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c#entity-frameworklinq-to-sqlmorelinq
Ofiris
Ofiris

Reputation: 6151

MoreLinq maxBy vs LINQ max + where

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);

Takes very long time (RecordTime is a non-indexed datetime)

Is that because MaxBy always runs on the client side (and firstly gets ALL records from the database)?

Upvotes: 5

Views: 11123

Answers (1)

dtb
dtb

Reputation: 217341

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);
}

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.

Upvotes: 9

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