Question

我需要同步在线数据库和本地数据库的约会。到目前为止，这是我的代码：

        List<Appointment> onlineAppointments = new List<Appointment>();
        List<Appointment> localAppointments = new List<Appointment>();
        Appointment appointment01 = new Appointment(new DateTime(2012, 12, 24, 17, 30, 00), new DateTime(2012, 12, 24, 17, 45, 00), name, 123, "comment", 0, "test", 123, 1, DateTime.Now);
        Appointment appointment02 = new Appointment(new DateTime(2012, 12, 24, 17, 30, 00), new DateTime(2012, 12, 24, 17, 45, 00), name, 123, "comment", 0, "test", 123, 1, DateTime.Now);

        onlineAppointments.Add(appointment01);
        localAppointments.Add(appointment02);

因为我只想比较我创建IEqualityComparer的对象的一些属性：

public class AppointmentEqualityComparer<T> : IEqualityComparer<T> where T : Appointment
{
    #region IEqualityComparer<T> Members

    public bool Equals(T x, T y)
    {
        return (x == null && y == null) || ((x != null && y != null) &&
        (x.getAppointmentStart() == y.getAppointmentStart() &&
        x.getAppointmentEnd() == y.getAppointmentEnd())
        );
    }

    /// </exception>
    public int GetHashCode(T obj)
    {
        if (obj == null)
        {
            throw new ArgumentNullException("obj");
        }

        return obj.GetHashCode();
    }

    #endregion
}

不幸的是，这不起作用：

var comparer = new AppointmentEqualityComparer<Appointment>();    
IEnumerable<Appointment> diffOnlineOffline = onlineAppointments.Except(localAppointments, comparer);

含义diffOnlineOffline不为空，但应该是因为两个列表都包含相同的约会。

有什么想法吗？

Answer 1

您的GetHashCode方法应使用用于相等的属性。目前，您想要考虑的对象可能没有相同的哈希码。

您可以使用以下内容：

public int GetHashCode(T obj)
{
    return 41 * (41 * (41 * (41 + obj.getAppointmentStart().GetHashCode())) 
    + obj.getAppointmentEnd().GetHashCode());
}

Answer 2

我怀疑问题出在getAppointmentStart和getAppointmentEnd方法上。以下是具有相同等式比较器的简洁版本的代码，但使用的属性按预期工作：

public class Appointment
{
    private int Id { get; set; }
    public DateTime Start { get; set; }
    public DateTime End { get; set; }

    public Appointment( int id, DateTime start, DateTime end )
    {
        Start = start;
        End = end;
        Id = id;
    }
}


public class AppointmentEqualityComparer<T> : IEqualityComparer<T> where T : Appointment
{
    #region IEqualityComparer<T> Members

    public bool Equals( T x, T y )
    {
        return ( x == null && y == null )
                || ( ( x != null && y != null ) && ( x.Start == y.Start && x.End == y.End ) );
    }

    public int GetHashCode( T obj )
    {
        if( obj == null )
        {
            throw new ArgumentNullException( "obj" );
        }

        return obj.GetHashCode();
    }

    #endregion
}

实施：

var onlineAppointments = new List<Appointment>();
var localAppointments = new List<Appointment>();
var appointment01 = new Appointment( 1, new DateTime( 2012, 12, 24, 17, 30, 00 ),
                                        new DateTime( 2012, 12, 24, 17, 45, 00 ) );
var appointment02 = new Appointment( 2, new DateTime( 2012, 12, 24, 17, 30, 00 ),
                                        new DateTime( 2012, 12, 24, 17, 45, 00 ) );

onlineAppointments.Add( appointment01 );
localAppointments.Add( appointment02 );

var comparer = new AppointmentEqualityComparer<Appointment>();
var diffOnlineOffline = onlineAppointments.Except( localAppointments, comparer ).ToList();

diffOnlineOffline仅显示第一个约会。这导致得出结论：getAppointmentStart和getAppointmentEnd方法返回的值不是构造函数中使用的实际日期。

Answer 3

您需要在Appointment类中实现IEqualityComparer

比较列表中对象的属性

3 个答案: