编辑:在EF 6.1.1版本中修复。这个答案是不实际的

对于SQL Server和EF4-6, Count()的执行速度比Any()快两倍。

当你运行Table.Any()时，它会生成类似这样的东西(警告:不要伤害大脑试图理解它)

SELECT 
CASE WHEN ( EXISTS (SELECT 
    1 AS [C1]
    FROM [Table] AS [Extent1]
)) THEN cast(1 as bit) WHEN ( NOT EXISTS (SELECT 
    1 AS [C1]
    FROM [Table] AS [Extent2]
)) THEN cast(0 as bit) END AS [C1]
FROM  ( SELECT 1 AS X ) AS [SingleRowTable1]

这需要对符合条件的行进行两次扫描。

我不喜欢写Count() > 0，因为它隐藏了我的意图。我更喜欢使用自定义谓词:

public static class QueryExtensions
{
    public static bool Exists<TSource>(this IQueryable<TSource> source, Expression<Func<TSource, bool>> predicate)
    {
        return source.Count(predicate) > 0;
    }
}

编辑:在EF 6.1.1版本中修复。这个答案是不实际的

对于SQL Server和EF4-6, Count()的执行速度比Any()快两倍。

当你运行Table.Any()时，它会生成类似这样的东西(警告:不要伤害大脑试图理解它)

SELECT 
CASE WHEN ( EXISTS (SELECT 
    1 AS [C1]
    FROM [Table] AS [Extent1]
)) THEN cast(1 as bit) WHEN ( NOT EXISTS (SELECT 
    1 AS [C1]
    FROM [Table] AS [Extent2]
)) THEN cast(0 as bit) END AS [C1]
FROM  ( SELECT 1 AS X ) AS [SingleRowTable1]

这需要对符合条件的行进行两次扫描。

我不喜欢写Count() > 0，因为它隐藏了我的意图。我更喜欢使用自定义谓词:

public static class QueryExtensions
{
    public static bool Exists<TSource>(this IQueryable<TSource> source, Expression<Func<TSource, bool>> predicate)
    {
        return source.Count(predicate) > 0;
    }
}

由于这是一个相当流行的话题，答案各不相同，我不得不重新审视这个问题。

测试env: EF 6.1.3, SQL Server, 300k记录

表模型:

class TestTable
{
    [Key]
    public int Id { get; set; }

    public string Name { get; set; }

    public string Surname { get; set; }
}

测试代码:

class Program
{
    static void Main()
    {
        using (var context = new TestContext())
        {
            context.Database.Log = Console.WriteLine;

            context.TestTables.Where(x => x.Surname.Contains("Surname")).Any(x => x.Id > 1000);
            context.TestTables.Where(x => x.Surname.Contains("Surname") && x.Name.Contains("Name")).Any(x => x.Id > 1000);
            context.TestTables.Where(x => x.Surname.Contains("Surname")).Count(x => x.Id > 1000);
            context.TestTables.Where(x => x.Surname.Contains("Surname") && x.Name.Contains("Name")).Count(x => x.Id > 1000);

            Console.ReadLine();
        }
    }
}

结果:

Any() ~ 3ms

Count()第一次查询~ 230ms，第二次查询~ 400ms

备注:

对于我的案例，EF没有像@Ben在他的帖子中提到的那样生成SQL。

注意:我写这个答案时实体框架4是实际的。这个答案的重点并不是要进行琐碎的. any () vs . count()性能测试。重点是要表明EF远非完美。更新的版本更好…但是如果你有部分代码很慢，并且使用EF，请直接使用TSQL测试并比较性能，而不是依赖于假设(. any()总是比. count() > 0快)。

虽然我同意大多数赞成的答案和评论-特别是在这一点上，任何信号开发人员的意图都比Count() > 0 -我有过这样的情况，在SQL Server (EntityFramework 4)上，Count的速度要快一个数量级。

下面是使用Any查询的w超时异常(在~200.000条记录上):

con = db.Contacts.
    Where(a => a.CompanyId == companyId && a.ContactStatusId <= (int) Const.ContactStatusEnum.Reactivated
        && !a.NewsletterLogs.Any(b => b.NewsletterLogTypeId == (int) Const.NewsletterLogTypeEnum.Unsubscr)
    ).OrderBy(a => a.ContactId).
    Skip(position - 1).
    Take(1).FirstOrDefault();

以毫秒为单位执行的计数版本:

con = db.Contacts.
    Where(a => a.CompanyId == companyId && a.ContactStatusId <= (int) Const.ContactStatusEnum.Reactivated
        && a.NewsletterLogs.Count(b => b.NewsletterLogTypeId == (int) Const.NewsletterLogTypeEnum.Unsubscr) == 0
    ).OrderBy(a => a.ContactId).
    Skip(position - 1).
    Take(1).FirstOrDefault();

我需要找到一种方法来查看两个linq产生的确切SQL -但很明显，在某些情况下，Count和Any之间存在巨大的性能差异，不幸的是，似乎您不能在所有情况下都坚持使用Any。

编辑:这里是生成的sql。你可以看到的美;)

ANY:

exec sp_executesql N'SELECT TOP (1) 
[Project2].[ContactId] AS [ContactId], 
[Project2].[CompanyId] AS [CompanyId], 
[Project2].[ContactName] AS [ContactName], 
[Project2].[FullName] AS [FullName], 
[Project2].[ContactStatusId] AS [ContactStatusId], 
[Project2].[Created] AS [Created]
FROM ( SELECT [Project2].[ContactId] AS [ContactId], [Project2].[CompanyId] AS [CompanyId], [Project2].[ContactName] AS [ContactName], [Project2].[FullName] AS [FullName], [Project2].[ContactStatusId] AS [ContactStatusId], [Project2].[Created] AS [Created], row_number() OVER (ORDER BY [Project2].[ContactId] ASC) AS [row_number]
    FROM ( SELECT 
        [Extent1].[ContactId] AS [ContactId], 
        [Extent1].[CompanyId] AS [CompanyId], 
        [Extent1].[ContactName] AS [ContactName], 
        [Extent1].[FullName] AS [FullName], 
        [Extent1].[ContactStatusId] AS [ContactStatusId], 
        [Extent1].[Created] AS [Created]
        FROM [dbo].[Contact] AS [Extent1]
        WHERE ([Extent1].[CompanyId] = @p__linq__0) AND ([Extent1].[ContactStatusId] <= 3) AND ( NOT EXISTS (SELECT 
            1 AS [C1]
            FROM [dbo].[NewsletterLog] AS [Extent2]
            WHERE ([Extent1].[ContactId] = [Extent2].[ContactId]) AND (6 = [Extent2].[NewsletterLogTypeId])
        ))
    )  AS [Project2]
)  AS [Project2]
WHERE [Project2].[row_number] > 99
ORDER BY [Project2].[ContactId] ASC',N'@p__linq__0 int',@p__linq__0=4

数:

exec sp_executesql N'SELECT TOP (1) 
[Project2].[ContactId] AS [ContactId], 
[Project2].[CompanyId] AS [CompanyId], 
[Project2].[ContactName] AS [ContactName], 
[Project2].[FullName] AS [FullName], 
[Project2].[ContactStatusId] AS [ContactStatusId], 
[Project2].[Created] AS [Created]
FROM ( SELECT [Project2].[ContactId] AS [ContactId], [Project2].[CompanyId] AS [CompanyId], [Project2].[ContactName] AS [ContactName], [Project2].[FullName] AS [FullName], [Project2].[ContactStatusId] AS [ContactStatusId], [Project2].[Created] AS [Created], row_number() OVER (ORDER BY [Project2].[ContactId] ASC) AS [row_number]
    FROM ( SELECT 
        [Project1].[ContactId] AS [ContactId], 
        [Project1].[CompanyId] AS [CompanyId], 
        [Project1].[ContactName] AS [ContactName], 
        [Project1].[FullName] AS [FullName], 
        [Project1].[ContactStatusId] AS [ContactStatusId], 
        [Project1].[Created] AS [Created]
        FROM ( SELECT 
            [Extent1].[ContactId] AS [ContactId], 
            [Extent1].[CompanyId] AS [CompanyId], 
            [Extent1].[ContactName] AS [ContactName], 
            [Extent1].[FullName] AS [FullName], 
            [Extent1].[ContactStatusId] AS [ContactStatusId], 
            [Extent1].[Created] AS [Created], 
            (SELECT 
                COUNT(1) AS [A1]
                FROM [dbo].[NewsletterLog] AS [Extent2]
                WHERE ([Extent1].[ContactId] = [Extent2].[ContactId]) AND (6 = [Extent2].[NewsletterLogTypeId])) AS [C1]
            FROM [dbo].[Contact] AS [Extent1]
        )  AS [Project1]
        WHERE ([Project1].[CompanyId] = @p__linq__0) AND ([Project1].[ContactStatusId] <= 3) AND (0 = [Project1].[C1])
    )  AS [Project2]
)  AS [Project2]
WHERE [Project2].[row_number] > 99
ORDER BY [Project2].[ContactId] ASC',N'@p__linq__0 int',@p__linq__0=4

似乎纯粹的Where with EXISTS比计算Count然后用Count == 0执行Where要差得多。

如果你们发现我的发现有错误，请告诉我。不管Any vs Count的讨论如何，我们可以从所有这些中得出的结论是，任何更复杂的LINQ在重写为存储过程时都要好得多。

你可以做一个简单的测试来弄清楚:

var query = //make any query here
var timeCount = new Stopwatch();
timeCount.Start();
if (query.Count > 0)
{
}
timeCount.Stop();
var testCount = timeCount.Elapsed;

var timeAny = new Stopwatch();
timeAny.Start();
if (query.Any())
{
}
timeAny.Stop();
var testAny = timeAny.Elapsed;

检查testCount和testAny的值。

如果您从具有. length或. count的东西开始(例如ICollection<T>， IList<T>， List<T>，等等)，那么这将是最快的选项，因为它不需要通过Any()所要求的GetEnumerator()/MoveNext()/Dispose()序列来检查非空IEnumerable<T>序列。

对于IEnumerable<T>，则Any()通常会更快，因为它只需要查看一次迭代。但是，请注意Count()的LINQ-to-Objects实现确实检查ICollection<T>(使用.Count作为优化)-因此，如果您的底层数据源直接是一个列表/集合，则不会有很大的区别。不要问我为什么不使用非泛型的ICollection…

当然，如果你已经使用LINQ来过滤它(Where等)，你将有一个基于迭代器块的序列，所以这个ICollection<T>优化是无用的。

通常，对于IEnumerable<T>:坚持使用Any();-p