A design pattern is a general reusable solution to a commonly occurring problem in software design.

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Progressive Enhancement vs. Single Page Apps

I just got back from a conference in Boston called An Event Apart. A really popular theme amongst the speakers was the idea of progressive enhancement - a site's content should go in the HTML, and ...
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180 views

What is the Loopback Pattern? [closed]

I was reading this blog post about Hexagonal architecture and at the bottom it says: The Loopback pattern is an explicit pattern for creating an internal replacement for an external device. When ...
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1answer
406 views

To Repository Or Not To Repository

When I first learnt about Domain Driven Design, I was also introduced to the repository and unit of work patterns that once seemed to be top notch for the cool kids that threw SQL queries like ...
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1answer
119 views

Where do utility libraries fit in a layered architecture?

Consider this mock-up of a software stack designed with layered architecture in mind : Every application layer is decoupled through API calls, but a memory handling library is used throughout. All ...
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PaypalCheckout object is composed of PaypalQuery objects. Hide PaypalQuery objects to users of PaypalCheckout?

I have a PaypalCheckout object that handles the checkout process: from initiating API calls, to providing an interface for front-end code (e.g. View/Controller). The PaypalCheckout object handles: ...
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1answer
100 views

Traversing an AST using Visitors

I'm writing a compiler for a C-like language, and I'm looking for an elegant way to traverse my abstract syntax tree. I'm trying to implement the Visitor pattern, although I'm not convinced that I'm ...
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131 views

Optimization ended up in casting an object at each method call

I've been doing some optimization for the following piece of code : public void DrawLine(int x1, int y1, int x2, int y2, int color) { _bitmap.DrawLineBresenham(x1, y1, x2, y2, color); } After ...
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1answer
127 views

Is the following example a strategy pattern?

In my problem I had lots of objects with slightly different behaviour, but identical attributes and methodes with identical interfaces. The objects variants were quite big in number, and I didn't want ...
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51 views

Easiest way to use objects as filters for queries

I'm just starting on a new little pet project of mine. I started the project using a familiar pattern for using objects as "filters" in SQL Queries. I've never been much happy about its easy of use, ...
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41 views

Modelling network and persistent entity representations

I have an app where I need to synchronize some entities (simply download latest versions of entities from server to client). Entity has bunch of text properties and bunch of resource links (referenced ...
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1answer
76 views

How to deal with interactions between many objects

I've been working on a game in my spare time. I'm pretty much done defining the primitives and until today everything was pretty well segmented and encapsulated but now it's come time to implement ...
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2answers
100 views

Visitor only applicable when using the Composite pattern?

For a long time I've tried to get my head wrapped around the visitor pattern, and somehow this thing keeps being rather fuzzy to me. I'm currently under the impression it is only useful to apply ...
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128 views

Relative encapsulation design

Let's say I am doing a 2D application with the following design: There is the Level object that manages the world, and there are world objects which are entities inside the Level object. A world ...
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Adding field to the class at runtime - design pattern

Imagine your customer want's to have a possibility to add new property (e.g. color) to product in their eshop in their CMS. Instead of having properties as fields: class Car extends Product { ...
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78 views

Best approach for tracking dependent state

Let's pretend I work on a project tracking application. The application is a database backed, server hosted, web application. In this application there are Projects which have many Activities which ...
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2answers
441 views

When is it worth NOT using a Factory?

I'm employing TDD quite a bit these days and really enjoying myself - everything seems to flow better and be naturally better constructed and organized. However, while writing a bit of IO code, ...
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2answers
213 views

Can this argument be enough?

We have two C++ classes named Important and Small The class Small use a few methods and attributes from the class Important, but not all. Since our application is performance critical, instead of ...
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How would another popular language avoid having to use the factory pattern while managing similar complexity as in Java/Java EE?

Factory pattern (or at least the use of FactoryFactory..) is the butt of many jokes, like here. Apart from having verbose and "creative" names like ...
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1answer
163 views

How to make my code decide which class to instantiate based on a parameter?

I have a system in which I will perform queries to a database. I want Query1, Query2 and Query3 to use the same methods in their way to the data source layer. To do that I would like to make ...
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213 views

Design Pattern: Algorithm varies according to the input arguments

I will give a simple example to help you understand my question. Suppose we have a rectangle and a Utility class with a method that creates a buffer arround a shape. The .createBuffer method has ...
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1answer
158 views

Should I use inheritance or an interface?

So in a nutshell I have an abstract class : public abstract class Member { public string PCode { get; set; } public string Reference { get; set; } public DateTime? ElectedDate { get; set; } } And ...
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1answer
176 views

Implementing a strategy pattern with dependency injection

Okay, so the goal here is to implement a strategy pattern that can be tested using any sort of automated testing tool. I've been struggling with this problem conceptually for a few weeks now and I ...
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180 views

Using the Decorator pattern to add public methods to an object

The Decorator pattern is usually used to extend the functionality of an object by extending one of it's current methods. To illustrate, please consider an object object and a decorator decorator. ...
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4answers
227 views

Why would I want a UnitOfWork layer if my service/business logic layer is specific enough?

I'm getting into the Repository pattern (which I love), and as I read up on it I see this UnitOfWork pattern in many articles. Before I knew anything about UnitOfWork I was just using my Repository ...
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1answer
152 views

Functions returning either “OK” or “error message” instead of procedures

I have joined writing middle-size multi-purpose database application as co-lead. It currently has about 150 tables (and growing) and overall functionality you can imagine as very small ERP. At many ...
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2answers
131 views

Refactoring sought for replacing shared data types in .NET component

I am in charge with updating a software product that is made up of two components the Controller process and the UI process. The Controller and the UI communicate via XML messages. Furthermore, the ...
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1answer
105 views

Design MVC site such that UI developer can work without access to data tier? [closed]

I'm working on an ASP.NET MVC site (using Team Foundation Service for source control) that I've divided into a few separate projects under one solution: Project.WebAPI (Main entrypoint, contains ...
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378 views

What is the main goal of MVVM pattern? [closed]

Could you tell me what is the goal of the MVVM pattern? What are the arguments or the reasons I can give to a team and product owner to respect and develop according to this pattern? I would like a ...
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203 views

Is it wrong to have HTML strings within PHP objects, or is it only wrong in controllers?

I've always thought that in typical MVC design it is bad practice to build & concatenate HTML strings in any PHP file or class that isn't strictly a template. I'm working on a large project with ...
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Ensure that each class has only one responsibility, why?

According to Microsoft documentation, the Wikipedia SOLID principe article, or most IT architects we must ensure that each class has only one responsibility. I would like to know why, because if ...
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4answers
240 views

What are the perks and drawbacks of using html templates versus building the html in-code [closed]

As far as I can see there are two ways of building a html page: "inside" the language (I'll call it building for lack of a better name) or outside the language (using templates). Let me explain a bit ...
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79 views

Inheritance vs 'specification' by fields

I'm currently reading 'Head first design patterns', and already the first chapter threw some questions towards me. This chapter introduces the 'prefer composition over inheritance' design principle, ...
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1answer
131 views

Differentiating between Factory Method and Abstract Factory

I've been confused for a while about the differences between the patterns Factory Method and Abstract Factory. Been doing a lot of research, still confused. I have one question: Is the only ...
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1answer
121 views

design patterns in Javascript - toggle functionality [duplicate]

My goal is to add some functionality to the bxslider script - in this case, I want to be able to enable/disable a keyboard event handler AFTER a slider is instantiated. I guess this code is self ...
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74 views

Container/Item pattern without `friend`

I have a class Container containing objects of type Item. They are different classes, and especially they have no common base class (e.g. a Container does not itself have a Container).: class ...
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1answer
175 views

Observer pattern: “Web of observers” - Is this ever in use?

I had an idea (which I'm sure already exists), to create a sort of 'network of observers/subjects'. I would like to describe how it works and than ask several questions about it. Say we have 5 ...
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1answer
57 views

Is it fine for a class that creates objects to delegate them?

I have a large list of intercommunicating components; so I decided to have one class create all of them and then subsequently delegate them to other classes to facilitate finer tweaking and wiring ...
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1answer
183 views

Python - Is this a bad strategy pattern?

I've got a Python project wherein a basic object is created and various different attributes are modified/given to it via what I thought was a good example of a strategy pattern. In this silly game ...
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86 views

How to design modular “screen configurator” for database application

I am currently working with a product that is effectively a glorified CRUD application. (It is a C# .NET 4.0 desktop application backed by an Oracle 11gR2 database.) The client program presents a list ...
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1answer
392 views

Design Pattern for Data Validation

What would be the best design pattern for this problem: I have an Object A. Object A can either be registered or deleted from the database depending on the user request. Data validation is performed ...
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2answers
106 views

System Communication: Avoiding Including a Large “HAS-A” Hierarchy Which Isn't Used

The situation: System A Huge, complicated system. Uses an important Message object with many other Message objects attached, many of which have further Message objects attached. In total, this is ...
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Dealing with an often occuring dependency that is not related to the class

I'm using view classes for my templating. These view classes often require the Routing class to get URI's from other pages. You could actually say that the Routing should be available to every view ...
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1answer
164 views

Good pattern(s) for pointing to mutable state

I asked this question once here, but believe the question was unclear. However I'm having a hard time extracting the general problem from my specific case. UPDATE: I've answered my own question ...
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1answer
151 views

Is there a Pattern or a Refactoring Method to pull data-loading out of existing Class

I am refactoring legacy codebase. Part of it is a loadProduct() function inside a larger "everything" class. loadProduct() loads data from a database. I want to move this loading-data part out of ...
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2answers
270 views

What should a repository really do?

I've heard a lot of the repository pattern, but I quite didn't understand what a repository should really do. When I say "what a repository should really do" I'm mainly concerned about which methods ...
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1answer
60 views

Contradiction of layered design and global data access for analytics reporting

While developing an application (mobile app for Android), our team always strives to use best development practices such as interfaces, layering and separation of concerns. When it comes to reporting ...
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1answer
149 views

Is the flyweight pattern a good security choice for managing permissions?

I'm designing a system, and it needs future expandability for the use of a permission system of some kind. I'm wondering if the flyweight pattern would be a good choice to implement this. I'm not ...
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3answers
234 views

How does Observer create loosely-coupled design?

I completely understand the Observer design pattern, what it is for and how to implement it. I also understand what the term 'loosely-coupled' means. But I'm not sure how Observer makes designs more ...
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0answers
61 views

Looking for design pattern to represent shared state in music sequencer

I like to give lots of context, but also to state the basic question up top as concisely as possible. Feel free to read a little or a lot. I'm working on a music sequencer, and have been happy so far ...
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Question/Answer for multiple Users - How should I design it?

I'm wondering about a good way to deal with a Question/Answer - Model for multiple Users. My goal is to have an efficient and readable model where all the results of my users are stored. Every user ...