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• At what point is it worth using a database?

  - by radix07

  I have a question relating to databases and at what point is worth diving into one. I am primarily an embedded engineer, but I am writing an application using QT to interface with our controller. We are at an odd point where we have enough data that it would be feasible to implement a database (around 700+ items and growing) to manage everything, but I am not sure it is worth the time right now to deal with. I have no problems implementing the GUI with files generated from excel and parsed in, but it gets tedious and hard to track even with VBA scripts. I have been playing around with converting our data into something more manageable for the application side with Microsoft Access and that seems to be working well. If that works out I am only a step (or several) away from using an SQL database and using the QT library to access and modify it. I don't have much experience managing data at this level and am curious what may be the best way to approach this. So what are some of the real benefits of using a database if any in this case? I realize much of this can be very application specific, but some general ideas and suggestions on how to straddle the embedded/application programming line would be helpful. Thanks

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• Web services or shared database for (game) server communication?

  - by jaaronfarr

  We have 2 server clusters: the first is made up of typical web applications backed by SQL databases. The second are highly optimized multiplayer game servers which keep all data in memory. Both clusters communicate with clients via HTTP (Ajax with JSON). There are a few cases in which we need to share data between the two server types, for example, reporting back and storing the results of a game (should ultimately end up in the database). We're considering several approaches for inter-server communication: Just share the MySQL databases between clusters (introduce SQL to the game servers) Sharing data in a distributed key-value store like Memcache, Redis, etc. Use an RPC technology like Google ProtoBufs or Apache Thrift Using RESTful web services (the game server would POST back to the web servers, for example) At the moment, we're leaning towards web services or just sharing the database. Sharing the database seems easy, but we're concerned this adds extra memory and a new dependency into the game servers. Web services provide good separation of concerns and fit with the existing Ajax we use, but add complexity, overhead and many more ways for communication to fail. Are there any other good reasons not to use one or the other approach? Which would be easier to scale?

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• In Python, how to make sure database connection will always close before leaving a code block?

  - by Cawas

  I want to prevent database connection being open as much as possible, because this code will run on an intensive used server and people here already told me database connections should always be closed as soon as possible. def do_something_that_needs_database (): dbConnection = MySQLdb.connect(host=args['database_host'], user=args['database_user'], passwd=args['database_pass'], db=args['database_tabl'], cursorclass=MySQLdb.cursors.DictCursor) dbCursor = dbConnection.cursor() dbCursor.execute('SELECT COUNT(*) total FROM table') row = dbCursor.fetchone() if row['total'] == 0: print 'error: table have no records' dbCursor.execute('UPDATE table SET field="%s"', whatever_value) return None print 'table is ok' dbCursor.execute('UPDATE table SET field="%s"', another_value) # a lot more of workflow done here dbConnection.close() # even more stuff would come below I believe that leaves a database connection open when there is no row on the table, tho I'm still really not sure how it works. Anyway, maybe that is bad design in the sense that I could open and close a DB connection after each small block of execute. And sure, I could just add a close right before the return in that case... But how could I always properly close the DB without having to worry if I have that return, or a raise, or continue, or whatever in the middle? I'm thinking in something like a code block, similar to using try, like in the following suggestion, which obviously doesn't work: def do_something_that_needs_database (): dbConnection = MySQLdb.connect(host=args['database_host'], user=args['database_user'], passwd=args['database_pass'], db=args['database_tabl'], cursorclass=MySQLdb.cursors.DictCursor) try: dbCursor = dbConnection.cursor() dbCursor.execute('SELECT COUNT(*) total FROM table') row = dbCursor.fetchone() if row['total'] == 0: print 'error: table have no records' dbCursor.execute('UPDATE table SET field="%s"', whatever_value) return None print 'table is ok' dbCursor.execute('UPDATE table SET field="%s"', another_value) # again, that same lot of line codes done here except ExitingCodeBlock: closeDb(dbConnection) # still, that "even more stuff" from before would come below I don't think there is anything similar to ExitingCodeBlock for an exception, tho I know there is the try else, but I hope Python already have a similar feature... Or maybe someone can suggest me a paradigm move and tell me this is awful and highly advise me to never do that. Maybe this is just something to not worry about and let MySQLdb handle it, or is it?

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• What's the best way to access a MS Access database using PHP?

  - by Jack Roscoe

  Hi, I need to access some data from an MS Access database and retrieve some data from it using PHP. I've looked around the web, and found the following line which seems to correctly connect to the database: $conn->Open("DRIVER={Microsoft Access Driver (*.mdb)}; DBQ=C:\wamp\www\data\MYDB.mdb"); However, I have tried to retrieve some data in the following way: $query = "SELECT pageid FROM pages_table"; $result = mysqli_query($conn, $query); $amount_of_pages = 0; if(mysqli_num_rows($result) <= 0) echo "No results found."; else while($row = mysqli_fetch_array($result, MYSQL_ASSOC)) $amount_of_pages++; And was presented with the following errors: Warning: mysqli_query() expects parameter 1 to be mysqli, object given in C:\wamp\www\data\index.php on line 19 Warning: mysqli_num_rows() expects parameter 1 to be mysqli_result, null given in C:\wamp\www\data\index.php on line 23 No results found. I don't really understand the connection to the Access database, is there something I should be doing differently? Thanks in advance for any help.

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• Best way to run multiple queries per second on database, performance wise?

  - by Michael Joell

  I am currently using Java to insert and update data multiple times per second. Never having used databases with Java, I am not sure what is required, and how to get the best performance. I currently have a method for each type of query I need to do (for example, update a row in a database). I also have a method to create the database connection. Below is my simplified code. public static void addOneForUserInChannel(String channel, String username) throws SQLException { Connection dbConnection = null; PreparedStatement ps = null; String updateSQL = "UPDATE " + channel + "_count SET messages = messages + 1 WHERE username = ?"; try { dbConnection = getDBConnection(); ps = dbConnection.prepareStatement(updateSQL); ps.setString(1, username); ps.executeUpdate(); } catch(SQLException e) { System.out.println(e.getMessage()); } finally { if(ps != null) { ps.close(); } if(dbConnection != null) { dbConnection.close(); } } } And my DB connection private static Connection getDBConnection() { Connection dbConnection = null; try { Class.forName(DB_DRIVER); } catch (ClassNotFoundException e) { System.out.println(e.getMessage()); } try { dbConnection = DriverManager.getConnection(DB_CONNECTION, DB_USER,DB_PASSWORD); return dbConnection; } catch (SQLException e) { System.out.println(e.getMessage()); } return dbConnection; } This seems to be working fine for now, with about 1-2 queries per second, but I am worried that once I expand and it is running many more, I might have some issues. My questions: Is there a way to have a persistent database connection throughout the entire run time of the process? If so, should I do this? Are there any other optimizations that I should do to help with performance? Thanks

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• Informix "Database locale information mismatch"

  - by lmmortal

  I have informix 11.5 running in my Win-2003 box and few databases running in it. System databases have locale en_us.819 My custom databases have locale en_us.57372 (UTF8). There is also application deployed to JBoss 4.0.2 which has few datasources configured for those custom databases. <local-tx-datasource> <jndi-name>InformixDS</jndi-name> <connection-url>jdbc:informix-sqli://@database.server@:@database.port@/tcs_catalog:[email protected]@</connection-url> <driver-class>com.informix.jdbc.IfxDriver</driver-class> <user-name>@database.username@</user-name> <password>@database.password@</password> <new-connection-sql>set lock mode to wait 5</new-connection-sql> <check-valid-connection-sql>select '1' from dual</check-valid-connection-sql> <metadata> <type-mapping>InformixDB</type-mapping> </metadata> I'm logged in as Administrator and when I start JBoss the following error is shown Caused by: java.sql.SQLException: Database locale information mismatch. at com.informix.util.IfxErrMsg.getSQLException(IfxErrMsg.java:373) at com.informix.jdbc.IfxSqli.a(IfxSqli.java:3208) at com.informix.jdbc.IfxSqli.E(IfxSqli.java:3518) at com.informix.jdbc.IfxSqli.dispatchMsg(IfxSqli.java:2353) at com.informix.jdbc.IfxSqli.receiveMessage(IfxSqli.java:2269) at com.informix.jdbc.IfxSqli.executeOpenDatabase(IfxSqli.java:1786) at com.informix.jdbc.IfxSqliConnect.<init>(IfxSqliConnect.java:1327) at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27) at java.lang.reflect.Constructor.newInstance(Constructor.java:501) at com.informix.jdbc.IfxDriver.connect(IfxDriver.java:254) at org.jboss.resource.adapter.jdbc.local.LocalManagedConnectionFactory.createManagedConnection(LocalManagedConnectionFactory.java:151) ... 160 more Caused by: java.sql.SQLException at com.informix.util.IfxErrMsg.getSQLException(IfxErrMsg.java:373) at com.informix.jdbc.IfxSqli.E(IfxSqli.java:3523) ... 170 more DB_LOCALE and CLIENT_LOCALE are set to en_us.utf8 for Administrator. When I set in Server Studio DB_LOCALE and CLIENT_LOCALE to en_us.utf8 I can connect my databases. Where should I set DB_LOCALE and CLIENT_LOCALE to avoid this Database locale information mismatch error? Thanks.

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• EF4 Generate Database

  - by shaneseaton

  Hi, I am trying my hardest to find the simplest way to create a basic "model first" entity framework example. However I am struggling with the actually generation of the database, particularly the running of the SQL against the database. Tools Visual Studio 2010 SQL Server 2008 Express Process Create a new class project Add a new Server-Database item (mdf) named "Database1.mdf" to the project Add an empty ADO.net Entity Model Create a simple entity (Person: Id, Name) Generate the Script selecting the Database1 connection created for me by visual studio Right click the script editor and select the "Execute SQL..." option Log in to SQLEXPRESS This is where is falls over saying it cant find a database name "Database1". The "problem" is that the SQL server has not had Database1 attached to it. I am 100% positive that Visual Studio use to attach a database to SQLExpress when it created a new database (Step 2). This appears to not be the case any more (even the beta of VS2010 did it). Can someone confirm this? or tell me how to get this to happen? Is there a way that I can modify the TSQL script to use an un-attached database. ie a file. I know I can use SQL Management Studio or sqlcmd to attach the database, but I would ideally like to avoid the solutions as I would like to see the cleanest method of just using visual studio. Ideal Solutions (in order of most prefered) Get visual studio to attach the newly created database Modify the generated SQL to point to file Thanks in advance.

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• How to Set Customer Table with Multiple Phone Numbers? - Relational Database Design

  - by user311509

  CREATE TABLE Phone ( phoneID - PK . . . ); CREATE TABLE PhoneDetail ( phoneDetailID - PK phoneID - FK points to Phone phoneTypeID ... phoneNumber ... . . . ); CREATE TABLE Customer ( customerID - PK firstName phoneID - Unique FK points to Phone . . . ); A customer can have multiple phone numbers e.g. Cell, Work, etc. phoneID in Customer table is unique and points to PhoneID in Phone table. If customer record is deleted, phoneID in Phone table should also be deleted. Do you have any concerns on my design? Is this designed properly? My problem is phoneID in Customer table is a child and if child record is deleted then i can not delete the parent (Phone) record automatically.

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• Database structure for ecommerce site

  - by imanc

  Hey Guys, I have been tasked with designing an ecommerce solution. The aspect that is causing me the most problems is the database. Currently the site consists of 10+ country based shops each with their own database (all residing on the same mysql instance). For the new site I'd rather all these shop databases be merged into one database so that all tables (products, orders, customers etc.) have a shop_id field. From a programming perspective this seems to make the most sense as we won't have to manage data across multiple databases. Currently the entire site generates about 120k orders a year, but is experiencing fairly heavy growth and we need to design a solution that will scale. In 5 years there may be more than a million orders per year and a database that contains 5 years order history (archiving maybe a solution here). The question is - do we use a single database, or do we keep the database-per-shop structure? I am currently trying to find supporting evidence for either avenue. The company I am designing the solution for prefer the per-shop database structure because they believe it will allow the sites to scale. But my argument is that the shop's database probably won't get that busy over the next few years that they exceed the capacity of a mysql database and a "no expenses spared" hardware set-up. I am wondering if anyone has any advice either way? Does anyone have experience with websites / ecommerce sites that have tables containing millions of records? I know there is probably not a clear answer here, but at what stage do we have too many records or too large table files to have a fast loading site? Also, if anyone has any advice on sources of information - books, websites, etc. where I can do further research, it would be highly appreciated! Cheers, imanc

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• Oracle Embedded - Duração de meio dia - 14/Abr/10

  - by Claudia Costa

  Convidamo-lo a participar num evento que a Oracle irá realizar no próximo dia 14 de Abril, dedicado a soluções para sistemas Embedded.   A Oracle tem sido desde sempre o líder indisputado - em termos de desempenho, fiabilidade e escalabilidade - em sistemas de gestão de base de dados para aplicações críticas de gestão das grandes organizações. Hoje, no entanto, as aplicações críticas são implementadas não apenas nos data centers, mas cada vez mais em dispositivos móveis, nas infraestruturas de rede e em sistemas de aplicação específica. Por isso, o compromisso da Oracle em desenvolver os melhores produtos de gestão de dados alarga-se hoje do data center às aplicações designadas edge e embedded.   A Oracle oferece hoje a gama mais completa do mercado em tecnologias embedded, tanto para ISVs como para fabricantes de dispositivos e equipamentos, proporcionando-lhe a escolha dos produtos de base de dados e middleware embeddable que melhor se ajustem aos seus requisitos técnicos:   ·         Oracle Database 11g ·         Oracle Database Lite 11g ·         Oracle Berkeley DB ·         Oracle TimesTen In-Memory Database ·         Oracle Fusion Middleware 11g ·         Java for Business   Mais informação sobre produtos embedded Oracle aqui.   Segundo a IDC, a Oracle é hoje o líder mundial no mercado das bases de dados embedded com uma quota de mercado de 28,2% em 2008, estando a crescer a um ritmo 40% superior ao seu concorrente mais próximo e 50% superior à media do mercado.   A par com a riqueza da sua oferta tecnológica, a Oracle oferece igualmente modelos de licenciamento e de preços que se ajustam às necessidades de quem usa esses componentes tecnológicos como peças de uma solução final integrada a se vendida aos seus cliente finais.   A Oracle está empenhada em contribuir para o sucesso da sua empresa. Ao pôr os seus interesses acima de tudo, ganha a sua empresa e ganha a Oracle. E, mais importante que tudo, ganham os clientes, que recebem as melhores soluções possíveis.   Em resumo, as soluções embedded da Oracle proporcionam-lhe:   ·         Melhores produtos ·         Clientes mais satisfeitos ·         Maior rentabilidade das suas soluções   Agenda: ·         Oracle and Embedded ·         Embedded Market Trends ·         Oracle portfolio Oracle Database 11g o    Oracle Berkeley DB  o    Oracle Database Lite o    Oracle TimesTen o    Oracle Fusion Middleware ·         Demo: Berkeley DB ·         Embedded Software Licensing (ESL) Models   -----------------------------------------------------------------------------------   Clique aqui e registe-se.   Horário e Local: 9h30 - 13h00 Oracle Lagoas Park - Edf. 8 Porto Salvo   Para mais informações, por favor contacte: Melissa Lopes 214235194  

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• How accurate is "Business logic should be in a service, not in a model"?

  - by Jeroen Vannevel

  Situation Earlier this evening I gave an answer to a question on StackOverflow. The question: Editing of an existing object should be done in repository layer or in service? For example if I have a User that has debt. I want to change his debt. Should I do it in UserRepository or in service for example BuyingService by getting an object, editing it and saving it ? My answer: You should leave the responsibility of mutating an object to that same object and use the repository to retrieve this object. Example situation: class User { private int debt; // debt in cents private string name; // getters public void makePayment(int cents){ debt -= cents; } } class UserRepository { public User GetUserByName(string name){ // Get appropriate user from database } } A comment I received: Business logic should really be in a service. Not in a model. What does the internet say? So, this got me searching since I've never really (consciously) used a service layer. I started reading up on the Service Layer pattern and the Unit Of Work pattern but so far I can't say I'm convinced a service layer has to be used. Take for example this article by Martin Fowler on the anti-pattern of an Anemic Domain Model: There are objects, many named after the nouns in the domain space, and these objects are connected with the rich relationships and structure that true domain models have. The catch comes when you look at the behavior, and you realize that there is hardly any behavior on these objects, making them little more than bags of getters and setters. Indeed often these models come with design rules that say that you are not to put any domain logic in the the domain objects. Instead there are a set of service objects which capture all the domain logic. These services live on top of the domain model and use the domain model for data. (...) The logic that should be in a domain object is domain logic - validations, calculations, business rules - whatever you like to call it. To me, this seemed exactly what the situation was about: I advocated the manipulation of an object's data by introducing methods inside that class that do just that. However I realize that this should be a given either way, and it probably has more to do with how these methods are invoked (using a repository). I also had the feeling that in that article (see below), a Service Layer is more considered as a façade that delegates work to the underlying model, than an actual work-intensive layer. Application Layer [his name for Service Layer]: Defines the jobs the software is supposed to do and directs the expressive domain objects to work out problems. The tasks this layer is responsible for are meaningful to the business or necessary for interaction with the application layers of other systems. This layer is kept thin. It does not contain business rules or knowledge, but only coordinates tasks and delegates work to collaborations of domain objects in the next layer down. It does not have state reflecting the business situation, but it can have state that reflects the progress of a task for the user or the program. Which is reinforced here: Service interfaces. Services expose a service interface to which all inbound messages are sent. You can think of a service interface as a façade that exposes the business logic implemented in the application (typically, logic in the business layer) to potential consumers. And here: The service layer should be devoid of any application or business logic and should focus primarily on a few concerns. It should wrap Business Layer calls, translate your Domain in a common language that your clients can understand, and handle the communication medium between server and requesting client. This is a serious contrast to other resources that talk about the Service Layer: The service layer should consist of classes with methods that are units of work with actions that belong in the same transaction. Or the second answer to a question I've already linked: At some point, your application will want some business logic. Also, you might want to validate the input to make sure that there isn't something evil or nonperforming being requested. This logic belongs in your service layer. "Solution"? Following the guidelines in this answer, I came up with the following approach that uses a Service Layer: class UserController : Controller { private UserService _userService; public UserController(UserService userService){ _userService = userService; } public ActionResult MakeHimPay(string username, int amount) { _userService.MakeHimPay(username, amount); return RedirectToAction("ShowUserOverview"); } public ActionResult ShowUserOverview() { return View(); } } class UserService { private IUserRepository _userRepository; public UserService(IUserRepository userRepository) { _userRepository = userRepository; } public void MakeHimPay(username, amount) { _userRepository.GetUserByName(username).makePayment(amount); } } class UserRepository { public User GetUserByName(string name){ // Get appropriate user from database } } class User { private int debt; // debt in cents private string name; // getters public void makePayment(int cents){ debt -= cents; } } Conclusion All together not much has changed here: code from the controller has moved to the service layer (which is a good thing, so there is an upside to this approach). However this doesn't look like it had anything to do with my original answer. I realize design patterns are guidelines, not rules set in stone to be implemented whenever possible. Yet I have not found a definitive explanation of the service layer and how it should be regarded. Is it a means to simply extract logic from the controller and put it inside a service instead? Is it supposed to form a contract between the controller and the domain? Should there be a layer between the domain and the service layer? And, last but not least: following the original comment Business logic should really be in a service. Not in a model. Is this correct? How would I introduce my business logic in a service instead of the model?

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• Extracting Data from a Source System to History Tables

  - by Derek D.

  This is a topic I find very little information written about, however it is very important that the method for extracting data be done in a way that does not hinder performance of the source system.  In this example, the goal is to extract data from a source system, into another database (or server) all [...]

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• Is throwing an error in unpredictable subclass-specific circumstances a violation of LSP?

