How to save a large nhibernate collection without causing OutOfMemoryException
- by Michael Hedgpeth
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" 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);
}
