Equals 和 GetHashCode 都不会在 IEqualityComparer 上被调用

Question

我正在将两个 List<Dictionary<string, object>> 与我自己的 IEqualityComparer<Dictionary<string, object>> 实现进行比较，但是 GetHashCode 和 Equals 方法都没有被调用。

这是我自己的 IEqualityComparer 实现。

public class TestEqualityComparer : IEqualityComparer<Dictionary<string, object>>
{
    public bool Equals(Dictionary<string, object> a, Dictionary<string, object> b)
    {
        return true; // breakpoint here
    }

    public int GetHashCode(Dictionary<string, object> obj)
    {
        return 0; // breakpoint here
    }
}

这是一个实际的比较代码。

var a = new List<Dictionary<string, object>>();
var b = new List<Dictionary<string, object>>();

a.Add(new Dictionary<string, object> { ["id"] = 1, ["msg"] = "aaaaa" });
a.Add(new Dictionary<string, object> { ["id"] = 2, ["msg"] = "bbbbb" });
a.Add(new Dictionary<string, object> { ["id"] = 3, ["msg"] = "ccccc" });

b.Add(new Dictionary<string, object> { ["id"] = 1, ["msg"] = "zzzzz" });
b.Add(new Dictionary<string, object> { ["id"] = 2, ["msg"] = "bbbbb" });
b.Add(new Dictionary<string, object> { ["id"] = 4, ["msg"] = "ddddd" });

var except = a.Except(b, new TestEqualityComparer());

当我运行上面的代码时，断点从未被触发。有什么问题？

Answer 1

由于 LINQ uses deferred execution except 集合的内容将无法确定，除非您决定对其进行迭代，因此不会调用您的 IEqualityComparer.

要强制评估您的 Except 语句，您可以使用 foreach 对其进行迭代或将 ToList/ToArray 附加到您的语句，如下所示：

var except = a.Except(b, new TestEqualityComparer()).ToList(); // ToList forces processing of LINQ query

Equals 和 GetHashCode 都不会在 IEqualityComparer 上被调用

Neither Equals nor GetHashCode get called on IEqualityComparer

c#

linq

iequalitycomparer