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  • Self-Configuring Classes W/ Command Line Args: Pattern or Anti-Pattern?

    - by dsimcha
    I've got a program where a lot of classes have really complicated configuration requirements. I've adopted the pattern of decentralizing the configuration and allowing each class to take and parse the command line/configuration file arguments in its c'tor and do whatever it needs with them. (These are very coarse-grained classes that are only instantiated a few times, so there is absolutely no performance issue here.) This avoids having to do shotgun surgery to plumb new options I add through all the levels they need to be passed through. It also avoids having to specify each configuration option in multiple places (where it's parsed and where it's used). What are some advantages/disadvantages of this style of programming? It seems to reduce separation of concerns in that every class is now doing configuration stuff, and to make programs less self-documenting because what parameters a class takes becomes less explicit. OTOH, it seems to increase encapsulation in that it makes each class more self-contained because no other part of the program needs to know exactly what configuration parameters a class might need.

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  • Would ViewModels fit in the Model View Presenter pattern?

    - by Jonn
    Having used ViewModels in MVC, I was wondering if applying the same to the MVP pattern is practical. I only have a few considerations, one being that MVP is already fairly hard to implement (with all the additional coding, not much on the seeming complexity) or that ViewModels already have a slightly similar way of modeling data or entities. Would adding another layer in the form of ViewModels be redundant or is it a logical abstraction that I, as one implementing the MVP pattern, should adhere to?

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  • Are we using IoC effectively?

    - by Juliet
    So my company uses Castle Windsor IoC container, but in a way that feels "off": All the data types are registered in code, not the config file. All data types are hard-coded to use one interface implementation. In fact, for nearly all given interfaces, there is and will only ever be one implementation. All registered data types have a default constructor, so Windsor doesn't instantiate an object graph for any registered types. The people who designed the system insist the IoC container makes the system better. We have 1200+ public classes, so its a big system, the kind where you'd expect to find a framework like Windsor. But I'm still skeptical. Is my company using IoC effectively? Is there an advantage to new'ing objects with Windsor than new'ing objects with the new keyword?

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  • JavaScript Module Pattern - What about using "return this"?

    - by Rob
    After doing some reading about the Module Pattern, I've seen a few ways of returning the properties which you want to be public. One of the most common ways is to declare your public properties and methods right inside of the "return" statement, apart from your private properties and methods. A similar way (the "Revealing" pattern) is to provide simply references to the properties and methods which you want to be public. Lastly, a third technique I saw was to create a new object inside your module function, to which you assign your new properties before returning said object. This was an interesting idea, but requires the creation of a new object. So I was thinking, why not just use "this.propertyName" to assign your public properties and methods, and finally use "return this" at the end? This way seems much simpler to me, as you can create private properties and methods with the usual "var" or "function" syntax, or use the "this.propertyName" syntax to declare your public methods. Here's the method I'm suggesting: (function() { var privateMethod = function () { alert('This is a private method.'); } this.publicMethod = function () { alert('This is a public method.'); } return this; })(); Are there any pros/cons to using the method above? What about the others?

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  • Haskell: Pattern Matching with Lists

    - by user1670032
    I'm trying to make a function that takes in a list, and if one of the elements is negative, then any elements in that list that are equal to its positive counterpart should be changed to 0. Eg, if there is a -2 in a list, then all 2's in that list should be changed to 0. Any ideas why it only works for some cases and not others? I'm not understanding why this is, I've looked it over several times. changeToZero [] = [] changeToZero [x] = [x] changeToZero (x:zs:y:ws) | (x < 0) && ((-1)*(x) == y) = x : zs : 0 : changeToZero ws changeToZero (x:xs) = x : changeToZero xs *Main changeToZero [-1,1,-2,2,-3,3] [-1,1,-2,2,-3,3] *Main changeToZero [-2,1,2,3] [-2,1,0,3] *Main changeToZero [-2,1,2,3,2] [-2,1,0,3,2] *Main changeToZero [1,-2,2,2,1] [1,-2,2,0,1]

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  • Building a wiki like data model in rails question.