  - by Motti Strom

  Say, I wanted to create a Java List<String> (see spec) implementation that uses a complex subsystem, such as a database or file system, for its store so that it becomes a simple persistent collection rather than an basic in-memory one. (We're limiting it specifically to a List of Strings for the purposes of discussion, but it could extended to automatically de-/serialise any object, with some help. We can also provide persistent Sets, Maps and so on in this way too.) So here's a skeleton implementation: class DbBackedList implements List<String> { private DbBackedList() {} /** Returns a list, possibly non-empty */ public static getList() { return new DbBackedList(); } public String get(int index) { return Db.getTable().getRow(i).asString(); // may throw DbExceptions! } // add(String), add(int, String), etc. ... } My problem lies with the fact that the underlying DB API may encounter connection errors that are not specified in the List interface that it should throw. My problem is whether this violates Liskov's Substitution Principle (LSP). Bob Martin actually gives an example of a PersistentSet in his paper on LSP that violates LSP. The difference is that his newly-specified Exception there is determined by the inserted value and so is strengthening the precondition. In my case the connection/read error is unpredictable and due to external factors and so is not technically a new precondition, merely an error of circumstance, perhaps like OutOfMemoryError which can occur even when unspecified. In normal circumstances, the new Error/Exception might never be thrown. (The caller could catch if it is aware of the possibility, just as a memory-restricted Java program might specifically catch OOME.) Is this therefore a valid argument for throwing an extra error and can I still claim to be a valid java.util.List (or pick your SDK/language/collection in general) and not in violation of LSP? If this does indeed violate LSP and thus not practically usable, I have provided two less-palatable alternative solutions as answers that you can comment on, see below. Footnote: Use Cases In the simplest case, the goal is to provide a familiar interface for cases when (say) a database is just being used as a persistent list, and allow regular List operations such as search, subList and iteration. Another, more adventurous, use-case is as a slot-in replacement for libraries that work with basic Lists, e.g if we have a third-party task queue that usually works with a plain List: new TaskWorkQueue(new ArrayList<String>()).start() which is susceptible to losing all it's queue in event of a crash, if we just replace this with: new TaskWorkQueue(new DbBackedList()).start() we get a instant persistence and the ability to share the tasks amongst more than one machine. In either case, we could either handle connection/read exceptions that are thrown, perhaps retrying the connection/read first, or allow them to throw and crash the program (e.g. if we can't change the TaskWorkQueue code).

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• What layer to introduce human readable error messages?

  - by MrLane

  One of the things that I have never been happy with on any project I have worked on over the years and have really not been able to resolve myself is exactly at what tier in an application should human readable error information be retrieved for display to a user. A common approach that has worked well has been to return strongly typed/concrete "result objects" from the methods on the public surface of the business tier/API. A method on the interface may be: public ClearUserAccountsResult ClearUserAccounts(ClearUserAccountsParam param); And the result class implementation: public class ClearUserAccountsResult : IResult { public readonly List<Account> ClearedAccounts{get; set;} public readonly bool Success {get; set;} // Implements IResult public readonly string Message{get; set;} // Implements IResult, human readable // Constructor implemented here to set readonly properties... } This works great when the API needs to be exposed over WCF as the result object can be serialized. Again this is only done on the public surface of the API/business tier. The error message can also be looked up from the database, which means it can be changed and localized. However, it has always been suspect to me, this idea of returning human readable information from the business tier like this, partly because what constitutes the public surface of the API may change over time...and it may be the case that the API will need to be reused by other API components in the future that do not need the human readable string messages (and looking them up from a database would be an expensive waste). I am thinking a better approach is to keep the business objects free from such result objects and keep them simple and then retrieve human readable error strings somewhere closer to the UI layer or only in the UI itself, but I have two problems here: 1) The UI may be a remote client (Winforms/WPF/Silverlight) or an ASP.NET web application hosted on another server. In these cases the UI will have to fetch the error strings from the server. 2) Often there are multiple legitimate modes of failure. If the business tier becomes so vague and generic in the way it returns errors there may not be enough information exposed publicly to tell what the error actually was: i.e: if a method has 3 modes of legitimate failure but returns a boolean to indicate failure, you cannot work out what the appropriate message to display to the user should be. I have thought about using failure enums as a substitute, they can indicate a specific error that can be tested for and coded against. This is sometimes useful within the business tier itself as a way of passing via method returns the specifics of a failure rather than just a boolean, but it is not so good for serialization scenarios. Is there a well worn pattern for this? What do people think? Thanks.

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• 24 Hours of PASS next week, pre-con preview style

  - by drsql

  I will be doing my Characteristics of a Great Relational Database , which is a session that I haven’t done since last PASS. When I was asked about doing this Summit Preview version of 24 hours of PASS, I decided that I would do this session, largely because it is kind of light and fun, but also because it is either going to be the basis of the end section of my pre-con at the summit or it is going to be the section of the pre-con we don’t get to because we are so involved in working out designs that...(read more)

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• Are there any concerns with using a static read-only unit of work so that it behaves like a cache?

  - by Rowan Freeman

  Related question: How do I cache data that rarely changes? I'm making an ASP.NET MVC4 application. On every request the security details about the user will need to be checked with the area/controller/action that they are accessing to see if they are allowed to view it. The security information is stored in the database. For example: User Permission UserPermission Action ActionPermission A "Permission" is a token that is applied to an MVC action to indicate that the token is required in order to access the action. Once a user is given the permission (via the UserPermission table) then they have the token and can therefore access the action. I've been looking in to how to cache this data (since it rarely changes) so that I'm only querying in-memory data and not hitting a database (which is a considerable performance hit at the moment). I've tried storing things in lists, using a caching provider but I either run in to problems or performance doesn't improve. One problem that I constantly run in to is that I'm using lazy loading and dynamic proxies with EntityFramework. This means that even if I ToList() everything and store them somewhere static, the relationships are never populated. For example, User.Permissions is an ICollection but it's always null. I don't want to Include() everything because I'm trying to keep things simple and generic (and easy to modify). One thing I know is that an EntityFramework DbContext is a unit of work that acts with 1st-level caching. That is, for the duration of the unit of work, everything that is accessed is cached in memory. I want to create a read-only DbContext that will exist indefinitely and will only be used to read about permission data. Upon testing this it worked perfectly; my page load times went from 200ms+ to 20ms. I can easily force the data to refresh at certain intervals or simply leave it to refresh when the application pool is recycled. Basically it will behave like a cache. Note that the rest of the application will interact with other contexts that exist per request as normal. Is there any disadvantage to this approach? Could I be doing something different?

