问题描述
我在使用 except() 方法时遇到了麻烦.它没有返回差值,而是返回原始集合.
I'm having troubles with the Except() method. Instead of returning the difference, it returns the original set.
我尝试在 Account 类中实现 IEquatable 和 IEqualityComparer.我还尝试为 Account 创建一个单独的 IEqualityComparer 类.
I've tried implementing the IEquatable and IEqualityComparer in the Account class. I've also tried creating a separate IEqualityComparer class for Account.
当从main调用Except()方法时,它似乎没有调用我自定义的Equals()方法,但是当我尝试Count()时,它确实调用了自定义的GetHashCode()方法!
When the Except() method is called from main, it doesn't seem to call my custom Equals() method, but when I tried Count(), it did call the custom GetHashCode() method!
我确定我在某个地方犯了一个小错误,我希望一双新的眼睛可以帮助我.
I'm sure I made a trivial mistake somewhere and I hope a fresh pair of eyes can help me.
主要:
IEnumerable<Account> everyPartnerID = from partner in dataContext.Partners select new Account { IDPartner = partner.ID, Name = partner.Name }; IEnumerable<Account> hasAccountPartnerID = from partner in dataContext.Partners from account in dataContext.Accounts where !partner.ID.Equals(Guid.Empty) && account.IDPartner.Equals(partner.ID) && account.Username.Equals("Special") select new Account { IDPartner = partner.ID, Name = partner.Name }; IEnumerable<Account> noAccountPartnerID = everyPartnerID.Except( hasAccountPartnerID, new LambdaComparer<Account>((x, y) => x.IDPartner.Equals(y.IDPartner)));
帐户:
public class Account : IEquatable<Account> { public Guid IDPartner{ get; set; } public string Name{ get; set; } /* #region IEquatable<Account> Members public bool Equals(Account other) { return this.IDPartner.Equals(other.IDPartner); } #endregion*/ }
LambdaComparer:
LambdaComparer:
public class LambdaComparer<T> : IEqualityComparer<T> { private readonly Func<T, T, bool> _lambdaComparer; private readonly Func<T, int> _lambdaHash; public LambdaComparer(Func<T, T, bool> lambdaComparer) : this(lambdaComparer, o => o.GetHashCode()) { } public LambdaComparer(Func<T, T, bool> lambdaComparer, Func<T, int> lambdaHash) { if (lambdaComparer == null) throw new ArgumentNullException("lambdaComparer"); if (lambdaHash == null) throw new ArgumentNullException("lambdaHash"); _lambdaComparer = lambdaComparer; _lambdaHash = lambdaHash; } public bool Equals(T x, T y) { return _lambdaComparer(x, y); } public int GetHashCode(T obj) { return _lambdaHash(obj); } }
推荐答案
当你只传入一个函数时,基本上你的 LambdaComparer 类被破坏了,因为它使用身份哈希码"提供者,如果你不提供任何其他东西.Except 使用了哈希码,这就是导致问题的原因.
Basically your LambdaComparer class is broken when you pass in just a single function, because it uses the "identity hash code" provider if you don't provide anything else. The hash code is used by Except, and that's what's causing the problem.
这里有三个选项:
实现您自己的 ExceptBy 方法,然后最好将其贡献给 MoreLINQ 包含那种东西.
Implement your own ExceptBy method and then preferably contribute it to MoreLINQ which contains that sort of thing.
使用 IEqualityComparer
Use a different implementation of IEqualityComparer<T>. I have a ProjectionEqualityComparer class you can use in MiscUtil - or you can use the code as posted in another question.
将 lambda 表达式传递到您的 LambdaComparer 代码中以用于哈希:
Pass a lambda expression into your LambdaComparer code to use for the hash:
new LambdaComparer<Account>((x, y) => x.IDPartner.Equals(y.IDPartner)), x => x.IDPartner.GetHashCode());