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• Many-to-many relationship in oop

  - by Manu

  what is best way to model many-to-many relationship? lets say we have a two classes , Team and Player any given Player can be in multiple Team s any Team can have as many Player s as they like I like to call methods like playerX.getTeamList() to get the list of all the Team s he/she is in teamY.getPlayerList() to get the list of all the Player s in the team (or have some other way to do this effectively) I can think of two ways of doing this , but they just don't feels like good oop pattens. can you think of any good ways , perhaps a design patten ?

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• Should I share UI for objects that use common fields?

  - by wb

  I have a parent class that holds all of the fields that are common between all device types. From that, I have a few derived classes that each hold their unique fields. Say I have device type "Switch" and "Transformer". Both derived classes only have 2-3 of their own unique fields. When doing the UI design (windows forms) in this case. Should I create two separate forms for each device type or create a user control with all fields that are shared among all devices? Thank you.

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• Python: Catching / blocking SIGINT during system call

  - by danben

  I've written a web crawler that I'd like to be able to stop via the keyboard. I don't want the program to die when I interrupt it; it needs to flush its data to disk first. I also don't want to catch KeyboardInterruptedException, because the persistent data could be in an inconsistent state. My current solution is to define a signal handler that catches SIGINT and sets a flag; each iteration of the main loop checks this flag before processing the next url. However, I've found that if the system happens to be executing socket.recv() when I send the interrupt, I get this: ^C Interrupted; stopping... // indicates my interrupt handler ran Traceback (most recent call last): File "crawler_test.py", line 154, in <module> main() ... File "/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/socket.py", line 397, in readline data = recv(1) socket.error: [Errno 4] Interrupted system call and the process exits completely. Why does this happen? Is there a way I can prevent the interrupt from affecting the system call?

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• Catching / blocking SIGINT during system call

  - by danben

  I've written a web crawler that I'd like to be able to stop via the keyboard. I don't want the program to die when I interrupt it; it needs to flush its data to disk first. I also don't want to catch KeyboardInterruptedException, because the persistent data could be in an inconsistent state. My current solution is to define a signal handler that catches SIGINT and sets a flag; each iteration of the main loop checks this flag before processing the next url. However, I've found that if the system happens to be executing socket.recv() when I send the interrupt, I get this: ^C Interrupted; stopping... // indicates my interrupt handler ran Traceback (most recent call last): File "crawler_test.py", line 154, in <module> main() ... File "/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/socket.py", line 397, in readline data = recv(1) socket.error: [Errno 4] Interrupted system call and the process exits completely. Why does this happen? Is there a way I can prevent the interrupt from affecting the system call?

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• Credit card system implementation?

  - by Mark

  My site is going to have a credit system that basically works a lot like a credit card. Each user has an unlimited credit limit, but at the end of each week, they have to pay it off. For example, a user might make several purchases between March 1st and 7th, and then at the end of March 7th, they would be emailed an invoice that lists all their purchases during the week and a total that is due by the 14th. If they don't pay it off, their account is simply deactivated until they do. I'm just trying to wrap my head around how to implement this. I have a list of all their purchases, that's not a problem, but I'm just trying to figure out what to do with it. On the end of the 7th day, I could set up a cronjob to generate an invoice, which would basically have an id, and due date, and then I would need another many-to-many table to link all the purchases to the invoice. Then when a user adds money to their account, I guess it's applied against their current outstanding invoice? And what if they don't pay off their invoice by the time a new invoice rolls around, so now they have 2 outstanding ones, how do I know which to apply it against? Or do I make the cronjob check for any previous outstanding invoices, cancel them, and add a new item to the new invoice as "balance forward (+interest)"? How would you apply the money against an invoice? Would each payment have to be linked to an invoice, or could I just deposit it to their account credit, and then somehow figure out whats been paid and what hasn't? What if they pay in advance, before their invoice has been generated? Do I deduct it from their credit from the invoice upon generation, or at the end of the week when its due? There are so many ways to do this... Can anyone describe what approach they would take?

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• Semantic Grid System, Media Query issue

  - by Andy

  I'm using the Semantic Grid System to build a responsive site. However, something isn't quite right with the media queries that should obviously kick in once it hits a particular screen size. I'll reference what i mean with their example on the website : if I view this on my iPhone for example, given that it is supposed to adjust to a single column structure on a mobile device, it still throws out the web version of the page. That is true for both Safari and Chrome on my iPhone. However, if I use the RWD bookmarklet to check it's appearance at different resolutions it appears as expected for the mobile resolution. Also, ironically, if I resize the page in Safari on my desktop it also adjusts accordingly once I get down to the approriate screen size, but not in Firefox. The media query that it uses once it hits 720px is @media screen and (max-width: 720px) { #maincolumn, #sidebar { .column(12); margin-bottom: 1em; } } and I might be wide of the mark here but I think that must be the issue. But given that this is directly from the semantic.gs website I'm not inclined to question their own code. Any idea what the problem might be?

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• Testing system where App-level and Request-level IoC containers exist

  - by Bobby

  My team is in the process of developing a system where we're using Unity as our IoC container; and to provide NHibernate ISessions (Units of work) over each HTTP Request, we're using Unity's ChildContainer feature to create a child container for each request, and sticking the ISession in there. We arrived at this approach after trying others (including defining per-request lifetimes in the container, but there are issues there) and are now trying to decide on a unit testing strategy. Right now, the application-level container itself is living in the HttpApplication, and the Request container lives in the HttpContext.Current. Obviously, neither exist during testing. The pain increases when we decided to use Service Location from our Domain layer, to "lazily" resolve dependencies from the container. So now we have more components wanting to talk to the container. We are also using MSTest, which presents some concurrency dilemmas during testing as well. So we're wondering, what do the bright folks out there in the SO community do to tackle this predicament? How does one setup an application that, during "real" runtime, relies on HTTP objects to hold the containers, but during test has the flexibility to build-up and tear-down the containers consistently, and have the ServiceLocation bits get to those precise containers. I hope the question is clear, thanks!

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• WCF timedout waiting for System.Diagnostics.Process to finish

