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• SQL: empty string vs NULL value

  - by Jacek Prucia

  I know this subject is a bit controversial and there are a lot of various articles/opinions floating around the internet. Unfortunatelly, most of them assume the person doesn't know what the difference between NULL and empty string is. So they tell stories about surprising results with joins/aggregates and generally do a bit more advanced SQL lessons. By doing this, they absolutely miss the whole point and are therefore useless for me. So hopefully this question and all answers will move subject a bit forward. Let's suppose I have a table with personal information (name, birth, etc) where one of the columns is an email address with varchar type. We assume that for some reason some people might not want to provide an email address. When inserting such data (without email) into the table, there are two available choices: set cell to NULL or set it to empty string (''). Let's assume that I'm aware of all the technical implications of choosing one solution over another and I can create correct SQL queries for either scenario. The problem is even when both values differ on the technical level, they are exactly the same on logical level. After looking at NULL and '' I came to a single conclusion: I don't know email address of the guy. Also no matter how hard i tried, I was not able to sent an e-mail using either NULL or empty string, so apparently most SMTP servers out there agree with my logic. So i tend to use NULL where i don't know the value and consider empty string a bad thing. After some intense discussions with colleagues i came with two questions: am I right in assuming that using empty string for an unknown value is causing a database to "lie" about the facts? To be more precise: using SQL's idea of what is value and what is not, I might come to conclusion: we have e-mail address, just by finding out it is not null. But then later on, when trying to send e-mail I'll come to contradictory conclusion: no, we don't have e-mail address, that @!#$ Database must have been lying! Is there any logical scenario in which an empty string '' could be such a good carrier of important information (besides value and no value), which would be troublesome/inefficient to store by any other way (like additional column). I've seen many posts claiming that sometimes it's good to use empty string along with real values and NULLs, but so far haven't seen a scenario that would be logical (in terms of SQL/DB design). P.S. Some people will be tempted to answer, that it is just a matter of personal taste. I don't agree. To me it is a design decision with important consequences. So i'd like to see answers where opion about this is backed by some logical and/or technical reasons.

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• What are DRY, KISS, SOLID, etc. classified as?

  - by Morgan Herlocker

  Is something like DRY a design pattern, a methodology, or something in between? They do not have specific implementations that could neccessarily be demonstrated(even if you can easily demonstrate a case NOT using something like KISS... see The Daily WTF for a plethora of examples), nor do they fully explain a development process like a methodology generally would. Where does that leave these types of "rule of thumb"'s?

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• What are the essential things one needs to know about UML?

  - by Hanno Fietz

  I want my scribbles of a program's design and behaviour to become more streamlined and have a common language with other developers. I looked at UML and in principle it seems to be what I'm looking for, but it seems to be overkill. The information I found online also seems very bloated and academic. How can I understand UML in plain-English way, enough to be able to explain it to my colleagues? What are the canonical resources for understanding UML at a ground level?

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• What's the most useful 10% of UML and is there a quick tutorial on it?

  - by Hanno Fietz

  I want my scribbles of a program's design and behaviour to become more streamlined and have a common language with other developers. I looked at UML and in principle it seems to be what I'm looking for, just way overkill. The information I found online also seems very bloated and academic. Is there a no-bullshit, 15-minutes introduction to the handful of UML symbols I'll need when discussing the architecture of some garden variety software on a whiteboard with my colleagues?

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• Starting all over again?

  - by kyndigs

  Have you ever been developing something and just came to a point where you think that this is rubbish, the design is bad and although I will lose time it will be better to just start all over again? What should you consider before making this step? I know it can be drastic in some cases, is it best to just totally ignore what you did before, or take some of the best bits from it? Some real life examples would be great.

