.net - 如何解决不良的 nHibernate 集合初始化

Question

n休眠3；从 EAV 数据模式中检索 4xxx 记录。当 nHibernate 或 .NET 首次初始化这些集合时，我们会看到严重的损失。随后的调用似乎执行得更有效率。在 SQL Server Management Studio 中运行相同的查询会导致预期的快速返回时间。

使用 Fluent 和运行时映射代替 .hbm.xml；好奇序列化映射是否对这里有帮助？

nHibernate Profiler 和 log4net 日志记录似乎没有让我继续下去。在此过程中，总共约有 140,000 个实体被水化。

附上我的 dotTrace 性能跟踪截图，其中显示了集合初始化惩罚:

已尝试连接和急切获取类型，但没有明显结果，但我不能 100% 确定我是否正确实现了这些类型——是否只需要如此指定父表，还是也需要标记子表？

var products = ((HandleSession)_handleSession).Session.CreateCriteria(typeof(Product))
                    .SetFetchMode("Product", FetchMode.Eager)
                    .List<Product>()
                    .AsEnumerable();

通过 web.config 启用反射优化器(我认为):

这是花费最多时间的地方:

return new ProductList(products.Select(p => p.ToProductContract()));

这只是一个扩展方法:

public static ProductContract ToProductContract(this Product product)
        {
            return new ProductContract
                       {
                           Name = product.ProductName,
                           ProductTypeName = product.ProductType.ProductTypeName,
                           UpdateTimeStamp = product.UpdateDateTime,
                           ProductNumber = product.ProductNumber,
                           Attributes = product.ProductAttributes.ToCommonAttribute().ToList(),
                           GroupCategories = product.ProductGroups.ToGroupCategory().ToList(),
                           PublicUniqueId = product.PublicUniqueId
                       };
        }

映射:

internal class ProductMapping : ClassMap<Product>
    {
        private const string _iscurrentindicator = "IsCurrentIndicator=1";

        public ProductMapping()
        {
            Table("Product");
            Id(Reveal.Member<Product>("ProductId")).GeneratedBy.Identity().Column("ProductID");
            Map(x => x.ProductNumber).Column("ProductNumber").Not.Nullable();
            Map(x => x.ProductName).Column("ProductName").Not.Nullable();
            Map(x => x.InsertDateTime).Column("InsertedDateTime").Nullable().ReadOnly();
            Map(x => x.UpdateDateTime).Column("UpdatedDateTime").Nullable();
            Map(x => x.PublicUniqueId).Column("ProductGUID").Generated.Insert();

            References(x => x.ProductType).Column("ProductTypeId").Not.Nullable();
            HasMany(x => x.ProductAttributes)
                .KeyColumn("ProductId")
                .Inverse()
                .Fetch
                .Subselect()
                .Where(_iscurrentindicator)
                .Cascade
                .SaveUpdate();

            HasMany(x => x.ProductGroups).KeyColumn("ProductId").Fetch.Subselect().Where(_iscurrentindicator);
            DynamicUpdate();
            DynamicInsert();
            BatchSize(500);
        }
    }

internal class ProductGroupMapping : ClassMap<ProductGroup>
    {
        public ProductGroupMapping()
        {
            Table("ProductGroup");
            Id(x => x.ProductGroupId).Column("ProductGroupId").GeneratedBy.Identity();
            References(x => x.Product).Column("ProductId").Not.Nullable();
            References(x => x.Group).Column("GroupId").Not.Nullable();
            //Where("IsCurrentIndicator=1");
        }
    }

internal class ProductAttributeMapping : ClassMap<ProductAttribute>
    {
        public ProductAttributeMapping()
        {
            Table("ProductAttribute");
            LazyLoad();
            Id(x => x.ProductAttributeId).GeneratedBy.Identity().Column("ProductAttributeID");
            References(x => x.Product).Column("ProductID").Not.Nullable();
            References(x => x.Attribute).Column("AttributeID").Not.Nullable().Fetch.Join();
            Map(x => x.PositionNumber).Column("PositionNumber").Nullable();
            Map(x => x.ValueText).Column("ValueText").Nullable();
            Map(x => x.ValueBinary).Column("ValueBinary").Nullable();

            Component(x => x.OperationalAuditHistory, m =>
                        {
                            Table("ProductAttribute");
                            m.Map(x => x.ExpirationDateTime).Column("ExpirationDateTime").Nullable();
                            m.Map(x => x.IsCurrent).Column("IsCurrentIndicator").Not.Nullable();
                            m.Map(x => x.OperationCode).Column("OperationCode").Nullable();
                            m.Map(x => x.OperationDateTime).Column("OperationDateTime").Nullable();
                            m.Map(x => x.OperationSystemName).Column("OperationSystemName").Nullable();
                            m.Map(x => x.OperationUserName).Column("OperationUserName").Nullable();
                            m.Map(x => x.LastUserPriority).Column("LastUserPriority").Nullable();
                        });

            DynamicInsert();
            BatchSize(50);
        }
    }

不幸的是，对于 .Future，我似乎仍然得到了类似的结果。这是一条新的踪迹；目前，我已经为关键项目切换到 Release 和 x64，所以时间更短，但比例仍然几乎相同；以及 .Eager:

var products = ((HandleSession) _handleSession).Session.CreateCriteria(typeof (Product))
                    .SetFetchMode("ProductAttribute", FetchMode.Join)
                    .SetFetchMode("ProductGroup", FetchMode.Join)
                    .SetFetchMode("ProductType", FetchMode.Join)
                    .Future<Product>()
                    .AsEnumerable();

使用 .Eager 和 .Future 生成的 SQL:

SELECT this_.ProductID as ProductID0_1_, this_.ProductNumber as ProductN2_0_1_, this_.ProductName as ProductN3_0_1_, this_.InsertedDateTime as Inserted4_0_1_, this_.UpdatedDateTime as UpdatedD5_0_1_, this_.ProductGUID as ProductG6_0_1_, this_.ProductTypeId as ProductT7_0_1_, producttyp2_.ProductTypeID as ProductT1_6_0_, producttyp2_.ProductTypeName as ProductT2_6_0_ FROM Product this_ inner join ProductType producttyp2_ on this_.ProductTypeId=producttyp2_.ProductTypeID;

SELECT productatt0_.ProductId as ProductId2_, productatt0_.ProductAttributeID as ProductA1_2_, productatt0_.ProductAttributeID as ProductA1_2_1_, productatt0_.PositionNumber as Position2_2_1_, productatt0_.ValueText as ValueText2_1_, productatt0_.ValueBinary as ValueBin4_2_1_, productatt0_.ProductID as ProductID2_1_, productatt0_.AttributeID as Attribut6_2_1_, productatt0_.ExpirationDateTime as Expirati7_2_1_, productatt0_.IsCurrentIndicator as IsCurren8_2_1_, productatt0_.OperationCode as Operatio9_2_1_, productatt0_.OperationDateTime as Operati10_2_1_, productatt0_.OperationSystemName as Operati11_2_1_, productatt0_.OperationUserName as Operati12_2_1_, productatt0_.LastUserPriority as LastUse13_2_1_, attribute1_.AttributeId as Attribut1_1_0_, attribute1_.AttributeName as Attribut2_1_0_, attribute1_.DisplayName as DisplayN3_1_0_, attribute1_.DataTypeName as DataType4_1_0_, attribute1_.ConstraintText as Constrai5_1_0_, attribute1_.ConstraintMin as Constrai6_1_0_, attribute1_.ConstraintMax as Constrai7_1_0_, attribute1_.ValuesMin as ValuesMin1_0_, attribute1_.ValuesMax as ValuesMax1_0_, attribute1_.Precision as Precision1_0_ FROM ProductAttribute productatt0_ inner join Attribute attribute1_ on productatt0_.AttributeID=attribute1_.AttributeId WHERE (productatt0_.IsCurrentIndicator=1) and productatt0_.ProductId in (select this_.ProductID FROM Product this_ inner join ProductType producttyp2_ on this_.ProductTypeId=producttyp2_.ProductTypeID)

SELECT productgro0_.ProductId as ProductId1_, productgro0_.ProductGroupId as ProductG1_1_, productgro0_.ProductGroupId as ProductG1_3_0_, productgro0_.ProductId as ProductId3_0_, productgro0_.GroupId as GroupId3_0_ FROM ProductGroup productgro0_ WHERE (productgro0_.IsCurrentIndicator=1) and productgro0_.ProductId in (select this_.ProductID FROM Product this_ inner join ProductType producttyp2_ on this_.ProductTypeId=producttyp2_.ProductTypeID)

Answer 1

1) 序列化映射只会帮助减少构建 SessionFactory 所需的时间。如果上述查询不是第一次访问数据库，则在这方面它不会完成任何事情。

2) 设置 FetchMode 需要应用到 child ，像这样:

var products = ((HandleSession)_handleSession).Session.CreateCriteria(typeof(Product))
                .SetFetchMode("ProductChildren", FetchMode.Eager)
                .List<Product>()
                .AsEnumerable();

3) 如果我正确解释屏幕截图中的方法，这看起来像是一个 N+1 问题。您是否将查询结果中的 Products 转换为 ProductDTO 列表？如果是这样，则子集合似乎是在一个循环中从数据库中延迟加载的。

编辑:

为了对抗 N+1 Select，我们必须告诉 NHibernate 预先加载所有内容，最好是使用 Futures。这是一个潜在的解决方案，它基本上使用少量 Select 语句从数据库中获取所有数据。我没有包括任何 Where 条件。那些你必须相应地添加。

// any where-condition will have to be applied here and in the subsequent queries
var products = session.QueryOver<Product>()
    .Future();

var products2 = session.QueryOver<Product>()
    .Fetch(p => p.ProductType).Eager
    .Future();

var products3 = session.QueryOver<Product>()
    .Fetch(p => p.ProductAttributes).Eager
    .Future();

var products4 = session.QueryOver<Product>()
    .Fetch(p => p.ProductGroups).Eager
    .Future();

// Here we execute all of the above queries in one roundtrip.
// Since we already have all the data we could possibly want, there is no need
// for a N+1 Select.
return new ProductList(products.Select(p => p.ToProductContract()));