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• How to design a scalable notification system?

  - by Trent

  I need to write a notification system manager. Here is my requirements: I need to be able to send a Notification on different platforms, which may be totally different (for exemple, I need to be able to send either an SMS or an E-mail). Sometimes the notification may be the same for all recipients for a given platform, but sometimes it may be a notification per recipients (or several) per platform. Each notification can contain platform specific payload (for exemple an MMS can contains a sound or an image). The system need to be scalable, I need to be able to send a very large amount of notification without crashing either the application or the server. It is a two step process, first a customer may type a message and choose a platform to send to, and the notification(s) should be created to be processed either real-time either later. Then the system needs to send the notification to the platform provider. For now, I end up with some though but I don't know how scalable it will be or if it is a good design. I've though of the following objects (in a pseudo language): a generic Notification object: class Notification { String $message; Payload $payload; Collection<Recipient> $recipients; } The problem with the following objects is what if I've 1.000.000 recipients ? Even if the Recipient object is very small, it'll take too much memory. I could also create one Notification per recipient, but some platform providers requires me to send it in batch, meaning I need to define one Notification with several Recipients. Each created notification could be stored in a persistent storage like a DB or Redis. Would it be a good it to aggregate this later to make sure it is scalable? On the second step, I need to process this notification. But how could I distinguish the notification to the right platform provider? Should I use an object like MMSNotification extending an abstract Notification? or something like Notification.setType('MMS')? To allow to process a lot of notification at the same time, I think a messaging queue system like RabbitMQ may be the right tool. Is it? It would allow me to queue a lot of notification and have several worker to pop notification and process them. But what if I need to batch the recipients as seen above? Then I imagine a NotificationProcessor object for which I could I add NotificationHandler each NotificationHandler would be in charge to connect the platform provider and perform notification. I can also use an EventManager to allow pluggable behavior. Any feedbacks or ideas? Thanks for giving your time. Note: I'm used to work in PHP and it is likely the language of my choice.

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• Best Design Pattern for Coupling User Interface Components and Data Structures

  - by szahn

  I have a windows desktop application with a tree view. Due to lack of a sound data-binding solution for a tree view, I've implemented my own layer of abstraction on it to bind nodes to my own data structure. The requirements are as follows: Populate a tree view with nodes that resemble fields in a data structure. When a node is clicked, display the appropriate control to modify the value of that property in the instance of the data structure. The tree view is populated with instances of custom TreeNode classes that inherit from TreeNode. The responsibility of each custom TreeNode class is to (1) format the node text to represent the name and value of the associated field in my data structure, (2) return the control used to modify the property value, (3) get the value of the field in the control (3) set the field's value from the control. My custom TreeNode implementation has a property called "Control" which retrieves the proper custom control in the form of the base control. The control instance is stored in the custom node and instantiated upon first retrieval. So each, custom node has an associated custom control which extends a base abstract control class. Example TreeNode implementation: //The Tree Node Base Class public abstract class TreeViewNodeBase : TreeNode { public abstract CustomControlBase Control { get; } public TreeViewNodeBase(ExtractionField field) { UpdateControl(field); } public virtual void UpdateControl(ExtractionField field) { Control.UpdateControl(field); UpdateCaption(FormatValueForCaption()); } public virtual void SaveChanges(ExtractionField field) { Control.SaveChanges(field); UpdateCaption(FormatValueForCaption()); } public virtual string FormatValueForCaption() { return Control.FormatValueForCaption(); } public virtual void UpdateCaption(string newValue) { this.Text = Caption; this.LongText = newValue; } } //The tree node implementation class public class ExtractionTypeNode : TreeViewNodeBase { private CustomDropDownControl control; public override CustomControlBase Control { get { if (control == null) { control = new CustomDropDownControl(); control.label1.Text = Caption; control.comboBox1.Items.Clear(); control.comboBox1.Items.AddRange( Enum.GetNames( typeof(ExtractionField.ExtractionType))); } return control; } } public ExtractionTypeNode(ExtractionField field) : base(field) { } } //The custom control base class public abstract class CustomControlBase : UserControl { public abstract void UpdateControl(ExtractionField field); public abstract void SaveChanges(ExtractionField field); public abstract string FormatValueForCaption(); } //The custom control generic implementation (view) public partial class CustomDropDownControl : CustomControlBase { public CustomDropDownControl() { InitializeComponent(); } public override void UpdateControl(ExtractionField field) { //Nothing to do here } public override void SaveChanges(ExtractionField field) { //Nothing to do here } public override string FormatValueForCaption() { //Nothing to do here return string.Empty; } } //The custom control specific implementation public class FieldExtractionTypeControl : CustomDropDownControl { public override void UpdateControl(ExtractionField field) { comboBox1.SelectedIndex = comboBox1.FindStringExact(field.Extraction.ToString()); } public override void SaveChanges(ExtractionField field) { field.Extraction = (ExtractionField.ExtractionType) Enum.Parse(typeof(ExtractionField.ExtractionType), comboBox1.SelectedItem.ToString()); } public override string FormatValueForCaption() { return string.Empty; } The problem is that I have "generic" controls which inherit from CustomControlBase. These are just "views" with no logic. Then I have specific controls that inherit from the generic controls. I don't have any functions or business logic in the generic controls because the specific controls should govern how data is associated with the data structure. What is the best design pattern for this?

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• Design for a plugin based application

  - by Varun Naik

  I am working on application, details of which I cannot discuss here. We have core framework and the rest is designed as plug in. In the core framework we have a domain object. This domain object is updated by the plugins. I have defined an interface in which I have function as DomainObject doProcessing(DomainObject object) My intention here is I pass the domain object, the plug in will update it and return it. This updated object is then passed again to different plugin to be updated. I am not sure if this is a good approach. I don't like passing the DomainObject to plugin. Is there a better way I can achieve this? Should I just request data from plugin and update the domain object myself?