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• Go/Obj-C style interfaces with ability to extend compiled objects after initial release

  - by Skrylar

  I have a conceptual model for an object system which involves combining Go/Obj-C interfaces/protocols with being able to add virtual methods from any unit, not just the one which defines a class. The idea of this is to allow Ruby-ish open classes so you can take a minimalist approach to library development, and attach on small pieces of functionality as is actually needed by the whole program. Implementation of this involves a table of methods marked virtual in an RTTI table, which system functions are allowed to add to during module initialization. Upon typecasting an object to an interface, a Go-style lookup is done to create a vtable for that particular mapping and pass it off so you can have comparable performance to C/C++. In this case, methods may be added /afterwards/ which were not previously known and these new methods allow newer interfaces to be satisfied; while I like this idea because it seems like it would be very flexible (disregarding the potential for spaghetti code, which can happen with just about any model you use regardless). By wrapping the system calls for binding methods up in a set of clean C-compatible calls, one would also be able to integrate code with shared libraries and retain a decent amount of performance (Go does not do shared linking, and Objective-C does a dynamic lookup on each call.) Is there a valid use-case for this model that would make it worth the extra background plumbing? As much as this Dylan-style extensibility would be nice to have access to, I can't quite bring myself to a use case that would justify the overhead other than "it could make some kinds of code more extensible in future scenarios."

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• What browser do you build in? [closed]

  - by Ryan

  Lately I have been using Chrome, but I am starting to think I should use FF. What are the advantages and disadvantages of the various mainstream browsers (with an emphasis on Chrome and FF) when doing web development? Is it easier to start with clean code for a relatively conforming browser, and later add hacks/workarounds for acceptable display with less conforming browsers, or is it easier to work with a variety of browsers from the beginning, so we never have a page that's completely unacceptable with, for example, IE 6?

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• How should I structure my database to gain maximum efficiently in this scenario?

  - by Bob Jansen

  I'm developing a PHP script that analyzes the web traffic of my clients websites. By placing a link to a javascript on the clients website (think of Google Analyses), my script harvests information like: the visitors IP address, reference link, current page link, user agent, etc. Now my clients can view these statistics via a control panel that I have build. These clients can also adjust profile settings, set firewall rules, create support tickets and pay invoices. Currently all the the traffic is stored in one table. You can imagine that this tabel would become very large as some my clients receive thousands of pageviews per day. Furthermore, all the traffic data of each client would be stored in the same table, creating a mess. This is the same for the firewall rules currently, and the invoice and support system. I'm looking for way to structure my database in a more organized way to hold large amounts of data of multiple users. This is the first project that I'm developing that deals with so much data, and would like to hear suggestions and tips. I was thinking of using multiple databases to structure the data. The main database will store users data (email,pass,id,etc) admin/website settings. Than each client will have an unique database labeled prefix_userid, which carry tables holding their traffic, invoice, and support ticket data. Would this be a solution, and would it slow down or speed up overall performances (that is spreading the data over muliple databases). I have a solid VPS, but would like to safe and be as effient as possible.

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• How to store prices that have effective dates?

  - by lal00

  I have a list of products. Each of them is offered by N providers. Each providers quotes us a price for a specific date. That price is effective until that provider decides to set a new price. In that case, the provider will give the new price with a new date. The MySQL table header currently looks like: provider_id, product_id, price, date_price_effective Every other day, we compile a list of products/prices that are effective for the current day. For each product, the list contains a sorted list of the providers that have that particular product. In that way, we can order certain products from whoever happens to offer the best price. To get the effective prices, I have a SQL statement that returns all rows that have date_price_effective >= NOW(). That result set is processed with a ruby script that does the sorting and filtering necessary to obtain a file that looks like this: product_id_1,provider_1,provider_3,provider8,provider_10... product_id_2,provider_3,provider_2,provider1,provider_10... This works fine for our purposes, but I still have an itch that a SQL table is probably not the best way to store this kind of information. I have that feeling that this kind of problema has been solved previously in other more creative ways. Is there a better way to store this information other than in SQL? or, if using SQL, is there a better approach than the one I'm using?