  - by Bartek

  Dear All, We have a WCF Service deployed on Windows Server 2003 that handles file transfers. When file is in Unix format, I am converting it to Dos format in the initialization stage using System.Diagnostics.Process (.WaitForExit()). Client calls the service: obj_DataSenderService = New DataSendClient() obj_DataSenderService.InnerChannel.OperationTimeout = New TimeSpan(0, System.Configuration.ConfigurationManager.AppSettings("DatasenderServiceOperationTimeout"), 0) str_DataSenderGUID = obj_DataSenderService.Initialize(xe_InitDetails.GetXMLNode) This works fine, however for large files the conversion takes more than 10 minutes and I am getting exception: A first chance exception of type 'System.ServiceModel.CommunicationException' occurred in mscorlib.dll Additional information: The socket connection was aborted. This could be caused by an error processing your message or a receive timeout being exceeded by the remote host, or an underlying network resource issue. Local socket timeout was '00:59:59.8749992'. I tried configuring both client: <system.serviceModel> <bindings> <netTcpBinding> <binding name="NetTcpBinding_IDataSend" closeTimeout="01:00:00" openTimeout="01:00:00" receiveTimeout="01:00:00" sendTimeout="01:00:00" transactionFlow="false" transferMode="Buffered" transactionProtocol="OleTransactions" hostNameComparisonMode="StrongWildcard" listenBacklog="10" maxBufferPoolSize="524288" maxBufferSize="65536" maxConnections="10" maxReceivedMessageSize="65536"> <readerQuotas maxDepth="32" maxStringContentLength="8192" maxArrayLength="16384" maxBytesPerRead="4096" maxNameTableCharCount="16384" /> <reliableSession ordered="true" inactivityTimeout="00:10:00" enabled="false" /> <security mode="None"> <transport clientCredentialType="Windows" protectionLevel="EncryptAndSign" /> <message clientCredentialType="Windows" /> </security> </binding> </netTcpBinding> </bindings> <client> <endpoint address="net.tcp://localhost:4000/DataSenderEndPoint" binding="netTcpBinding" bindingConfiguration="NetTcpBinding_IDataSend" contract="IDataSend" name="NetTcpBinding_IDataSend"> <identity> <servicePrincipalName value="host/localhost" /> <!--<servicePrincipalName value="host/axopwrapp01.Corp.Acxiom.net" />--> </identity> </endpoint> </client> </system.serviceModel> And service: <system.serviceModel> <bindings> <netTcpBinding> <binding name="NetTcpBinding_IDataSend" closeTimeout="01:00:00" openTimeout="01:00:00" receiveTimeout="01:00:00" sendTimeout="01:00:00" transactionFlow="false" transferMode="Buffered" transactionProtocol="OleTransactions" hostNameComparisonMode="StrongWildcard" listenBacklog="10" maxBufferPoolSize="524288" maxBufferSize="65536" maxConnections="10" maxReceivedMessageSize="65536"> </binding> </netTcpBinding> </bindings> </system.serviceModel> but without luck. In the Service trace viewer I can see: Close process timed out waiting for service dispatch to complete. with stack trace: System.ServiceModel.ServiceChannelManager.CloseInput(TimeSpan timeout) System.ServiceModel.Dispatcher.InstanceContextManager.CloseInput(TimeSpan timeout) System.ServiceModel.ServiceHostBase.OnClose(TimeSpan timeout) System.ServiceModel.Channels.CommunicationObject.Close(TimeSpan timeout) System.ServiceModel.Channels.CommunicationObject.Close() DataSenderService.DataSender.OnStop() System.ServiceProcess.ServiceBase.DeferredStop() System.Runtime.Remoting.Messaging.StackBuilderSink._PrivateProcessMessage(IntPtr md, Object[] args, Object server, Int32 methodPtr, Boolean fExecuteInContext, Object[]& outArgs) System.Runtime.Remoting.Messaging.StackBuilderSink.PrivateProcessMessage(RuntimeMethodHandle md, Object[] args, Object server, Int32 methodPtr, Boolean fExecuteInContext, Object[]& outArgs) System.Runtime.Remoting.Messaging.StackBuilderSink.AsyncProcessMessage(IMessage msg, IMessageSink replySink) System.Runtime.Remoting.Proxies.AgileAsyncWorkerItem.DoAsyncCall() System.Runtime.Remoting.Proxies.AgileAsyncWorkerItem.ThreadPoolCallBack(Object o) System.Threading._ThreadPoolWaitCallback.WaitCallback_Context(Object state) System.Threading.ExecutionContext.runTryCode(Object userData) System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData) System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state) System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state) System.Threading._ThreadPoolWaitCallback.PerformWaitCallbackInternal(_ThreadPoolWaitCallback tpWaitCallBack) System.Threading._ThreadPoolWaitCallback.PerformWaitCallback(Object state) Many thanks Bartek

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• Aligning inputs on bootstrap using the Fluid Grid System

  - by sguha

  I am creating a form that requires the user to input their name and email address. The first line of the form has two inputs side by side for each part of the name and the 2nd line has one input for the email address that should be the same width as the first line combined. I'm trying to use the fluid grid system but can't line up the 2nd row with the first. <form action="/subscriptions" method="post"> <fieldset> <div class="control-group"> <label class="control-label" for="name">Name</label> <div class="controls row-fluid"> <input class="span2" id="first_name" name="first_name" placeholder="First" required="required" type="text"> <input class="span2" id="last_name" name="last_name" placeholder="Last" required="required" type="text"> </div> </div> <div class="control-group"> <label class="control-label" for="email">Email</label> <div class="controls row-fluid"> <input class="span4" id="email" name="email" type="email"> </div> </div> </fieldset> </form>? http://jsfiddle.net/sguha095/v4amX/

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• Performance improvement of client server system

  - by Tanuj

  I have a legacy client server system where the server maintains a record of some data stored in a sqlite database. The data is related to monitoring access patterns of files stored on the server. The client application is basically a remote viewer of the data. When the client is launched, it connects to the server and gets the data from the server to display in a grid view. The data gets updated in real time on the server and the view in the client automatically gets refreshed. There are two problems with the current implementation: When the database gets too big, it takes a lot of time to load the client. What are the best ways to deal with this. One option is to maintain a cache at the client side. How to best implement a cache ? How can the server maintain a diff so that it only sends the diff during the refresh cycle. There can be multiple clients and each client needs to display the latest data available on the server. The server is a windows service daemon. Both the client and the server are implemented in C#

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• Can certain system-hungry modules be disabled in Ubuntu?

