Cascade Save - StaleObjectStateException: Row was updated or deleted by another transaction - nhibernate

Question

Having an issue with updating the NHibernate version. Current version is 3.3.1.4000 and trying to update to 4.
After updating the unit test which does save with cascade fails with:
NHibernate.StaleObjectStateException: Row was updated or deleted by another transaction (or unsaved-value mapping was incorrect): [NHibernateTests.TestMappings.ProductLine#cdcaf08d-4831-4882-84b8-14de91581d2e]
The mappings:
<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="NHibernateTests" namespace="NHibernateTests.TestMappings">
<class name="Product" lazy="false" table="UserTest">
<id name="Id">
<generator class="guid"></generator>
</id>
<version name="Version" column="Version" unsaved-value="0"/>
<property name="Name" not-null="false"></property>
<property name="IsDeleted"></property>
<bag name="ProductLines" table="ProductLine" inverse="true" cascade="all" lazy="true" where="IsDeleted=0" >
<cache usage="nonstrict-read-write" />
<key column="UserId" />
<one-to-many class="ProductLine" />
</bag>
</class>
</hibernate-mapping>
<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="NHibernateTests" namespace="NHibernateTests.TestMappings">
<class name="ProductLine" where="IsDeleted=0" lazy="false">
<cache usage="nonstrict-read-write" />
<id name="Id">
<generator class="guid"></generator>
</id>
<version name="Version" column="Version" unsaved-value="0"/>
<property name="IsDeleted"></property>
<many-to-one name="Product" class="Product" column="UserId" not-null="true" lazy="proxy"></many-to-one>
</class>
</hibernate-mapping>
Classes:
public class Product
{
public Guid Id { get; set; }
public int Version { get; set; }
public bool IsDeleted { get; set; }
public string Name { get; set; }
public bool IsActive { get; set; }
public IList<ProductLine> ProductLines { get; private set; }
public Product()
{
ProductLines = new List<ProductLine>();
}
}
public class ProductLine
{
public Guid Id { get; set; }
public int Version { get; set; }
public bool IsDeleted { get; set; }
public Product Product { get; set; }
}
The test:
[TestMethod]
public void CascadeSaveTest()
{
var product = new Product
{
Id = Guid.NewGuid(),
Name = "aaa",
IsActive = true
};
var productLine = new ProductLine
{
Id = Guid.NewGuid(),
Product = product,
};
product.ProductLines.Add(productLine);
using (var connection = new RepositoryConnection())
{
using (var repositories = new Repository<Product>(connection))
{
repositories.Create(product);
//the below just calls the Session.Transaction.Commit();
connection.Commit(); //NH3.3.1.400 passes, NH4 fails
}
}
}
Thanks for you ideas in advance.

Answer 1

Well, I guess I have now understood what causes the error with NH 4. And If I am right, that is a bit contrived case causing this behavior to be hard to qualify as a bug.
In your example, products lines are mapped through a bag. A bag can contains duplicates, which requires an intermediate table between Product and ProductLine. (Something like a ProductProductLine table with an UserId (ProductId) column, and a ProductLineId column.)
You have set this intermediate table as being the ProductLine table. I suspect the commit to db causes NHibernate to insert the product, then the product line, then to try to insert the relationship by inserting again in ProductLine table. (You may check that by profiling SQL queries on your db.)
Things are a bit muddy, since doc states (emphasis is mine):
table (optional - defaults to property name) the name of the
collection table (not used for one-to-many associations)
But then, how to honor the bag semantics allowing duplicates in the collection? From the same doc:
A bag is an unordered, unindexed collection which may contain the same
element multiple times.
Anyway, within your example, you really should map your one-to-many with a set, as shown in doc.
<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="NHibernateTests" namespace="NHibernateTests.TestMappings">
<class name="Product" lazy="false" table="UserTest">
<id name="Id">
<generator class="guid"></generator>
</id>
<version name="Version" column="Version" unsaved-value="0"/>
<property name="Name" not-null="false"></property>
<property name="IsDeleted"></property>
<set name="ProductLines" inverse="true" cascade="all" lazy="true" where="IsDeleted=0" >
<cache usage="nonstrict-read-write" />
<key column="UserId" />
<one-to-many class="ProductLine" />
</set>
</class>
</hibernate-mapping>
And change your collection type for using .Net fx 4 System.Collections.Generic.ISet<T>.
public ISet<ProductLine> ProductLines { get; private set; }
public Product()
{
ProductLines = new HashSet<ProductLine>();
}
If this causes your trouble to disappear, it would mean something has changed in bag handling in NH 4. But should we consider this change as being a bug? Not sure, since using a bag in this case does not look right for me.

Answer 2

Drilling it further down turned out that NHibernate4 has problems identifying whether it is a new entity or an already existent when concerned with Cascade.
With the scenario in question it was calling a SQL Update for the ProductLine, rather than Create.
It works fine with the below changes, however I'm quite puzzled with such a changes in between NHibernate versions.
Change to ProductLine Mapping
<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="NHibernateTests" namespace="NHibernateTests.TestMappings">
<class name="ProductLine" where="IsDeleted=0" lazy="false">
<cache usage="nonstrict-read-write" />
<!-- here comes the updated line -->
<id name="Id" type="guid" unsaved-value="00000000-0000-0000-0000-000000000000">
<generator class="guid"></generator>
</id>
<version name="Version" column="Version" unsaved-value="0"/>
<property name="IsDeleted"></property>
<many-to-one name="Product" class="Product" column="UserId" not-null="true" lazy="proxy"></many-to-one>
</class>
</hibernate-mapping>
Change to test method
[TestMethod]
public void CascadeSaveTest()
{
var product = new Product
{
Id = Guid.NewGuid(),
Name = "aaa",
IsActive = true
};
var productLine = new ProductLine
{
Id = Guid.Empty, //The updated line
Product = product,
};
product.ProductLines.Add(productLine);
using (var connection = new RepositoryConnection())
{
using (var repositories = new Repository<Product>(connection))
{
repositories.Create(product);
connection.Commit();
}
}
}