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  • Object behaviour or separate class?

    - by Andrew Stephens
    When it comes to OO database access you see two common approaches - the first is to provide a class (say "Customer") with methods such as Retrieve(), Update(), Delete(), etc. The other is to keep the Customer class fairly lightweight (essentially just properties) and perform the database access elsewhere, e.g. using a repository. This choice of approaches doesn't just apply to database access, it can crop up in many different OOD scenarios. So I was wondering if one way is preferable over the other (although I suspect the answer will be "it depends")! Another dev on our team argues that to be truly OO the class should be "self-contained", i.e. providing all the methods necessary to manipulate and interact with that object. I personally prefer the repository approach - I don't like bloating the Customer class with all that functionality, and I feel it results in cleaner code having it elsewhere, but I can't help thinking I'm seriously violating core OO concepts! And what about memory implications? If I retrieve thousands of Customer objects I'm assuming those with the data access methods will take up a lot more memory than the property-only objects?

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  • Reusable skill class structure

    - by Martino Wullems
    Hello, Pretty new to the whole game development scene, but I have experience in other branches of programming. Anyway, I was wondering what methods are used to implement a skill structure. I imagine a skill in itself would a class. I'm using actionscript 3 for this project btw. public class Skill { public var power:int; public var delay:int; public var cooldown:int; public function Attack(user:Mob, target:Mob) { } } } Each skill would extend the Skill class and add it's own functionality. public class Tackle extends Skill { public function Tackle(user:Mob, target:Mob) { super(user, target); executeAttack(); } private function executeAttack():void { //multiply user.strength with power etc //play attack animation } } } This where I get stuck. How do I termine which mobs has which skills? And which skill will they later be able to retrieve (by reaching a certain level etc). How does the player actually execute the skill and how is it determine if it hits. It's all very new to me so I have no idea where to begin. Any links would also be appreciated. Thanks in advance.

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  • Canonical representation of a class object containing a list element in XML

    - by dendini
    I see that most implementations of JAX-RS represent a class object containing a list of elements as follows (assume a class House containing a list of People) <houses> <house> <person> <name>Adam</name> </person> <person> <name>Blake</name> </person> </house> <house> </house> </houses> The result above is obtained for instance from Jersey 2 JAX-RS implementation, notice Jersey creates a wrapper class "houses" around each house, however strangely it doesn't create a wrapper class around each person! I don't feel this is a correct mapping of a list, in other words I'd feel more confortable with something like this: <houses> <house> <persons> <person> <name>Adam</name> </person> <person> <name>Blake</name> </person> </persons> </house> <house> </house> </houses> Is there any document explaining how an object should be correctly mapped apart from any opninion?

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  • Should you create a class within a method?

    - by Amndeep7
    I have made a program using Java that is an implementation of this project: http://nifty.stanford.edu/2009/stone-random-art/sml/index.html. Essentially, you create a mathematical expression and, using the pixel coordinate as input, make a picture. After I initially implemented this in serial, I then implemented it in parallel due to the fact that if the picture size is too large or if the mathematical expression is too complex (especially considering the fact that I made the expression recursively), it takes a really long time. During this process, I realized that I needed two classes which implemented the Runnable interface as I had to put in parameters for the run method, which you aren't allowed to do directly. One of these classes ended up being a medium sized static inner class (not large enough to make an independent class file for it though). The other though, just needed a few parameters to determine some indexes and the size of the for loop that I was making run in parallel - here it is: class DataConversionRunnable implements Runnable { int jj, kk, w; DataConversionRunnable(int column, int matrix, int wid) { jj = column; kk = matrix; w = wid; } public void run() { for(int i = 0; i < w; i++) colorvals[kk][jj][i] = (int) ((raw[kk][jj][i] + 1.0) * 255 / 2.0); increaseCounter(); } } My question is should I make it a static inner class or can I just create it in a method? What is the general programming convention followed in this case?

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  • Avoid overwriting all the methods in the child class

    - by Heckel
    The context I am making a game in C++ using SFML. I have a class that controls what is displayed on the screen (manager on the image below). It has a list of all the things to draw like images, text, etc. To be able to store them in one list I created a Drawable class from which all the other drawable class inherit. The image below represents how I would organize each class. Drawable has a virtual method Draw that will be called by the manager. Image and Text overwrite this method. My problem is that I would like Image::draw method to work for Circle, Polygon, etc. since sf::CircleShape and sf::ConvexShape inherit from sf::Shape. I thought of two ways to do that. My first idea would be for Image to have a pointer on sf::Shape, and the subclasses would make it point onto their sf::CircleShape or sf::ConvexShape classes (Like on the image below). In the Polygon constructor I would write something like ptr_shape = &polygon_shape; This doesn't look very elegant because I have two variables that are, in fact, just one. My second idea is to store the sf::CircleShape and sf::ConvexShape inside the ptr_shape like ptr_shape = new sf::ConvexShape(...); and to use a function that is only in ConvexShape I would cast it like so ((sf::ConvexShape*)ptr_shape)->convex_method(); But that doesn't look very elegant either. I am not even sure I am allowed to do that. My question I added details about the whole thing because I thought that maybe my whole architecture was wrong. I would like to know how I could design my program to be safe without overwriting all the Image methods. I apologize if this question has already been asked; I have no idea what to google.

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  • Reflective discovery of an inner class in an API

    - by wassup
    Let me ask you, as this bothers me for quite a while but appears to be subjectively the best solution for my problem, if reflective discovery of an inner class for API purposes is that bad idea? First, let me explain what I mean by saying "reflective discovery" and all that stuff. I am sketching an API for a Java database system, that'll be centered around block-based entities (don't ask me what that means - that's a long story), and those entities can be read and returned to the Java code as objects subclassed from the Entity class. I have an Entity.Factory class, that, by means of fluent interfaces, takes a Class<? extends Entity> argument and then, uses an instance of Section.Builder, Property.Builder, or whatever builder the entity has, to put it into the back-end storage. The idea about registering all entity types and their builders just doesn't appeal to me, so I thought that the closest solution to the problem that'd suffice my design needs would be to discover, using reflection, all inner classes of Entity classes and find one that's called Builder. Looking for some expert insight :) And if I missed some important design details (which could happen as I tried to make this question as concise as possible), just tell me and I'll add them.

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  • REST API wrapper - class design for 'lite' object responses

    - by sasfrog
    I am writing a class library to serve as a managed .NET wrapper over a REST API. I'm very new to OOP, and this task is an ideal opportunity for me to learn some OOP concepts in a real-life situation that makes sense to me. Some of the key resources/objects that the API returns are returned with different levels of detail depending on whether the request is for a single instance, a list, or part of a "search all resources" response. This is obviously a good design for the REST API itself, so that full objects aren't returned (thus increasing the size of the response and therefore the time taken to respond) unless they're needed. So, to be clear: .../car/1234.json returns the full Car object for 1234, all its properties like colour, make, model, year, engine_size, etc. Let's call this full. .../cars.json returns a list of Car objects, but only with a subset of the properties returned by .../car/1234.json. Let's call this lite. ...search.json returns, among other things, a list of car objects, but with minimal properties (only ID, make and model). Let's call this lite-lite. I want to know what the pros and cons of each of the following possible designs are, and whether there is a better design that I haven't covered: Create a Car class that models the lite-lite properties, and then have each of the more detailed responses inherit and extend this class. Create separate CarFull, CarLite and CarLiteLite classes corresponding to each of the responses. Create a single Car class that contains (nullable?) properties for the full response, and create constructors for each of the responses which populate it to the extent possible (and maybe include a property that returns the response type from which the instance was created). I expect among other things there will be use cases for consumers of the wrapper where they will want to iterate through lists of Cars, regardless of which response type they were created from, such that the three response types can contribute to the same list. Happy to be pointed to good resources on this sort of thing, and/or even told the name of the concept I'm describing so I can better target my research.

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  • Class structure for the proposed data and its containers ?

    - by Prix
    First I would like to wish a happy new year to everyone that may read this :) I am having trouble on how to make a container for some data that I am importing into my application, and I am not sure on how to explain this very well and my english is not really a that good so I hope you can bear with my mistake and help me with some guidance. Currently with a foreach I am importing the follow fields from the data I receive: guid, itemid, name, owner(optional, can be null), zoneid, titleid, subid, heading, x, y, z, typeA, typeB, typeC From the above fields I need to store a Waypoint list of all coords a given item has moved to BUT for each guid I have a new list of waypoints. And from the waypoint list the first entry is also my initial item start location which would be my item initial position (if you notice i have a separate list for it which I was not sure would be better or not) not all items have a waypoint list but all items have the first position. So the first idea I came with to store this data was a list with a class with 2 inner classes with their list: public List<ItemList> myList = new List<ItemList>(); public class ItemList { public int guid { get; set; } public int itemid { get; set; } public string name { get; set; } public int titleid { get; set; } public itemType status { get; set; } public class Waypoint { public float posX { get; set; } public float posY { get; set; } public float posZ { get; set; } } public List<Waypoint> waypoint = new List<Waypoint>(); public class Location { public int zone { get; set; } public int subid { get; set; } public int heading { get; set; } public float posX { get; set; } public float posY { get; set; } public float posZ { get; set; } } public List<Location> position = new List<Location>(); } So here is an example of how I would add a new waypoint to a GUID that exists in the list bool itemExists = myList.Exists(item => item.guid == guid && item.itemid == itemid); if (itemExists) { int lastDistance = 3; ItemList.Waypoint nextWaypoint; ItemList myItem = myList.Find(item => item.guid == guid && item.itemid == itemid); if (myItem.waypoint.Count == 0) { nextWaypoint = new ItemList.Waypoint(); nextWaypoint.posX = PosX; nextWaypoint.posY = PosY; nextWaypoint.posZ = PosZ; } else { ItemList.Waypoint lastWaypoint = myItem.waypoint[myItem.waypoint.Count - 1]; if (lastWaypoint != null) { lastDistance = getDistance(x, y, z, lastWaypoint.posX, lastWaypoint.posY, lastWaypoint.posZ); } if (lastDistance > 2) { nextWaypoint = new ItemList.Waypoint(); nextWaypoint.posX = PosX; nextWaypoint.posY = PosY; nextWaypoint.posZ = PosZ; } } myItem.waypoint.Add(nextWaypoint); } Then to register a new item I would take advantage of the itemExist above so I won't register the same GUID again: ItemList newItem = new ItemList(); newItem.guid = guid; newItem.itemid = itemid; newItem.name = name; newItem.status = status; newItem.titleid = titleid; // Item location ItemList.Location itemLocation = new ItemList.Location(); itemLocation.subid = 0; itemLocation.zone= zone; itemLocation.heading = convertHeading(Heading); itemLocation.posX = PosX; itemLocation.posY = PosY; itemLocation.posZ = PosZ; newItem.position.Add(itemLocation); myList.Add(newItem); Could you help me with advices on how my class structure and lists should look like ? Are there better ways to interate with the lists to get lastWaypoint of a GUID or verify wether an item exist or not ? What else would you advise me in general ? PS: If you have any questions or if there is something I missed to post please let me know and I will update it.

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  • Class-Level Model Validation with EF Code First and ASP.NET MVC 3

    - by ScottGu
    Earlier this week the data team released the CTP5 build of the new Entity Framework Code-First library.  In my blog post a few days ago I talked about a few of the improvements introduced with the new CTP5 build.  Automatic support for enforcing DataAnnotation validation attributes on models was one of the improvements I discussed.  It provides a pretty easy way to enable property-level validation logic within your model layer. You can apply validation attributes like [Required], [Range], and [RegularExpression] – all of which are built-into .NET 4 – to your model classes in order to enforce that the model properties are valid before they are persisted to a database.  You can also create your own custom validation attributes (like this cool [CreditCard] validator) and have them be automatically enforced by EF Code First as well.  This provides a really easy way to validate property values on your models.  I showed some code samples of this in action in my previous post. Class-Level Model Validation using IValidatableObject DataAnnotation attributes provides an easy way to validate individual property values on your model classes.  Several people have asked - “Does EF Code First also support a way to implement class-level validation methods on model objects, for validation rules than need to span multiple property values?”  It does – and one easy way you can enable this is by implementing the IValidatableObject interface on your model classes. IValidatableObject.Validate() Method Below is an example of using the IValidatableObject interface (which is built-into .NET 4 within the System.ComponentModel.DataAnnotations namespace) to implement two custom validation rules on a Product model class.  The two rules ensure that: New units can’t be ordered if the Product is in a discontinued state New units can’t be ordered if there are already more than 100 units in stock We will enforce these business rules by implementing the IValidatableObject interface on our Product class, and by implementing its Validate() method like so: The IValidatableObject.Validate() method can apply validation rules that span across multiple properties, and can yield back multiple validation errors. Each ValidationResult returned can supply both an error message as well as an optional list of property names that caused the violation (which is useful when displaying error messages within UI). Automatic Validation Enforcement EF Code-First (starting with CTP5) now automatically invokes the Validate() method when a model object that implements the IValidatableObject interface is saved.  You do not need to write any code to cause this to happen – this support is now enabled by default. This new support means that the below code – which violates one of our above business rules – will automatically throw an exception (and abort the transaction) when we call the “SaveChanges()” method on our Northwind DbContext: In addition to reactively handling validation exceptions, EF Code First also allows you to proactively check for validation errors.  Starting with CTP5, you can call the “GetValidationErrors()” method on the DbContext base class to retrieve a list of validation errors within the model objects you are working with.  GetValidationErrors() will return a list of all validation errors – regardless of whether they are generated via DataAnnotation attributes or by an IValidatableObject.Validate() implementation.  Below is an example of proactively using the GetValidationErrors() method to check (and handle) errors before trying to call SaveChanges(): ASP.NET MVC 3 and IValidatableObject ASP.NET MVC 2 included support for automatically honoring and enforcing DataAnnotation attributes on model objects that are used with ASP.NET MVC’s model binding infrastructure.  ASP.NET MVC 3 goes further and also honors the IValidatableObject interface.  This combined support for model validation makes it easy to display appropriate error messages within forms when validation errors occur.  To see this in action, let’s consider a simple Create form that allows users to create a new Product: We can implement the above Create functionality using a ProductsController class that has two “Create” action methods like below: The first Create() method implements a version of the /Products/Create URL that handles HTTP-GET requests - and displays the HTML form to fill-out.  The second Create() method implements a version of the /Products/Create URL that handles HTTP-POST requests - and which takes the posted form data, ensures that is is valid, and if it is valid saves it in the database.  If there are validation issues it redisplays the form with the posted values.  The razor view template of our “Create” view (which renders the form) looks like below: One of the nice things about the above Controller + View implementation is that we did not write any validation logic within it.  The validation logic and business rules are instead implemented entirely within our model layer, and the ProductsController simply checks whether it is valid (by calling the ModelState.IsValid helper method) to determine whether to try and save the changes or redisplay the form with errors. The Html.ValidationMessageFor() helper method calls within our view simply display the error messages our Product model’s DataAnnotations and IValidatableObject.Validate() method returned.  We can see the above scenario in action by filling out invalid data within the form and attempting to submit it: Notice above how when we hit the “Create” button we got an error message.  This was because we ticked the “Discontinued” checkbox while also entering a value for the UnitsOnOrder (and so violated one of our business rules).  You might ask – how did ASP.NET MVC know to highlight and display the error message next to the UnitsOnOrder textbox?  It did this because ASP.NET MVC 3 now honors the IValidatableObject interface when performing model binding, and will retrieve the error messages from validation failures with it. The business rule within our Product model class indicated that the “UnitsOnOrder” property should be highlighted when the business rule we hit was violated: Our Html.ValidationMessageFor() helper method knew to display the business rule error message (next to the UnitsOnOrder edit box) because of the above property name hint we supplied: Keeping things DRY ASP.NET MVC and EF Code First enables you to keep your validation and business rules in one place (within your model layer), and avoid having it creep into your Controllers and Views.  Keeping the validation logic in the model layer helps ensure that you do not duplicate validation/business logic as you add more Controllers and Views to your application.  It allows you to quickly change your business rules/validation logic in one single place (within your model layer) – and have all controllers/views across your application immediately reflect it.  This help keep your application code clean and easily maintainable, and makes it much easier to evolve and update your application in the future. Summary EF Code First (starting with CTP5) now has built-in support for both DataAnnotations and the IValidatableObject interface.  This allows you to easily add validation and business rules to your models, and have EF automatically ensure that they are enforced anytime someone tries to persist changes of them to a database.  ASP.NET MVC 3 also now supports both DataAnnotations and IValidatableObject as well, which makes it even easier to use them with your EF Code First model layer – and then have the controllers/views within your web layer automatically honor and support them as well.  This makes it easy to build clean and highly maintainable applications. You don’t have to use DataAnnotations or IValidatableObject to perform your validation/business logic.  You can always roll your own custom validation architecture and/or use other more advanced validation frameworks/patterns if you want.  But for a lot of applications this built-in support will probably be sufficient – and provide a highly productive way to build solutions. Hope this helps, Scott P.S. In addition to blogging, I am also now using Twitter for quick updates and to share links. Follow me at: twitter.com/scottgu

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  • Creating instance of a service-side DataContract class on client-side in WCF

