問題描述
我將 EF5 與 MoreLinq 擴展一起使用，在生產中測試我的程序(非常大的數(shù)據(jù)庫)時，我發(fā)現(xiàn)該行:
I am using EF5 with the MoreLinq extenstion, while testing my program in production (very big database), I found out that the line:
var x = db.TheBigTable.MaxBy(x => x.RecordTime);
需要很長時間(RecordTime 是一個非索引的datetime)
Takes very long time (RecordTime is a non-indexed datetime)
是不是因為MaxBy 總是在客戶端運行(并且首先從數(shù)據(jù)庫中獲取所有記錄)?
Is that because MaxBy always runs on the client side (and firstly gets ALL records from the database)?
推薦答案
這里是 MaxBy 擴展方法:
Here is the signature of the MaxBy extension method:
public static TSource MaxBy<TSource, TKey>(this IEnumerable<TSource> source,
Func<TSource, TKey> selector)
{
return source.MaxBy(selector, Comparer<TKey>.Default);
}
它返回 IEnumerable 的最大元素(基于給定的投影)，而不是 IQueryable.所以查詢db.TheBigTable的結果確實都是先加載到內存中，然后迭代求最大值.
It returns the maximal element (based on the given projection) of an IEnumerable<T>, not an IQueryable<T>. So the results of the query db.TheBigTable are indeed all loaded into memory first, and then they are iterated to find the maximum.
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