How to save a large nhibernate collection without causing OutOfMemoryException_问答_开发者

How do I save a large collection with NHibernate which has elements that surpass the amount of memory allowed for the process?

I am trying to save a Video object with nhibernate which has a large number of Screenshots (see below for code). Each Screenshot contains a byte[], so after nhibernate tries to save 10,000 or so records at once, an OutOfMemoryException is thrown. Normally I would try to break up the save and flush the session after every 500 or so records, but in this case, I need to save the collection because it automatically saves the SortOrder and VideoId for me (without the Screenshot having to know that it was a part of a Video). What is the best approach given my situation? Is there a way to break up this save without forcing the Screenshot to have knowledge of its parent Video?

For your reference, here is the code from the simple sample I created:

public class Video
{
    public long Id { get; set; }
    public string Name { get; set; }

    public Video()
    {
        Screenshots = new ArrayList();
    }

    public IList Screenshots { get; set; }
}

public class Screenshot
{
    public long Id { get; set; }
    public byte[] Data { get; set; }
}

And mappings:

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
                   assembly="SavingScreenshotsTrial"
                   namespace="SavingScreenshotsTrial"
                   default-access="property">
  <class name="Screenshot"
         lazy="false">
    <id name="Id"
        type="Int64">
      <generator class="hilo"/>
    </id>

    <property name="Data"开发者_StackOverflow社区 column="Data" type="BinaryBlob" length="2147483647" not-null="true" />
  </class>
</hibernate-mapping>

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
                   assembly="SavingScreenshotsTrial"
                   namespace="SavingScreenshotsTrial" >
  <class name="Video"
         lazy="false"
         table="Video"
         discriminator-value="0"
         abstract="true">
    <id name="Id"
        type="Int64"
        access="property">
      <generator class="hilo"/>
    </id>
    <property name="Name" />
    <list name="Screenshots"
          cascade="all-delete-orphan"
          lazy="false">
      <key column="VideoId" />
      <index column="SortOrder" />
      <one-to-many class="Screenshot" />
    </list>
  </class>
</hibernate-mapping>

When I try to save a Video with 10000 screenshots, it throws an OutOfMemoryException. Here is the code I'm using:

        using (var session = CreateSession())
        {
            Video video = new Video();
            for (int i = 0; i < 10000; i++)
            {
                video.Screenshots.Add(new Screenshot() {Data = camera.TakeScreenshot(resolution)});
            }
            session.SaveOrUpdate(video);
        }

For this reason, we have typically had the child entity reference the parent rather than vice versa.

Create a custom type by using AbstractType and IParameterizedType these are in NHibernate.Type namespace. Use stateless session and provide batch size.

The chapter 13 of nhibernate documentation handle this issue.

"A naive approach to inserting 100 000 rows in the database using NHibernate might look like this:

using (ISession session = sessionFactory.OpenSession())
using (ITransaction tx = session.BeginTransaction())
{
for (int i = 0; i < 100000; i++)
{
Customer customer = new Customer(.....);
session.Save(customer);
}
tx.Commit();
}

This would fall over with an OutOfMemoryException somewhere around the 50 000th row[...]"

To resume... the solution is work with batch size and no second level cache by setting this properties:

Batch size: