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  • Which pattern to use for logging? Dependency Injection or Service Locator?

    - by andlju
    Consider this scenario. I have some business logic that now and then will be required to write to a log. interface ILogger { void Log(string stuff); } interface IDependency { string GetInfo(); } class MyBusinessObject { private IDependency _dependency; public MyBusinessObject(IDependency dependency) { _dependency = dependency; } public string DoSomething(string input) { // Process input var info = _dependency.GetInfo(); var intermediateResult = PerformInterestingStuff(input, info); if (intermediateResult== "SomethingWeNeedToLog") { // How do I get to the ILogger-interface? } var result = PerformSomethingElse(intermediateResult); return result; } } How would you get the ILogger interface? I see two main possibilities; Pass it using Dependency Injection on the constructor. Get it via a singleton Service Locator. Which method would you prefer, and why? Or is there an even better pattern? Update: Note that I don't need to log ALL method calls. I only want to log a few (rare) events that may or may not occur within my method.

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  • Is it ok to throw NotImplemented exception in virtual methods?

    - by Axarydax
    I have a base class for some plugin-style stuff, and there are some methods that are absolutely required to be implemented. I currently declare those in the base class as virtual, for example public virtual void Save { throw new NotImplementedException(); } and in the descendand I have a public override void Save() { //do stuff } Is it a good practice to throw a NotImplementedException there? The descendand classes could for example be the modules for handling different file formats. Thanks

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  • Question about a possible design pattern...

    - by Aftershock
    I have such a design in my mind.... My aim is to reuse the program with some features included and without some features. What is it called in the literature? class feature1 { void feature1function1(); void feature1function2(); } class feature2 { void feature2function1(); void feature2function2(); } class program: feature1, feature2 { void function1() { feature2function1(); } void function2() { feature1function1(); feature2function1(); } void execute() { function1(); function2(); } }

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  • Reference table values in a war against magic numbers

    - by Alex N.
    This question bugged me for years now and can't seem to find good solution still. I working in PHP and Java but it sounds like this maybe language-agnostic :) Say we have a standard status reference table that holds status ids for some kind of entity. Further let's assume the table will have just 5 values, and will remain like this for a long time, maybe edited occasionally with addition of a new status. When you fetch a row and need to see what status it is you have 2 options(as I see it at least) - put it straight ID values(magic numbers that is) or use a named constant. Latter seem much cleaner, the question though is where those named constants should leave? In a model class? In a class that uses this particular constant? Somewhere else?

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  • Request/Response pattern in SOA implementation

    - by UserControl
    In some enterprise-like project (.NET, WCF) i saw that all service contracts accept a single Request parameter and always return Response: [DataContract] public class CustomerRequest : RequestBase { [DataMember] public long Id { get; set; } } [DataContract] public class CustomerResponse : ResponseBase { [DataMember] public CustomerInfo Customer { get; set; } } where RequestBase/ResponseBase contain common stuff like ErrorCode, Context, etc. Bodies of both service methods and proxies are wrapped in try/catch, so the only way to check for errors is looking at ResponseBase.ErrorCode (which is enumeration). I want to know how this technique is called and why it's better compared to passing what's needed as method parameters and using standard WCF context passing/faults mechanisms?

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  • MySQL indexes - what are the best practises?

    - by Haroldo
    I've been using indexes on my mysql databases for a while now but never properly learnt about them. Generally I put an index on any fields that i will be searching or selecting using a WHERE clause but sometimes it doesn't seem so black and white. What are the best practises for mysql indexes? example situations/dilemas: If a table has six columns and all of them are searchable, should i index all of them or none of them? . What are the negetive performance impacts of indexing? . If i have a VARCHAR 2500 column which is searchable from parts of my site, should i index it?

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  • Lock thread using somthing other than a object

    - by Scott Chamberlain
    when using a lock does the thing you are locking on have to be a object. For example is this legal static DateTime NextCleanup = DateTime.Now; const TimeSpan CleanupInterval = new TimeSpan(1, 0, 0); private static void DoCleanup() { lock ((object)NextCleanup) { if (NextCleanup < DateTime.Now) { NextCleanup = DateTime.Now.Add(CleanupInterval); System.Threading.ThreadPool.QueueUserWorkItem(new System.Threading.WaitCallback(cleanupThread)); } } return; } EDIT-- From reading SLaks' responce I know the above code would be not valid but would this be? static MyClass myClass = new MyClass(); private static void DoCleanup() { lock (myClass) { // } return; }

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  • C# Design Reduce a Long List of Methods

    - by guazz
    I have a simple application that loads data from an XML file to a database. public class EmployeeLoader() { public void LoadEmpoyees() {...} public void LoadSalaries() {...} public void LoadRegistrationData() {...} public void LoadTaxData() {...} } Is it a good idea to have multiple "Load" methods as this looks like a code smell as I have about tweney Load methods? If so, how do I make my code more readable? Each Load method loads data to the corresponding table in the database via a repository?

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  • how to make objects globally accessible?

    - by fayer
    i have this code: class IC_Core { /** * Database * @var IC_Database */ public static $db = NULL; /** * Core * @var IC_Core */ protected static $_instance = NULL; private function __construct() { } public static function getInstance() { if ( ! is_object(self::$_instance)) { self::$_instance = new self(); self::initialize(self::$_instance); } return self::$_instance; } private static function initialize(IC_Core $IC_Core) { self::$db = new IC_Database($IC_Core); } } but when i wanna access IC_Database with: $IC = IC_Core::getInstance(); $IC->db->add() // it says that its not an object. i think the problem lies in self::$db = new IC_Database($IC_Core); but i dont know how to make it work. could someone give me a hand=) thanks!

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  • Is this a problem typically solved with IOC?

    - by Dirk
    My current application allows users to define custom web forms through a set of admin screens. it's essentially an EAV type application. As such, I can't hard code HTML or ASP.NET markup to render a given page. Instead, the UI requests an instance of a Form object from the service layer, which in turn constructs one using a several RDMBS tables. Form contains the kind of classes you would expect to see in such a context: Form= IEnumerable<FormSections>=IEnumerable<FormFields> Here's what the service layer looks like: public class MyFormService: IFormService{ public Form OpenForm(int formId){ //construct and return a concrete implementation of Form } } Everything works splendidly (for a while). The UI is none the wiser about what sections/fields exist in a given form: It happily renders the Form object it receives into a functional ASP.NET page. A few weeks later, I get a new requirement from the business: When viewing a non-editable (i.e. read-only) versions of a form, certain field values should be merged together and other contrived/calculated fields should are added. No problem I say. Simply amend my service class so that its methods are more explicit: public class MyFormService: IFormService{ public Form OpenFormForEditing(int formId){ //construct and return a concrete implementation of Form } public Form OpenFormForViewing(int formId){ //construct and a concrete implementation of Form //apply additional transformations to the form } } Again everything works great and balance has been restored to the force. The UI continues to be agnostic as to what is in the Form, and our separation of concerns is achieved. Only a few short weeks later, however, the business puts out a new requirement: in certain scenarios, we should apply only some of the form transformations I referenced above. At this point, it feels like the "explicit method" approach has reached a dead end, unless I want to end up with an explosion of methods (OpenFormViewingScenario1, OpenFormViewingScenario2, etc). Instead, I introduce another level of indirection: public interface IFormViewCreator{ void CreateView(Form form); } public class MyFormService: IFormService{ public Form OpenFormForEditing(int formId){ //construct and return a concrete implementation of Form } public Form OpenFormForViewing(int formId, IFormViewCreator formViewCreator){ //construct a concrete implementation of Form //apply transformations to the dynamic field list return formViewCreator.CreateView(form); } } On the surface, this seems like acceptable approach and yet there is a certain smell. Namely, the UI, which had been living in ignorant bliss about the implementation details of OpenFormForViewing, must possess knowledge of and create an instance of IFormViewCreator. My questions are twofold: Is there a better way to achieve the composability I'm after? (perhaps by using an IoC container or a home rolled factory to create the concrete IFormViewCreator)? Did I fundamentally screw up the abstraction here?

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  • Does database affect classes?

    - by satyanarayana
    I had created one class User and UserDAOImpl class for querying DB using class User. As there is one table to be queried, these two classes are sufficient for me. What if there is a case where new fields are to be added to that one table is to be divided into 3 tables( user_info, user_profile and user_address) to store user? As new fields are added, I need to change classes User and UserDAOImpl, it seems these two are not sufficient. It seems database changes affect my classes. In this case, do I need to divide class User into 3 classes as tables are changes? Can any one suggest me how can I solve this without making too many changes?

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  • Should every class have its own namespace?

    - by thehouse
    Something that has been troubling me for a while: The current wisdom is that types should be kept in a namespace that only contains functions which are part of the type's non-member interface (see C++ Coding Standards Sutter and Alexandrescu or here) to prevent ADL pulling in unrelated definitions. Does this imply that all classes must have a namespace of their own? If we assume that a class may be augmented in the future by the addition of non-member functions, then it can never be safe to put two types in the same namespace as either one of them may introduce non-member functions that could interfere with the other. The reason I ask is that namespaces are becoming cumbersome for me. I'm writing a header-only library and I find myself using classes names such as project::component::class_name::class_name. Their implementations call helper functions but as these can't be in the same namespace they also have to be fully qualified!

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  • What pattern to use in this scenario?

    - by jess
    Hi, We have got many forms(windows app C#) in our application.We have similar steps in most of them - user adds a new object(in a grid),fills values and save.On,save,we validate,and save if everything ok,else show message.Now,adding of object usually means we add a new row with some default values.

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  • Finding relative libraries when using symlinks to ruby executables

    - by dgtized
    Imagine you have an executable foo.rb, with libraries bar.rb layed out in the following manner: <root>/bin/foo.rb <root>/lib/bar.rb In the header of foo.rb you place the following require to bring in functionality in bar.rb: require File.dirname(__FILE__)+"../lib/bar.rb" This works fine so long as all calls to foo.rb are direct. If you put as say $HOME/project, and symlink foo.rb into $HOME/usr/bin, then __FILE__ resolves to $HOME/usr/bin/foo.rb, and is thus unable to locate bar.rb in relation to the dirname for foo.rb. I realize that packaging systems such as rubygems fix this by creating a namespace to search for the library, and that it is also possible to adjust the load_path using $: to include $HOME/project/lib, but it seems as if a more simple solution should exist. Has anyone had experience with this problem and found a useful solution or recipe?

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  • Passing arguments between classes - use public properties or pass a properties class as argument?

    - by devoured elysium
    So let's assume I have a class named ABC that will have a list of Point objects. I need to make some drawing logic with them. Each one of those Point objects will have a Draw() method that will be called by the ABC class. The Draw() method code will need info from ABC class. I can only see two ways to make them have this info: Having Abc class make public some properties that would allow draw() to make its decisions. Having Abc class pass to draw() a class full of properties. The properties in both cases would be the same, my question is what is preferred in this case. Maybe the second approach is more flexible? Maybe not? I don't see here a clear winner, but that sure has more to do with my inexperience than any other thing. If there are other good approaches, feel free to share them. Here are both cases: class Abc1 { public property a; public property b; public property c; ... public property z; public void method1(); ... public void methodn(); } and here is approach 2: class Abc2 { //here we make take down all properties public void method1(); ... public void methodn(); } class Abc2MethodArgs { //and we put them here. this class will be passed as argument to //Point's draw() method! public property a; public property b; public property c; ... public property z; } Also, if there are any "formal" names for these two approaches, I'd like to know them so I can better choose the tags/thread name, so it's more useful for searching purposes. That or feel free to edit them.

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  • Are upper bounds of indexed ranges always assumed to be exclusive?

    - by polygenelubricants
    So in Java, whenever an indexed range is given, the upper bound is almost always exclusive. From java.lang.String: substring(int beginIndex, int endIndex) Returns a new string that is a substring of this string. The substring begins at the specified beginIndex and extends to the character at index endIndex - 1 From java.util.Arrays: copyOfRange(T[] original, int from, int to) from - the initial index of the range to be copied, inclusive to - the final index of the range to be copied, exclusive. From java.util.BitSet: set(int fromIndex, int toIndex) fromIndex - index of the first bit to be set. toIndex - index after the last bit to be set. As you can see, it does look like Java tries to make it a consistent convention that upper bounds are exclusive. My questions are: Is this the official authoritative recommendation? Are there notable violations that we should be wary of? Is there a name for this system? (ala "0-based" vs "1-based")

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  • Should I use block identifiers ("end;") in my code?

    - by JosephStyons
    Code Complete says it is good practice to always use block identifiers, both for clarity and as a defensive measure. Since reading that book, I've been doing that religiously. Sometimes it seems excessive though, as in the case below. Is Steve McConnell right to insist on always using block identifiers? Which of these would you use? //naughty and brief with myGrid do for currRow := FixedRows to RowCount - 1 do if RowChanged(currRow) then if not(RecordExists(currRow)) then InsertNewRecord(currRow) else UpdateExistingRecord(currRow); //well behaved and verbose with myGrid do begin for currRow := FixedRows to RowCount - 1 do begin if RowChanged(currRow) then begin if not(RecordExists(currRow)) then begin InsertNewRecord(currRow); end //if it didn't exist, so insert it else begin UpdateExistingRecord(currRow); end; //else it existed, so update it end; //if any change end; //for each row in the grid end; //with myGrid

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  • In Java how instance of and type cast(i.e (ClassName)) works on proxy object ?

    - by learner
    Java generates a proxy class for a given interface and provides the instance of the proxy class. But when we type cast the proxy object to our specific Object, how java handles this internally? Is this treated as special scenario? For example I have class 'OriginalClass' and it implements 'OriginalInterface', when I create proxy object by passing 'OriginalInterface' interface java created proxy class 'ProxyClass' using methods in the provided interface and provides object of this class(i.e ProxyClass). If my understanding is correct then can you please answer following queries 1) When I type cast object of ProxyClass to my class OriginalClass this works, but how java is allowing this? Same in case of instace of? 2) As my knowledge java creates a proxy class only with the methods, but what happen when I try to access attributes on this object? 3) Only interface methods are getting implemented in Proxy, but what happens when I try to access a method which not in interface and only mentioned in the class? Thanks, Student

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  • Number of characters recommended for a statement

    - by liaK
    Hi, I have been using Qt 4.5 and so do C++. I have been told that it's a standard practice to maintain the length of each statement in the application to 80 characters. Even in Qt creator we can make a right border visible so that we can know whether we are crossing the 80 characters limit. But my question is, Is it really a standard being followed? Because in my application, I use indenting and all, so it's quite common that I cross the boundary. Other cases include, there might be a error statement which will be a bit explanatory one and which is in an inner block of code, so it too will cross the boundary. Usually my variable names look bit lengthier so as to make the names meaningful. When I call the functions of the variable names, again I will cross. Function names will not be in fewer characters either. I agree a horizontal scroll bar shows up and it's quite annoying to move back and forth. So, for function calls including multiple arguments, when the boundary is reached I will make the forth coming arguments in the new line. But besides that, for a single statement (for e.g a very long error message which is in double quotes " " or like longfun1()->longfun2()->...) if I use an \ and split into multiple lines, the readability becomes very poor. So is it a good practice to have those statement length restrictions? If this restriction in statement has to be followed? I don't think it depends on a specific language anyway. I added C++ and Qt tags since if it might. Any pointers regarding this are welcome.

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  • best practice when referring to a program's name in C

    - by guest
    what is considered best practice when referring to a program's name? i've seen #define PROGRAM_NAME "myprog" printf("this is %s\n", PROGRAM_NAME); as well as printf("this is %s\n", argv[0]); i know, that the second approach will give me ./myprog rather than myprog when the program is not called from $PATH and that the first approach will guarantee consistence regarding the program's name. but is there anything else, that makes one approach superior to the other?

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  • What is the role of the Router Object in MVC based frameworks

    - by Saif Bechan
    In most MVC based framework I see a router object. If I look at it splits up the uri and decides what controller should be used, and which action should be fired. Even though this makes a lot of sense, I can not give this a place in the MVC patern. Is splitting up the uri not the job of the controller. And then the controller should just decide which class and function to run.

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  • Java: Inputting text from a file using split

    - by 00PS
    I am inputting an adjacency list for a graph. There are three columns of data (vertex, destination, edge) separated by a single space. Here is my implementation so far: FileStream in = new FileStream("input1.txt"); Scanner s = new Scanner(in); String buffer; String [] line = null; while (s.hasNext()) { buffer = s.nextLine(); line = buffer.split("\\s+"); g.add(line[0]); System.out.println("Added vertex " + line[0] + "."); g.addEdge(line[0], line[1], Integer.parseInt(line[2])); System.out.println("Added edge from " + line[0] + " to " + line[1] + " with a weight of " + Integer.parseInt(line[2]) + "."); } System.out.println("Size of graph = " + g.size()); Here is the output: Added vertex a. Added edge from a to b with a weight of 9. Exception in thread "main" java.lang.NullPointerException at structure5.GraphListDirected.addEdge(GraphListDirected.java:93) at Driver.main(Driver.java:28) I was under the impression that line = buffer.split("\\s+"); would return a 2 dimensional array of Strings to the variable line. It seemed to work the first time but not the second. Any thoughts? I would also like some feedback on my implementation of this problem. Is there a better way? Anything to help out a novice! :)

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