Question

Nhibernate强制您使用Iesi Set，而不是net 4 ISet接口。在下面的代码片段中，我检查一个iesi集是否包含一个项目：

    public virtual void Remove(Substance substance)
    {
        var test = _substances.First() == substance;

        if (!_substances.Contains(substance)) return;

        _substances.Remove(substance);
        substance.SubstanceGroup = null;
    }

变量_substances引用HashedSet。我添加了测试var只是为了检查代码作为临时措施。我像这样覆盖了Equals方法：

    public override int GetHashCode()
    {
        return Equals(Id, default(TId)) ? base.GetHashCode() : Id.GetHashCode();
    }

这会导致项目将Id（Guid）作为哈希返回。如果我签入调试器，我会得到以下结果：

test
true
_substances.Contains(substance)
false
_substances.First().GetHashCode()
-2974953
substance.GetHashCode()
-2974953

如何使用该集合的contains方法在集合中找不到完全相同的对象？我甚至可以在调试器中执行此操作：

_substances.Contains(_substances.First())
false

显然，_substances.Remove（物质）也不起作用。经过一些额外的研究后，我发现NH用它自己的Persistent Generic集取代了该集合。使用此套件时会出现问题。如果我从该集合中检索一个项目并且我在同一个集合上调用Contains，它总是返回false。我已经覆盖了GetHashCode和Equals，甚至在Equals方法中返回true。

Answer 1

您的Equals和GetHashCode实现有问题，因为我向您保证Iesi ISet集合正常运行。它被PersistentGenericSet取代的原因是ISet只是一个接口，集合必须由具体类型替换。如果没有更多的代码，很难看出问题出在哪里，所以我在下面粘贴了一个更好的平等实现。我可以在你的问题中看到的一个问题是，在分配Id之后哈希码会改变，我的版本通过缓存哈希码来处理它。

public class Substance
{
    private int? _cachedHashCode;

    public Substance()
    {
        Id = Guid.Empty;
    }

    public Substance(Guid id)
    {
        Id = id;
    }

    public Guid Id { get; set; }

    public bool IsTransient
    {
        get { return Id == Guid.Empty; }
    }

    public bool Equals(Substance other)
    {
        if (IsTransient ^ other.IsTransient)
        {
            return false;
        }
        if (IsTransient && other.IsTransient)
        {
            return ReferenceEquals(this, other);
        }
        return other.Id.Equals(Id);
    }

    public override bool Equals(object obj)
    {
        if (obj == null || obj.GetType() != GetType())
        {
            return false;
        }
        var other = (Substance)obj;
        return Equals(other);
    }

    public override int GetHashCode()
    {
        if (!_cachedHashCode.HasValue)
        {
            _cachedHashCode = IsTransient ? base.GetHashCode() : Id.GetHashCode();
        }
        return _cachedHashCode.Value;
    }
}

public class Mixture
{
    public Mixture()
    {
        Substances = new HashedSet<Substance>();
    }

    public ISet<Substance> Substances { get; set; }
}

public class Tests
{
    [Test]
    public void set_contains_transient_substance()
    {
        var mixture = new Mixture();
        var s1 = new Substance();
        mixture.Substances.Add(s1);
        Assert.IsTrue(mixture.Substances.Contains(s1));
    }

    [Test]
    public void set_contains_persistent_substance()
    {
        var id = Guid.NewGuid();
        var mixture = new Mixture();

        var s1 = new Substance(id);
        mixture.Substances.Add(s1);

        var s2 = new Substance(id);
        // these were created with the same id so hash code is not cached
        // and id equality is used
        Assert.IsTrue(mixture.Substances.Contains(s2));
    }

    [Test]
    public void remove_substance()
    {
        var id = Guid.NewGuid();
        var mixture = new Mixture();

        var s1 = new Substance(id);
        mixture.Substances.Add(s1);

        var s2 = new Substance(id);
        mixture.Substances.Remove(s2);
        Assert.IsTrue(mixture.Substances.Count() == 0);
    }

    [Test]
    public void hash_code_is_cached()
    {
        var s1 = new Substance(Guid.NewGuid());
        var s2 = new Substance(Guid.NewGuid());

        var mixture = new Mixture();
        mixture.Substances.Add(s1);

        Assert.IsFalse(mixture.Substances.Contains(s2));
        // assign s1 id to s2, s2 hashcode is cached so they are not equal
        s2.Id = s1.Id;
        Assert.IsFalse(mixture.Substances.Contains(s2));
    }

}

Nhibernate iesicollection包含返回false

1 个答案: