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我在一個項目中使用Nhibernate，我試圖運行一個簡單的查詢來驗證用戶登錄。它工作正常，但非常慢，如果我刪除SingleOrDefault（），它會變得非常快。爲什麼在QueryOver SingleOrDefault非常慢？
所以我的問題是：爲什麼.SingleOrDefault使下面的代碼非常慢，我可以用它來代替它，使其更快？
var user = Session.QueryOver<Customer>()
.Where(c => c.Username == username)
.SingleOrDefault();
謝謝
編輯：
這可能是有點過分，但我不太清楚如何對其進行過濾。從NHibernate的過程中的SingleOrDefault步驟輸出整體：
2012-03-07 16:24:09,808 DEBUG NHibernate.Loader.Criteria.CriteriaQueryTranslator - put criteria=Username = Koste alias=this0_
2012-03-07 16:24:09,808 DEBUG NHibernate.Loader.Criteria.CriteriaQueryTranslator - returning alias=this_ for criteria=Username = Koste
2012-03-07 16:24:09,808 DEBUG NHibernate.AdoNet.AbstractBatcher - Opened new IDbCommand, open IDbCommands: 1
2012-03-07 16:24:09,808 DEBUG NHibernate.AdoNet.AbstractBatcher - Building an IDbCommand object for the SqlString: SELECT TOP (?) this_.CustomerID as CustomerID16_0_, this_.FirstName as FirstName16_0_, this_.LastName as LastName16_0_, this_.Username as Username16_0_, this_.Password as Password16_0_, this_.PersonalInformation as Personal6_16_0_, this_.LastLogin as LastLogin16_0_, this_.IsApproved as IsApproved16_0_, this_.IsReceiveRightsBulletins as IsReceiv9_16_0_, this_.CompanyID as CompanyID16_0_, this_.CustomerTypeID as Custome11_16_0_ FROM Customers.Customer this_ WHERE this_.Username = ?
2012-03-07 16:24:09,808 DEBUG NHibernate.Engine.QueryParameters - BindParameters(Positional0:NHibernate.Type.StringType) Koste -> [1]
2012-03-07 16:24:09,808 DEBUG NHibernate.Type.StringType - binding 'Koste' to parameter: 1
2012-03-07 16:24:09,808 INFO NHibernate.Loader.Loader - SELECT TOP (@p0) this_.CustomerID as CustomerID16_0_, this_.FirstName as FirstName16_0_, this_.LastName as LastName16_0_, this_.Username as Username16_0_, this_.Password as Password16_0_, this_.PersonalInformation as Personal6_16_0_, this_.LastLogin as LastLogin16_0_, this_.IsApproved as IsApproved16_0_, this_.IsReceiveRightsBulletins as IsReceiv9_16_0_, this_.CompanyID as CompanyID16_0_, this_.CustomerTypeID as Custome11_16_0_ FROM Customers.Customer this_ WHERE this_.Username = @p1
2012-03-07 16:24:09,808 DEBUG NHibernate.SQL - SELECT TOP (@p0) this_.CustomerID as CustomerID16_0_, this_.FirstName as FirstName16_0_, this_.LastName as LastName16_0_, this_.Username as Username16_0_, this_.Password as Password16_0_, this_.PersonalInformation as Personal6_16_0_, this_.LastLogin as LastLogin16_0_, this_.IsApproved as IsApproved16_0_, this_.IsReceiveRightsBulletins as IsReceiv9_16_0_, this_.CompanyID as CompanyID16_0_, this_.CustomerTypeID as Custome11_16_0_ FROM Customers.Customer this_ WHERE this_.Username = @p1;@p0 = 1 [Type: Int32 (0)], @p1 = 'Koste' [Type: String (250)]
2012-03-07 16:24:09,808 DEBUG NHibernate.Connection.DriverConnectionProvider - Obtaining IDbConnection from Driver
2012-03-07 16:24:09,840 DEBUG NHibernate.AdoNet.AbstractBatcher - ExecuteReader took 14 ms
2012-03-07 16:24:09,840 DEBUG NHibernate.AdoNet.AbstractBatcher - Opened IDataReader, open IDataReaders: 1
2012-03-07 16:24:09,840 DEBUG NHibernate.Loader.Loader - processing result set
2012-03-07 16:24:09,840 DEBUG NHibernate.Loader.Loader - result set row: 0
2012-03-07 16:24:09,840 DEBUG NHibernate.Type.Int32Type - returning '1' as column: CustomerID16_0_
2012-03-07 16:24:09,840 DEBUG NHibernate.Loader.Loader - result row: EntityKey[IPRBA.Core.Domain.Model.Customers.Customer#1]
2012-03-07 16:24:09,840 DEBUG NHibernate.Loader.Loader - Initializing object from DataReader: [IPRBA.Core.Domain.Model.Customers.Customer#1]
2012-03-07 16:24:09,840 DEBUG NHibernate.Persister.Entity.AbstractEntityPersister - Hydrating entity: [IPRBA.Core.Domain.Model.Customers.Customer#1]
2012-03-07 16:24:09,840 DEBUG NHibernate.Type.StringType - returning 'Koste' as column: FirstName16_0_
2012-03-07 16:24:09,840 DEBUG NHibernate.Type.StringType - returning 'Budinoski' as column: LastName16_0_
2012-03-07 16:24:09,840 DEBUG NHibernate.Type.StringType - returning 'Koste' as column: Username16_0_
2012-03-07 16:24:09,840 DEBUG NHibernate.Type.StringType - returning 'Koste123' as column: Password16_0_
2012-03-07 16:24:09,840 DEBUG NHibernate.Type.StringType - returning null as column: Personal6_16_0_
2012-03-07 16:24:09,840 DEBUG NHibernate.Type.DateTimeType - returning '1/1/2012 12:00:00 AM' as column: LastLogin16_0_
2012-03-07 16:24:09,840 DEBUG NHibernate.Type.BooleanType - returning 'True' as column: IsApproved16_0_
2012-03-07 16:24:09,840 DEBUG NHibernate.Type.BooleanType - returning 'False' as column: IsReceiv9_16_0_
2012-03-07 16:24:09,840 DEBUG NHibernate.Type.Int32Type - returning null as column: CompanyID16_0_
2012-03-07 16:24:09,840 DEBUG NHibernate.Type.Int32Type - returning '1' as column: Custome11_16_0_
2012-03-07 16:24:09,840 DEBUG NHibernate.Loader.Loader - done processing result set (1 rows)
2012-03-07 16:24:09,840 DEBUG NHibernate.Driver.NHybridDataReader - running NHybridDataReader.Dispose()
2012-03-07 16:24:09,840 DEBUG NHibernate.AdoNet.AbstractBatcher - Closed IDataReader, open IDataReaders :0
2012-03-07 16:24:09,840 DEBUG NHibernate.AdoNet.AbstractBatcher - DataReader was closed after 15 ms
2012-03-07 16:24:09,840 DEBUG NHibernate.AdoNet.AbstractBatcher - Closed IDbCommand, open IDbCommands: 0
2012-03-07 16:24:09,840 DEBUG NHibernate.AdoNet.ConnectionManager - aggressively releasing database connection
2012-03-07 16:24:09,840 DEBUG NHibernate.Connection.ConnectionProvider - Closing connection
2012-03-07 16:24:09,841 DEBUG NHibernate.Loader.Loader - total objects hydrated: 1
2012-03-07 16:24:09,841 DEBUG NHibernate.Engine.TwoPhaseLoad - resolving associations for [IPRBA.Core.Domain.Model.Customers.Customer#1]
2012-03-07 16:24:09,841 DEBUG NHibernate.Engine.Loading.LoadContexts - creating collection wrapper:[IPRBA.Core.Domain.Model.Customers.Customer.CustomerBookRights#1]
2012-03-07 16:24:09,841 DEBUG NHibernate.Engine.Loading.LoadContexts - creating collection wrapper:[IPRBA.Core.Domain.Model.Customers.Customer.CustomerContactInfos#1]
2012-03-07 16:24:09,841 DEBUG NHibernate.Engine.Loading.LoadContexts - creating collection wrapper:[IPRBA.Core.Domain.Model.Customers.Customer.CustomerMembershipTypes#1]
2012-03-07 16:24:09,841 DEBUG NHibernate.Engine.Loading.LoadContexts - creating collection wrapper:[IPRBA.Core.Domain.Model.Customers.Customer.CustomerSubscriptionTypes#1]
2012-03-07 16:24:09,841 DEBUG NHibernate.Event.Default.DefaultLoadEventListener - loading entity: [IPRBA.Core.Domain.Model.Customers.CustomerType#1]
2012-03-07 16:24:09,841 DEBUG NHibernate.Event.Default.DefaultLoadEventListener - creating new proxy for entity
2012-03-07 16:24:09,841 DEBUG NHibernate.Engine.TwoPhaseLoad - done materializing entity [IPRBA.Core.Domain.Model.Customers.Customer#1]
2012-03-07 16:24:09,841 DEBUG NHibernate.Engine.StatefulPersistenceContext - initializing non-lazy collections
2012-03-07 16:24:09,841 DEBUG NHibernate.AdoNet.ConnectionManager - after autocommit
2012-03-07 16:24:09,841 DEBUG NHibernate.Impl.SessionImpl - transaction completion
2012-03-07 16:24:09,841 DEBUG NHibernate.AdoNet.ConnectionManager - aggressively releasing database connection
我會檢查結果的數量，然後得到users.First（），我以前做過，並且對結果滿意。 – AnarchistGeek 2012-03-07 14:55:43
另外，你可以檢查http://perezj.blogspot.com/2010/10/linq-lamba-expressions-performance.html嗎？ – AnarchistGeek 2012-03-07 14:57:08
「非常緩慢」是什麼意思，跟蹤似乎表明查詢需要15ms（DataReader在15 ms後關閉）。 – Phil 2012-03-07 15:36:38