    - by lillq
    I have a data model in which I would like to have an item that has a description that can be edited. I would like to also keep track of all edits to the item. I am running into issues with my current strategy, which is: class Item < ActiveRecord::Base has_one :current_edit, :class_name => "Edit", :foreign_key => "current_edit_id" has_many :edits end class Edit < ActiveRecord::Base belongs_to :item end Can the Item have multiple associations to the same class like this? I was thinking that I should switch to keeping track of the edit version in the Edit object and then just sorting the has_many relationship base on this version.

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  • An appropriate C API for inspecting attribute values

    - by uk82
    There are two obvious ways in C to provide outside access to internal attribute values (A) provide a generic interface that accepts a list of attributes that changes over time (some added / some die) or (B) a specific interface for each and every attribute. Example A: int x_get_attribute_value(ATT att) { if (a) return a_val; if (b) return b_val; } Example B: A_Enum x_get_a_type_attribute() {} B_Enum x_get_b_type_attribute() {} I recall that Eclipse's API is very much like A (I could be wrong). What I can't do is come up with a compelling argument against either. A is clean - any user will no where to go to find out a property value. It can evolve cleanly without leaving dead interfaces around. B has type checking to a degree - this is C enums! Is there a big hitter argument that pushes the balance away from opinion?

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  • Patterns: Local Singleton vs. Global Singleton?

    - by Mike Rosenblum
    There is a pattern that I use from time to time, but I'm not quite sure what it is called. I was hoping that the SO community could help me out. The pattern is pretty simple, and consists of two parts: A singleton factory, which creates objects based on the arguments passed to the factory method. Objects created by the factory. So far this is just a standard "singleton" pattern or "factory pattern". The issue that I'm asking about, however, is that the singleton factory in this case maintains a set of references to every object that it ever creates, held within a dictionary. These references can sometimes be strong references and sometimes weak references, but it can always reference any object that it has ever created. When receiving a request for a "new" object, the factory first searches the dictionary to see if an object with the required arguments already exits. If it does, it returns that object, if not, it returns a new object and also stores a reference to the new object within the dictionary. This pattern prevents having duplicative objects representing the same underlying "thing". This is useful where the created objects are relatively expensive. It can also be useful where these objects perform event handling or messaging - having one object per item being represented can prevent multiple messages/events for a single underlying source. There are probably other reasons to use this pattern, but this is where I've found this useful. My question is: what to call this? In a sense, each object is a singleton, at least with respect to the data it contains. Each is unique. But there are multiple instances of this class, however, so it's not at all a true singleton. In my own personal terminology, I tend to call the factory method a "global singleton". I then call the created objects "local singletons". I sometimes also say that the created objects have "reference equality", meaning that if two variables reference the same data (the same underlying item) then the reference they each hold must be to the same exact object, hence "reference equality". But these are my own invented terms, and I am not sure that they are good ones. Is there standard terminology for this concept? And if not, could some naming suggestions be made? Thanks in advance...

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  • How to organize and manage multiple database credentials in application?

    - by Polaris878
    Okay, so I'm designing a stand-alone web service (using RestLET as my framework). My application is divided in to 3 layers: Data Layer (just above the database, provides APIs for connecting to/querying database, and a database object) Object layer (responsible for serialization from the data layer... provides objects which the client layer can use without worrying about database) Client layer (This layer is the RestLET web service... basically just creates objects from the object layer and fulfills webservice request) Now, for each object I create in the object layer, I want to use different credentials (so I can sandbox each object...). The object layer should not know the exact credentials (IE the login/pw/DB URL etc). What would be the best way to manage this? I'm thinking that I should have a super class Database object in my data layer... and each subclass will contain the required log-in information... this way my object layer can just go Database db = new SubDatabase(); and then continue using that database. On the client level, they would just be able to go ItemCollection items = new ItemCollection(); and have no idea/control over the database that gets connected. I'm asking this because I am trying to make my platform extensible, so that others can easily create services off of my platform. If anyone has any experience with these architectural problems or how to manage this sort of thing I'd appreciate any insight or advice... Feel free to ask questions if this is confusing. Thanks! My platform is Java, the REST framework I'm using is RestLET, my database is MySQL.

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  • Best practice to modularise a large Grails app?

    - by Mulone
    Hi all, A Grails app I'm working on is becoming pretty big, and it would be good to refactor it into several modules, so that we don't have to redeploy the whole thing every time. In your opinion, what is the best practice to split a Grails app in several modules? In particular I'd like to create a package of domain classes + relevant services and use it in the app as a module. Is this possible? Is it possible to do it with plugins? Cheers, Mulone

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  • What's a good icon to represent a legend or a key for a diagram?

    - by Bears will eat you
    I'm implementing a small web app widget that shows a legend/key for a diagram (or chart/map/graph/whatever), but only during mouseover of the widget. It's basically just going to be a div with a background image. What would be a good icon that communicates "I show the legend" or "I am the legend" to the unfamiliar users? I'm looking for something in the 10x10 to 20x20 pixel range. Assuming that a legend is the same thing as a key (is it?) then I could use a small icon of a key (like you'd unlock a door with) but that seems cheesy or unclear at worst. I'm not sure that's really the clearest way to do it. Is there an icon that should instantly remind users of a legend?

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  • Maintaining sort order of database table rows

    - by Lox
    Say I have at database table containing information about a news article in each row. The table has an integer "sort" column to dictate the order in which the articles are to be presented on a web site. How do I best implement and maintain this sort order. The problem I want to avoid is having the the articles numbered 1,2,3,4,..,100 and when article number 50 suddenly becomes interesting it gets its sort number set to 1 and then all articles between them must have their sort number increased by one. Sure, setting initial sort numbers to 100,200,300,400 etc. leaves some space for moving around but at some point it will break. Is there a correct way to do this, maybe a completely different approach? Added-1: All article titles are shown in a list linking to the contents, so yes all sorted items are show at once. Added-2: An item is not necessarily moved to the top of the list; any item can be placed anywhere in the ordered list.

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  • Is it OK to re-create many SQL connections (SQL 2008)

    - by Mr. Flibble
    When performing many inserts into a database I would usually have code like this: using (var connection = new SqlConnection(connStr)) { connection.Open(); foreach (var item in items) { var cmd = new SqlCommand("INSERT ...") cmd.ExecuteNonQuery(); } } I now want to shard the database and therefore need to choose the connection string based on the item being inserted. This would make my code run more like this foreach (var item in items) { connStr = GetConnectionString(item); using (var connection = new SqlConnection(connStr)) { connection.Open(); var cmd = new SqlCommand("INSERT ...") cmd.ExecuteNonQuery(); } } Which basically means it's creating a new connection to the database for each item. Will this work or will recreating connections for each insert cause terrible overhead?

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  • Working with foreign keys - cannot insert

    - by Industrial
    Hi everyone! Doing my first tryouts with foreign keys in a mySQL database and are trying to do a insert, that fails for this reason: Integrity constraint violation: 1452 Cannot add or update a child row: a foreign key constraint fails Does this mean that foreign keys restrict INSERTS as well as DELETES and/or UPDATES on each table that is enforced with foreign keys relations? Thanks! Updated description: Products ---------------------------- id | type ---------------------------- 0 | 0 1 | 3 ProductsToCategories ---------------------------- productid | categoryid ---------------------------- 0 | 0 1 | 1 Product table has following structure CREATE TABLE IF NOT EXISTS `alpha`.`products` ( `id` MEDIUMINT UNSIGNED NOT NULL AUTO_INCREMENT , `type` TINYINT(2) UNSIGNED NOT NULL DEFAULT 0 , PRIMARY KEY (`id`) , CONSTRAINT `prodsku` FOREIGN KEY (`id` ) REFERENCES `alpha`.`productsToSku` (`product` ) ON DELETE CASCADE, ON UPDATE CASCADE) ENGINE = InnoDB;

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  • Doctrine: Relating a model to itself using a link table, like "This event is related to to the following other events"

    - by mattalexx
    So in English, the relationship would sound like "This event is related to to the following other events". My first instinct is to create an EventEvent model, with a first_event_id field and a second_event_id field. Then I would define the following two relationships in the Event model: $this->hasMany('Event as FirstRelatedEvents', array('local' => 'first_event_id', 'foreign' => 'second_event_id', 'refClass' => 'EventEvent')); $this->hasMany('Event as SecondRelatedEvents', array('local' => 'second_event_id', 'foreign' => 'first_event_id', 'refClass' => 'EventEvent')); But I would rather not have to use two relationships on the Event model. Is there a better way to do this?

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  • Explain "Leader/Follower" Pattern

    - by Alex B
    I can't seem to find a good explanation of "Leader/Follower" pattern. All explanations either simply refer to it in the context of some problem, or are completely meaningless. Can anyone explain to the the mechanics of how this pattern works, and why and how it improves performance over more traditional asynchronous IO models? Examples and links to diagrams are appreciated too.

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  • How should rules for Aggregate Roots be enforced?

    - by MylesRip
    While searching the web, I came across a list of rules from Eric Evans' book that should be enforced for aggregates: The root Entity has global identity and is ultimately responsible for checking invariants Root Entities have global identity. Entities inside the boundary have local identity, unique only within the Aggregate. Nothing outside the Aggregate boundary can hold a reference to anything inside, except to the root Entity. The root Entity can hand references to the internal Entities to other objects, but they can only use them transiently (within a single method or block). Only Aggregate Roots can be obtained directly with database queries. Everything else must be done through traversal. Objects within the Aggregate can hold references to other Aggregate roots. A delete operation must remove everything within the Aggregate boundary all at once When a change to any object within the Aggregate boundary is committed, all invariants of the whole Aggregate must be satisfied. This all seems fine in theory, but I don't see how these rules would be enforced in the real world. Take rule 3 for example. Once the root entity has given an exteral object a reference to an internal entity, what's to keep that external object from holding on to the reference beyond the single method or block? (If the enforcement of this is platform-specific, I would be interested in knowing how this would be enforced within a C#/.NET/NHibernate environment.)

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  • Brilliant features of C++

    - by John
    (Following Features to remove from C++ and Desired features for C++, I thought why not complete the trio...) What C++ features would you not change? What features are elegantly and brilliantly implemented and still look better than other popular languages?

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  • @media queries - one rule overrides another?

    - by John
    I have multiple @media queries all working fine but as soon as i put in a higher max screen-width than 1024px the rules for the higher width gets applied to everything. @media screen and (max-width: 1400px) { #wrap { width: 72%; } } @media screen and (max-width: 1024px) { #slider h2 { width: 100%; } #slider img { margin: 60px 0.83333333333333% 0 2.08333333333333%; } .recent { width: 45.82%; margin: 10px 2.08333333333334% 0 1.875%; } } as you can see 1024px (and also the 800px max-width query) do not change the #wrap width and work fine. As soon as i add the 1400px max-width query it changes them to 72% for ALL sizes and does the same for any element - for instance if i set #slider img to have a margin of 40px it will show at ALL sizes even though it is only in the max-width of 1400px. Am i missing something really obvious? Been trying to work this out for the past 2 days! Thanks, John

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  • what is the easiest way to do this function in c# ?

    - by From.ME.to.YOU
    Hello let say that we have an array [5,5] 01,02,03,04,05 06,07,08,09,10 11,12,13,14,15 16,17,18,19,20 21,22,23,24,25 the user should send 2 values to the function (start,searchFOR) for example (13,25) the function should search for that value in this way 07,08,09 12, ,14 17,18,19 if the value is n't found in this level it will goes a level higher 01,02,03,04,05 06, , , ,10 11, , , ,15 16, , , ,20 21,22,23,24,25 if the array is bigger than this and the value didn't found it will go to a level higher Thanks for your help

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  • Aligning inputs on bootstrap using the Fluid Grid System

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

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  • Problem with IE 6 page loading.

    - by Puneet Dudeja
    I have a website which works fine in all browsers except in IE6. The pages content is inside a div loaded with a background image. The page layout gets very nasty and image does not load when the page is opened for first time, but when the same page is opened for the second time and any subsequent times, then it loads perfectly. This scenario is with every page in the site. Please help.

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