    - by hgulyan
    Hi, I have my custom class Customer with its properties. I added DataContract mark above the class and DataMember to properties and it was working fine, but I'm calling a service class's function, passing customer instance as parameter and some of my properties get 0 values. While debugging I can see my properties values and after it gets to the function, some properties' values are 0. Why it can be so? There's no code between this two actions. DataContract mark workes fine, everything's ok. Any suggestions on this issue? I tried to change ByRef to ByVal, but it doesn't change anything. Why it would pass other values right and some of integer types just 0? Maybe the answer is simple, but I can't figure it out. Thank You. <DataContract()> Public Class Customer Private Type_of_clientField As Integer = -1 <DataMember(Order:=1)> Public Property type_of_client() As Integer Get Return Type_of_clientField End Get Set(ByVal value As Integer) Type_of_clientField = value End Set End Property End Class <ServiceContract(SessionMode:=SessionMode.Allowed)> <DataContractFormat()> Public Interface CustomerService <OperationContract()> Function addCustomer(ByRef customer As Customer) As Long End Interface type_of_client properties value is 6 before I call addCustomer function. After it enters that function the value is 0. UPDATE: The issue is in instance creating. When I create an instance of a class on client side, that is stored on service side, some of my properties pass 0 or nothing, but when I call a function of a service class, that returns a new instance of that class, it works fine. What's is the difference? Could that be serialization issue?

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  • Class; Struct; Enum confusion, what is better?

    - by Angel Brighteyes
    I have 46 rows of information, 2 columns each row ("Code Number", "Description"). These codes are returned to the client dependent upon the success or failure of their initial submission request. I do not want to use a database file (csv, sqlite, etc) for the storage/access. The closest type that I can think of for how I want these codes to be shown to the client is the exception class. Correct me if I'm wrong, but from what I can tell enums do not allow strings, though this sort of structure seemed the better option initially based on how it works (e.g. 100 = "missing name in request"). Thinking about it, creating a class might be the best modus operandi. However I would appreciate more experienced advice or direction and input from those who might have been in a similar situation. Currently this is what I have: class ReturnCode { private int _code; private string _message; public ReturnCode(int code) { Code = code; } public int Code { get { return _code; } set { _code = value; _message = RetrieveMessage(value); } } public string Message { get { return _message; } } private string RetrieveMessage(int value) { string message; switch (value) { case 100: message = "Request completed successfuly"; break; case 201: message = "Missing name in request."; break; default: message = "Unexpected failure, please email for support"; break; } return message; } }

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  • Java - Class type from inside static initialization block

    - by DutrowLLC
    Is it possible to get the class type from inside the static initialization block? This is a simplified version of what I currently have:: class Person extends SuperClass { String firstName; static{ // This function is on the "SuperClass": // I'd for this function to be able to get "Person.class" without me // having to explicitly type it in but "this.class" does not work in // a static context. doSomeReflectionStuff(Person.class); // IN "SuperClass" } } This is closer to what I am doing, which is to initialize a data structure that holds information about the object and its annotations, etc... Perhaps I am using the wrong pattern? public abstract SuperClass{ static void doSomeReflectionStuff( Class<?> classType, List<FieldData> fieldDataList ){ Field[] fields = classType.getDeclaredFields(); for( Field field : fields ){ // Initialize fieldDataList } } } public abstract class Person { @SomeAnnotation String firstName; // Holds information on each of the fields, I used a Map<String, FieldData> // in my actual implementation to map strings to the field information, but that // seemed a little wordy for this example static List<FieldData> fieldDataList = new List<FieldData>(); static{ // Again, it seems dangerous to have to type in the "Person.class" // (or Address.class, PhoneNumber.class, etc...) every time. // Ideally, I'd liken to eliminate all this code from the Sub class // since now I have to copy and paste it into each Sub class. doSomeReflectionStuff(Person.class, fieldDataList); } }

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  • Development/runtime Licensing mechanism for a C# class library?

    - by Darryl
    I'm developing a .Net class library (a data provider) and I'm starting to think about how I would handle licensing the library to prospective purchasers. By licensing, I mean the mechanics of trying to prevent my library from being used by those who haven't purchased it, not the software license (i.e., Apache, Gnu, etc). I've never dealt with licensing, and in the past, I've always developed apps, not libraries. I don't want to make things difficult for my customers; know it is not possible to make it ironclad. Just some mechanism that gives me decent protection without making the customer jump through hoops or gnash their teeth. I think the mechanism would check for a valid license when the class is being used in development mode, and not in runtime mode (when the customer's software is released to their customers). I think libraries are typically sold per developer, but I'm not sure how that could be accomplished without making the mechanism odious for my customers; maybe that gets left to the honor system. I Googled this and found many approaches. Ideally, I'd like to do something that is generally accepted and common, the "right" way class libraries are licensed, if that exists, rather than making my customers deal with yet another license mechanism. A firm push in the right direction will be greatly appreciated!

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  • Dynamically class creating by using Java Reflection, java.lang.ClassNotFoundException

    - by rubby
    Hi all; i want to use reflection in java, i want to do that third class will read the name of the class as String from console. Upon reading the name of the class, it will automatically and dynamically (!) generate that class and call its writeout method. If that class is not read from input, it will not be initialized. I wrote that codes but i am always taking to "java.lang.Class.Not.Found.Exception", and i don't know how i can fix it. Can anyone help me? class class3 { public Object dynamicsinif(String className, String fieldName, String value) throws Exception { Class cls = Class.forName(className,true,null); Object obj = cls.newInstance(); Field fld = cls.getField(fieldName); fld.set(obj, value); return obj; } public void writeout3() { System.out.println("class3"); } } public class Main { public static void main(String[] args) throws Exception { System.out.println("enter the class name : "); BufferedReader reader= new BufferedReader(new InputStreamReader(System.in)); String line=reader.readLine(); String x="Text1"; try{ class3 trycls=new class3(); Object gelen=trycls.dynamicsinif(line, x, "rubby"); Class yeni=(Class)gelen; System.out.println(yeni); }catch(ClassNotFoundException ex){ System.out.print(ex.toString()); } } }

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  • Could this be considered a well-written PHP5 class?

    - by Ben Dauphinee
    I have been learning OOP principals on my own for a while, and taken a few cracks at writing classes. What I really need to know now is if I am actually using what I have learned correctly, or if I could improve as far as OOP is concerned. I have chopped a massive portion of code out of a class that I have been working on for a while now, and pasted it here. To all you skilled and knowledgeable programmers here I ask: Am I doing it wrong? class acl extends genericAPI{ // -- Copied from genericAPI class protected final function sanityCheck($what, $check, $vars){ switch($check){ case 'set': if(isset($vars[$what])){return(1);}else{return(0);} break; } } // --------------------------------- protected $db = null; protected $dataQuery = null; public function __construct(Zend_Db_Adapter_Abstract $db, $config = array()){ $this->db = $db; if(!empty($config)){$this->config = $config;} } protected function _buildQuery($selectType = null, $vars = array()){ // Removed switches for simplicity sake $this->dataQuery = $this->db->select( )->from( $this->config['table_users'], array('tf' => '(CASE WHEN count(*) > 0 THEN 1 ELSE 0 END)') )->where( $this->config['uidcol'] . ' = ?', $vars['uid'] ); } protected function _sanityRun_acl($sanitycheck, &$vars){ switch($sanitycheck){ case 'uid_set': if(!$this->sanityCheck('uid', 'set', $vars)){ throw new Exception(ERR_ACL_NOUID); } $vars['uid'] = settype($vars['uid'], 'integer'); break; } } private function user($action = null, $vars = array()){ switch($action){ case 'exists': $this->_sanityRun_acl('uid_set', $vars); $this->_buildQuery('user_exists_idcheck', $vars); return($this->db->fetchOne($this->dataQuery->__toString())); break; } } public function user_exists($uid){ return($this->user('exists', array('uid' => $uid))); } } $return = $acl_test->user_exists(1);

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  • Could this be considered a well-written class (am I using OOP correctly)?

    - by Ben Dauphinee
    I have been learning OOP principals on my own for a while, and taken a few cracks at writing classes. What I really need to know now is if I am actually using what I have learned correctly, or if I could improve as far as OOP is concerned. I have chopped a massive portion of code out of a class that I have been working on for a while now, and pasted it here. To all you skilled and knowledgeable programmers here I ask: Am I doing it wrong? class acl extends genericAPI{ // -- Copied from genericAPI class protected final function sanityCheck($what, $check, $vars){ switch($check){ case 'set': if(isset($vars[$what])){return(1);}else{return(0);} break; } } // --------------------------------- protected $db = null; protected $dataQuery = null; public function __construct(Zend_Db_Adapter_Abstract $db, $config = array()){ $this->db = $db; if(!empty($config)){$this->config = $config;} } protected function _buildQuery($selectType = null, $vars = array()){ // Removed switches for simplicity sake $this->dataQuery = $this->db->select( )->from( $this->config['table_users'], array('tf' => '(CASE WHEN count(*) > 0 THEN 1 ELSE 0 END)') )->where( $this->config['uidcol'] . ' = ?', $vars['uid'] ); } protected function _sanityRun_acl($sanitycheck, &$vars){ switch($sanitycheck){ case 'uid_set': if(!$this->sanityCheck('uid', 'set', $vars)){ throw new Exception(ERR_ACL_NOUID); } $vars['uid'] = settype($vars['uid'], 'integer'); break; } } private function user($action = null, $vars = array()){ switch($action){ case 'exists': $this->_sanityRun_acl('uid_set', $vars); $this->_buildQuery('user_exists_idcheck', $vars); return($this->db->fetchOne($this->dataQuery->__toString())); break; } } public function user_exists($uid){ return($this->user('exists', array('uid' => $uid))); } } $return = $acl_test->user_exists(1);

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  • Are there any other ways to iterate through the attributes of a custom class, excluding the in-built ones?

    - by Ricardo Altamirano
    Is there another way to iterate through only the attributes of a custom class that are not in-built (e.g. __dict__, __module__, etc.)? For example, in this code: class Terrain: WATER = -1 GRASS = 0 HILL = 1 MOUNTAIN = 2 I can iterate through all of these attributes like this: for key, value in Terrain.__dict__.items(): print("{: <11}".format(key), " --> ", value) which outputs: MOUNTAIN --> 2 __module__ --> __main__ WATER --> -1 HILL --> 1 __dict__ --> <attribute '__dict__' of 'Terrain' objects> GRASS --> 0 __weakref__ --> <attribute '__weakref__' of 'Terrain' objects> __doc__ --> None If I just want the integer arguments (a rudimentary version of an enumerated type), I can use this: for key, value in Terrain.__dict__.items(): if type(value) is int: # type(value) == int print("{: <11}".format(key), " --> ", value) this gives the expected result: MOUNTAIN --> 2 WATER --> -1 HILL --> 1 GRASS --> 0 Is it possible to iterate through only the non-in-built attributes of a custom class independent of type, e.g. if the attributes are not all integral. Presumably I could expand the conditional to include more types, but I want to know if there are other ways I'm missing.

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  • Mutate an object into an instance of one its subclasses

    - by Gohu
    Hi, Is it possible to mutate an object into an instance of a derived class of the initial's object class? Something like: class Base(): def __init__(self): self.a = 1 def mutate(self): self = Derived() class Derived(Base): def __init__(self): self.b = 2 But that doesn't work. >>> obj = Base() >>> obj.mutate() >>> obj.a 1 >>> obj.b AttributeError... If this isn't possible, how should I do otherwise? My problem is the following: My Base class is like a "summary", and the Derived class is the "whole thing". Of course getting the "whole thing" is a bit expensive so working on summaries as long as it is possible is the point of having these two classes. But you should be able to get it if you want, and then there's no point in having the summary anymore, so every reference to the summary should now be (or contain, at least) the whole thing. I guess I would have to create a class that can hold both, right? class Thing(): def __init__(self): self.summary = Summary() self.whole = None def get_whole_thing(self): self.whole = Whole()

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  • Amazon EC2 High-Memory Extra Large Instance

    - by Simpanoz
    I am new to Mongodb and EC2. If I use following single MongoDb server : High-Memory Extra Large Instance 17.1 GiB memory, 6.5 ECU (2 virtual cores with 3.25 EC2 Compute Units each), 420 GB of local instance storage, 64-bit platform As a layman, if we quantify I/O, data in MB/sec. How much I/O transactions mongodb server can handle easily, without being burnt out. Consider default settings of EC2 server with Ubuntu and MongoDb version available in AWS marketplace. Thanks in advance

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  • Determining which database instance makes biggest IO

    - by user2008937
    Assuming that I have a dedicated server on which I am running multiple instances of mysql and postresql servers. How without iotop determine which instance in particular time (proc/pid/io shows data collected in some peroid of time) makes the biggest IO (so it increases IOWAIT)? When lots of ppl do something on DB then I clearly see which instance is making the load because of high cpu usage, but I had a situation when the cpu usage was just normal, but very high iowait made a huge load on server and i had problem finding process that was making some outstanding IO

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  • Canonical configuration for multiple-instance Postfix?

    - by threecheeseopera
    I recently attempted to reconfigure an existing single-instance Postfix server (multi-homed) to support multiple MTA instances, but failed miserably (read: open relay, nastygram from ISP). It appears that there are several methods that can be used to accomplish this, and the various (and numerous) secondary sources that I found online were 'all over the map' with respect to which they used/glued together. Can anyone provide a working configuration (or tips) that use postmulti to manage a multi-instance Postfix setup?

