Question

我目前正在使用c＃和Nhibernate 3.2访问SqlServer数据库，我正在尝试使用multiquery和Futures来加载子集合。

无论如何我可以使用Linq到Nhibernate来使用它，但是当查看sql被发送到数据库时，看起来它除了加载子集合的子对象之外还加载了所有父对象（如它是渴望加载）。我很好奇是否可以将此行为更改为仅拉出所需的子对象列。

以下是说明此问题的代码示例。

  public class Parent : Entity
   {
      public virtual string Name { get; set; }
      public virtual IList<Child> Children { get; set; }
   }


public class Child : Entity
   {
      public virtual int Age { get; set; }
      public virtual string Name { get; set; }
      public virtual Parent Parent { get; set; }
   }


public class ChildClassMap : ClassMap<Child>
   {
      public ChildClassMap()
      {
         Id(x => x.Id,"Id");
         Map(x => x.Age);
         Map(x => x.Name);
         this.References(x => x.Parent).Column("ParentId").ForeignKey("Id");
      }
   }


 public class ParentClassMap : ClassMap<Parent>
   {
      public ParentClassMap()
      {
         Id(x => x.Id, "Id");
         Map(x => x.Name);
         this.HasMany(x => x.Children).KeyColumn("ParentId");
      }
   }



  public class FamilyRepository : NHibernateRepository<Parent>
   {
      public Parent GetParent(int id)
      {
         using (var session = this.Session.OpenSession())
         {
            var parent = session.Query<Parent>()
               .Where(p => p.Id == id);

            parent.FetchMany(x => x.Children)
               .ToFuture();

            return parent.ToFuture().SingleOrDefault();
         }
      }
   }

测试用例

   [TestClass]
   public class FamilyTests
   {
      [TestMethod]
      public void Should_Get_Parent_And_Children()
      {
         // arrange
         var repo = new FamilyRepository();

         // act
         var parent = repo.GetParent(1);

         // assert
         Assert.AreNotEqual(null, parent);
         Assert.AreEqual("TheOldOne", parent.Name);
         Assert.AreEqual(3, parent.Children.Count);
         Assert.AreEqual(4, parent.Children[1].Age);
         Assert.AreEqual("TheMiddleOne", parent.Children[1].Name);

      }
   }

SQL：

CREATE TABLE [dbo].[Parent](
   [Id] [int] IDENTITY(1,1) NOT NULL,
   [Name] [varchar](50) NOT NULL,
CONSTRAINT [PK_Parent] PRIMARY KEY CLUSTERED 
(
   [Id] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
GO

CREATE TABLE [dbo].[Child](
   [Id] [int] IDENTITY(1,1) NOT NULL,
   [ParentId] [int] NOT NULL,
   [Age] [int] NOT NULL,
   [Name] [varchar](50) NOT NULL,
CONSTRAINT [PK_Child] PRIMARY KEY CLUSTERED 
(
   [Id] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]

GO

SET ANSI_PADDING OFF
GO

ALTER TABLE [dbo].[Child]  WITH CHECK ADD  CONSTRAINT [FK_Child_Parent] FOREIGN KEY([ParentId])
REFERENCES [dbo].[Parent] ([Id])
GO

ALTER TABLE [dbo].[Child] CHECK CONSTRAINT [FK_Child_Parent]
GO


Set Identity_Insert [dbo].[Parent] on 
insert into [dbo].[Parent]
(Id, Name)
values (1, 'TheOldOne');

insert into [dbo].[Parent]
(Id, Name)
values (2, 'TheOtherOne');
Set Identity_Insert [dbo].[Parent] off
GO

Set Identity_Insert [dbo].[Child] on
insert into [dbo].[Child]
(Id, ParentId, Age, Name)
values(1,1,3,'TheYoungOne')


insert into [dbo].[Child]
(Id, ParentId, Age, Name)
values(2,1,4,'TheMiddleOne')


insert into [dbo].[Child]
(Id, ParentId, Age, Name)
values(3,1,7,'TheFirstOne')
Set Identity_Insert [dbo].[Child] off

sql profiler的输出是：

exec sp_executesql N'
    select parent0_.Id as Id3_0_, children1_.Id as Id2_1_, parent0_.Name as Name3_0_, children1_.Age as Age2_1_, children1_.Name as Name2_1_, children1_.ParentId as ParentId2_1_, children1_.ParentId as ParentId0__, children1_.Id as Id0__ 
    from [Parent] parent0_ left outer join [Child] children1_ on parent0_.Id=children1_.ParentId where parent0_.Id=@p0;
    select parent0_.Id as Id3_, parent0_.Name as Name3_ from [Parent] parent0_ where parent0_.Id=@p1;
',N'@p0 bigint,@p1 bigint',@p0=1,@p1=1

有人有任何建议吗？

感谢您的时间

Answer 1

只需将代码缩短为

public Parent GetParentWithChildrenInitialised(int id)
{
    using (var session = SessionFactory.OpenSession())
    {
        return session.Query<Parent>()
           .Where(p => p.Id == id)
           .FetchMany(x => x.Children)
           .SingleOrDefault();
    }
}

我个人会摆脱存储库，因为它增加了不必要的抽象并使调整性能变得更难，ISession已经像存储库一样。

更好的选择是使用session.Get(parentId);，因为如果需要子节点，它会使用lvl1 / session缓存或上面的查询。

还使用sessionfactory创建会话，因为它是线程安全的，会话不是。

使用ToFuture延迟加载子集合

1 个答案: