public class EqualityComparer123 : IEqualityComparer<ClassA>
    {
        Func<ClassA, ClassA, bool> pred;
        public EqualityComparer123(Func<ClassA, ClassA, bool> pred)
        {
            this.pred = pred;
        }

        public bool Equals(ClassA x, ClassA y)
        {
            //return x.id == y.id;
            return pred(x, y);
        }

        public int GetHashCode(ClassA obj)
        {
            return base.GetHashCode();
        }
    }

    public class TEqualityComparer<T> : IEqualityComparer<T>
    {
        Func<T, T, bool> pred;

        public TEqualityComparer(Func<T, T, bool> pred)
        {
            this.pred = pred;
        }

        public bool Equals(T x, T y)
        {
            return pred(x, y);
        }

        public int GetHashCode(T obj)
        {
            return obj.GetHashCode();
        }
    }

类有：

public class ClassA
    {
        public int id { set; get; }
        public string name { set; get; }
    }

代码：

var ca = new List<ClassA>();
ca.Add(new ClassA() { id = 1, name = "nima" });
ca.Add(new ClassA() { id = 2, name = "tama" });

var cb = new List<ClassA>();
cb.Add(new ClassA() { id = 1, name = "nima2" });
cb.Add(new ClassA() { id = 3, name = "tama2" });

var Compare = new EqualityComparer123((x, y) => { return x.id == y.id; });
var query = ca.Join(cb, x => x, y => y, (x, y) => new { CA = x, CB = y }, Compare);
var Compare3 = new TEqualityComparer<ClassA>((x, y) => { return x.id == y.id; });

var query3 = ca.Join(cb, x => x, y => y, (x, y) => new { CA = x, CB = y }, Compare3);

其中query1能够查询出数据，而query3却查询不出数据，望解惑。。