Refactoring a JavaScript video store
The simple example of calculating and formatting a bill for a video store opened my refactoring book in 1999. If done in modern JavaScript, there are several directions you could take the refactoring. I explore four here: refactoring to top level functions, to a nested function with a dispatcher, using classes, and transformation using an intermediate data structure. 18 May 2016 Many years ago, wh
bliki: Orm Hate
While I was at the QCon conference in London a couple of months ago, it seemed that every talk included some snarky remarks about Object/Relational mapping (ORM) tools. I guess I should read the conference emails sent to speakers more carefully, doubtless there was something in there telling us all to heap scorn upon ORMs at least once every 45 minutes. But as you can tell, I want to push back a b
Collection Pipeline
Collection pipelines are a programming pattern where you organize some computation as a sequence of operations which compose by taking a collection as output of one operation and feeding it into the next. (Common operations are filter, map, and reduce.) This pattern is common in functional programming, and also in object-oriented languages which have lambdas. This article describes the pattern wit
Microservices
a definition of this new architectural term The term “Microservice Architecture” has sprung up over the last few years to describe a particular way of designing software applications as suites of independently deployable services. While there is no precise definition of this architectural style, there are certain common characteristics around organization around business capability, automated depl
bliki: Segregated DOM
Single-page web applications often turn into jQuery soup, where application logic, DOM manipulation, and server access are all mixed together. This mixing of concerns makes such applications harder to understand and test than they ought to be. Segregated DOM is a modularization tactic that separates all manipulation of the DOM into dedicated JavaScript objects. For an example, consider the recent
bliki: Page Object
When you write tests against a web page, you need to refer to elements within that web page in order to click links and determine what's displayed. However, if you write tests that manipulate the HTML elements directly your tests will be brittle to changes in the UI. A page object wraps an HTML page, or fragment, with an application-specific API, allowing you to manipulate page elements without di
DIP in the Wild
The Dependency Inversion Principle (DIP) has been around since the early '90s, even so it seems easy to forget in the middle of solving a problem. After a few definitions, I'll present a number of applications of the DIP I've personally used on real projects so you'll have some examples from which to form your own conclusions. 21 May 2013 Brett is a generalist striving to get the basics right. He'
bliki: Evans Classification
In his excellent book Domain Driven Design, Eric Evans creates a classification of the different kinds of domain objects that you're likely to run into. Entity: Objects that have a distinct identity that runs through time and different representations. You also hear these called "reference objects". Value Object: Objects that matter only as the combination of their attributes. Two value objects wi
bliki: Aggregate Oriented Database
One of the first topics to spring to mind as we worked on Nosql Distilled was that NoSQL databases use different data models than the relational model. Most sources I've looked at mention at least four groups of data model: key-value, document, column-family, and graph. Looking at this list, there's a big similarity between the first three - all have a fundamental unit of storage which is a rich s
bliki: CQRS
CQRS stands for Command Query Responsibility Segregation. It's a pattern that I first heard described by Greg Young. At its heart is the notion that you can use a different model to update information than the model you use to read information. For some situations, this separation can be valuable, but beware that for most systems CQRS adds risky complexity. The mainstream approach people use for i
Richardson Maturity Model
steps toward the glory of REST A model (developed by Leonard Richardson) that breaks down the principal elements of a REST approach into three steps. These introduce resources, http verbs, and hypermedia controls. 18 March 2010 Recently I've been reading drafts of Rest In Practice: a book that a couple of my colleagues have been working on. Their aim is to explain how to use Restful web services t
bliki: Anemic Domain Model
This is one of those anti-patterns that's been around for quite a long time, yet seems to be having a particular spurt at the moment. I was chatting with Eric Evans on this, and we've both noticed they seem to be getting more popular. As great boosters of a proper Domain Model, this is not a good thing. The basic symptom of an Anemic Domain Model is that at first blush it looks like the real thing
bliki: Feature Branch
A feature branch is a source code branching pattern where a developer opens a branch when she starts working on a new feature. She does all the work on the feature on this branch and integrates the changes with the rest of the team when the feature is done. During the work, she may merge in changes confirmed by the rest of the team into her branch, in order to reduce her integration once the featu
Ruby at ThoughtWorks
ThoughtWorks started using Ruby for production projects in 2006, from then till the end of 2008 we had done 41 ruby projects. In preparation for a talk at QCon I surveyed these projects to examine what lessons we can draw from the experience. I describe our thoughts so far on common questions about Ruby's productivity, speed and maintainability. So far our conclusions are that Ruby is a viable pla
DSL Book WIP
Narratives An Introductory Example: Using Domain Specific Languages: Implementing DSLs: Implementing an Internal DSL: Implementing an External DSL: Code Generation: External DSL Topics Delimiter Directed Translation: Translate source text by breaking it up into chunks (usually lines) and then parsing each line. (Syntax Directed Translation): Translate source text by defining a grammar, and u
Using the Rake Build Language
Rake is a build language, similar in purpose to make and ant. Like make and ant it's a Domain Specific Language, unlike those two it's an internal DSL programmed in the Ruby language. In this article I introduce rake and describe some interesting things that came out of my use of rake to build this web site: dependency models, synthesized tasks, custom build routines and debugging the build script
Presentation Model
This is part of the Further Enterprise Application Architecture development writing that I was doing in the mid 2000’s. Sadly too many other things have claimed my attention since, so I haven’t had time to work on them further, nor do I see much time in the foreseeable future. As such this material is very much in draft form and I won’t be doing any corrections or updates until I’m able to find ti
Event Sourcing
Capture all changes to an application state as a sequence of events. This is part of the Further Enterprise Application Architecture development writing that I was doing in the mid 2000’s. Sadly too many other things have claimed my attention since, so I haven’t had time to work on them further, nor do I see much time in the foreseeable future. As such this material is very much in draft form and
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Using Domain Specific Languages
Patterns in Enterprise Software