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  • Repeating fields in similar database tables

    - by user1738833
    I have been tasked with working on a database that I have never seen before and I'm looking at the DB structure. Some of the central and most heavily queried and joined tables look like virtual duplicates of each other. Here's a massively simplified representation of the situation, with business-sensitive information changed, listing hypothetical table names and fields: TopLevelGroup: PK_TLGroupId, DisplaysXOnBill, DisplaysYOnBill, IsInvoicedForJ, IsInvoicedForK SubGroup: PK_SubGroupId, FK_ParentTopLevelGroupId, DisplaysXOnBill, DisplaysYOnBill, IsInvoicedForJ, IsInvoicedForK SubSubGroup: PK_SubSUbGroupId, FK_ParentSubGroupId, DisplaysXOnBill, DisplaysYOnBill, IsInvoicedForJ, IsInvoicedForK I haven't listed the types of the fields as I don't think it's particularly important to the situation. In addition, it's worth saying that rather than four repeated fields as in the example above, I'm looking at 86 repeated fields. For the most part, those fields genuinely do represent "facts" about the primary table entity, so it's not automatically wrong for that reason. In addition, the "groups" represented here have a property inheritance relationship. If DisplaysXOnBill is NULL in the SubSubGroup, it takes the value of DisplaysXOnBillfrom it's parent, the SubGroup, and so-on up to the TopLevelGroup. Further, the requirements will never require that the model extends beyond three levels, so there is no need for flexibility in that area. Is there a design smell from several tables which describe very similar entities having almost identical fields? If so, what might be a better design of the example above? I'm using the phrase "design smell" to indicate a possible problem. Of course, in any given situation, a particular design might well be the best solution. I'm looking for a more general answer - wondering what might be wrong with this design and what might be the better design were that the case. Possibly related, but not primary questions: Is this database schema in a reasonably normal form (e.g. to 3NF), insofar as can be told from the information I've provided. I can't see a problem with the requirements of 2NF and 3NF, except in their inheriting the requirements of 1NF. Is 1NF satisfied though? Are repeating groups allowed in different tables? Is there a best-practice method for implementing the inheritance relationship in a database as I require? The method above feels clunky to me because any query on the SubSubGroup necessarily needs to join onto the SubGroup and the TopLevelGroup tables to collect inherited facts, which can make even trivial joins requiring facts from the SubSubGroup table rather long-winded. There are, of course, political considerations to making a relatively large change like this. For the purpose of this question, I'm happy to ignore that fact in the interests of keeping the answers ring-fenced to the technical problem.

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  • What features would you like to see removed from C++?

    - by Justin Ethier
    This question was inspired by what-features-would-you-like-to-see-added-to-c. anBasically, C++ is a great general-purpose language. But perhaps too general and feature-rich... multiple inheritance, operator overloading, manual memory management, templates, smart pointers, virtual destructors, legacy frameworks (think MFC), and I could just go on. Is there any one feature / aspect of C++ that you would like taken away, to make our lives easier as C++ developers? One feature per answer, please.

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  • C# - calling ext. DLL function containing Delphi "variant record" parameter

    - by CaldonCZE
    Hello, In external (Delphi-created) DLL I've got the following function that I need to call from C# application. function ReadMsg(handle: longword; var Msg: TRxMsg): longword; stdcall; external 'MyDll.dll' name 'ReadMsg'; The "TRxMsg" type is variant record, defined as follows: TRxMsg = record case TypeMsg: byte of 1: (accept, mask: longword); 2: (SN: string[6]); 3: (rx_rate, tx_rate: word); 4: (rx_status, tx_status, ctl0, ctl1, rflg: byte); end; In order to call the function from C#, I declared auxiliary structure "my9Bytes" containing array of bytes and defined that it should be marshalled as 9 bytes long array (which is exactly the size of the Delphi record). private struct my9Bytes { [MarshalAs(UnmanagedType.ByValArray, ArraySubType = UnmanagedType.U1, SizeConst = 9)] public byte[] data; } Then I declared the imported "ReadMsg" function, using the "my9bytes" struct. [DllImport("MyDll.dll")] private static extern uint ReadMsg(uint handle, ref my9Bytes myMsg); I can call the function with no problem... Then I need to create structure corresponding to the original "TRxMsg" variant record and convert my auxiliary "myMsg" array into this structure. I don't know any C# equivalent of Delphi variant array, so I used inheritance and created the following classes. public abstract class TRxMsg { public byte typeMsg; } public class TRxMsgAcceptMask:TRxMsg { public uint accept, mask; //... } public class TRxMsgSN:TRxMsg { public string SN; //... } public class TRxMsgMRate:TRxMsg { public ushort rx_rate, tx_rate; //... } public class TRxMsgStatus:TRxMsg { public byte rx_status, tx_status, ctl0, ctl1, rflg; //... } Finally I create the appropriate object and initialize it with values manually converted from "myMsg" array (I used BitConverter for this). This does work fine, this solution seems to me a little too complicated, and that it should be possible to do this somehow more directly, without the auxiliary "my9bytes" structures or the inheritance and manual converting of individual values. So I'd like to ask you for a suggestions for the best way to do this. Thanks a lot!

