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.


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 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 …

Entity Framework (EF) TransactionScope vs Database.BeginTransaction

In today blog post we will talk a little about a new feature that is available on EF6+ related to Transactions.
Until now, when we had to use transaction we used ‘TransactionScope’. It works great and I would say that is something that is now in our blood.
using (var scope = new TransactionScope(TransactionScopeOption.Required)) { using (SqlConnection conn = new SqlConnection("...")) { conn.Open(); SqlCommand sqlCommand = new SqlCommand(); sqlCommand.Connection = conn; sqlCommand.CommandText = ... sqlCommand.ExecuteNonQuery(); ... } scope.Complete(); } Starting with EF6.0 we have a new way to work with transactions. The new approach is based on Database.BeginTransaction(), Database.Rollback(), Database.Commit(). Yes, no more TransactionScope.
In the followi…

GET call of REST API that contains '/'-slash character in the value of a parameter

Let’s assume that we have the following scenario: I have a public HTTP endpoint and I need to post some content using GET command. One of the parameters contains special characters like “\” and “/”. If the endpoint is an ApiController than you may have problems if you encode the parameter using the http encoder.
using (var httpClient = new HttpClient()) { httpClient.BaseAddress = baseUrl; Task<HttpResponseMessage> response = httpClient.GetAsync(string.Format("api/foo/{0}", "qwert/qwerqwer"))); response.Wait(); response.Result.EnsureSuccessStatusCode(); } One possible solution would be to encode the query parameter using UrlTokenEncode method of HttpServerUtility class and GetBytes method ofUTF8. In this way you would get the array of bytes of the parameter and encode them as a url token.
The following code show to you how you could write the encode and decode methods.