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• Three level database - foreign keys

  - by poke

  I have a three level database with the following structure (simplified to only show the primary keys): Table A: a_id Table B: a_id, b_id Table C: a_id, b_id, c_id So possible values for table C would be something like this: a_id b_id c_id 1 1 1 1 1 2 1 1 3 1 2 1 1 2 2 2 1 1 2 2 1 2 2 2 ... I am now unsure, how foreign keys should be set; or if they should be set for the primary keys at all. My idea was to have a foreign key on table B B.a_id -> A.a_id, and two foreign key on C C.a_id -> A.a_id and ( C.a_id, C.b_id ) -> ( B.a_id, B.b_id ). Is that the way I should set up the foreign keys? Is the foreign key from C->A necessary? Or do I even need foreign keys at all given that all those columns are part of the primary keys? Thanks.

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• Meaning of Primary Key to Microsoft SQL Server 2008

  - by usr

  What meaning does the concept of a primary key have to the database engine of SQL Server? I don't mean the clustered/nonclustered index created on the "ID" column, i mean the constraint object "primary key". Does it matter if it exists or not? Alternatives: alter table add primary key clustered alter table create clustered index Does it make a difference?

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• index 'enabled' fields good idea?

  - by sibidiba

  Content of a website is stored in a MySQL database. 99% of the content will be enabled, but some (users, posts etc.) will be disabled. Most of the queries end as WHERE (...) AND enabled Is it a good idea to create an index on the field 'enabled'?

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• Dealing with dependencies between WCF services when using Castle Windsor

  - by Georgia Brown

  I have several WCF services which use castle windsor to resolve their dependencies. Now I need some of these services to talk to each other. The typical structure is service -- Business Logic -- DAL The calls to the other services need to occur at Business Logic level. What is the best approach for implementing this? Should I simply inject a service proxy into the business logic? Is this wasteful if for example, only one of two method from my service need to use this proxy? What if the services need to talk to each other? - Will castle windsor get stuck in a loop trying to resolve each services dependencies?

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• Where should I put contextual data related to an Object that is not really a property of the object?

  - by RenderIn

  I have a Car class. It has three properties: id, color and model. In a particular query I want to return all the cars and their properties, and I also want to return a true/false field called "searcherKnowsOwner" which is a field I calculate in my database query based on whether or not the individual conducting the search knows the owner. I have a database function that takes the ID of the searcher and the ID of the car and returns a boolean. My car class looks like this (pseudocode): class Car{ int id; Color color; Model model; } I have a screen where I want to display all the cars, but I also want to display a flag next to each car if the person viewing the page knows the owner of that car. Should I add a field to the Car class, a boolean searcherKnowsOwner? It's not a property of the car, but is actually a property of the user conducting the search. But this seems like the most efficient place to put this information.

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• Pros / Cons displaying list of users at login page

  - by Radu094

  We seem to have a lot of clients asking us to change the login screen in this manner: Display a list of all available users (thumbnail picture + name) User selects a username from the list A password prompt appears near the username User enters password then presses enter This sounds remarcably similar to the Windows XP login, which is probably where they got the ideea in the first place. There are only about 4 - 5 different users that can login at any given station, so implementing that list on one screen is feasable. So I was wondering if there are any usability experts with some word on this method of login. As far as I can tell, MS droped this behaviour in Vista/Win7, didn't they?

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• PHP: Best solution for links breaking in a mod_rewrite app

  - by psil

  I'm using mod rewrite to redirect all requests targeting non-existent files/directories to index.php?url=* This is surely the most common thing you do with mod_rewrite yet I have a problem: Naturally, if the page url is "mydomain.com/blog/view/1", the browser will look for images, stylesheets and relative links in the "virtual" directory "mydomain.com/blog/view/". Problem 1: Is using the base tag the best solution? I see that none of the PHP frameworks out there use the base tag, though. I'm currently having a regex replace all the relative links to point to the right path before output. Is that "okay"? Problem 2: It is possible that the server doesn't support mod_rewrite. However, all public files like images, stylesheets and the requests collector index.php are located in the directory /myapp/public. Normally mod_rewrite points all request to /public so it seems as if public was actually the root directory too all users. However if there is no mod_rewrite, I then have to point the users to /public from the root directory with a header() call. That means, however that all links are broken again because suddenly all images, etc. have to be called via /public/myimage.jpg Additional info: When there is no mod_rewrite the above request would look like this: mydomain.com/public/index.php/blog/view/1 What would be the best solutions for both problems?

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• Understanding MongoDB(and NoSQL in general) and How to make the best use of it

  - by Earlz

  Hello, I am beginning to think that my next project I am wanting to do would work better with a NoSQL solution. The project would either involve a ton of 2-column tables or a ton of dynamic queries with dynamically generated columns in a traditional SQL database. So I feel a NoSQL database would be much cleaner. I'm looking at MongoDB and it looks pretty promising. Anyway, I'm attempting to make sense of it all. Also, I will be using MongoMapper in Ruby. Anyway though, I'm confused as to how to layout things in such a freeform database. I've read http://stackoverflow.com/questions/2170152/nosql-best-practices and the answer there says that normalization is usually bad in a NoSQL DB. So how would be the best way of laying out say a simple blog with users, posts, and comments? My natural thought was to have 3 collections for each and then link them by a unique ID. But this apparently is wrong? So, what are some of the ways to lay out such a thing? My concern with the answer given in the other question is what if the author's name changed. You'd have to go through updating a ton of posts and comments. But is this an ok thing to do with NoSQL?

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• C#: How to inherit constructors?

  - by Ian Boyd

  Imagine a base class with many constructors and a virtual method public class Foo { ... public Foo() {...} public Foo(int i) {...} ... public virtual void SomethingElse() {...} ... } and now I want to create a descendant class that overrides the virtual method: public class Bar : Foo { public override void SomethingElse() {...} } And another descendant that does some more stuff: public class Bah : Bar { public void DoMoreStuff() {...} } Do I really have to copy all constructors from Foo into Bar and Bah? And then if I change a constructor signature in Foo, do I have to update it in Bar and Bah? Is there no way to inherit constructors? Is there no way to encourage code reuse?

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• Start thread with two parameters

  - by Matt

  I've got a method that gets called on an event, which presents me with two variables varA, varB (both strings). This method gets called with new information quite frequently, thus I have created a separate method that takes in the two parameters. I want to run this method in a thread, however have struck the issue that Thread.Start will not accept parameters. I've tried a few supposed methods, but have so far had no luck.. I think my best bet is to create a separate class, and handle it there.. However I have a List which I am inserting data into, and hit a dead end when the separate class tried to access that list, since it was in a different class. Can someone help me out here please?

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• Using inheritance and polymorphism to solve a common game problem

  - by Barry Brown

  I have two classes; let's call them Ogre and Wizard. (All fields are public to make the example easier to type in.) public class Ogre { int weight; int height; int axeLength; } public class Wizard { int age; int IQ; int height; } In each class I can create a method called, say, battle() that will determine who will win if an Ogre meets and Ogre or a Wizard meets a Wizard. Here's an example. If an Ogre meets an Ogre, the heavier one wins. But if the weight is the same, the one with the longer axe wins. public Ogre battle(Ogre o) { if (this.height > o.height) return this; else if (this.height < o.height) return o; else if (this.axeLength > o.axeLength) return this; else if (this.axeLength < o.axeLength) return o; else return this; // default case } We can make a similar method for Wizards. But what if a Wizard meets an Ogre? We could of course make a method for that, comparing, say, just the heights. public Wizard battle(Ogre o) { if (this.height > o.height) return this; else if (this.height < o.height) return o; else return this; } And we'd make a similar one for Ogres that meet Wizard. But things get out of hand if we have to add more character types to the program. This is where I get stuck. One obvious solution is to create a Character class with the common traits. Ogre and Wizard inherit from the Character and extend it to include the other traits that define each one. public class Character { int height; public Character battle(Character c) { if (this.height > c.height) return this; else if (this.height < c.height) return c; else return this; } } Is there a better way to organize the classes? I've looked at the strategy pattern and the mediator pattern, but I'm not sure how either of them (if any) could help here. My goal is to reach some kind of common battle method, so that if an Ogre meets an Ogre it uses the Ogre-vs-Ogre battle, but if an Ogre meets a Wizard, it uses a more generic one. Further, what if the characters that meet share no common traits? How can we decide who wins a battle?

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• ASP.NET MVC: post-redirect-get pattern, with only two overloaded action methods

  - by Rafi

  Is it possible to implement post-redirect-get pattern, with two overloaded action methods(One for GET action and the other for POST action) in ASP.NET MVC. In all of the MVC post-redirect-get pattern samples, I have seen three different action methods for the post-redirect-get process, each having different names. Is this really required? For Eg:(Does the code shown below, follows Post-Redirect-Get pattern?) public class SalaryTransferController : Controller { // // GET: /SalaryTransfer/ [HttpGet] public ActionResult Index(int id) { SalaryTransferIndexViewModel vm = new SalaryTransferIndexViewModel(id) { SelectedDivision = DivisionEnum.Contracting }; //Do some processing here return View(vm); } // // POST: /SalaryTransfer/ [HttpPost] public ActionResult Index(SalaryTransferIndexViewModel vm) { bool validationsuccess = false; //validate if (validationsuccess) return RedirectToAction("Index", new {id=1234 }); else return View(vm); } } Thank you for your responses.

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• What to name column in database table that holds versioning number

  - by rwmnau

  I'm trying to figure out what to call the column in my database table that holds an INT to specific "record version". I'm currently using "RecordOrder", but I don't like that, because people think higher=newer, but the way I'm using it, lower=newer (with "1" being the current record, "2" being the second most current, "3" older still, and so on). I've considered "RecordVersion", but I'm afraid that would have the same problem. Any other suggestions? "RecordAge"? I'm doing this because when I insert into the table, instead of having to find out what version is next, then run the risk of having that number stolen from me before I write, I just insert insert with a "RecordOrder" of 0. There's a trigger on the table AFTER INSERT that increments all the "RecordOrder" numbers for that key by 1, so the record I just inserted becomes "1", and all others are increased by 1. That way, you can get a person's current record by selection RecordOrder=1, instead of getting the MAX(RecordOrder) and then selecting that. PS - I'm also open to criticism about why this is a terrible idea and I should be incrementing this index instead. This just seemed to make lookups much easier, but if it's a bad idea, please enlighten me! Some details about the data, as an example: I have the following database table: CREATE TABLE AmountDue ( CustomerNumber INT, AmountDue DECIMAL(14,2), RecordOrder SMALLINT, RecordCreated DATETIME ) A subset of my data looks like this: CustomerNumber Amountdue RecordOrder RecordCreated 100 0 1 2009-12-19 05:10:10.123 100 10.05 2 2009-12-15 06:12:10.123 100 100.00 3 2009-12-14 14:19:10.123 101 5.00 1 2009-11-14 05:16:10.123 In this example, there are three rows for customer 100 - they owed $100, then $10.05, and now they owe nothing. Let me know if I need to clarify it some more. UPDATE: The "RecordOrder" and "RecordCreated" columns are not available to the user - they're only there for internal use, and to help figure out which is the current customer record. Also, I could use it to return an appropriately-ordered customer history, though I could just as easily do that with the date. I can accomplish the same thing as an incrementing "Record Version" with just the RecordCreated date, I suppose, but that removes the convenience of knowing that RecordOrder=1 is the current record, and I'm back to doing a sub-query with MAX or MIN on the DateTime to determine the most recent record.

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• What are the responsibilities of the data layer?

  - by alimac83

  I'm working on a project where I had to add a data layer to my application. I've always thought that the data layer is purely responsible for CRUD functions ie. shouldn't really contain any logic but should simply retrieve data for the business layer to manipulate. However I'm a little confused with my project because I'm not sure whether I've structured my app correctly for this scenario. Basically I'm trying to retrieve a list of products from the database that fall within a certain pricing threshold. At the moment I have a function in my data layer that basically returns all products where price min threshold and price < max threshold. But it got me thinking that maybe this is incorrect. Should the data layer simply return a list of ALL products and then the business logic do the filtering? I'm pretty confused over whether the data layer should simply provide methods that allow the business layer to get raw data or whether it should be responsible for getting filtered data too? If anyone has an article or something explaining this in detail it'd be very helpful. Thanks

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• Better to use constructor or method factory pattern?

  - by devoured elysium

  I have a wrapper class for the Bitmap .NET class called BitmapZone. Assuming we have a WIDTH x HEIGHT bitmap picture, this wrapper class should serve the purpose of allowing me to send to other methods/classes itself instead of the original bitmap. I can then better control what the user is or not allowed to do with the picture (and I don't have to copy the bitmap lots of times to send for each method/class). My question is: knowing that all BitmapZone's are created from a Bitmap, what do you find preferrable? Constructor syntax: something like BitmapZone bitmapZone = new BitmapZone(originalBitmap, x, y, width, height); Factory Method Pattern: BitmapZone bitmapZone = BitmapZone.From(originalBitmap, x , y, width, height); Factory Method Pattern: BitmapZone bitmapZone = BitmapZone.FromBitmap(originalBitmap, x, y, width, height); Other? Why? Thanks

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• Delegates in Action -Help

  - by Amutha

  I am learning delegates.I am very curious to apply delegates to the following chain-of-responsibility pattern. Kindly help me the way to apply delegates to the following piece. Thanks in advance.Thanks for your effort. #region Chain of Responsibility Pattern namespace Chain { public class Player { public string Name { get; set; } public int Score { get; set; } } public abstract class PlayerHandler { protected PlayerHandler _Successor = null; public abstract void HandlePlayer(Player _player); public void SetupHandler(PlayerHandler _handler) { _Successor = _handler; } } public class Employee : PlayerHandler { public override void HandlePlayer(Player _player) { if (_player.Score <= 100) { MessageBox.Show(string.Format("{0} is greeted by Employee", _player.Name)); } else { _Successor.HandlePlayer(_player); } } } public class Supervisor : PlayerHandler { public override void HandlePlayer(Player _player) { if (_player.Score >100 && _player.Score<=200) { MessageBox.Show(string.Format("{0} is greeted by Supervisor", _player.Name)); } else { _Successor.HandlePlayer(_player); } } } public class Manager : PlayerHandler { public override void HandlePlayer(Player _player) { if (_player.Score > 200) { MessageBox.Show(string.Format("{0} is greeted by Manager", _player.Name)); } else { MessageBox.Show(string.Format("{0} got low score", _player.Name)); } } } } #endregion #region Main() void Main() { Chain.Player p1 = new Chain.Player(); p1.Name = "Jon"; p1.Score = 100; Chain.Player p2 = new Chain.Player(); p2.Name = "William"; p2.Score = 170; Chain.Player p3 = new Chain.Player(); p3.Name = "Robert"; p3.Score = 300; Chain.Employee emp = new Chain.Employee(); Chain.Manager mgr = new Chain.Manager(); Chain.Supervisor sup = new Chain.Supervisor(); emp.SetupHandler(sup); sup.SetupHandler(mgr); emp.HandlePlayer(p1); emp.HandlePlayer(p2); emp.HandlePlayer(p3); } #endregion

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• Languages and VMs: Features that are hard to optimize and why

  - by mrjoltcola

  I'm doing a survey of features in preparation for a research project. Name a mainstream language or language feature that is hard to optimize, and why the feature is or isn't worth the price paid, or instead, just debunk my theories below with anecdotal evidence. Before anyone flags this as subjective, I am asking for specific examples of languages or features, and ideas for optimization of these features, or important features that I haven't considered. Also, any references to implementations that prove my theories right or wrong. Top on my list of hard to optimize features and my theories (some of my theories are untested and are based on thought experiments): 1) Runtime method overloading (aka multi-method dispatch or signature based dispatch). Is it hard to optimize when combined with features that allow runtime recompilation or method addition. Or is it just hard, anyway? Call site caching is a common optimization for many runtime systems, but multi-methods add additional complexity as well as making it less practical to inline methods. 2) Type morphing / variants (aka value based typing as opposed to variable based) Traditional optimizations simply cannot be applied when you don't know if the type of someting can change in a basic block. Combined with multi-methods, inlining must be done carefully if at all, and probably only for a given threshold of size of the callee. ie. it is easy to consider inlining simple property fetches (getters / setters) but inlining complex methods may result in code bloat. The other issue is I cannot just assign a variant to a register and JIT it to the native instructions because I have to carry around the type info, or every variable needs 2 registers instead of 1. On IA-32 this is inconvenient, even if improved with x64's extra registers. This is probably my favorite feature of dynamic languages, as it simplifies so many things from the programmer's perspective. 3) First class continuations - There are multiple ways to implement them, and I have done so in both of the most common approaches, one being stack copying and the other as implementing the runtime to use continuation passing style, cactus stacks, copy-on-write stack frames, and garbage collection. First class continuations have resource management issues, ie. we must save everything, in case the continuation is resumed, and I'm not aware if any languages support leaving a continuation with "intent" (ie. "I am not coming back here, so you may discard this copy of the world"). Having programmed in the threading model and the contination model, I know both can accomplish the same thing, but continuations' elegance imposes considerable complexity on the runtime and also may affect cache efficienty (locality of stack changes more with use of continuations and co-routines). The other issue is they just don't map to hardware. Optimizing continuations is optimizing for the less-common case, and as we know, the common case should be fast, and the less-common cases should be correct. 4) Pointer arithmetic and ability to mask pointers (storing in integers, etc.) Had to throw this in, but I could actually live without this quite easily. My feelings are that many of the high-level features, particularly in dynamic languages just don't map to hardware. Microprocessor implementations have billions of dollars of research behind the optimizations on the chip, yet the choice of language feature(s) may marginalize many of these features (features like caching, aliasing top of stack to register, instruction parallelism, return address buffers, loop buffers and branch prediction). Macro-applications of micro-features don't necessarily pan out like some developers like to think, and implementing many languages in a VM ends up mapping native ops into function calls (ie. the more dynamic a language is the more we must lookup/cache at runtime, nothing can be assumed, so our instruction mix is made up of a higher percentage of non-local branching than traditional, statically compiled code) and the only thing we can really JIT well is expression evaluation of non-dynamic types and operations on constant or immediate types. It is my gut feeling that bytecode virtual machines and JIT cores are perhaps not always justified for certain languages because of this. I welcome your answers.

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• Risking the exception anti-pattern.. with some modifications

  - by Sridhar Iyer

  Lets say that I have a library which runs 24x7 on certain machines. Even if the code is rock solid, a hardware fault can sooner or later trigger an exception. I would like to have some sort of failsafe in position for events like this. One approach would be to write wrapper functions that encapsulate each api a: returnCode=DEFAULT; try { returnCode=libraryAPI1(); } catch(...) { returnCode=BAD; } return returnCode; The caller of the library then restarts the whole thread, reinitializes the module if the returnCode is bad. Things CAN go horribly wrong. E.g. if the try block(or libraryAPI1()) had: func1(); char *x=malloc(1000); func2(); if func2() throws an exception, x will never be freed. On a similar vein, file corruption is a possible outcome. Could you please tell me what other things can possibly go wrong in this scenario?

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• What do you choose, protected or internal?

  - by brickner

  If I have a class with a method I want protected and internal. I want that only derived classes in the assembly would be able to call it. Since protected internal means protected or internal, you have to make a choice. What do you choose in this case - protected or internal?

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• where does the professional sheen of a GUI application realistically come from?

  - by JW

  I have been playing around with php-gtk recently and in the past I have experimented with Java to make GUI 'hello world' apps. However both these types of applications have had a bit of a clunky (almost childish) look and feel to them. I cannot deny that they are handy for making apps for in-house use (and I totally respect the amount of community effort that goes into these projects). But I would not necessarily be proud to sell it as a commercial application with a price tag of, say, £450 or £1,000. If I wanted to make an application that had the look and feel of, say, Firefox for Windows, or Adobe xyz, what GUI/language should I use? Is the 'professional sheen' or smart look and feel down to the designer or is it the case that, no matter how good a designer is, picking the right GUI framework is essential to get that look?

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• How to show unread subforums?

  - by bilygates

  I have written a simple forum in PHP using PostgreSQL. The forum consists of a number of subforums (or categories, if you like) that contain topics. I have a table that stores when was the last time a user visited a topic. It's something like this: user_id, topic_id, timestamp. I can easily determine what topics should be marked as unread by comparing the timestamp of the last topic reply with the timestamp of the last user visit. My question is: how do I efficiently determine what subforums (categories) should be marked as unread? All I've come up with is this: every time a user visits a topic, update the visit timestamp and check if all the topics from the current subforum are read or unread. If they are all read, mark the subforum as read for the user. Else, mark it as unread. But I think there must be another way. Thank you in advance.

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• Two Tables Serving as one Model in Rails

  - by matsko

  Is is possible in rails to setup on model which is dependant on a join from two tables? This would mean that for the the model record to be found/updated/destroyed there would need to be both records in both database tables linked together in a join. The model would just be all the columns of both tables wrapped together which may then be used for the forms and so on. This way when the model gets created/updated it is just one form variable hash that gets applied to the model? Is this possible in Rails 2 or 3?

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• c# - pull records from database without timeout

  - by BhejaFry

  Hi folks, i have a sql query with multiple joins & it pulls data from a database for processing. This is supposed to be running on some scheduled basis. So day 1, it might pull 500, day 2 say 400. Now, if the service is stopped for some reason & the data not processed, then on day3 there could be as much as 1000 records to process. This is causing timeout on the sql query. How best to handle this situation without causing timeout & gradually reducing workload to process? TIA

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• Active Record/ORM vs Normal Forms?

  - by Arsenal

  Hello, I've been playing around with Active Record a bit, and I have noticed that A.C./ORM always uses the following database model when creating a one-to-one relationship Person id | country_id | name | ... Country id | tld | name | ... No I wondered, isn't this a violiation of the third Normal Form? This clearly states "Every non-prime attribute is non-transitively dependent on every key of the table". Well this country_id isn't dependent of personid is it? So is this wrong or am I just not getting the point?

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• Avoid loading unnecessary data from db into objects (web pages)

  - by GmGr

  Really newbie question coming up. Is there a standard (or good) way to deal with not needing all of the information that a database table contains loaded into every associated object. I'm thinking in the context of web pages where you're only going to use the objects to build a single page rather than an application with longer lived objects. For example, lets say you have an Article table containing id, title, author, date, summary and fullContents fields. You don't need the fullContents to be loaded into the associated objects if you're just showing a page containing a list of articles with their summaries. On the other hand if you're displaying a specific article you might want every field loaded for that one article and maybe just the titles for the other articles (e.g. for display in a recent articles sidebar). Some techniques I can think of: Don't worry about it, just load everything from the database every time. Have several different, possibly inherited, classes for each table and create the appropriate one for the situation (e.g. SummaryArticle, FullArticle). Use one class but set unused properties to null at creation if that field is not needed and be careful. Give the objects access to the database so they can load some fields on demand. Something else? All of the above seem to have fairly major disadvantages. I'm fairly new to programming, very new to OOP and totally new to databases so I might be completely missing the obvious answer here. :)

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