  - by Ole Thomsen Buus

  Hi, Let me add some context: I am currently using Ubuntu 9.10 64-bit (Desktop) on a relatively powerful stationary PC (Intel Core i7 920, 12GB ram). My purpose is highspeed imaging with a pointgrey Grashopper machine-vision camera (for research, PhD project). This camera is capable of 200 fps at full VGA (640x480) resolution. The camera is connected using Firewire (1394b) and the drivers and software from Pointgrey works great. I have developed a console C++ application that can grap a certain number of frames to preallocated memory and after this also save the grapped frames to harddrive. Currently it works fine but sometimes I am observing a few framedrops (1-3). When this happens I reset the experiment and repeat the recording and usually i am lucky the second time with no framedrops (the camera-driver has a internal framecounter that I am using). Question: I usually go to tty1 and use "sudo service gdm stop" to disable the graphical frontend. It seems to release some memory though that is not my main concern. My concern is CPU resources. Are there other system hungry modules that can be disabled temporarily such that the CPU gets less busy on Ubuntu 9.10? At some point in the future I will update to 10.10. Should I perhaps option for the server edition instead? Thanks.

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• C# Lack of Static Inheritance - What Should I Do?

  - by yellowblood

  Alright, so as you probably know, static inheritance is impossible in C#. I understand that, however I'm stuck with the development of my program. I will try to make it as simple as possible. Lets say our code needs to manage objects that are presenting aircrafts in some airport. The requirements are as follows: There are members and methods that are shared for all aircrafts There are many types of aircrafts, each type may have its own extra methods and members. There can be many instances for each aircraft type. Every aircraft type must have a friendly name for this type, and more details about this type. For example a class named F16 will have a static member FriendlyName with the value of "Lockheed Martin F-16 Fighting Falcon". Other programmers should be able to add more aircrafts, although they must be enforced to create the same static details about the types of the aircrafts. In some GUI, there should be a way to let the user see the list of available types (with the details such as FriendlyName) and add or remove instances of the aircrafts, saved, lets say, to some XML file. So, basically, if I could enforce inherited classes to implement static members and methods, I would enforce the aircraft types to have static members such as FriendlyName. Sadly I cannot do that. So, what would be the best design for this scenario?

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• How do you keep your business rules DRY?

  - by Mario

  I periodically ponder how to best design an application whose every business rule exists in just a single location. (While I know there is no proverbial “best way” and that designs are situational, people must have a leaning toward one practice or another.) I work for a shop where they prefer to house as much of the business rules as possible in the database. This requires developers in many cases to perform identical front-end validations to avoid sending data to the database that will result in an exception—not very DRY. It grates me anytime I find myself duplicating any kind of logic—even lowly validation logic. I am a single-point-of-truth purist to an anal degree. On the other end of the spectrum, I know of shops that create dumb databases (the Rails community leans in this direction) and handle all of the business logic in a separate tier (in Rails the models would house “most” of this). Note the word “most” which implies that some business logic does end up spilling into other places (in Rails it might spill over into the controllers). In way, a clean separation of concerns where all business logic exists in a single core location is a Utopian fantasy that’s hard to uphold (n-tiered architecture or not). Furthermore, is see the “Database as a fortress” and would agree that it should be built on constraints that cause it to reject bad data. As such, I hold principles that cause a degree of angst as I attempt to balance them. How do you balance the database-as-a-fortress view with the desire to have a single-point-of-truth?