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• I need an approach to the problem of preventing inserting duplicate records into the database

  - by Maurice

  Apologies is this question is asked on the incorrect "stack" A webservice that I call returns a list of data. The data from the webservice is updated periodically, so a call to the webservice done in one hour could return the same data as a call done in an hour. Also, the data is returned based on a start and end date. We have multiple users that can run the webservice search, and duplicate data is most likely to be returned (especially for historical data). However I don't want to insert this duplicate data in the database. I've created a db table in which the data is stored (most important columns are) Id int autoincrement PK Date date not null --The date to which the data set belongs. LastUpdate date not null --The date the data set was last updated. UserName varchar(50) --The name of the user doing the search. I use sql server 2008 express with c# 4.0 and visual studio 2010. Entity Framework is used as the ORM. If stored procedures could be avoided in the proposed solution, then that will be a plus. Another way of looking interpreting what I'm asking a solution for is as follows: I have a million unique records in my table. A user does a new search. The search results from the user contains around 300k of the data that is already in the db. An efficient solution to finding an inserting only the unique records is needed.

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• Should I use multiple column primary keys or add a new colum?

  - by Covar

  My current database design makes use of a multiple column primary key to use existing data (that would be unique anyway) instead of creating an additional column assigning each entry an arbitrary key. I know that this is allowed, but was wondering if this is a practice that I might want to use cautiously and possibly avoid (much like goto in C). So what are some of the disadvantages I might see in this approach or reasons I might want a single column key?

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• Nested Entities and calculation on leaf entity property - SQL or NoSQL approach

  - by Chandu

  I am working on a hobby project called Menu/Recipe Management. This is how my entities and their relations look like. A Nutrient has properties Code and Value An Ingredient has a collection of Nutrients A Recipe has a Collection of Ingredients and occasionally can have a collection of other recipes A Meal has a Collection of Recipes and Ingredients A Menu has a Collection of Meals The relations can be depicted as In one of the pages, for a selected menu I need to display the effective nutrients information calculated based on its constituents (Meals, Recipes, Ingredients and the corresponding nutrients). As of now am using SQL Server to store the data and I am navigating the chain from my C# code, starting from each meal of the menu and then aggregating the nutrient values. I think this is not an efficient way as this calculation is being done every time the page is requested and the constituents change occasionally. I was thinking about a having a background service that maintains a table called MenuNutrients ({MenuId, NutrientId, Value}) and will populate/update this table with the effective nutrients when any of the component (Meal, Recipe, Ingredient) changes. I feel that a GraphDB would be a good fit for this requirement, but my exposure to NoSQL is limited. I want to know what are the alternative solutions/approaches to this requirement of displaying the nutrients of a given menu. Hope my description of the scenario is clear.

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• Attaching new animations onto skeleton via props, a good idea?

  - by Cardin

  I'm thinking of coding a game with an idea of mine. I've coded 2D games before, but I'm new to 3D programming, so I'd like to ask if this idea of mine is feasible or out of my depth. I'm making a game where there are many different characters for the player to choose from (JRPG style). So to save time, I have an idea of creating many different varied characters using a completely naked body mesh and animation skeleton, standardised across all characters. For example, by placing different hair, boots, armor props on the character mesh, new characters can be formed. Kinda like playing dress-up with a barbie doll. I'm thinking this can be done by having a bone on the prop that I can programmically attach to the main mesh. Also, I plan to have some props add new animations to the base skeleton, so equipping some particular props would give it new attack, damage, idle animations. This is because I can't expect the character to have the same swinging animation if he had a big sword or an axe. I think this might be possible if the prop has its own instance of the animation skeleton with just only the new animations, and parenting the base body mesh to this new skeleton. So all the base body mesh has are just the basic animations, other animations come from the props. My concerns are, 1) the props might not attach to the mesh properly and jitter a lot, 2) since prop and body are animated differently, the props and base mesh will cause visual artefacts, like the naked thighs showing through the pants when the character walks, 3) a custom pipeline have to be developed to export skeletons without mesh, and also to attach the base body mesh to a new skeleton during runtime in the game. So my question: are these features considered 'easy' to code? Or am I trying to do something few have ever succeeded with on their own? It feels like all these can be done given enough time and I know I definitely have to do a bit of bone matrix calculations, but I really don't want to drag out the development timeline unnecessarily from coding mathematically intense things or analyzing how to parse 3D export formats. I'm currently only at the Game Design stage, so if these features aren't a good idea, I can simply change the design of the game. (Unrelated to question) I could always, as last resort, have the characters have predetermined outfit and weapon selections so as to animate everything manually.

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• How can I improve my skills while working on actual projects, in the absence of more experienced developers?

  - by LolCoder

  I'm the lead developer at a small company, working with C# and ASP.Net. Our team is small, 2-3 people, without much experience in development and design. I don't have the opportunity to learn from more senior developers, there is no one in my team to guide me and help me choose the best approaches, as I take care most of the projects myself. How can I improve my software development skills while working on actual projects, in the absence of more experienced developers?

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• Interaction of a GUI-based App and Windows Service

  - by psubsee2003

  I am working on personal project that will be designed to help manage my media library, specifically recordings created by Windows Media Center. So I am going to have the following parts to this application: A Windows Service that monitors the recording folder. Once a new recording is completed that meets specific criteria, it will call several 3rd party CLI Applications to remove the commercials and re-encode the video into a more hard-drive friendly format. A controller GUI to be able to modify settings of the service, specifically add new shows to watch for, and to modify parameters for the CLI Applications A standalone (GUI-based) desktop application that can perform many of the same functions as the windows service, expect manually on specific files instead of automatically based on specific criteria. (It should be mentioned that I have limited experience with an application of this complexity, and I have absolutely zero experience with Windows Services) Since the 1st and 3rd bullet share similar functionality, my design plan is to pull the common functionality into a separate library shared by both parts applications, but these 2 components do not need to interact otherwise. The 2nd and 3rd bullets seem to share some common functionality, both will have a GUI, both will have to help define similar parameters (one to send to the service and the other to send directly to the CLI applications), so I can see some advantage to combining them into the same application. On the other hand, the standalone application (bullet #3) really does not need to interact with the service at all, except for possibly sharing a few common default parameters that can easily be put into an XML in a common location, so it seems to make more sense to just keep everything separate. The controller GUI (2nd bullet) is where I am stuck at the moment. Do I just roll this functionality (allow for user interaction with the service to update settings and criteria) into the standalone application? Or would it be a better design decision to keep them separate? Specifically, I'm worried about adding the complexity of communicating with the Windows Service to the standalone application when it doesn't need it. Is WCF the right approach to allow the controller GUI to interact with the Windows Service? Or is there a better alternative? At the moment, I don't envision a need for a significant amount of interaction, maybe just adding a new task once in a while and occasionally tweaking a parameter, but when something is changed, I do expect the windows service to immediately use the new settings.

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• iOS - Unit tests for KVO/delegate codes

  - by ZhangChn

  I am going to design a MVC pattern. It could be either designed as a delegate pattern, or a Key-Value-Observing(KVO), to notify the controller about changing models. The project requires certain quality control procedures to conform to those verification documents. My questions: Does delegate pattern fit better for unit testing than KVO? If KVO fits better, would you please suggest some sample codes?

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• Dynamic Query Generation : suggestion for better approaches

  - by Gaurav Parmar

  I am currently designing a functionality in my Web Application where the verified user of the application can execute queries which he wishes to from the predefined set of queries with where clause varying as per user's choice. For example,Table ABC contains the following Template query called SecretReport "Select def as FOO, ghi as BAR from MNO where " SecretReport can have parameters XYZ, ILP. Again XYZ can have values as 1,2 and ILP can have 3,4 so if the user chooses ILP=3, he will get the result of the following query on his screen "Select def as FOO, ghi as BAR from MNO where ILP=3" Again the user is allowed permutations of XYZ / ILP My initial thought is that User will be shown a list of Report names and each report will have parameters and corresponding values. But this approach although technically simple does not appear intuitive. I would like to extend this functionality to a more generic level. Such that the user can choose a table and query based on his requirements. Of course we do not want the end user to take complete control of DB. But only tables and fields that are relevant to him. At present we are defining what is relevant in the code. But I want the Admin to take over this functionality such that he can decide what is relevant and expose the same to the user. On user's side it should be intuitive what is available to him and what queries he can form. Please share your thoughts what is the most user friendly way to provide this feature to the end user.