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• How to explain bad software to non-technical people?

  - by mtutty

  In discussing software development with non-technical people (customers, business owners, project sponsors, etc.), I often resort to analogies and metaphors. It's relatively easy and effective to use a "house" or other metaphor for describing the size and complexity of new development. However, we often inherit someone else's code or data, and this approach doesn't seem to hold up as well when trying to explain why we're gutting something that already seems to work. Of course we can point to cycle time and cost to be saved in the future but this generally means nothing to business folks. I know doctors can say "just take this pill," but I'm not sure that software devs have the same authority. Ideas? EDIT: Let me add a bit to the discussion. The specific project I'm talking about has customers that don't realize (or care) about specific aspects of the system we're retiring (i.e., they think it was just fine): The system would save a NEW RECORD every time someone updated a field The system contained tables for reference data. These tables had new records added every day, even though they were duplicates of previous records. And there was no way to tie the reference data used for a particular case at the time it was closed. This is like 99% of the data in the old system. The field NAMES also have spaces, apostrophes and other inappropriate characters in them, making everything harder to work with. In addition to the incredible amount of duplicate data, they have around 1000 XLS files with data they want added to the system. Previously, they would do a spreadsheet for each case in the database, IN ADDITION TO what they typed into the database. Getting rid of this old, unneeded information and piping in the XLS data comprises about 80% of the total project effort, and was not something we could accurately predict. I'm trying to find a concrete way to describe how bad this thing was, mostly so that the customer will understand why the migration process has been so time-consuming. The actual coding was done pretty quickly and the new system works fine, but without the old data they won't be happy. Sorry to get into the weeds, but most of the answers I've seen so far are pretty basic scope/schedule/cost things. I've been doing this for 15 years, so this really is more of a reflective, philosophical question - but without some of the details it can be difficult to really appreciate the awful beauty of this problem.

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• Help identify the pattern for reacting on updates

  - by Mike

  There's an entity that gets updated from external sources. Update events are at random intervals. And the entity has to be processed once updated. Multiple updates may be multiplexed. In other words there's a need for the most current state of entity to be processed. There's a point of no-return during processing where the current state (and the state is consistent i.e. no partial update is made) of entity is saved somewhere else and processing goes on independently of any arriving updates. Every consequent set of updates has to trigger processing i.e. system should not forget about updates. And for each entity there should be no more than one running processing (before the point of no-return) i.e. the entity state should not be processed more than once. So what I'm looking for is a pattern to cancel current processing before the point of no return or abandon processing results if an update arrives. The main challenge is to minimize race conditions and maintain integrity. The entity sits mainly in database with some files on disk. And the system is in .NET with web-services and message queues. What comes to my mind is a database queue-like table. An arriving update inserts row in that table and the processing is launched. The processing gathers necessary data before the point of no-return and once it reaches this barrier it looks into the queue table and checks whether there're more recent updates for the entity. If there are new updates the processing simply shuts down and its data is discarded. Otherwise the processing data is persisted and it goes beyond the point of no-return. Though it looks like a solution to me it is not quite elegant and I believe this scenario may be supported by some sort of middleware. If I would use message queues for this then there's a need to access the queue API in the point of no-return to check for the existence of new messages. And this approach also lacks elegance. Is there a name for this pattern and an existing solution?

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• Strategy to use two different measurement systems in software

  - by Dennis

  I have an application that needs to accept and output values in both US Custom Units and Metric system. Right now the conversion and input and output is a mess. You can only enter in US system, but you can choose the output to be US or Metric, and the code to do the conversions is everywhere. So I want to organize this and put together some simple rules. So I came up with this: Rules user can enter values in either US or Metric, and User Interface will take care of marking this properly All units internally will be stored as US, since the majority of the system already has most of the data stored like that and depends on this. It shouldn't matter I suppose as long as you don't mix unit. All output will be in US or Metric, depending on user selection/choice/preference. In theory this sounds great and seems like a solution. However, one little problem I came across is this: There is some data stored in code or in the database that already returns data like this: 4 x 13/16" screws, which means "four times screws". I need the to be in either US or Metric. Where exactly do I put the conversion code for doing the conversion for this unit? The above already mixing presentation and data, but the data for the field I need to populate is that whole string. I can certainly split it up into the number 4, the 13/16", and the " x " and the " screws", but the question remains... where do I put the conversion code? Different Locations for Conversion Routines 1) Right now the string is in a class where it's produced. I can put conversion code right into that class and it may be a good solution. Except then, I want to be consistent so I will be putting conversion procedures everywhere in the code at-data-source, or right after reading it from the database. The problem though is I think that my code will have to deal with two systems, all throughout the codebase after this, should I do this. 2) According to the rules, my idea was to put it in the view script, aka last change to modify it before it is shown to the user. And it may be the right thing to do, but then it strikes me it may not always be the best solution. (First, it complicates the view script a tad, second, I need to do more work on the data side to split things up more, or do extra parsing, such as in my case above). 3) Another solution is to do this somewhere in the data prep step before the view, aka somewhere in the middle, before the view, but after the data-source. This strikes me as messy and that could be the reason why my codebase is in such a mess right now. It seems that there is no best solution. What do I do?