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• AntFarm anti-pattern -- strategies to avoid, antidotes to help heal from

  - by alchemical

  I'm working on a 10 page web site with a database back-end. There are 500+ objects in use, trying to implement the MVP pattern in ASP.Net. I'm tracing the code-execution from a single-page, my finger has been on F-11 in Visual Studio for about 40 minutes, there seems to be no end, possibly 1000+ method calls for one web page! If it was just 50 objects that would be one thing, however, code execution snakes through all these objects just like millions of ants frantically woring in their giant dirt mound house, riddled with object tunnels. Hence, a new anti-pattern is born : AntFarm. AntFarm is also known as "OO-Madnes", "OO-Fever", OO-ADD, or simply design-pattern junkie. This is not the first time I've seen this, nor my associates at other companies. It seems that this style is being actively propogated, or in any case is a misunderstanding of the numerous OO/DP gospels going around... I'd like to introduce an anti-pattern to the anti-pattern: GST or "Get Stuff Done" AKA "Get Sh** done" AKA GRD (GetRDone). This pattern focused on just what it says, getting stuff done, in a simple way. I may try to outline it more in a later post, or please share your ideas on this antidote pattern. Anyway, I'm in the midst of a great example of AntFarm anti-pattern as I write (as a bonus, there is no documentation or comments). Please share you thoughts on how this anti-pattern has become so prevelant, how we can avoid it, and how can one undo or deal with this pattern in a live system one must work with!

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• Pros and cons of making database IDs consistent and "readable"

  - by gmale

  Question Is it a good rule of thumb for database IDs to be "meaningless?" Conversely, are there significant benefits from having IDs structured in a way where they can be recognized at a glance? What are the pros and cons? Background I just had a debate with my coworkers about the consistency of the IDs in our database. We have a data-driven application that leverages spring so that we rarely ever have to change code. That means, if there's a problem, a data change is usually the solution. My argument was that by making IDs consistent and readable, we save ourselves significant time and headaches, long term. Once the IDs are set, they don't have to change often and if done right, future changes won't be difficult. My coworkers position was that IDs should never matter. Encoding information into the ID violates DB design policies and keeping them orderly requires extra work that, "we don't have time for." I can't find anything online to support either position. So I'm turning to all the gurus here at SA! Example Imagine this simplified list of database records representing food in a grocery store, the first set represents data that has meaning encoded in the IDs, while the second does not: ID's with meaning: Type 1 Fruit 2 Veggie Product 101 Apple 102 Banana 103 Orange 201 Lettuce 202 Onion 203 Carrot Location 41 Aisle four top shelf 42 Aisle four bottom shelf 51 Aisle five top shelf 52 Aisle five bottom shelf ProductLocation 10141 Apple on aisle four top shelf 10241 Banana on aisle four top shelf //just by reading the ids, it's easy to recongnize that these are both Fruit on Aisle 4 ID's without meaning: Type 1 Fruit 2 Veggie Product 1 Apple 2 Banana 3 Orange 4 Lettuce 5 Onion 6 Carrot Location 1 Aisle four top shelf 2 Aisle four bottom shelf 3 Aisle five top shelf 4 Aisle five bottom shelf ProductLocation 1 Apple on aisle four top shelf 2 Banana on aisle four top shelf //given the IDs, it's harder to see that these are both fruit on aisle 4 Summary What are the pros and cons of keeping IDs readable and consistent? Which approach do you generally prefer and why? Is there an accepted industry best-practice?

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• Pattern for UI configuration

  - by TERACytE

  I have a Win32 C++ program that validates user input and updates the UI with status information and options. Currently it is written like this: void ShowError() { SetIcon(kError); SetMessageString("There was an error"); HideButton(kButton1); HideButton(kButton2); ShowButton(kButton3); } void ShowSuccess() { SetIcon(kError); std::String statusText (GetStatusText()); SetMessageString(statusText); HideButton(kButton1); HideButton(kButton2); ShowButton(kButton3); } // plus several more methods to update the UI using similar mechanisms I do not likes this because it duplicates code and causes me to update several methods if something changes in the UI. I am wondering if there is a design pattern or best practice to remove the duplication and make the functionality easier to understand and update. I could consolidate the code inside a config function and pass in flags to enable/disable UI items, but I am not convinced this is the best approach. Any suggestions and ideas?

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• Using an ORM with a database that has no defined relationships?

  - by Ahmad

  Consider a database(MSSQL 2005) that consists of 100+ tables which have primary keys defined to a certain degree. There are 'relationships' between tables, however these are not enforced with foreign key constraints. Consider the following simplified example of typical types of tables I am dealing with. The are clear relations between the User and City and Province tables. However, they key issues is the inconsistent data types in the tables and naming conventions. User: UserRowId [int] PK Name [varchar(50)] CityId [smallint] ProvinceRowId [bigint] City: CityRowId [bigint] PK CityDescription [varchar(100)] Province: ProvinceId [int] PK ProvinceDesc [varchar(50)] I am considering a rewrite of the application (in ASP.net MVC) that uses this data source as is similar in design to MVC storefront. However I am going through a proof of concept phase and this is one of the stumbling blocks I have come across. What are my options in terms of ORM choice that can be easily used and why? Should I even be considering an ORM? (The reason I ask this is that most explanations and tutorials all work with relatively cleanly designed existing databases, or newly created ones when compared to mine. I am thus having a very hard time trying to find a way forward with this problem) There is a huge amount of existing SQL queries, would a datamappper(eg IBatis.net) be more suitable since we could easily modify them to work and reuse the investment already made? I have found this question on SO which indicates to me that an ORM can be used - however I get the impression that this a question of mapping? Note: at the moment, the object model is not clearly defined as it was non-existent. The existing system pretty much did almost everything in SQL or consisted of overly complicated, and numerous queries to complete fucntionality. I am pretty much a noob and have zero experience around ORMs and MVC - so this an awesome learning curve I am on.

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• When is factory method better than simple factory and vice versa?

  - by Bruce

  Hi all Working my way through the Head First Design Patterns book. I believe I understand the simple factory and the factory method, but I'm having trouble seeing what advantages factory method brings over simple factory. If an object A uses a simple factory to create its B objects, then clients can create it like this: A a = new A(new BFactory()); whereas if an object uses a factory method, a client can create it like this: A a = new ConcreteA(); // ConcreteA contains a method for instantiating the same Bs that the BFactory above creates, with the method hardwired into the subclass of A, ConcreteA. So in the case of the simple factory, clients compose A with a B factory, whereas with the factory method, the client chooses the appropriate subclass for the types of B it wants. There really doesn't seem to be much to choose between them. Either you have to choose which BFactory you want to compose A with, or you have to choose the right subclass of A to give you the Bs. Under what circumstances is one better than the other? Thanks all!

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• Why does C# not provide the C++ style 'friend' keyword?

  - by Ash

  The C++ friend keyword allows a class A to designate class B as it's friend. This allows Class B to access the private/protected members of class A. I've never read anything as to why this was left out of C# (and VB.NET). Most answers to this earlier StackOverflow question seem to be saying it is a useful part of C++ and there are good reasons to use it. In my experience I'd have to agree. Another question seems to me to be really asking how to do something similar to friend in a C# application. While the answers generally revolve around nested classes, it doesn't seem quite as elegant as using the friend keyword. The original Design Patterns book uses the friend keyword regularly throughout its examples. So in summary, why is friend missing from C#, and what is the "best practice" way (or ways) of simulating it in C#? (By the way, the "internal" keyword is not the same thing, it allows ALL classes within the entire assembly to access internal members, friend allows you to give access to a class to just one other class.)