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  • Writing SDK documentation, need useful beginner tutorials

    - by David Rutten
    I'm currently writing SDK documentation for one of our products, but for obvious reasons I don't want to talk about the essentials of OOP. Does anyone know any good online teaching material that explain (aimed at absolute beginners) concepts such as classes, inheritance, constructors, instances etc.? Preferably urls that are likely to survive for a couple of years to come... It's a DotNET SDK and we're including only VB and C# samples, so C++ or Delphi or Lisp material is not that useful.

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  • Did Java invent interfaces?

    - by Jordão
    I know about C++ pure virtual classes, but Java went one step further and created a first-class (no pun intended) concept for multiple-interface (not implementation) inheritance, the interface. It's now a staple of major statically-typed languages. Did Java invent the interface concept? Or did it appear in older languages also as a first-class concept?

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  • Database design question (Book Trading System)

    - by Paul
    Hello all! I´m developing a Book Trading System... The user will input your Book to trading... I already have a table tblBook with "all" existing books ... So the user will select one book from that list and fill the book´s CONDITIONS and Edition... So, what is a good Database design to tha case? tblBook = All books tblUserBook = All User Books And making tblUserBook to inheritance tblBook? Thanks

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  • CSS style info library

    - by Bobby Jack
    Is anyone aware of a good javascript library to obtain original (i.e. not computed) style for a given element in the DOM? In other words, something one could use to produce the results in Firebug's style tab. Like Firebug, it should take into account inheritance, shortcut properties, and all the other nuances of CSS.

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  • DOT NET NUKE URL PROBLEM

    - by user311166
    URL's are posting in address bar however all pages show up as the home page. I tried to add a document to the documents tab and after seeing inheritance overrides I canceled out of it and now all the pages post the home page.

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  • Good Entity Framework sample applications?

    - by Abdu
    I am looking for some good asp.net sample applications which use Entity Framework. I saw a couple apps for NorthWind (one was MVC based). Looking for one with is more sophisticated than the simple apps at MSDN (HRSkillsCombined, CourseManager,AdWksSalesWinDataBind, ResearchCollaborationAssistant). Possibly using Entity Inheritance, multi table change tracking.. etc.

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  • ruby language syntax(how platform_info variable is used

    - by amit singh tomar
    class EncodeDemoTest < Test #inheritance in ruby def setup(platform_info, logdir) @telnet_ip = platform_info["telnet_ip"] @telnet_login = platform_info["telnet_login"] @telnet_password = nil @filesys_path = platform_info["filesys_path"] @host_files_path = platform_info["host_files_path"] @host_machine_ip = platform_info["host_machine_ip"] @linuxserver_ip = platform_info["linuxserver_ip"] @target_prompt = platform_info["target_prompt"] @demo_execuable_path = platform_info["demo_execuable_path"] @mts4ea_machine_ip = platform_info["mts4ea_machine_ip"] @mts4ea_files_path = platform_info["mts4ea_files_path"] @ffmpeg_machine_ip = platform_info["ffmpeg_machine_ip"] @ffmpeg_service_machine_ip = platform_info["ffmpeg_service_machine_ip"] @ffmpeg_files_path = platform_info["ffmpeg_files_path"] @ffmpeg_login = platform_info["ffmpeg_login"] @ffmpeg_password = platform_info["ffmpeg_password"] @ffmpeg_prompt = platform_info["ffmpeg_prompt"] @platform_info = platform_info could anyone tell me how argument passed in setup method .means what does that syntax means platform["telnet_ip"]

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  • Why are static classes considered “classes” and “reference types”?

    - by Timwi
    I’ve been pondering about the C# and CIL type system today and I’ve started to wonder why static classes are considered classes. There are many ways in which they are not really classes: A “normal” class can contain non-static members, a static class can’t. In this respect, a class is more similar to a struct than it is to a static class, and yet structs have a separate name. You can have a reference to an instance of a “normal” class, but not a static class (despite it being considered a “reference type”). In this respect, a class is more similar to an interface than it is to a static class, and yet interfaces have a separate name. The name of a static class can never be used in any place where a type name would normally fit: you can’t declare a variable of this type, you can’t use it as a base type, and you can’t use it as a generic type parameter. In this respect, static classes are somewhat more like namespaces. A “normal” class can implement interfaces. Once again, that makes classes more similar to structs than to static classes. A “normal” class can inherit from another class. It is also bizarre that static classes are considered to derive from System.Object. Although this allows them to “inherit” the static methods Equals and ReferenceEquals, the purpose of that inheritance is questionable as you would call those methods on object anyway. C# even allows you to specify that useless inheritance explicitly on static classes, but not on interfaces or structs, where the implicit derivation from object and System.ValueType, respectively, actually has a purpose. Regarding the subset-of-features argument: Static classes have a subset of the features of classes, but they also have a subset of the features of structs. All of the things that make a class distinct from the other kinds of type, do not seem to apply to static classes. Regarding the typeof argument: Making a static class into a new and different kind of type does not preclude it from being used in typeof. Given the sheer oddity of static classes, and the scarcity of similarities between them and “normal” classes, shouldn’t they have been made into a separate kind of type instead of a special kind of class?

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  • When should I use a struct instead of a class?

    - by Esteban Araya
    MSDN says that you should use structs when you need lightweight objects. Are there any other scenarios when a struct is preferable over a class? Edit: Some people have forgotten that: 1. structs can have methods! 2. structs have no inheritance capabilites. Another Edit: I understand the technical differences, I just don't have a good feel for WHEN to use a struct.

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  • problem in extending a class

    - by Vineeth
    there are two classes public class Account { public Acconut() { //constructor } } public class SavingsAccount extends Account { } while doing the inheritance i have got an error message "cannont find symbol Symbol: constructor Account()" what might be the error in my code...??

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  • Finding an unnamed union in a struct::Haiku

    - by Freeman Lou
    So I have this assignment, and I have to find an unnamed union in struct _pthread_rwlock in pthread.h in the Haiku open source project. I began this assignment with some knowledge of c++ (past inheritance, polymorphism, and classes), but I find that what I learned do not help at all in my situation. I've opened the header file, and a source file named pthread_rwlock.cpp, and tried to look for the unnamed union, but there seems to be no unions in either file. What would be the correct way to find the problem?

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  • Can't I send NULL as a parameter with a constructor?

    - by Jason94
    Lets say i have a Shape object that has a constructor like this: Shape( width, height, radius, depth ) Now, I just have a silly rect so i dont need redius and depth... is it okey to do Shape myRect(50, 50, NULL, NULL) ? I know its not the best idea and I should use inheritance and stuff but this is the mess im in so can i use NULL like this?

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  • How does Symfony pass members set in an action to a template?

    - by Martin Chatterton
    How does a member set inside an action... $this->foo = 'bar'; ...become a variable accessible from a template... echo $foo; // bar I would like to know how it is achieved at a framework level. There is a lot of documentation on how to use Symfony, but I've not managed to find much about how it all fits together behind the scenes (class structure/inheritance etc). Thanks in advance for your help!

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  • C++ code parser/processor library

    - by uray
    is there any library that parse a source code of C++ to produce lets say, call graph, class inheritance tree, flow control, class member list or anything as a ready to use graph or structure in code (not in diagram image). to make it more clear, suppose to generate call graph image, there will be a process like this: ` C++ source -> parser -> intermediate structure -> renderer -> call graph image ^ | [i need this] `

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  • Problem creating a webpage in OOP pattern?

    - by Starx
    I want to develop a website in OOP pattern, but I am stuck in a point whether I need to inherit from multiple classes. For example I have a main class "index" this class has several methods which need to inherited from other classes and I have created seperate classes for it like class "banner", class "content", class "footer" Not only this but class "content" has several methods to be inherited from other classes like class "gallery", class "news", etc I found out that multiple inheritance is not allowed, and using interface I cannot write codes in its methods, so how can i achieve a solution for this problem.

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  • Short intruduction to OOP basics

    - by woo
    Hi. Can somebody point me to good intruductions into OOP main paradigms, like inheritance, polymorphism, incapsulation? I am looking for short article, about 2-3 pages, for very quick reading. Thank you very much.

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