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• A solution for a PHP website without a framework

  - by lortabac

  One of our customers asked us to add some dynamic functionality to an existent website, made of several static HTML pages. We normally work with an MVC framework (mostly CodeIgniter), but in this case moving everything to a framework would require too much time. Since it is not a big project, not having the full functionality of a framework is not a problem. But the question is how to keep code clean. The solution I came up with is to divide code in libraries (the application's API) and models. So inside HTML there will only be API calls, and readability will not be sacrificed. I implemented this with a sort of static Registry (sorry if I'm wrong, I am not a design pattern expert): <?php class Custom_framework { //Global database instance private static $db; //Registered models private static $models = array(); //Registered libraries private static $libraries = array(); //Returns a database class instance static public function get_db(){ if(isset(self::$db)){ //If instance exists, returns it return self::$db; } else { //If instance doesn't exists, creates it self::$db = new DB; return self::$db; } } //Returns a model instance static public function get_model($model_name){ if(isset(self::$models[$model_name])){ //If instance exists, returns it return self::$models[$model_name]; } else { //If instance doesn't exists, creates it if(is_file(ROOT_DIR . 'application/models/' . $model_name . '.php')){ include_once ROOT_DIR . 'application/models/' . $model_name . '.php'; self::$models[$model_name] = new $model_name; return self::$models[$model_name]; } else { return FALSE; } } } //Returns a library instance static public function get_library($library_name){ if(isset(self::$libraries[$library_name])){ //If instance exists, returns it return self::$libraries[$library_name]; } else { //If instance doesn't exists, creates it if(is_file(ROOT_DIR . 'application/libraries/' . $library_name . '.php')){ include_once ROOT_DIR . 'application/libraries/' . $library_name . '.php'; self::$libraries[$library_name] = new $library_name; return self::$libraries[$library_name]; } else { return FALSE; } } } } Inside HTML, API methods are accessed like this: <?php echo Custom_framework::get_library('My_library')->my_method(); ?> It looks to me as a practical solution. But I wonder what its drawbacks are, and what the possible alternatives.

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• Entity Framework 5, separating business logic from model - Repository?

  - by bnice7

  I am working on my first public-facing web application and I’m using MVC 4 for the presentation layer and EF 5 for the DAL. The database structure is locked, and there are moderate differences between how the user inputs data and how the database itself gets populated. I have done a ton of reading on the repository pattern (which I have never used) but most of my research is pushing me away from using it since it supposedly creates an unnecessary level of abstraction for the latest versions of EF since repositories and unit-of-work are already built-in. My initial approach is to simply create a separate set of classes for my business objects in the BLL that can act as an intermediary between my Controllers and the DAL. Here’s an example class: public class MyBuilding { public int Id { get; private set; } public string Name { get; set; } public string Notes { get; set; } private readonly Entities _context = new Entities(); // Is this thread safe? private static readonly int UserId = WebSecurity.GetCurrentUser().UserId; public IEnumerable<MyBuilding> GetList() { IEnumerable<MyBuilding> buildingList = from p in _context.BuildingInfo where p.Building.UserProfile.UserId == UserId select new MyBuilding {Id = p.BuildingId, Name = p.BuildingName, Notes = p.Building.Notes}; return buildingList; } public void Create() { var b = new Building {UserId = UserId, Notes = this.Notes}; _context.Building.Add(b); _context.SaveChanges(); // Set the building ID this.Id = b.BuildingId; // Seed 1-to-1 tables with reference the new building _context.BuildingInfo.Add(new BuildingInfo {Building = b}); _context.GeneralInfo.Add(new GeneralInfo {Building = b}); _context.LocationInfo.Add(new LocationInfo {Building = b}); _context.SaveChanges(); } public static MyBuilding Find(int id) { using (var context = new Entities()) // Is this OK to do in a static method? { var b = context.Building.FirstOrDefault(p => p.BuildingId == id && p.UserId == UserId); if (b == null) throw new Exception("Error: Building not found or user does not have access."); return new MyBuilding {Id = b.BuildingId, Name = b.BuildingInfo.BuildingName, Notes = b.Notes}; } } } My primary concern: Is the way I am instantiating my DbContext as a private property thread-safe, and is it safe to have a static method that instantiates a separate DbContext? Or am I approaching this all wrong? I am not opposed to learning up on the repository pattern if I am taking the total wrong approach here.

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• I want something ready to start with

  - by BDotA

  I am looking for something quick like a weblog in wordpress or blogspot maybe, that when I write a blog post I can put it there, for example if I write something about .NET or Java or Database,..some quick tutorial with some small code samples that visitors can use ... And I don't know anything about webdesign and I just want a ready-made thing to use for this purpose. What do you suggest? any samples of that that I can take a look?

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• Integrating with a payment provider; Proper and robust OOP approach

  - by ExternalUse

  History We are currently using a so called redirect model for our online payments (where you send the payer to a payment gateway, where he inputs his payment details - the gateway will then return him to a success/failure callback page). That's easy and straight-forward, but unfortunately quite inconvenient and at times confusing for our customers (leaving the site, changing their credit card details with an additional login on another site etc). Intention & Problem description We are now intending to switch to an integrated approach using an exchange of XML requests and responses. My problem is on how to cater with all (or rather most) of the things that may happen during processing - bearing in mind that normally simplicity is robust whereas complexity is fragile. Examples User abort: The user inputs Credit Card details and hits submit. An XML message to the provider's gateway is sent and waiting for response. The user hits "stop" in his browser or closes the window. ignore_user_abort() in PHP may be an option - but is that reliable? might it be better to redirect the user to a "please wait"-page, that in turn opens an AJAX or other request to the actual processor that does not rely on the connection? Database goes away sounds over-complicated, but with e.g. a webserver in the States and a DB in the UK, it has happened and will happen again: User clicks together his order, payment request has been sent to the provider but the response cannot be stored in the database. What approach could I use, using PHP to sort of start an SQL like "Transaction" that only at the very end gets committed or rolled back, depending on the individual steps? Should then neither commit or roll back have happened, I could sort of "lock" the user to prevent him from paying again or to improperly account for payments - but how? And what else do I need to consider technically? None of the integration examples of e.g. Worldpay, Realex or SagePay offer any insight, and neither Google or my search terms were good enough to find somebody else's thoughts on this. Thank you very much for any insight on how you would approach this!

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• A KSH adattárháza: Oracle Essbase és Oracle Database alapon

  - by Fekete Zoltán

  A magyar Központi Statisztikai Hivatal metaadat vezérelt adattárháza három fontos Oracle terméken nyugszik. Az interneten elérhetok az adatok a KSH Tájékoztatási adatbázis-ból. Data from KSH in English. Amikor ezeket a sorokat írom, péntek éjjel 21:36-kor 81 online felhasználó kérdezte le az adatokat. :) - Oracle Essbase multidimenziós OLAP szerver, technikai infó - Hyperion Interactive Reporting lekérdezo eszköz, technikai infó - Oracle Database Enterprise Edition Az angol nyelvu customer snapshot, azaz ügyfél történet: Hungarian Central Statistical Office Provides 200,000 External Users with Secure Online Access to Data. A magyar nyelvu sikersztori: A KSH statisztikai adatainak 60 százaléka elérheto böngészo és platform függetlenül évi mintegy 200 000 internetes felhasználó számára. A termék kiválasztásában, a projekt kialakításában és bevezetésében nagy szerepet vállalt a DSS Consulting Kft. és az Oracle Konzultáció. A projekt során elért legfontosabb eredmények: - adattárház: 150-200 egyideju felhasználó, éves szinten 200 000 felhasználót jelent - Essbase memória alapú tárolási struktúrája: közel valósideju hozzáférés - A rendszer platform és böngészo független, ezért a felhasználók széles köre érheti el a statisztikai adatokat. - Natív Java API és XMLA támogatással egyedi karbantartó alkalmazás - A statisztikus munkatársak speciális informatikai eloképzettség nélkül építik fel és gondozzák a multidimenzionális adatbázisokat - Az Oracle Hyperion Interactive Reporting: oszlopos, kereszttáblás, szekcionált, grafikonos, webes lekérdezések Letöltheto a következo KSH eloadás a HOUG konferenciáról 2009-bol: Hyperalea iacta est - a KSH Essbase alapú adattárház rendszere. A most megjelent sikersztori: angolul és magyarul.

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• Connecting to SQL database using SQLCMD

  - by kaleidoscope

  As we all know, there are a number of ways you can connect to your SQL Azure Database. One of the quick options is to try to connect to SQL server is SQLCMD. To start the SQLCMD utility and connect to a named instance of SQL Server Open a Command Prompt window, and type sqlcmd -S myServer\instanceName. Replace myServer\instanceName with the name of the computer and the instance of SQL Server that you want to connect to. Press ENTER. The sqlcmd prompt (1>) indicates that you are connected to the specified instance of SQL Server. SQL Management Studio offers the facility to use SQLCMD from within SQL scripts by using SQLCMD Mode. How to: Enable SQLCMD mode in the Transact-SQL Editor (About how to start the editor, see How to: Start the Transact-SQL Editor.) To toggle SQLCMD mode from the Data menu 1. Open the query in the Transact-SQL editor. 2. On the Data menu, point to Transact-SQL Editor, and click SQLCMD Mode. To toggle SQLCMD mode from the toolbar 1. Open the query in the Transact-SQL editor. 2. On the Transact-SQL Editor toolbar, click SQLCMD Mode. To toggle SQLCMD mode from the shortcut menu 1. Open the query in the Transact-SQL editor. 2. Right-click anywhere in the editor window, and then click SQLCMD Mode. For more information follow below link http://msdn.microsoft.com/en-us/library/ms170207.aspx   Geeta, G

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