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2015, Sunday May 3

SOLID Design Principles

I've just updated the documentation part about the SOLID Design Principles.
The former blog article (almost 4 years old!) sounds like a bit deprecated now...
This is why I would extract here an updated version of this material.

Ensure you checked the corresponding part of the mORMot documentation, which is the updated reference, and probably the easiest to read - including links to all the other documentation.

The acronym SOLID is derived from the following OOP principles (quoted from the corresponding Wikipedia article):

  • Single responsibility principle: the notion that an object should have only a single responsibility;
  • Open/closed principle: the notion that "software entities ... should be open for extension, but closed for modification";
  • Liskov substitution principle: the notion that "objects in a program should be replaceable with instances of their subtypes without altering the correctness of that program” - also named as "design by contract";
  • Interface segregation principle: the notion that "many client specific interfaces are better than one general purpose interface.";
  • Dependency inversion principle: the notion that one should "Depend upon Abstractions. Do not depend upon concretions.". Dependency injection is one method of following this principle, which is also called Inversion Of Control (aka IoC).

If you have some programming skills, those principles are general statements you may already found out by yourself. If you start doing serious object-oriented coding, those principles are best-practice guidelines you would gain following.

They certainly help to fight the three main code weaknesses:

  • Rigidity: Hard to change something because every change affects too many other parts of the system;
  • Fragility: When you make a change, unexpected parts of the system break;
  • Immobility: Hard to reuse in another application because it cannot be disentangled from the current application.

Continue reading...

2014, Saturday September 13

Some thoughts about "modern" pascal, generics, code and data structures

In a comment of a Google+ announcement about new C# features, Stephan did react about my naive enthusiasm about SmartPascal.

Apart from the fact that he did miss the numerous ways of creating Windows executable in this dialect (I quoted at least 5 diverse ways), he was chocked by the fact that the SmartPascal syntax, in its actual idiom, does not support generics.

But are generics mandatory?
I'm not speaking about any drug identified by its chemical name rather than its brand name (Wikipedia).
I would neither comment on the current Delphi implementation of generics (which may appear not so polished, nor very widely used, even in the Delphi RTL/FMX, but for TList<T> TDictionary<>).
Just share some thoughts about what is, to my opinion - which may be wrong and biased! - the most important part of today's programming.

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2014, Saturday July 12

Static class variables are just global variables in disguise

Cape Cod Gunny just wrote a blog article about how to replace a global variable by a static class instance.

But I had to react!
Using such static declaration is just another way of creating a global variable.
This is just a global variable in disguise.
In fact, the generated asm will be just like a global variable!

It encapsulates the global declaration within a class name space, but it is still IMHO a very wrong design.
I've seen so many C# or Java code which used such a pattern (there is no global variable in those languages), and it has the same disadvantages as global variables.
Just like the singleton syndrome
Code is just not re-entrant nor thread-safe.
Nightmare to debug and let evolve.

Continue reading...

2014, Friday April 18

Introducing mORMot's architecture and design principles

We have just released a set of slides introducing 

  • ORM, SOA, REST, JSON, MVC, MVVM, SOLID, Mocks/Stubs, Domain-Driven Design concepts with Delphi, 
  • and showing some sample code using our Open Source mORMot framework.

You can follow the public link on Google Drive!

This is a great opportunity to discovers some patterns you may not be familiar with, and find out how mORMot try to implement them.
This set of slides may be less intimidating than our huge documentation - do not be terrified by our Online Documentation!
The first set of pages (presenting architecture and design principles) is worth reading.

Feedback is welcome on our forum, as usual.

2014, Saturday January 4

Domain-Driven Design: part 4

One year ago, we already made a quick presentation of Domain-Driven Design, in the context of our mORMot framework.
After one year of real-world application of those patterns, it is now time to give more light to DDD.

Let's continue with part 4, which will define Domain-Driven Design as could be implemented with our Synopse mORMot framework

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Domain-Driven Design: part 3

One year ago, we already made a quick presentation of Domain-Driven Design, in the context of our mORMot framework.
After one year of real-world application of those patterns, it is now time to give more light to DDD.

Let's continue with part 3, which will define Domain-Driven Design patterns and principles - this will be the main article of the whole serie!

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Domain-Driven Design: part 2

One year ago, we already made a quick presentation of Domain-Driven Design, in the context of our mORMot framework.
After one year of real-world application of those patterns, it is now time to give more light to DDD.

Let's continue with part 2, which will define Domain-Driven Design high-level model principles.

Continue reading...

Domain-Driven Design: part 1

One year ago, we already made a quick presentation of Domain-Driven Design, in the context of our mORMot framework.
After one year of real-world application of those patterns, and a training made by a great French software designer named Jérémie Grodziski, it is now time to give more light to DDD.

Let's start with part 1, which will be a general introduction to Domain-Driven Design, trying to state how it may be interesting (or not) for your projects.

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2012, Sunday October 14

Interfaces in practice: dependency injection, stubs and mocks

In order to fulfill the SOLID principles, two features are to be available when handling interfaces:

  • Dependency injection; 
  • Stubbing and mocking of interfaces for proper testing.

We will show now how mORMot provides all needed features for such patterns, testing a simple "forgot my password" scenario: a password shall be computed for a given user name, then transmitted via SMS, and its record shall be updated in the database.

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