing all ''things' in a central table

    - by naiquevin
    Hi, I am not sure if there is a term to describe this, but I have observed that content management systems store all kinds of data in a single table with their bare minimum properties while the meta data is stored in another table in form of key value pairs. for eg. everything (blog posts, pages, images, events etc) is stored in one table and considered as a post. I understand that this allows for abstraction and easy extensibility we are considering designing our new project this way. It is not exactly a CMS but we plan to keep adding modules to it in stages. Lets say initially there will be only posts and images on which comments can be posted. Later on we might add videos which will also have the commenting feature. what are the drawbacks of this approach ? and will it work for a requirement like ours ? Thanks

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  • Android::Creating a clickable collage?

    - by Legend
    I am trying to create something like a rectangular grid with pictures. When a picture is clicked, it should zoom in pushing the other ones out. I don't know what you name you call this particular model with but does anyone have suggestions on where I should start? Collage Example

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  • Should the program logic reside inside the gui object class or be external to the class?

    - by hd112
    I have a question about how to structure code in relation to GUI objects. Suppose I have a dialog that has a list control that has a bunch of names obtained from a database. The user can edit the names. Does the logic reside inside that dialog class or should it be from the outside. To illustrate what I mean, here’s some pseudo code showing the structure of the code when the logic is handled outside the dialog class: NamesDialog : wxDialog { Private: ..stuff.. Public: ... SetNames(wxStringArray names); wxStringArray GetNames(); ..stuff.. } So the user of the class would do something like: wxStringArray names = DatabaseManager::Get()->GetNames(); names.Sort(); NamesDialogObject.SetNames(names); NamesDialogObject.ShowModal(); wxStringArray modified_names = NamesDialogObject.GetNames(); AddToDatabase(modified_names); //or something like this. On the other hand, the database logic can reside inside the NamesDialog class itself. In the show method I can query the database for the names and as the user interacts with the controls (list control in this case), the database can be updated from the event handlers. As a result the NamesDialog class only has the Show() method as there is no need to use SetNames or GetNames() etc. Which method is generally preferred? I don’t have much work experience so I’m not sure which is the proper way to handle it. Sometimes it's easier to handle everything in the class but getting access to objects it interacts with can be challenging. Generally can do it by having the relevant objects be singletons like the database manager in the above example.

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  • Singleton Pattern Implementation Issues?

    - by locky28
    Hi I am revising for an exam and need to know some implementation issues with the singleton pattern. they do not need to be too complex just basic things that would affect a developers decision to include them, Thanks P.S. Could any code examples be given in Java thanks.

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