Question

我在基础数据访问层（LazySave<T>）中为对象数据库创建了BaseDAL。

public void LazySave<T>(IEnumerable<T> TList, Func<T, T, bool> condition, IEqualityComparer<T> comparer) where T : class
{
  //Select where GetOne<T> returns null, meaning this item doesn't exist
  var itemsToStore = TList.Where(TItem => GetOne<T>(e => condition(TItem, e)) == null);
  //Select where GetOne<T> returns not null, meaning this item exists
  var itemsToUpdate = TList.Where(TItem => GetOne<T>(e => condition(TItem, e)) != null);
  //Get all of the items
  var allItems = GetMany<T>();
  //Any items which aren't in TList but are in the original list need to be deleted
  var itemsToDelete = TList.Intersect(allItems, comparer);
  itemsToStore.ToList().ForEach(i => Store<T>(i));
  itemsToUpdate.ToList().ForEach(i => Update<T>(i, condition));
  itemsToDelete.ToList().ForEach(i => Delete<T>(i, condition));
}

我将以下对象和比较器传递给方法。

public class BankHoliday : IBankHoliday, IEquatable<BankHoliday>
{
  public DateTime Date { get; set; }

  public bool Equals(BankHoliday other)
  {
    return other.Date == Date;
  }
}

public class BankHolidayComparer : IEqualityComparer<BankHoliday>
{
  public bool Equals(BankHoliday x, BankHoliday y)
  {
    return x.Date == y.Date;
  }

  public int GetHashCode(BankHoliday obj)
  {
    if (object.ReferenceEquals(obj, null)) return 0;
    return obj.Date.GetHashCode();
  }
}

被称为：

var comparer = (IEqualityComparer<BankHoliday>)new BankHolidayComparer();
bhDAL.LazySave<BankHoliday>(holidays, ((T, T2) => T.Date == T2.Date), comparer);

数据库中的列表有11个日期。我删除了一个，然后拨打LazySave，将10个项目传递到TList，但Intersect没有返回结果，甚至没有点击Equals或GetHashCode。任何想法＆gt;我认为这与我的比较器有关...

Answer 1

根据您的评论，您误解了Intersect的目的：

//Any items which aren't in TList but are in the original list need to be deleted
var itemsToDelete = TList.Intersect(allItems, comparer);

Intersect在两个序列中找到的项目。根据你的评论，我怀疑你想要Except：

var itemsToDelete = allItems.Except(TList, comparer);

如果在使用Equals时未调用您的自定义GetHashCode和Intersect方法，则表明 allItems 或 TList（顺便说一句是奇数参数名称）是空的。

Answer 2

我相信IEqualityComparer是用于比较对象实例的外部类吗？

在BankHoliday类上，尝试使用覆盖实现IEquatable：

public override bool Equals(object obj)

和

public override int GetHashCode()

编辑：并使用@ Jon的除外代码示例。

Answer 3

这可能是一个愚蠢的问题，但只是为了确认 - 你是将你的断点放在比较器的Equals和GetHashCode上？（不是BankHoliday的方法）

由于交叉点的延迟评估，在击中断点之前必须调用下面的行。

itemsToDelete.ToList().ForEach(i => Delete<T>(i, condition));

IEnumerable <t>与泛型方法</t>中的comparer相交

3 个答案: