刚升级到v2,这不再有效;如果我尝试使用Count(),我会收到类似的错误
public class Deck_Ratings : AbstractIndexCreationTask<DeckRating, Deck_Ratings.ReduceResult>
{
public class ReduceResult
{
public string DeckId { get; set; }
public int Rating { get; set; }
}
public Deck_Ratings()
{
Map = deckRatings => deckRatings.Select(deckRating => new
{
deckRating.DeckId,
deckRating.Rating
});
Reduce = reduceResults => reduceResults
.GroupBy(reduceResult => reduceResult.DeckId)
.Select(grouping => new
{
DeckId = grouping.Key,
Rating = grouping.Average(reduceResult => reduceResult.Rating)
});
}
}
解决方法:
禁止可能受reduce批量大小影响的聚合(例如Count和Average),因为它们会产生错误的结果.您可能已经能够在1.0下使用它,但您的平均值可能是错误的,除非您拥有的项目非常少,以至于它们都在一个减少批次中完成.要了解有关减少批次的更多信息,请阅读Map / Reduce – A Visual Explanation
您必须通过将每个项目的总和相加来计算项目.您必须通过将值的总和作为总和,将1的总和作为计数,然后除以它们来平均项目.
public class Deck_Ratings : AbstractIndexCreationTask<DeckRating, Deck_Ratings.ReduceResult>
{
public class ReduceResult
{
public string DeckId { get; set; }
public int TotalRating { get; set; }
public int CountRating { get; set; }
public double AverageRating { get; set; }
}
public Deck_Ratings()
{
Map = deckRatings => deckRatings.Select(deckRating => new
{
deckRating.DeckId,
TotalRating = deckRating.Rating,
CountRating = 1,
AverageRating = 0
});
Reduce = reduceResults => reduceResults
.GroupBy(reduceResult => reduceResult.DeckId)
.Select(grouping => new
{
DeckId = grouping.Key,
TotalRating = grouping.Sum(reduceResult => reduceResult.TotalRating)
CountRating = grouping.Sum(reduceResult => reduceResult.CountRating)
})
.Select(x => new
{
x.DeckId,
x.TotalRating,
x.CountRating,
AverageRating = x.TotalRating / x.CountRating
});
}
}
标签:c,net,ravendb 来源: https://codeday.me/bug/20190529/1180085.html
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