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  • SQL Express 2008 R2 on Amazon EC2 instance: tons of free memory, poor performance

    - by gravyface
    The old SQL Express 2005 was running on a low-end single Xeon CPU Dell server, RAID 5 7200 disks, 2 GB RAM (SBS 2003). I have not done any baseline measurements on the old physical server, but the Web app is used by half a dozen people (maybe 2 concurrently), so I figured "how bad can an Amazon EC2 instance be?". It's pretty horrible: a difference of 8 seconds of load time on one screen. First of all, I'm not a SQL guru, but here's what I've tried: Had a Small Instance, now running a c1.medium (High Cpu Medium) Windows 2008 32-bit R2 EBS-backed instance running IIS 7.5 and SQL Express 2008 R2. No noticeable improvement. Changed Page File from fixed 256 to Automatic. Setup a Striped Mirror from within Disk Management with two attached 1 GB EBS volumes. Moved database and transaction log, left everything else on the boot EBS volume. No noticeable change. Looked at memory, ~1000 MB of physical memory free (1.7 GB total). Changed SQL instance to use a minimum of 1024 RAM; restarted server, no change in memory usage. SQL still only using ~28MB of RAM(!). So I'm thinking: this database is tiny (28MB), why isn't the whole thing cached in RAM? Surely that would speed up performance. The transaction log is 241 MB. Seems kind of large in comparison -- has this not been committed? Is it a cause of performance degradation? I recall something about Recovery Models and log sizes somewhere in my travels, but not positive. Another thing: the old server was running SQL Express 2005. Not sure if that has any impact, but I tried changing the compatibility level from SQL 2000 to 2008, but that had no effect. Anyways, what else can I try here? Seems ridiculous to throw more virtual hardware at this thing. I know I/O is going to be rough on EBS volumes, but surely others are successfully running small .NET/SQL apps on reasonably priced instances?

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  • Invariant code contracts – using class-wide contracts

    - by DigiMortal
    It is possible to define invariant code contracts for classes. Invariant contracts should always hold true whatever member of class is called. In this posting I will show you how to use invariant code contracts so you understand how they work and how they should be tested. This is my randomizer class I am using to demonstrate code contracts. I added one method for invariant code contracts. Currently there is one contract that makes sure that random number generator is not null. public class Randomizer {     private IRandomGenerator _generator;       private Randomizer() { }       public Randomizer(IRandomGenerator generator)     {         _generator = generator;     }       public int GetRandomFromRangeContracted(int min, int max)     {         Contract.Requires<ArgumentOutOfRangeException>(             min < max,             "Min must be less than max"         );           Contract.Ensures(             Contract.Result<int>() >= min &&             Contract.Result<int>() <= max,             "Return value is out of range"         );           return _generator.Next(min, max);     }       [ContractInvariantMethod]     private void ObjectInvariant()     {         Contract.Invariant(_generator != null);     } } Invariant code contracts are define in methods that have ContractInvariantMethod attribute. Some notes: It is good idea to define invariant methods as private. Don’t call invariant methods from your code because code contracts system does not allow it. Invariant methods are defined only as place where you can keep invariant contracts. Invariant methods are called only when call to some class member is made! The last note means that having invariant method and creating Randomizer object with null as argument does not automatically generate exception. We have to call at least one method from Randomizer class. Here is the test for generator. You can find more about contracted code testing from my posting Code Contracts: Unit testing contracted code. There is also explained why the exception handling in test is like it is. [TestMethod] [ExpectedException(typeof(Exception))] public void Should_fail_if_generator_is_null() {     try     {         var randomizer = new Randomizer(null);         randomizer.GetRandomFromRangeContracted(1, 4);     }     catch (Exception ex)     {         throw new Exception(ex.Message, ex);     } } Try out this code – with unit tests or with test application to see that invariant contracts are checked as soon as you call some member of Randomizer class.

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  • Third-Grade Math Class

    - by andyleonard
    An Odd Thing Happened... ... when I was in third grade math class: I was handed a sheet of arithmetic problems to solve. There were maybe 20 problems on the page and we were given the remainder of the class to complete them. I don't remember how much time remained in the class, I remember I finished working on the problems before my classmates. That wasn't the odd part. The odd part was that I started working on the first problem, concentrating pretty hard. I worked the sum and moved to the next...(read more)

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