Skip to main content

Definirea unui mecanism de comparare a entitatiilor din punct de vedere a structurii folosind IStructuralEquatable

Uneori avem nevoie sa putem compara clasele de tip POCO ca pe niste structuri. De exemplu daca avem clasa Student, dorim sa comparam entitatile de acest tip din punct de vedere a datelor pe care le contin.
class Student
{
public string Nume{ get;set;}
public string Prenume{ get;set;}
public int Varsta{ get;set;}
}
Pentru acest lucru sa folosim IStructuralEquatable. Aceasta interfata a fost creata pentru a fi folosita in tupluri. In cazul acestora, doua tupluri sunt egale daca fiecare element din tuplu este egal din celalalt tuplu.
Interfata contine doua metode:
bool Equals(Object other, IEqualityComparer comparer);
int GetHashCode(IEqualityComparer comparer);
Prin intermediul parametrului comparer se defineste mecanismul de comparare. Exista cateva implementari in .NET pentru IEqualityComparer prin care putem sa comparam siruriile de elemente - element cu element.
Valoarea default a acestui parametru este EqualityComparer>Object<.Default.Equals in cazul in care se foloseste mecanismul standard de comparare. O alta implementare este StructuralComparisons.StructuralEqualityComparer. Aceasta este folosita cand lucram cu tupluri sau cu clase ce implementeaza IStructuralEquatable.
Dar ne putem defini si noi propriul mecanism de comparare daca implementam IEqualityComparer. De exemplu in cazul nostru am putea sa avem:
public class FullNameComparer
{
public new bool Equals(object s1, object s2)
{
...
var student1 = s1 as Student;
var student2 = s2 as Student;
return student1.Nume == student2.Nume && student1.Prenume == student2.Prenume;
}
}
Pentru a putea compara doi studenti putem sa apelam( clasa Student trebuie sa implementeze IStructuralEquatable):

var student1 = new Student() { ... };
var student2 = new Student() { ... };
bool areEquals = student1.Equals(student2, new FullNameComparer());
Unde ne este utiliza aceasta interfata. Cand avem nevoie sa definim mai multe mecanism de comparare pentru o clasa de un anumit fel. Prin acest mecanism putem foarte usor sa trimitem printr-un parametru modul in care sa se faca compararea. Cel mai bine aceasta interfata se preteaza cand lucram cu tupluri.
Exista nenumarate solutii la aceasta problema, depinde de la caz.

Comments

Popular posts from this blog

ADO.NET provider with invariant name 'System.Data.SqlClient' could not be loaded

Today blog post will be started with the following error when running DB tests on the CI machine:
threw exception: System.InvalidOperationException: The Entity Framework provider type 'System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer' registered in the application config file for the ADO.NET provider with invariant name 'System.Data.SqlClient' could not be loaded. Make sure that the assembly-qualified name is used and that the assembly is available to the running application. See http://go.microsoft.com/fwlink/?LinkId=260882 for more information. at System.Data.Entity.Infrastructure.DependencyResolution.ProviderServicesFactory.GetInstance(String providerTypeName, String providerInvariantName) This error happened only on the Continuous Integration machine. On the devs machines, everything has fine. The classic problem – on my machine it’s working. The CI has the following configuration:

TeamCity.NET 4.51EF 6.0.2VS2013
It seems that there …

How to check in AngularJS if a service was register or not

There are cases when you need to check in a service or a controller was register in AngularJS.
For example a valid use case is when you have the same implementation running on multiple application. In this case, you may want to intercept the HTTP provider and add a custom step there. This step don’t needs to run on all the application, only in the one where the service exist and register.
A solution for this case would be to have a flag in the configuration that specify this. In the core you would have an IF that would check the value of this flag.
Another solution is to check if a specific service was register in AngularJS or not. If the service was register that you would execute your own logic.
To check if a service was register or not in AngularJS container you need to call the ‘has’ method of ‘inhector’. It will return TRUE if the service was register.
if ($injector.has('httpInterceptorService')) { $httpProvider.interceptors.push('httpInterceptorService&#…

Fundamental Books of a Software Engineer (version 2018)

More then six years ago I wrote a blog post about fundamental books that any software engineer (developer) should read. Now it is an excellent time to update this list with new entries.

There are 5 different categories of books, that represent the recommended path. For example, you start with Coding books, after that, you read books about Programming, Design and so on.
There are some books about C++ that I recommend not because you shall know C++, only because the concepts that you can learn from it.

Coding

Writing solid codeCode completeProgramming Pearls, more programming pearls(recommended)[NEW] Introduction to Algorithms

Programming

Refactoring (M. Fowler)Pragmatic ProgrammerClean code[NEW] Software Engineering: A Practitioner's Approach[NEW] The Mythical Man-Month[NEW] The Art of Computer Programming

Design

Applying UML and Patterns (GRASP patterns)C++ coding standards (Sutter, Alexandrescu)The C++ programming language (Stroustrup, Part IV)Object-oriented programming (Peter Coad)P…