为什么 NHibernate 在更新 child 期间不在 one-to-many 中发送额外的 select 查询？

Question

我对 NHibernate 很陌生，我制作了简单的应用程序来测试 NHibernate 和 Entity Framework 性能。我注意到更新 one-to-many 关系中的 child 存在一些问题。在更新期间 child Entity Framework 正在发送额外的 select 查询以获取 children。由于延迟加载，这似乎没问题。但是 NHibernate 不会发送额外的 select 查询来获取 children 即使启用了延迟加载。我的问题来了。为什么它不发送额外的 select 查询？为什么不需要它？感谢您的帮助。

用于更新的 NHibernate 代码：

var students = nHibernateSQLServerSession.Query<Student>().Where(s => s.Grades.Count > 0).Take(records).ToList();
using (nHibernateSQLServerSession.BeginTransaction())
{
    foreach (var student in students)
    {
        student.Grades.ElementAt(rand.Next(student.Grades.Count)).Score = rand.Next(7);
    }
    nHibernateSQLServerSession.GetCurrentTransaction().Commit();
}

Entity Framework更新代码：

using (var db = new ORMTesterContext("name=ORMTesterSQLServer"))
{
    students = db.Students.Where(s => s.Grades.Count > 0).Take(records).ToList();
    foreach (var student in students)
    {
        student.Grades.ElementAt(rand.Next(student.Grades.Count)).Score = rand.Next(7);
    }
    db.SaveChanges();
}

NHibernate 中的关系映射：
学生

<set name="Grades" inverse="true">
    <key column="StudentId" />
    <one-to-many class="NHibernate.DataAccess.Entities.Grades.Grade, NHibernate.DataAccess" />
</set>

成绩

<many-to-one name="Student" class="NHibernate.DataAccess.Entities.Students.Student, NHibernate.DataAccess" column="StudentId" cascade="delete" />

执行的查询：
NHibernate:

exec sp_executesql 
N'select TOP (@p0) student0_.Id as id1_4_, student0_.Name as name2_4_, student0_.Surname as surname3_4_ 
from Students student0_ 
where (select (count(*)) 
    from Grades grades1_ 
    where student0_.Id=grades1_.StudentId)>@p1',N'@p0 int,@p1 int',@p0=1,@p1=0

exec sp_executesql 
N'UPDATE Grades 
SET Score = @p0, StudentId = @p1, TeacherId = @p2 
WHERE Id = @p3',N'@p0 int,@p1 int,@p2 int,@p3 int',@p0=1,@p1=78761,@p2=601,@p3=1202

Entity Framework:

SELECT TOP (1) 
    [Project1].[Id] AS [Id], 
    [Project1].[Name] AS [Name], 
    [Project1].[Surname] AS [Surname]
    FROM ( SELECT 
        [Extent1].[Id] AS [Id], 
        [Extent1].[Name] AS [Name], 
        [Extent1].[Surname] AS [Surname], 
        (SELECT 
            COUNT(1) AS [A1]
            FROM [dbo].[Grades] AS [Extent2]
            WHERE [Extent1].[Id] = [Extent2].[StudentId]) AS [C1]
        FROM [dbo].[Students] AS [Extent1]
    )  AS [Project1]
    WHERE [Project1].[C1] > 0

exec sp_executesql N'SELECT 
    [Extent1].[Id] AS [Id], 
    [Extent1].[Score] AS [Score], 
    [Extent1].[StudentId] AS [StudentId], 
    [Extent1].[TeacherId] AS [TeacherId]
    FROM [dbo].[Grades] AS [Extent1]
    WHERE [Extent1].[StudentId] = @EntityKeyValue1',N'@EntityKeyValue1 int',@EntityKeyValue1=78761

exec sp_executesql N'UPDATE [dbo].[Grades]
SET [Score] = @0
WHERE ([Id] = @1)
',N'@0 int,@1 int',@0=6,@1=1201

Answer 1

好吧，我错了。我完全忘记了 NHibernate 缓存。成绩已经缓存在第一次查询中，并且正在检查下一次尝试的查询，这就是为什么我在第一次尝试时没有注意到额外的查询。

为什么 NHibernate 在更新 child 期间不在 one-to-many 中发送额外的 select 查询？

Why NHibernate is not sending extra select query in one-to-many during updating child?

c#

nhibernate

lazy-loading

entity-framework-6