Skip to main content

SOLID (5/5) - Dependency inversion principle

Dependency inversion principle

In object-oriented design, the dependency inversion principle is a specific form of decoupling software modules. When following this principle, the conventional dependency relationships established from high-level, policy-setting modules to low-level, dependency modules are reversed, thus rendering high-level modules independent of the low-level module implementation details. The principle states:

  • High-level modules should not depend on low-level modules. Both should depend on abstractions (e.g., interfaces).
  • Abstractions should not depend on details. Details (concrete implementations) should depend on abstractions.
By dictating that both high-level and low-level objects must depend on the same abstraction, this design principle inverts the way some people may think about object-oriented programming.

The idea behind points A and B of this principle is that when designing the interaction between a high-level module and a low-level one, the interaction should be thought of as an abstract interaction between them. This not only has implications on the design of the high-level module, but also on the low-level one: the low-level one should be designed with the interaction in mind and it may be necessary to change its usage interface.

using System;
using System.Linq;
using System.Collections.Generic;

namespace dependencyinversion
{
    public enum Relationship { Parent, Child}

    public class Person
    {
        public string Name { get; set; }
    }

    public interface IRelationshipBrowser
    {
        IEnumerable<Person> FindAllChildrenOf(string name);       
    }

    public class Relationships : IRelationshipBrowser
    {
        private List<(Person, Relationship, Person)> relations
            = new List<(Person, Relationship, Person)>();

        public void AddParentAndChild(Person parent, Person child)
        {
            relations.Add((parent, Relationship.Parent, child));
            relations.Add((child, Relationship.Child, parent));
        }

        //public List<(Person, Relationship, Person)> Relations => relations;

        public IEnumerable<Person> FindAllChildrenOf(string name)
        {
            foreach (var r in relations.Where(
                x => x.Item1.Name == name &&
                    x.Item2 == Relationship.Parent))
            {
                yield return r.Item3;
            }
        }
    }

    public class Research
    {
        // public Research(Relationships relationships)
        // {
        //     var relations = relationships.Relations;

        //     foreach (var r in relations.Where(
        //         x => x.Item1.Name == "John" &&
        //             x.Item2 == Relationship.Parent))
        //     {
        //         Console.WriteLine($"John has a child called {r.Item3.Name}");
        //     }
        // }

        public Research(IRelationshipBrowser browser)
        {
            foreach (var person in browser.FindAllChildrenOf("John"))
            {
                Console.WriteLine($"John has a child called {person.Name}");
            }
        }

        static void Main(string[] args)
        {
            var parent = new Person { Name = "John"};
            var child1 = new Person { Name = "Chris"};
            var child2 = new Person { Name = "Mary"};

            var relationships = new Relationships();
            relationships.AddParentAndChild(parent, child1);
            relationships.AddParentAndChild(parent, child2);

            new Research(relationships);
        }
    }
}

Labels:

Comments

Post a Comment

Popular posts from this blog

XML Webservice (ASMX) - SOAP Request and Response Invocation logging

You are an integration developer. Eventualy you came into the state where there is nothing else you can debug, and you have to check which SOAP request it is built on the request, and which SOAP response you are getting from the server. C# XML Webservice (ASMX) - SOAP Request and Response Invocation logging In the legaccy .NET framework System.Web.Services , this means using soapExtensions to help you intersept the interaction with the webservice. This is done like so:  public class TraceExtension : SoapExtension     {         Stream oldStream;         Stream newStream;         string filename;         // Save the Stream representing the SOAP request or SOAP response into          // a local memory buffer.          public override Stream ChainStream(Stream stream)         {           ...
Post a Comment
Read more

Abstract Factory Pattern

Abstract Factory Pattern  Gamma Categorization: Creational Design Patten Summary: When the object construction is complicated, needing multiple arguments, we should create a separate function (Factory Method) or class (Factory), which is responsible for the creation of the all object. Problem examples Suport of multiple databases Multiple data sources: Serial port, ethernet port, device driver Diferent report types Solution Abstract class Generalized interface A Factory creates instances of the concrete classes Sample Code The abstract factory public   interface   IPhotoFactory {      IAnaloguePhoto   CreateAnaloguePhoto ();      IDigitalPhoto   CreateDigitalPhoto (); } The abstract products public   interface   IAnaloguePhoto {      string   GetName (); } public   interface   IDigitalPhoto {      ...
Post a Comment
Read more

Software Development

Software Development Agile Agile is an insurance policy for market changes. By designing your solution according to this methodology, your project remains flexible and is always ready for change. It is always better to correct the mistake early in the process. With this method, you keep your finger on the pulse of a dynamic market and changing user expectations. As a result, you can continuously adapt, change your strategy, and create a product that will be in demand by the target audience, even if preferences have changed during the development process. DevOps DevOps is one more way to optimize the development budget of your application. A key DevOps approach is that this practice and its culture allow team members to better interact with each other and the customer. The software development team and those responsible for the operation of the application share responsibilities clearly, and it helps you avoid shifting responsibilities from one team member to another. DevOps involves th...
Post a Comment
Read more