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• DDD: Enum like entities

  - by Chris

  Hi all, I have the following DB model: **Person table** ID | Name | StateId ------------------------------ 1 Joe 1 2 Peter 1 3 John 2 **State table** ID | Desc ------------------------------ 1 Working 2 Vacation and domain model would be (simplified): public class Person { public int Id { get; } public string Name { get; set; } public State State { get; set; } } public class State { private int id; public string Name { get; set; } } The state might be used in the domain logic e.g.: if(person.State == State.Working) // some logic So from my understanding, the State acts like a value object which is used for domain logic checks. But it also needs to be present in the DB model to represent a clean ERM. So state might be extended to: public class State { private int id; public string Name { get; set; } public static State New {get {return new State([hardCodedIdHere?], [hardCodeNameHere?]);}} } But using this approach the name of the state would be hardcoded into the domain. Do you know what I mean? Is there a standard approach for such a thing? From my point of view what I am trying to do is using an object (which is persisted from the ERM design perspective) as a sort of value object within my domain. What do you think? Question update: Probably my question wasn't clear enough. What I need to know is, how I would use an entity (like the State example) that is stored in a database within my domain logic. To avoid things like: if(person.State.Id == State.Working.Id) // some logic or if(person.State.Id == WORKING_ID) // some logic

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• Question About Example In Robert C Martin's _Clean Code_

  - by Jonah

  This is a question about the concept of a function doing only one thing. It won't make sense without some relevant passages for context, so I'll quote them here. They appear on pgs 37-38: To say this differently, we want to be able to read the program as though it were a set of TO paragraphs, each of which is describing the current level of abstraction and referencing subsequent TO paragraphs at the next level down. To include the setups and teardowns, we include setups, then we include the test page content, and then we include the teardowns. To include the setups, we include the suite setup if this is a suite, then we include the regular setup. It turns out to be very dif?cult for programmers to learn to follow this rule and write functions that stay at a single level of abstraction. But learning this trick is also very important. It is the key to keeping functions short and making sure they do “one thing.” Making the code read like a top-down set of TO paragraphs is an effective technique for keeping the abstraction level consistent. He then gives the following example of poor code: public Money calculatePay(Employee e) throws InvalidEmployeeType { switch (e.type) { case COMMISSIONED: return calculateCommissionedPay(e); case HOURLY: return calculateHourlyPay(e); case SALARIED: return calculateSalariedPay(e); default: throw new InvalidEmployeeType(e.type); } } and explains the problems with it as follows: There are several problems with this function. First, it’s large, and when new employee types are added, it will grow. Second, it very clearly does more than one thing. Third, it violates the Single Responsibility Principle7 (SRP) because there is more than one reason for it to change. Fourth, it violates the Open Closed Principle8 (OCP) because it must change whenever new types are added. Now my questions. To begin, it's clear to me how it violates the OCP, and it's clear to me that this alone makes it poor design. However, I am trying to understand each principle, and it's not clear to me how SRP applies. Specifically, the only reason I can imagine for this method to change is the addition of new employee types. There is only one "axis of change." If details of the calculation needed to change, this would only affect the submethods like "calculateHourlyPay()" Also, while in one sense it is obviously doing 3 things, those three things are all at the same level of abstraction, and can all be put into a TO paragraph no different from the example one: TO calculate pay for an employee, we calculate commissioned pay if the employee is commissioned, hourly pay if he is hourly, etc. So aside from its violation of the OCP, this code seems to conform to Martin's other requirements of clean code, even though he's arguing it does not. Can someone please explain what I am missing? Thanks.

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• Why does System.Web.Hosting.ApplicationHost.CreateApplicationHost throw System.IO.FileNotFoundExcept

  - by Scott Langham

  I saw something about needing to have the assembly available for the type of the first argument passed to the function. I think it is, I can't figure out what am I missing. This code is in a service. I was running the service under the 'NETWORK SERVICES' user account, when I changed the account to that of the session I was logged on with it worked ok. But, what's the difference, and how can I get it to work for the NETWORK SERVICES user.

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• Roadblocks in creating a custom operating system

  - by Dinah

  It seems to me that the most common overly ambitious project that programmers (esp. Comp. Sci. grads) try to tackle is building your own operating system. (Trying to create your own programming language + compiler is probably even more common but not nearly as ambitious.) For those (like myself) foolish enough to try: aside from the sheer size, what are the biggest *gotcha*s or unexpected roadblocks you've encountered in trying to create your own OS from the ground up? Edit: A great OS question: http://stackoverflow.com/questions/43180/how-to-get-started-in-operating-system-development/

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• ASP.NET FormView: "Object of type 'System.Int32' cannot be converted to type 'System.String"

  - by Vinzcent

  Hey I have a problem with my FromView. I would like to show some data from a Database Table in my FormView. But some data is from the tupe Int32, while this data should be in a TextBox, a string. How do you convert these Int32's. FormView and my ObjectDataSource <asp:FormView ID="fvDetailOrder" runat="server"> <ItemTemplate> Aantal:<br /> <asp:Label CssClass="txtBox" ID="Label15" runat="server" Text='<%# Eval("COUNT") %>' /><br /> Prijs:<br /> <asp:Label CssClass="txtBox" ID="Label16" runat="server" Text='<%# Eval("PRICE") %>' /><br /> Korting:<br /> <asp:Label CssClass="txtBox" ID="Label17" runat="server" Text='' /><br /> Totaal:<br /> <asp:Label CssClass="txtBox" ID="Label18" runat="server" Text='<%# Eval("AMOUNT") %>' /><br /> Betaald:<br /> <asp:Label CssClass="txtBox" ID="Label19" runat="server" Text='<%# Eval("PAID") %>' /><br /> Datum betaling:<br /> <asp:Label CssClass="txtBox" ID="Label20" runat="server" Text='<%# Eval("PDATE") %>' /><br /> </ItemTemplate> </asp:FormView> <asp:ObjectDataSource ID="objdsOrderID" runat="server" OnSelecting="objdsOrderID_Selecting" SelectMethod="getOrdersByID" TypeName="DAL.OrdersDAL"> <SelectParameters> <asp:Parameter Name="id" Type="Int32" /> </SelectParameters> </asp:ObjectDataSource> My Code behind protected void gvOrdersAdmin_SelectedIndexChanged(object sender, EventArgs e) { fvDetailOrder.DataSource = objdsOrderID; fvDetailOrder.DataBind(); // <-- HERE I GET THE ERROR } protected void objdsOrderID_Selecting(object sender, ObjectDataSourceSelectingEventArgs e) { e.InputParameters["id"] = gvOrdersAdmin.DataKeys[gvOrdersAdmin.SelectedRow.RowIndex].Values[0]; ; } My Data Acces Layer public static DataTable getOrdersByID(string id) { string sql = "SELECT 'AUTHOR' = tblAuthors.FIRSTNAME + ' ' + tblAuthors.LASTNAME, tblBooks.*, tblGenres.*, tblLanguages.*, tblOrders.* FROM tblAuthors INNER JOIN tblBooks ON tblAuthors.AUTHOR_ID = tblBooks.AUTHOR_ID INNER JOIN tblGenres ON tblBooks.GENRE_ID = tblGenres.GENRE_ID INNER JOIN tblLanguages ON tblBooks.LANG_ID = tblLanguages.LANG_ID INNER JOIN tblOrders ON tblBooks.BOOK_ID = tblOrders.BOOK_ID" + " WHERE tblOrders.ID = @id;"; SqlDataAdapter da = new SqlDataAdapter(sql, GetConnectionString()); da.SelectCommand.Parameters["id"].Value = id; DataSet ds = new DataSet(); da.Fill(ds, "Orders"); return ds.Tables["Orders"]; } Thanks a lot, Vincent

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• System.Security.Permissions.SecurityPermission and Reflection on Godaddy

  - by David Murdoch

  I have the following method: public static UserControl LoadControl(string UserControlPath, params object[] constructorParameters) { var p = new Page(); var ctl = p.LoadControl(UserControlPath) as UserControl; // Find the relevant constructor if (ctl != null) { ConstructorInfo constructor = ctl.GetType().BaseType.GetConstructor(constructorParameters.Select(constParam => constParam == null ? "".GetType() : constParam.GetType()).ToArray()); //And then call the relevant constructor if (constructor == null) { throw new MemberAccessException("The requested constructor was not found on : " + ctl.GetType().BaseType.ToString()); } constructor.Invoke(ctl, constructorParameters); } // Finally return the fully initialized UC return ctl; } Which when executed on a Godaddy shared host gives me System.Security.SecurityException: Request for the permission of type 'System.Security.Permissions.SecurityPermission, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' failed.

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