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• Class Design and Structure Online Web Store

  - by Phorce

  I hope I have asked this in the right forum. Basically, we're designing an Online Store and I am designing the class structure for ordering a product and want some clarification on what I have so far: So a customer comes, selects their product, chooses the quantity and selects 'Purchase' (I am using the Facade Pattern - So subsystems execute when this action is performed). My class structure: < Order > < Product > <Customer > There is no inheritance, more Association < Order has < Product , < Customer has < Order . Does this structure look ok? I've noticed that I don't handle the "Quantity" separately, I was just going to add this into the "Product" class, but, do you think it should be a class of it's own? Hope someone can help.

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• design a model for a system of dependent variables

  - by dbaseman

  I'm dealing with a modeling system (financial) that has dozens of variables. Some of the variables are independent, and function as inputs to the system; most of them are calculated from other variables (independent and calculated) in the system. What I'm looking for is a clean, elegant way to: define the function of each dependent variable in the system trigger a re-calculation, whenever a variable changes, of the variables that depend on it A naive way to do this would be to write a single class that implements INotifyPropertyChanged, and uses a massive case statement that lists out all the variable names x1, x2, ... xn on which others depend, and, whenever a variable xi changes, triggers a recalculation of each of that variable's dependencies. I feel that this naive approach is flawed, and that there must be a cleaner way. I started down the path of defining a CalculationManager<TModel> class, which would be used (in a simple example) something like as follows: public class Model : INotifyPropertyChanged { private CalculationManager<Model> _calculationManager = new CalculationManager<Model>(); // each setter triggers a "PropertyChanged" event public double? Height { get; set; } public double? Weight { get; set; } public double? BMI { get; set; } public Model() { _calculationManager.DefineDependency<double?>( forProperty: model => model.BMI, usingCalculation: (height, weight) => weight / Math.Pow(height, 2), withInputs: model => model.Height, model.Weight); } // INotifyPropertyChanged implementation here } I won't reproduce CalculationManager<TModel> here, but the basic idea is that it sets up a dependency map, listens for PropertyChanged events, and updates dependent properties as needed. I still feel that I'm missing something major here, and that this isn't the right approach: the (mis)use of INotifyPropertyChanged seems to me like a code smell the withInputs parameter is defined as params Expression<Func<TModel, T>>[] args, which means that the argument list of usingCalculation is not checked at compile time the argument list (weight, height) is redundantly defined in both usingCalculation and withInputs I am sure that this kind of system of dependent variables must be common in computational mathematics, physics, finance, and other fields. Does someone know of an established set of ideas that deal with what I'm grasping at here? Would this be a suitable application for a functional language like F#? Edit More context: The model currently exists in an Excel spreadsheet, and is being migrated to a C# application. It is run on-demand, and the variables can be modified by the user from the application's UI. Its purpose is to retrieve variables that the business is interested in, given current inputs from the markets, and model parameters set by the business.

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• Design for object with optional and modifiable attributtes?

  - by Ikuzen

  I've been using the Builder pattern to create objects with a large number of attributes, where most of them are optional. But up until now, I've defined them as final, as recommended by Joshua Block and other authors, and haven't needed to change their values. I am wondering what should I do though if I need a class with a substantial number of optional but non-final (mutable) attributes? My Builder pattern code looks like this: public class Example { //All possible parameters (optional or not) private final int param1; private final int param2; //Builder class public static class Builder { private final int param1; //Required parameters private int param2 = 0; //Optional parameters - initialized to default //Builder constructor public Builder (int param1) { this.param1 = param1; } //Setter-like methods for optional parameters public Builder param2(int value) { param2 = value; return this; } //build() method public Example build() { return new Example(this); } } //Private constructor private Example(Builder builder) { param1 = builder.param1; param2 = builder.param2; } } Can I just remove the final keyword from the declaration to be able to access the attributes externally (through normal setters, for example)? Or is there a creational pattern that allows optional but non-final attributes that would be better suited in this case?

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• Caching factory design

  - by max

  I have a factory class XFactory that creates objects of class X. Instances of X are very large, so the main purpose of the factory is to cache them, as transparently to the client code as possible. Objects of class X are immutable, so the following code seems reasonable: # module xfactory.py import x class XFactory: _registry = {} def get_x(self, arg1, arg2, use_cache = True): if use_cache: hash_id = hash((arg1, arg2)) if hash_id in _registry: return _registry[hash_id] obj = x.X(arg1, arg2) _registry[hash_id] = obj return obj # module x.py class X: # ... Is it a good pattern? (I know it's not the actual Factory Pattern.) Is there anything I should change? Now, I find that sometimes I want to cache X objects to disk. I'll use pickle for that purpose, and store as values in the _registry the filenames of the pickled objects instead of references to the objects. Of course, _registry itself would have to be stored persistently (perhaps in a pickle file of its own, in a text file, in a database, or simply by giving pickle files the filenames that contain hash_id). Except now the validity of the cached object depends not only on the parameters passed to get_x(), but also on the version of the code that created these objects. Strictly speaking, even a memory-cached object could become invalid if someone modifies x.py or any of its dependencies, and reloads it while the program is running. So far I ignored this danger since it seems unlikely for my application. But I certainly cannot ignore it when my objects are cached to persistent storage. What can I do? I suppose I could make the hash_id more robust by calculating hash of a tuple that contains arguments arg1 and arg2, as well as the filename and last modified date for x.py and every module and data file that it (recursively) depends on. To help delete cache files that won't ever be useful again, I'd add to the _registry the unhashed representation of the modified dates for each record. But even this solution isn't 100% safe since theoretically someone might load a module dynamically, and I wouldn't know about it from statically analyzing the source code. If I go all out and assume every file in the project is a dependency, the mechanism will still break if some module grabs data from an external website, etc.). In addition, the frequency of changes in x.py and its dependencies is quite high, leading to heavy cache invalidation. Thus, I figured I might as well give up some safety, and only invalidate the cache only when there is an obvious mismatch. This means that class X would have a class-level cache validation identifier that should be changed whenever the developer believes a change happened that should invalidate the cache. (With multiple developers, a separate invalidation identifier is required for each.) This identifier is hashed along with arg1 and arg2 and becomes part of the hash keys stored in _registry. Since developers may forget to update the validation identifier or not realize that they invalidated existing cache, it would seem better to add another validation mechanism: class X can have a method that returns all the known "traits" of X. For instance, if X is a table, I might add the names of all the columns. The hash calculation will include the traits as well. I can write this code, but I am afraid that I'm missing something important; and I'm also wondering if perhaps there's a framework or package that can do all of this stuff already. Ideally, I'd like to combine in-memory and disk-based caching.

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• Learning how to design knowledge and data flow [closed]

  - by max

  In designing software, I spend a lot of time deciding how the knowledge (algorithms / business logic) and data should be allocated between different entities; that is, which object should know what. I am asking for advice about books, articles, presentations, classes, or other resources that would help me learn how to do it better. I code primarily in Python, but my question is not really language-specific; even if some of the insights I learn don't work in Python, that's fine. I'll give a couple examples to clarify what I mean. Example 1 I want to perform some computation. As a user, I will need to provide parameters to do the computation. I can have all those parameters sent to the "main" object, which then uses them to create other objects as needed. Or I can create one "main" object, as well as several additional objects; the additional objects would then be sent to the "main" object as parameters. What factors should I consider to make this choice? Example 2 Let's say I have a few objects of type A that can perform a certain computation. The main computation often involves using an object of type B that performs some interim computation. I can either "teach" A instances what exact parameters to pass to B instances (i.e., make B "dumb"); or I can "teach" B instances to figure out what needs to be done when looking at an A instance (i.e., make B "smart"). What should I think about when I'm making this choice?

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• High-Level Application Architecture Question

  - by Jesse Bunch

  So I'm really wanting to improve how I architect the software I code. I want to focus on maintainability and clean code. As you might guess, I've been reading a lot of resources on this topic and all it's doing is making it harder for me to settle on an architecture because I can never tell if my design is the one that the more experienced programmer would've chosen. So I have these requirements: I should connect to one vendor and download form submissions from their API. We'll call them the CompanyA. I should then map those submissions to a schema fit for submitting to another vendor for integration with the email service provider. We'll call them the CompanyB. I should then submit those responses to the ESP (CompanyB) and then instruct the ESP to send that submitter an email. So basically, I'm copying data from one web service to another and then performing an action at the latter web service. I've identified a couple high-level services: The service that downloads data from CompanyA. I called this the CompanyAIntegrator. The service that submits the data to CompanyB. I called this CompanyBIntegrator. So my questions are these: Is this a good design? I've tried to separate the concerns and am planning to use the facade pattern to make the integrators interchangeable if the vendors change in the future. Are my naming conventions accurate and meaningful to you (who knows nothing specific of the project)? Now that I have these services, where should I do the work of taking output from the CompanyAIntegrator and getting it in the format for input to the CompanyBIntegrator? Is this OK to be done in main()? Do you have any general pointers on how you'd code something like this? I imagine this scenario is common to us engineers---especially those working in agencies. Thanks for any help you can give. Learning how to architect well is really mind-cluttering.

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• How bad is it to have two methods with the same name but different signatures in two classes?

  - by Super User

  I have a design problem related to a public interface, the names of methods, and the understanding of my API and code. I have two classes like this: class A: ... function collision(self): .... ... class B: .... function _collision(self, another_object, l, r, t, b): .... The first class has one public method named collision, and the second has one private method called _collision. The two methods differs in argument type and number. As an example let's say that _collision checks if the object is colliding with another object with certain conditions l, r, t, b (collide on the left side, right side, etc) and returns true or false. The public collision method, on the other hand, resolves all the collisions of the object with other objects. The two methods have the same name because I think it's better to avoid overloading the design with different names for methods that do almost the same thing, but in distinct contexts and classes. Is this clear enough to the reader or I should change the method's name?

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• How bad it's have two methods with the same name but differents signatures in two classes?

  - by Super User

  I have a design problem relationated with the public interface, the names of methods and the understanding of my API and my code. I have two classes like this: class A: ... function collision(self): .... ... class B: .... function _collision(self, another_object, l, r, t, b): .... The first class have one public method named collision and the second have one private method called _collision. The two methods differs in arguments type and number. In the API _m method is private. For the example let's say that the _collision method checks if the object is colliding with another_ object with certain conditions l, r, t, b (for example, collide the left side, the right side, etc) and returns true or false according to the case. The collision method, on the other hand, resolves all the collisions of the object with other objects. The two methods have the same name because I think is better avoid overload the design with different names for methods who do almost the same think, but in distinct contexts and classes. This is clear enough to the reader or I should change the method's name?

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• In database table design, how does "Virtual Goods" affect table design -- should we create an instan

  - by Jian Lin

  When we design a database table for a DVD rental company, we actually have a movie, which is an abstract idea, and a physical DVD, so for each rental, we have a many-to-many table with fields such as: TransactionID UserID DvdID RentedDate RentalDuration AmountPaid but what about with virtual goods? For example, if we let a user rent a movie online for 3 days, we don't actually have a DVD, so we may have a table: TransactionID UserID MovieID RentedDate RentalDuration AmountPaid should we create a record for each instance of "virtual good"? For example, what if this virtual good (the movie) can be authorized to be watched on 3 devices (with 3 device IDs), then should we then create a virtual good record in the VirtualGoods table, each with a VirtualGoodID and then another table that has VirtualGoodID DeviceID to match up the movie with the DeviceIDs? We can also just use the TransactionID as the VirtualGoodID. Are there circumstances where we may want to create a record to record this "virtual good" in a VirtualGoods table?

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• Templates for forms, tabs etc? - Patterntap alternatives

  - by Marco Demaio

  I used to find http://www.patterntap.com quite useful to get design inspiration for forms, tabs, and other web elements etc. Unfortunately after the ZURB acquisition of Patterntap now they enforce you to sign in with your Twitter account in order to simply view larger images of patterns provided by the crowd. So in some way it's not free anymore. Do you know of alternatives to patterntap that are free and you are not obliged to sign in?

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• Representing complex object dependencies

  - by max

  I have several classes with a reasonably complex (but acyclic) dependency graph. All the dependencies are of the form: class X instance contains an attribute of class Y. All such attributes are set during initialization and never changed again. Each class' constructor has just a couple parameters, and each object knows the proper parameters to pass to the constructors of the objects it contains. class Outer is at the top of the dependency hierarchy, i.e., no class depends on it. Currently, the UI layer only creates an Outer instance; the parameters for Outer constructor are derived from the user input. Of course, Outer in the process of initialization, creates the objects it needs, which in turn create the objects they need, and so on. The new development is that the a user who knows the dependency graph may want to reach deep into it, and set the values of some of the arguments passed to constructors of the inner classes (essentially overriding the values used currently). How should I change the design to support this? I could keep the current approach where all the inner classes are created by the classes that need them. In this case, the information about "user overrides" would need to be passed to Outer class' constructor in some complex user_overrides structure. Perhaps user_overrides could be the full logical representation of the dependency graph, with the overrides attached to the appropriate edges. Outer class would pass user_overrides to every object it creates, and they would do the same. Each object, before initializing lower level objects, will find its location in that graph and check if the user requested an override to any of the constructor arguments. Alternatively, I could rewrite all the objects' constructors to take as parameters the full objects they require. Thus, the creation of all the inner objects would be moved outside the whole hierarchy, into a new controller layer that lies between Outer and UI layer. The controller layer would essentially traverse the dependency graph from the bottom, creating all the objects as it goes. The controller layer would have to ask the higher-level objects for parameter values for the lower-level objects whenever the relevant parameter isn't provided by the user. Neither approach looks terribly simple. Is there any other approach? Has this problem come up enough in the past to have a pattern that I can read about? I'm using Python, but I don't think it matters much at the design level.

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• What do you do if you reach a design dead-end in evolutionary methods like Agile or XP?

  - by Dipan Mehta

  As I was reading Martin Fowler's famous blog post Is Design Dead?, one of the striking impressions I got is that given the fact that in Agile Methodology and Extreme Programming, the design as well as programming is evolutionary, there are always points where things need to get refactored. It may be possible that when a programmer's level is good, and they understand design implications and don't make critical mistakes, the code continues to evolve. However, in a normal context, what is the ground reality in this context? In a normal day given some significant development goes into product, and when critical change occurs in requirement isn't it a constraint that how much ever we wish, fundamental design aspects cannot be modified? (without throwing away major part of the code). Is it not quite likely that one reaches dead-end on any further possible improvement on design and requirements? I am not advocating any non-Agile practice here, but I want to know from people who practice agile or iterative or evolutionary development methods, as for their real experiences. Have you ever reached such dead-ends? How have you managed to avoid it or escaped it? Or are there measures to ensure that design remains clean and flexible as it evolves?

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• Object oriented wrapper around a dll

  - by Tom Davies

  So, I'm writing a C# managed wrapper around a native dll. The dll contains several hundred functions. In most cases, the first argument to each function is an opaque handle to a type internal to the dll. So, an obvious starting point for defining some classes in the wrapper would be to define classes corresponding to each of these opaque types, with each instance holding and managing the opaque handle (passed to its constructor) Things are a little awkward when dealing with callbacks from the dll. Naturally, the callback handlers in my wrapper have to be static, but the callbacks arguments invariable contain an opaque handle. In order to get from the static callback back to an object instance, I've created a static dictionary in each class, associating handles with class instances. In the constructor of each class, an entry is put into the dictionary, and this entry is then removed in the Destructors. When I receive a callback, I can then consult the dictionary to retrieve the class instance corresponding to the opaque reference. Are there any obvious flaws to this? Something that seems to be a problem is that the existence static dictionary means that the garbage collector will not act on my class instances that are otherwise unreachable. As they are never garbage collected, they never get removed from the dictionary, so the dictionary grows. It seems I might have to manually dispose of my objects, which is something absolutely would like to avoid. Can anyone suggest a good design that allows me to avoid having to do this?

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• How do we keep dependent data structures up to date?

  - by Geo

  Suppose you have a parse tree, an abstract syntax tree, and a control flow graph, each one logically derived from the one before. In principle it is easy to construct each graph given the parse tree, but how can we manage the complexity of updating the graphs when the parse tree is modified? We know exactly how the tree has been modified, but how can the change be propagated to the other trees in a way that doesn't become difficult to manage? Naturally the dependent graph can be updated by simply reconstructing it from scratch every time the first graph changes, but then there would be no way of knowing the details of the changes in the dependent graph. I currently have four ways to attempt to solve this problem, but each one has difficulties. Nodes of the dependent tree each observe the relevant nodes of the original tree, updating themselves and the observer lists of original tree nodes as necessary. The conceptual complexity of this can become daunting. Each node of the original tree has a list of the dependent tree nodes that specifically depend upon it, and when the node changes it sets a flag on the dependent nodes to mark them as dirty, including the parents of the dependent nodes all the way down to the root. After each change we run an algorithm that is much like the algorithm for constructing the dependent graph from scratch, but it skips over any clean node and reconstructs each dirty node, keeping track of whether the reconstructed node is actually different from the dirty node. This can also get tricky. We can represent the logical connection between the original graph and the dependent graph as a data structure, like a list of constraints, perhaps designed using a declarative language. When the original graph changes we need only scan the list to discover which constraints are violated and how the dependent tree needs to change to correct the violation, all encoded as data. We can reconstruct the dependent graph from scratch as though there were no existing dependent graph, and then compare the existing graph and the new graph to discover how it has changed. I'm sure this is the easiest way because I know there are algorithms available for detecting differences, but they are all quite computationally expensive and in principle it seems unnecessary so I'm deliberately avoiding this option. What is the right way to deal with these sorts of problems? Surely there must be a design pattern that makes this whole thing almost easy. It would be nice to have a good solution for every problem of this general description. Does this class of problem have a name?

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• How to avoid having very large objects with Domain Driven Design

  - by Pablojim

  We are following Domain Driven Design for the implementation of a large website. However by putting the behaviour on the domain objects we are ending up with some very large classes. For example on our WebsiteUser object, we have many many methods - e.g. dealing with passwords, order history, refunds, customer segmentation. All of these methods are directly related to the user. Many of these methods delegate internally to other child object but this still results in some very large classes. I'm keen to avoid exposing lots of child objects e.g. user.getOrderHistory().getLatestOrder(). What other strategies can be used to avoid this problems?

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• Subclassing to avoid line length

  - by Super User

  The standard line length of code is 80 characters per line. This is accepted and followed by the most of programmers. I working on a state machine of a character and is necessary for me follow this too. I have four classes who pass this limit. I can subclass each class in two more and then avoid the line length limit. class Stand class Walk class Punch class Crouch The new classes would be StandLeft, StandRight and so on. Stand, Walk, Punch and Crouch would be then abstract classes. The question if there is a limit for the long of the hierarchies tree or this is depends of the case.

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• Why should ViewModel route actions to Controller when using the MVCVM pattern?

  - by Lea Hayes

  When reading examples across the Internet (including the MSDN reference) I have found that code examples are all doing the following type of thing: public class FooViewModel : BaseViewModel { public FooViewModel(FooController controller) { Controller = controller; } protected FooController Controller { get; private set; } public void PerformSuperAction() { // This just routes action to controller... Controller.SuperAction(); } ... } and then for the view: public class FooView : BaseView { ... private void OnSuperButtonClicked() { ViewModel.PerformSuperAction(); } } Why do we not just do the following? public class FooView : BaseView { ... private void OnSuperButtonClicked() { ViewModel.Controller.SuperAction(); // or, even just use a shortcut property: Controller.SuperAction(); } }

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• How do I handle priority and propagation in an event system?

  - by Peeter

  Lets say I have a simple event system with the following syntax: object = new Object(); object.bind("my_trigger", function() { print "hello"; }); object.bind("my_trigger", function() { print "hello2"; }); object.trigger("my_trigger"); How could I make sure hello2 is printed out first (I do not want my code to depend on which order the events are binded). Ontop of that, how would I prevent my events from propagating (e.g. I want to stop every other event from being executed)

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• DDD: service contains two repository

  - by tikhop

  Does it correct way to have two repository inside one service and will it be an application or domain service? Suppose I have a Passenger object that should contains Passport (government id) object. I am getting Passenger from PassengerRepository. PassengerRepository create request to server and obtain data (json) than parse received data and store inside repository. I have confused because I want to store Passport as Entity and put it to PassportRepository but all information about password contains inside json than i received above. I guess that I should create a PassengerService that will be include PassengerRepository and PassportRepository with several methods like removePassport, addPassport, getAllPassenger and etc. UPDATE: So I guess that the better way is represent Passport as VO and store all passports inside Passenger aggregate. However there is another question: Where I should put the methods (methods calls server api) for management passenger's passport. I think the better place is so within Passenger aggregate.

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• Should database-models (conceptual or physical) be reviewed by DBAs?

  - by user61852

  Where I work, new applications that are being developed that will use their own relational database, must have their database-models (conceptual, then physical ) reviewed and aproved by DBAs. Things looked after are normalization, antipatterns, table and column naming standards, etc. Is this really a DBA's responsability to do this ? or should it be, in a greater extend, the responsability of app designers and architects ?

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• NEC uPD720200 USB 3.0 not working on Ubuntu 12.04

  - by Jagged

  I've recently installed Ubuntu 12.04 64-bit on a HP Envy 15 1104tx. Most stuff appears to be working fine with the exception of the two USB3 ports (USB2 port works fine). I've read a lot of articles but so far have not been able to find a solution. I've tried adding 'pci=nomsi' to '/etc/default/grub' but this made no difference. Some articles suggest booting into Windows and upgrading the firmware on the uPD720200. Any body had any experience of this? Is there a way I can checked the firmware version of the NEC uPD720200 in Linux to see if there is an update available? Any help appreciated. uname -a: Linux HP-ENVY-15-1104tx 3.2.0-26-generic #41-Ubuntu SMP Thu Jun 14 17:49:24 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux lshw: hp-envy-15-1104tx description: Notebook product: HP ENVY 15 Notebook PC (WF591PA#ABG) vendor: Hewlett-Packard version: 0492110000241910001420000 serial: CNF0301C79 width: 64 bits capabilities: smbios-2.6 dmi-2.6 vsyscall32 configuration: boot=normal chassis=notebook family=103C_5335KV sku=WF591PA#ABG uuid=434E4630-3330-3143-3739-60EB6906688F *-core description: Motherboard product: 1522 vendor: Hewlett-Packard physical id: 0 version: 36.35 serial: CNF0301C79 slot: Base Board Chassis Location *-firmware description: BIOS vendor: Hewlett-Packard physical id: 0 version: F.2B date: 10/12/2010 size: 1MiB capacity: 1472KiB capabilities: pci upgrade shadowing cdboot bootselect edd int13floppynec int13floppytoshiba int13floppy360 int13floppy1200 int13floppy720 int13floppy2880 int9keyboard int10video acpi usb biosbootspecification *-memory description: System Memory physical id: 13 slot: System board or motherboard size: 16GiB *-bank:0 description: SODIMM DDR3 Synchronous 1333 MHz (0.8 ns) product: 9905428-043.A00LF physical id: 0 serial: E13C4316 slot: Bottom size: 4GiB width: 64 bits clock: 1333MHz (0.8ns) *-bank:1 description: SODIMM DDR3 Synchronous 1333 MHz (0.8 ns) product: 9905428-043.A00LF physical id: 1 serial: E03C3E16 slot: Bottom size: 4GiB width: 64 bits clock: 1333MHz (0.8ns) *-bank:2 description: SODIMM DDR3 Synchronous 1333 MHz (0.8 ns) product: 9905428-043.A00LF physical id: 2 serial: 672279CC slot: On Board size: 4GiB width: 64 bits clock: 1333MHz (0.8ns) *-bank:3 description: SODIMM DDR3 Synchronous 1333 MHz (0.8 ns) product: 9905428-043.A00LF physical id: 3 serial: 652286CC slot: On Board size: 4GiB width: 64 bits clock: 1333MHz (0.8ns) *-cpu description: CPU product: Intel(R) Core(TM) i7 CPU Q 820 @ 1.73GHz vendor: Intel Corp. physical id: 1d bus info: cpu@0 version: Intel(R) Core(TM) i7 CPU Q 820 @ 1.73GHz slot: CPU size: 1199MHz capacity: 1199MHz width: 64 bits clock: 1066MHz capabilities: x86-64 fpu fpu_exception wp vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx rdtscp constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf pni dtes64 monitor ds_cpl vmx smx est tm2 ssse3 cx16 xtpr pdcm sse4_1 sse4_2 popcnt lahf_lm ida tpr_shadow vnmi flexpriority ept vpid cpufreq configuration: cores=4 enabledcores=4 threads=8 *-cache:0 description: L3 cache physical id: 1e slot: L3 Cache size: 8MiB capacity: 8MiB capabilities: synchronous internal write-through unified *-cache:1 description: L2 cache physical id: 20 slot: L2 Cache size: 256KiB capacity: 256KiB capabilities: synchronous internal write-through unified *-cache:2 description: L1 cache physical id: 21 slot: L1 Cache size: 32KiB capacity: 32KiB capabilities: synchronous internal write-through instruction *-cache description: L1 cache physical id: 1f slot: L1 Cache size: 32KiB capacity: 32KiB capabilities: synchronous internal write-through data *-pci:0 description: Host bridge product: Core Processor DMI vendor: Intel Corporation physical id: 100 bus info: pci@0000:00:00.0 version: 11 width: 32 bits clock: 33MHz *-pci:0 description: PCI bridge product: Core Processor PCI Express Root Port 1 vendor: Intel Corporation physical id: 3 bus info: pci@0000:00:03.0 version: 11 width: 32 bits clock: 33MHz capabilities: pci msi pciexpress pm normal_decode bus_master cap_list configuration: driver=pcieport resources: irq:16 ioport:4000(size=4096) memory:d4100000-d41fffff ioport:c0000000(size=268435456) *-display description: VGA compatible controller product: Broadway PRO [Mobility Radeon HD 5800 Series] vendor: Hynix Semiconductor (Hyundai Electronics) physical id: 0 bus info: pci@0000:01:00.0 version: 00 width: 64 bits clock: 33MHz capabilities: pm pciexpress msi vga_controller bus_master cap_list rom configuration: driver=fglrx_pci latency=0 resources: irq:58 memory:c0000000-cfffffff memory:d4100000-d411ffff ioport:4000(size=256) memory:d4140000-d415ffff *-multimedia description: Audio device product: Juniper HDMI Audio [Radeon HD 5700 Series] vendor: Hynix Semiconductor (Hyundai Electronics) physical id: 0.1 bus info: pci@0000:01:00.1 version: 00 width: 64 bits clock: 33MHz capabilities: pm pciexpress msi bus_master cap_list configuration: driver=snd_hda_intel latency=0 resources: irq:56 memory:d4120000-d4123fff *-pci:1 description: PCI bridge product: Core Processor PCI Express Root Port 3 vendor: Intel Corporation physical id: 5 bus info: pci@0000:00:05.0 version: 11 width: 32 bits clock: 33MHz capabilities: pci msi pciexpress pm normal_decode bus_master cap_list configuration: driver=pcieport resources: irq:16 memory:d4000000-d40fffff *-usb description: USB controller product: uPD720200 USB 3.0 Host Controller vendor: NEC Corporation physical id: 0 bus info: pci@0000:02:00.0 version: 03 width: 64 bits clock: 33MHz capabilities: pm msi msix pciexpress xhci bus_master cap_list configuration: driver=xhci_hcd latency=0 resources: irq:16 memory:d4000000-d4001fff *-generic:0 UNCLAIMED description: System peripheral product: Core Processor System Management Registers vendor: Intel Corporation physical id: 8 bus info: pci@0000:00:08.0 version: 11 width: 32 bits clock: 33MHz capabilities: pciexpress cap_list configuration: latency=0 *-generic:1 UNCLAIMED description: System peripheral product: Core Processor Semaphore and Scratchpad Registers vendor: Intel Corporation physical id: 8.1 bus info: pci@0000:00:08.1 version: 11 width: 32 bits clock: 33MHz capabilities: pciexpress cap_list configuration: latency=0 *-generic:2 UNCLAIMED description: System peripheral product: Core Processor System Control and Status Registers vendor: Intel Corporation physical id: 8.2 bus info: pci@0000:00:08.2 version: 11 width: 32 bits clock: 33MHz capabilities: pciexpress cap_list configuration: latency=0 *-generic:3 UNCLAIMED description: System peripheral product: Core Processor Miscellaneous Registers vendor: Intel Corporation physical id: 8.3 bus info: pci@0000:00:08.3 version: 11 width: 32 bits clock: 33MHz configuration: latency=0 *-generic:4 UNCLAIMED description: System peripheral product: Core Processor QPI Link vendor: Intel Corporation physical id: 10 bus info: pci@0000:00:10.0 version: 11 width: 32 bits clock: 33MHz configuration: latency=0 *-generic:5 UNCLAIMED description: System peripheral product: Core Processor QPI Routing and Protocol Registers vendor: Intel Corporation physical id: 10.1 bus info: pci@0000:00:10.1 version: 11 width: 32 bits clock: 33MHz configuration: latency=0 *-multimedia description: Audio device product: 5 Series/3400 Series Chipset High Definition Audio vendor: Intel Corporation physical id: 1b bus info: pci@0000:00:1b.0 version: 05 width: 64 bits clock: 33MHz capabilities: pm msi pciexpress bus_master cap_list configuration: driver=snd_hda_intel latency=0 resources: irq:55 memory:d4200000-d4203fff *-pci:2 description: PCI bridge product: 5 Series/3400 Series Chipset PCI Express Root Port 1 vendor: Intel Corporation physical id: 1c bus info: pci@0000:00:1c.0 version: 05 width: 32 bits clock: 33MHz capabilities: pci pciexpress msi pm normal_decode bus_master cap_list configuration: driver=pcieport resources: irq:17 ioport:3000(size=4096) memory:d3000000-d3ffffff ioport:d0000000(size=16777216) *-network description: Wireless interface product: Centrino Advanced-N 6200 vendor: Intel Corporation physical id: 0 bus info: pci@0000:03:00.0 logical name: wlan0 version: 35 serial: 00:27:10:40:e4:68 width: 64 bits clock: 33MHz capabilities: pm msi pciexpress bus_master cap_list ethernet physical wireless configuration: broadcast=yes driver=iwlwifi driverversion=3.2.0-26-generic firmware=9.221.4.1 build 25532 latency=0 link=no multicast=yes wireless=IEEE 802.11abgn resources: irq:54 memory:d3000000-d3001fff *-pci:3 description: PCI bridge product: 5 Series/3400 Series Chipset PCI Express Root Port 2 vendor: Intel Corporation physical id: 1c.1 bus info: pci@0000:00:1c.1 version: 05 width: 32 bits clock: 33MHz capabilities: pci pciexpress msi pm normal_decode bus_master cap_list configuration: driver=pcieport resources: irq:16 ioport:2000(size=4096) memory:d2000000-d2ffffff ioport:d1000000(size=16777216) *-network description: Ethernet interface product: AR8131 Gigabit Ethernet vendor: Atheros Communications Inc. physical id: 0 bus info: pci@0000:04:00.0 logical name: eth0 version: c0 serial: 60:eb:69:06:68:8f size: 1Gbit/s capacity: 1Gbit/s width: 64 bits clock: 33MHz capabilities: pm msi pciexpress vpd bus_master cap_list ethernet physical tp 10bt 10bt-fd 100bt 100bt-fd 1000bt-fd autonegotiation configuration: autonegotiation=on broadcast=yes driver=atl1c driverversion=1.0.1.0-NAPI duplex=full firmware=N/A ip=10.161.0.147 latency=0 link=yes multicast=yes port=twisted pair speed=1Gbit/s resources: irq:57 memory:d2000000-d203ffff ioport:2000(size=128) *-usb description: USB controller product: 5 Series/3400 Series Chipset USB2 Enhanced Host Controller vendor: Intel Corporation physical id: 1d bus info: pci@0000:00:1d.0 version: 05 width: 32 bits clock: 33MHz capabilities: pm debug ehci bus_master cap_list configuration: driver=ehci_hcd latency=0 resources: irq:20 memory:d4205800-d4205bff *-pci:4 description: PCI bridge product: 82801 Mobile PCI Bridge vendor: Intel Corporation physical id: 1e bus info: pci@0000:00:1e.0 version: a5 width: 32 bits clock: 33MHz capabilities: pci subtractive_decode bus_master cap_list *-isa description: ISA bridge product: Mobile 5 Series Chipset LPC Interface Controller vendor: Intel Corporation physical id: 1f bus info: pci@0000:00:1f.0 version: 05 width: 32 bits clock: 33MHz capabilities: isa bus_master cap_list configuration: latency=0 *-storage description: RAID bus controller product: 82801 Mobile SATA Controller [RAID mode] vendor: Intel Corporation physical id: 1f.2 bus info: pci@0000:00:1f.2 logical name: scsi0 version: 05 width: 32 bits clock: 66MHz capabilities: storage msi pm bus_master cap_list emulated configuration: driver=ahci latency=0 resources: irq:45 ioport:5048(size=8) ioport:5054(size=4) ioport:5040(size=8) ioport:5050(size=4) ioport:5020(size=32) memory:d4205000-d42057ff *-disk description: ATA Disk product: OCZ-VERTEX3 physical id: 0.0.0 bus info: scsi@0:0.0.0 logical name: /dev/sda version: 2.15 serial: OCZ-0350P6H316X5KUQE size: 223GiB (240GB) capabilities: partitioned partitioned:dos configuration: ansiversion=5 signature=000592dd *-volume:0 description: EXT4 volume vendor: Linux physical id: 1 bus info: scsi@0:0.0.0,1 logical name: /dev/sda1 logical name: / version: 1.0 serial: e741f18c-cfc5-4bce-b1e7-f80e517a3a22 size: 207GiB capacity: 207GiB capabilities: primary bootable journaled extended_attributes large_files huge_files dir_nlink recover extents ext4 ext2 initialized configuration: created=2012-06-15 06:49:27 filesystem=ext4 lastmountpoint=/ modified=2012-06-14 21:23:42 mount.fstype=ext4 mount.options=rw,relatime,errors=remount-ro,user_xattr,barrier=1,data=ordered mounted=2012-07-10 16:18:20 state=mounted *-volume:1 description: Extended partition physical id: 2 bus info: scsi@0:0.0.0,2 logical name: /dev/sda2 size: 15GiB capacity: 15GiB capabilities: primary extended partitioned partitioned:extended *-logicalvolume description: Linux swap / Solaris partition physical id: 5 logical name: /dev/sda5 capacity: 15GiB capabilities: nofs *-serial UNCLAIMED description: SMBus product: 5 Series/3400 Series Chipset SMBus Controller vendor: Intel Corporation physical id: 1f.3 bus info: pci@0000:00:1f.3 version: 05 width: 64 bits clock: 33MHz configuration: latency=0 resources: memory:d4205c00-d4205cff ioport:5000(size=32) *-pci:1 description: Host bridge product: Core Processor QuickPath Architecture Generic Non-Core Registers vendor: Intel Corporation physical id: 101 bus info: pci@0000:ff:00.0 version: 04 width: 32 bits clock: 33MHz *-pci:2 description: Host bridge product: Core Processor QuickPath Architecture System Address Decoder vendor: Intel Corporation physical id: 102 bus info: pci@0000:ff:00.1 version: 04 width: 32 bits clock: 33MHz *-pci:3 description: Host bridge product: Core Processor QPI Link 0 vendor: Intel Corporation physical id: 103 bus info: pci@0000:ff:02.0 version: 04 width: 32 bits clock: 33MHz *-pci:4 description: Host bridge product: Core Processor QPI Physical 0 vendor: Intel Corporation physical id: 104 bus info: pci@0000:ff:02.1 version: 04 width: 32 bits clock: 33MHz *-pci:5 description: Host bridge product: Core Processor Integrated Memory Controller vendor: Intel Corporation physical id: 105 bus info: pci@0000:ff:03.0 version: 04 width: 32 bits clock: 33MHz *-pci:6 description: Host bridge product: Core Processor Integrated Memory Controller Target Address Decoder vendor: Intel Corporation physical id: 106 bus info: pci@0000:ff:03.1 version: 04 width: 32 bits clock: 33MHz *-pci:7 description: Host bridge product: Core Processor Integrated Memory Controller Test Registers vendor: Intel Corporation physical id: 107 bus info: pci@0000:ff:03.4 version: 04 width: 32 bits clock: 33MHz *-pci:8 description: Host bridge product: Core Processor Integrated Memory Controller Channel 0 Control Registers vendor: Intel Corporation physical id: 108 bus info: pci@0000:ff:04.0 version: 04 width: 32 bits clock: 33MHz *-pci:9 description: Host bridge product: Core Processor Integrated Memory Controller Channel 0 Address Registers vendor: Intel Corporation physical id: 109 bus info: pci@0000:ff:04.1 version: 04 width: 32 bits clock: 33MHz *-pci:10 description: Host bridge product: Core Processor Integrated Memory Controller Channel 0 Rank Registers vendor: Intel Corporation physical id: 10a bus info: pci@0000:ff:04.2 version: 04 width: 32 bits clock: 33MHz *-pci:11 description: Host bridge product: Core Processor Integrated Memory Controller Channel 0 Thermal Control Registers vendor: Intel Corporation physical id: 10b bus info: pci@0000:ff:04.3 version: 04 width: 32 bits clock: 33MHz *-pci:12 description: Host bridge product: Core Processor Integrated Memory Controller Channel 1 Control Registers vendor: Intel Corporation physical id: 10c bus info: pci@0000:ff:05.0 version: 04 width: 32 bits clock: 33MHz *-pci:13 description: Host bridge product: Core Processor Integrated Memory Controller Channel 1 Address Registers vendor: Intel Corporation physical id: 10d bus info: pci@0000:ff:05.1 version: 04 width: 32 bits clock: 33MHz *-pci:14 description: Host bridge product: Core Processor Integrated Memory Controller Channel 1 Rank Registers vendor: Intel Corporation physical id: 10e bus info: pci@0000:ff:05.2 version: 04 width: 32 bits clock: 33MHz *-pci:15 description: Host bridge product: Core Processor Integrated Memory Controller Channel 1 Thermal Control Registers vendor: Intel Corporation physical id: 10f bus info: pci@0000:ff:05.3 version: 04 width: 32 bits clock: 33MHz *-battery description: Lithium Ion Battery product: NK06053 vendor: SMP-ATL24 physical id: 1 slot: Primary capacity: 4800mWh configuration: voltage=11.1V lspci: 02:00.0 USB controller: NEC Corporation uPD720200 USB 3.0 Host Controller (rev 03) (prog-if 30 [XHCI]) Subsystem: Hewlett-Packard Company Device 1522 Flags: bus master, fast devsel, latency 0, IRQ 16 Memory at d4000000 (64-bit, non-prefetchable) [size=8K] Capabilities: [50] Power Management version 3 Capabilities: [70] MSI: Enable- Count=1/8 Maskable- 64bit+ Capabilities: [90] MSI-X: Enable+ Count=8 Masked- Capabilities: [a0] Express Endpoint, MSI 00 Capabilities: [100] Advanced Error Reporting Capabilities: [140] Device Serial Number ff-ff-ff-ff-ff-ff-ff-ff Capabilities: [150] Latency Tolerance Reporting Kernel driver in use: xhci_hcd lsusb (with thumb drive plugged into USB3 port): Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub Bus 003 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub Bus 001 Device 002: ID 8087:0020 Intel Corp. Integrated Rate Matching Hub Bus 001 Device 003: ID 5986:01d0 Acer, Inc Bus 001 Device 004: ID 03f0:231d Hewlett-Packard

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• My proposed design is usually worse than my colleague's - how do I get better?

  - by user151193

  I have been programming for couple of years and am generally good when it comes to fixing problems and creating small-to-medium scripts, however, I'm generally not good at designing large scale programs in object oriented way. Few questions Recently, a colleague who has same number of years of experience as me and I were working on a problem. I was working on a problem longer than him, however, he came up with a better solution and in the end we're going to use his design. This really affected me. I admit his design is better, but I wanted to come up with a design as good as his. I'm even contemplating quitting the job. Not sure why but suddenly I feel under some pressure e.g. what would juniors think of me and etc? Is it normal? Or I'm thinking a little too much into this? My job involves programming in Python. I try to read source code but how do you think I can improve me design skills? Are there any good books or software that I should study? Please enlighten me. I will really appreciate your help.

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