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• Why are MVC & TDD not employed more in game architecture?

  - by secoif

  I will preface this by saying I haven't looked a huge amount of game source, nor built much in the way of games. But coming from trying to employ 'enterprise' coding practices in web apps, looking at game source code seriously hurts my head: "What is this view logic doing in with business logic? this needs refactoring... so does this, refactor, refactorrr" This worries me as I'm about to start a game project, and I'm not sure whether trying to mvc/tdd the dev process is going to hinder us or help us, as I don't see many game examples that use this or much push for better architectural practices it in the community. The following is an extract from a great article on prototyping games, though to me it seemed exactly the attitude many game devs seem to use when writing production game code: Mistake #4: Building a system, not a game ...if you ever find yourself working on something that isn’t directly moving your forward, stop right there. As programmers, we have a tendency to try to generalize our code, and make it elegant and be able to handle every situation. We find that an itch terribly hard not scratch, but we need to learn how. It took me many years to realize that it’s not about the code, it’s about the game you ship in the end. Don’t write an elegant game component system, skip the editor completely and hardwire the state in code, avoid the data-driven, self-parsing, XML craziness, and just code the damned thing. ... Just get stuff on the screen as quickly as you can. And don’t ever, ever, use the argument “if we take some extra time and do this the right way, we can reuse it in the game”. EVER. is it because games are (mostly) visually oriented so it makes sense that the code will be weighted heavily in the view, thus any benefits from moving stuff out to models/controllers, is fairly minimal, so why bother? I've heard the argument that MVC introduces a performance overhead, but this seems to me to be a premature optimisation, and that there'd more important performance issues to tackle before you worry about MVC overheads (eg render pipeline, AI algorithms, datastructure traversal, etc). Same thing regarding TDD. It's not often I see games employing test cases, but perhaps this is due to the design issues above (mixed view/business) and the fact that it's difficult to test visual components, or components that rely on probablistic results (eg operate within physics simulations). Perhaps I'm just looking at the wrong source code, but why do we not see more of these 'enterprise' practices employed in game design? Are games really so different in their requirements, or is a people/culture issue (ie game devs come from a different background and thus have different coding habits)?

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• How to refactor a method which breaks "The law of Demeter" principle?

  - by dreza

  I often find myself breaking this principle (not intentially, just through bad design). However recently I've seen a bit of code that I'm not sure of the best approach. I have a number of classes. For simplicity I've taken out the bulk of the classes methods etc public class Paddock { public SoilType Soil { get; private set; } // a whole bunch of other properties around paddock information } public class SoilType { public SoilDrainageType Drainage { get; private set; } // a whole bunch of other properties around soil types } public class SoilDrainageType { // a whole bunch of public properties that expose soil drainage values public double GetProportionOfDrainage(SoilType soil, double blockRatio) { // This method does a number of calculations using public properties // exposed off SoilType as well as the blockRatio value in some conditions } } In the code I have seen in a number of places calls like so paddock.Soil.Drainage.GetProportionOfDrainage(paddock.Soil, paddock.GetBlockRatio()); or within the block object itself in places it's Soil.Drainage.GetProportionOfDrainage(this.Soil, this.GetBlockRatio()); Upon reading this seems to break "The Law of Demeter" in that I'm chaining together these properties to access the method I want. So my thought in order to adjust this was to create public methods on SoilType and Paddock that contains wrappers i.e. on paddock it would be public class Paddock { public double GetProportionOfDrainage() { return Soil.GetProportionOfDrainage(this.GetBlockRatio()); } } on the SoilType it would be public class SoilType { public double GetProportionOfDrainage(double blockRatio) { return Drainage.GetProportionOfDrainage(this, blockRatio); } } so now calls where it used would be simply // used outside of paddock class where we can access instances of Paddock paddock.GetProportionofDrainage() or this.GetProportionOfDrainage(); // if used within Paddock class This seemed like a nice alternative. However now I have a concern over how would I enforce this usage and stop anyone else from writing code such as paddock.Soil.Drainage.GetProportionOfDrainage(paddock.Soil, paddock.GetBlockRatio()); rather than just paddock.GetProportionOfDrainage(); I need the properties to remain public at this stage as they are too ingrained in usage throughout the code block. However I don't really want a mixture of accessing the method on DrainageType directly as that seems to defeat the purpose altogether. What would be the appropiate design approach in this situation? I can provide more information as required to better help in answers. Is my thoughts on refactoring this even appropiate or should is it best to leave it as is and use the property chaining to access the method as and when required?

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• How do I deal with the problems of a fast side-scroller?

  - by Ska

  I'm making a side scrolling airplane game and when I begin going very fast I begin to experience some problems as a player: Elements are not distinguishable, like power-ups from bullets, etc I start to feel dizzy and uncomfortable There isn't enough time to see what's coming How can I sort this out? Do I use less details in all the grahpics? Tiny Wings has the same horizontal movement speed as in my game but it doesn't suffer from these problems. Are there any other really fast side-scrollers I could take as a reference?

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• Chapter 7–Enforced Data Protection

  - by drsql

  As the book progresses, I find myself veering from the original stated outline quite a bit, because as I teach about this more (and I am teaching a daylong db design class in August at http://www.sqlsolstice.com/ … shameless plug, but it is on topic :) I start to find that a given order works better. Originally I had slated myself to talk more about modeling here for three chapters, then get back to the more implementation topics to finish out the book, but now I am going to keep plugging through...(read more)

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• Speaking at SQL Saturday #39 in NYC!

  - by andyleonard

  I am honored to present Applied SSIS Design Patterns and Introduction to Incremental Loads at SQL Saturday #39 in New York City! If you're there and you read this blog, be sure to stop by and introduce yourself! :{> Andy Share this post: email it! | bookmark it! | digg it! | reddit! | kick it! | live it!...(read more)

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• Should I use multiple column primary keys or add a new column?

  - by Covar

  My current database design makes use of a multiple column primary key to use existing data (that would be unique anyway) instead of creating an additional column assigning each entry an arbitrary key. I know that this is allowed, but was wondering if this is a practice that I might want to use cautiously and possibly avoid (much like goto in C). So what are some of the disadvantages I might see in this approach or reasons I might want a single column key?

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• Storing revisions of a document

  - by dev.e.loper

  This is a follow up question to my original question. I'm thinking of going with generating diffs and storing those diffs in the database 'History' table. I'm using diff-match-patch library to generate what is called a 'patch'. On every save, I compare previous and new version and generate this patch. The patch could be used to generate a document at specific point in time. My dilemma is how to store this data. Should I: a Insert a new database record for every patch? b. Store these patches in javascript array and store that array in history table. So there is only one db History record for document with an array of all the patches. Concerns with: a. Too many db records generated. Will be slow and CPU intensive to query. b. Only one record. If record is somehow corrupted/deleted. Entire revision history is gone. I'm looking for suggestions, concerns with either approach.

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• Designing for visually impaired gamers

  - by Aku

  Globally the number of people of all ages visually impaired is estimated to be 285 million, of whom 39 million are blind. — World Health Organisation, 2010. (That's 4.2% and 0.6% of the world population.) Most videogames put a strong emphasis on visuals in their content delivery. Visually impaired gamers are largely left out. How do I design a game to be accessible to visually impaired gamers?

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