c# - SequenceEqual linq 组

Question

我使用 c# 3.5 和 linq 编写了一个简单的程序。

我有课

public class Product
{
    public Product()
    {

    }

    public int RoleId { get; set; }
    public int ObjectId { get; set; }
    public bool Read { get; set; }

    public override bool Equals(object obj)
    {
        return Equals((Product) obj);
    }

    public bool Equals(Product other)
    {
        return ObjectId == other.ObjectId && Read == other.Read;
    }

}

我正在尝试比较列表。

List<Product> products = new List<Product>() 
{ 
    new Product { RoleId = 1, ObjectId = 2, Read = false }, 
    new Product { RoleId = 2, ObjectId = 1, Read = false }, 
    new Product { RoleId = 1, ObjectId = 1, Read = true } 
};

var groupedCustomerList = products.GroupBy(u => u.RoleId)
                                  .Select(grp => grp.ToList()).ToList();

var firstGroup = groupedCustomerList.ElementAt(0);

List<Product> productsListSearch = new List<Product>() 
{ 
    new Product {ObjectId = 1, Read = true }, 
    new Product {ObjectId = 2, Read = false } 
};

var result= productsListSearch.SequenceEqual(firstGroup);

为什么结果不正确？ 我需要对元素进行分类？

Answer 1

它们不是顺序相等的，因为对象的顺序不同。如果您像这样更改 productsListSearch

List<Product> productsListSearch = new List<Product>() 
{ 
    new Product {ObjectId = 2, Read = false } 
,   new Product {ObjectId = 1, Read = true }
};

SequenceEqual 将返回 True。

Demo on ideone .

通常，您不应依赖 LINQ 生成的组中项目的顺序，除非您自己设置顺序:

var groupedCustomerList = products.GroupBy(u => u.RoleId)
    .Select(grp => grp.OrderBy(p => ...).ToList()).ToList();

注意:您的 Product 类会覆盖 Equals 而不会覆盖 GetHashCode。如果您决定在散列集中使用 Product 或将其用作基于散列的字典的键，这将是有问题的。