Backend Development
C++
How to Ensure Correct Object Equality for LINQ's Distinct Method with Custom Objects?
How to Ensure Correct Object Equality for LINQ's Distinct Method with Custom Objects?
Jan 20, 2025 pm 07:41 PM
Use IEquatable to handle object equality in LINQ Distinct
LINQ's Distinct method is designed to identify unique objects based on their equality. However, with custom objects, it may not always work as expected.
In the provided example, the Distinct method failed to identify two Author objects with the same name as duplicates. This is because LINQ treats objects as distinct based on their reference addresses rather than their property values.
In order to solve this problem, the Author interface can be implemented in the IEquatable class. By overriding the Equals method, you can define custom logic to determine equality based on property values ??FirstName and LastName. The following implementation checks matching values ??in two fields to determine equality:
public class Author : IEquatable<Author>
{
public string FirstName { get; set; }
public string LastName { get; set; }
public bool Equals(Author other)
{
if (FirstName == other?.FirstName && LastName == other?.LastName)
return true;
return false;
}
// 為保持一致性而重寫GetHashCode
public override int GetHashCode()
{
return (FirstName?.GetHashCode() ?? 0) ^ (LastName?.GetHashCode() ?? 0);
}
}
Usage:
Applying this custom implementation solves Distinct's problem. The modified code correctly identifies duplicate Author objects and removes one of them from the results:
using System.Collections.Generic;
using System.Linq;
class Program
{
static void Main(string[] args)
{
// 使用重復(fù)作者初始化書籍列表
List<Book> books = new List<Book>
{
new Book
{
Name = "C# in Depth",
Authors = new List<Author>
{
new Author { FirstName = "Jon", LastName = "Skeet" },
new Author { FirstName = "Jon", LastName = "Skeet" },
}
},
// ...
};
// 選擇作者，應(yīng)用Distinct，并打印
var temp = books.SelectMany(book => book.Authors).Distinct();
foreach (var author in temp)
{
Console.WriteLine($"{author.FirstName} {author.LastName}");
}
Console.Read();
}
}
Conclusion:
Implementing IEquatable and overriding the Equals method allows customizing the definition of object equality in LINQ operations. This ensures that Distinct methods correctly handle custom objects based on their properties rather than reference addresses.
Note that the GetHashCode method has been improved in the code example to ensure consistency with the Equals method and uses the null-conditional operator (?.) to handle potentially null properties. This avoids potential NullReferenceException exceptions.
The above is the detailed content of How to Ensure Correct Object Equality for LINQ's Distinct Method with Custom Objects?. For more information, please follow other related articles on the PHP Chinese website!
Hot AI Tools
Undress AI Tool
Undress images for free
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
Clothoff.io
AI clothes remover
Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!
Hot Article
Hot Tools
Notepad++7.3.1
Easy-to-use and free code editor
SublimeText3 Chinese version
Chinese version, very easy to use
Zend Studio 13.0.1
Powerful PHP integrated development environment
Dreamweaver CS6
Visual web development tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
Hot Topics
C Polymorphism : is function overloading a kind of polymorphism?
Jun 20, 2025 am 12:05 AM
Yes, function overloading is a polymorphic form in C, specifically compile-time polymorphism. 1. Function overload allows multiple functions with the same name but different parameter lists. 2. The compiler decides which function to call at compile time based on the provided parameters. 3. Unlike runtime polymorphism, function overloading has no extra overhead at runtime, and is simple to implement but less flexible.
What Are the Different Kinds of Polymorphism in C ? Explained
Jun 20, 2025 am 12:08 AM
C has two main polymorphic types: compile-time polymorphism and run-time polymorphism. 1. Compilation-time polymorphism is implemented through function overloading and templates, providing high efficiency but may lead to code bloating. 2. Runtime polymorphism is implemented through virtual functions and inheritance, providing flexibility but performance overhead.
C : Is Polymorphism really useful?
Jun 20, 2025 am 12:01 AM
Yes, polymorphisms in C are very useful. 1) It provides flexibility to allow easy addition of new types; 2) promotes code reuse and reduces duplication; 3) simplifies maintenance, making the code easier to expand and adapt to changes. Despite performance and memory management challenges, its advantages are particularly significant in complex systems.
C Destructors: Common Errors
Jun 20, 2025 am 12:12 AM
C destructorscanleadtoseveralcommonerrors.Toavoidthem:1)Preventdoubledeletionbysettingpointerstonullptrorusingsmartpointers.2)Handleexceptionsindestructorsbycatchingandloggingthem.3)Usevirtualdestructorsinbaseclassesforproperpolymorphicdestruction.4
C tutorial for people who know Python
Jul 01, 2025 am 01:11 AM
People who study Python transfer to C The most direct confusion is: Why can't you write like Python? Because C, although the syntax is more complex, provides underlying control capabilities and performance advantages. 1. In terms of syntax structure, C uses curly braces {} instead of indentation to organize code blocks, and variable types must be explicitly declared; 2. In terms of type system and memory management, C does not have an automatic garbage collection mechanism, and needs to manually manage memory and pay attention to releasing resources. RAII technology can assist resource management; 3. In functions and class definitions, C needs to explicitly access modifiers, constructors and destructors, and supports advanced functions such as operator overloading; 4. In terms of standard libraries, STL provides powerful containers and algorithms, but needs to adapt to generic programming ideas; 5
Polymorphism in C : A Comprehensive Guide with Examples
Jun 21, 2025 am 12:11 AM
Polymorphisms in C are divided into runtime polymorphisms and compile-time polymorphisms. 1. Runtime polymorphism is implemented through virtual functions, allowing the correct method to be called dynamically at runtime. 2. Compilation-time polymorphism is implemented through function overloading and templates, providing higher performance and flexibility.
What Are the Various Forms of Polymorphism in C ?
Jun 20, 2025 am 12:21 AM
C polymorphismincludescompile-time,runtime,andtemplatepolymorphism.1)Compile-timepolymorphismusesfunctionandoperatoroverloadingforefficiency.2)Runtimepolymorphismemploysvirtualfunctionsforflexibility.3)Templatepolymorphismenablesgenericprogrammingfo
C Destructors: Practical Code Examples
Jun 22, 2025 am 12:16 AM
C destructorsarespecialmemberfunctionsthatautomaticallyreleaseresourceswhenanobjectgoesoutofscopeorisdeleted.1)Theyarecrucialformanagingmemory,filehandles,andnetworkconnections.2)Beginnersoftenneglectdefiningdestructorsfordynamicmemory,leadingtomemo
