NHibernate - one-to-many just not working with SQLite - sqlite

Question

TL;DR;
NHibernate reverse relationship is working on Azure-SQL and MSSQL2012 but not with SQLite
Description:
I am currently Unittesting my Asp.Net MVC App and set up my Unittest with FluentMigrator on SQLite.
After creating the Database I set up some base entries I need.
One of those is a Product.
A Product has many ProductSuppliers and a ProductSupplier has many ProductSupplierPrices
public class Product
{
public virtual long Id { get; set; }
public virtual string Number { get; set; }
public virtual string Name { get; set; }
public virtual string Description { get; set; }
//more properties
public virtual IList<ProductSupplier> Suppliers { get; set; }
//more properties
}
public class ProductSupplier
{
public virtual long Id { get; set; }
public virtual Product Product { get; set; }
public virtual Supplier Supplier { get; set; }
public virtual IList<ProductSupplierPrice> Prices { get; set; }
}
public class ProductSupplierPrice : IHaveId
{
public virtual long Id { get; set; }
public virtual ProductSupplier ProductSupplier { get; set; }
public virtual decimal FromAmount { get; set; }
public virtual decimal Price { get; set; }
}
Setup:
Create Supplier
Create Product
Create ProductSupplier
Create ProductSupplierPrice
Test:
Product product = this.session.Load<Product>((long)1);
ProductSupplier productSupplier = product.Suppliers.First(); //<-- Suppliers are null; therefore throws an exception
If I load them seperately to check the relationships:
productSupplierPrice.ProductSupplier <--- Correct Supplier
productSupplier.Prices <-- Null
productSupplier.Product <-- Product with Id 1
product.Suppliers <-- Null
So to me it seems, that the many-to-one direction works correctely, but the one-to-many (reverse relation) is not working.
The Problem exists only in my Unittest (SQLite) the App itself runs on Azure-SQL and is working fine.
EDIT:
Mappings with FluentnHibernate
public class ProductMap : ClassMap<Product>
{
public ProductMap()
{
Id(x => x.Id);
HasMany(x => x.Suppliers).Inverse().Cascade.DeleteOrphan().BatchSize(20);
//many more mappings
}
}
public ProductSupplierMap()
{
Id(x => x.Id);
References(x => x.Product);
References(x => x.Supplier);
Map(x => x.IsMainSupplier);
Map(x => x.SupplierProductNumber);
Map(x => x.CopperSurcharge);
HasMany(x => x.Prices).Inverse().Cascade.DeleteOrphan().BatchSize(20);
}
public ProductSupplierPriceMap()
{
Id(x => x.Id);
References(x => x.ProductSupplier);
Map(x => x.FromAmount);
Map(x => x.Price);
}
Edit2 - Creating the DB-Entries:
Product product = new Product()
{
Type = ProductType.Purchase,
Dispatcher = session.Load<Employee>(employeeId),
Number = "100.10-1000",
Name = "Testproduct",
//Lots of Properties
Suppliers = new List<ProductSupplier>()
};
session.SaveOrUpdate(product);
ProductSupplier productSupplier = new ProductSupplier()
{
Product = product,
Supplier = session.Load<Supplier>((long)1),
IsMainSupplier = true,
SupplierProductNumber = "Artikel123456",
CopperSurcharge = CopperSurchargeType.DEL700,
Prices = new List<ProductSupplierPrice>()
};
session.Save(productSupplier);
ProductSupplierPrice productSupplierPrice = new ProductSupplierPrice()
{
ProductSupplier = productSupplier,
FromAmount = 1,
Price = 5
};
session.Save(productSupplierPrice);
EDIT 3.1:
public static ISession InitializeDatabase()
{
NHibernateSessionHolder.CreateSessionFactory();
session = NHibernateSessionHolder.OpenSession();
CreateBaseEntries(); //Creates Employees, Supplier, Customer etc
return session;
}

Answer 1

Based on the Ayende's article you need to clear the session between insert/update and querying:
session.Clear();
Seems to be a session management, I'm not sure why the session should be clean, but the session is providing your original instance (the same you provided for saving, stored on the session cache) instead a proxy for lazy-loading.
private long CreatePurchaseOrder()
{
session.Clear();
var product = this.session.Load<Product>((long)1);
var productSupplier = product.Suppliers.First();
var productSupplierPrice = productSupplier.Prices.First();
return 0;
}

Answer 2

Sorry for late reply
In your unit test, you are using same session for creating and fetching entities. This is not right as subsequent fetch returns entities from first level cache which do not have their graph set up properly.
So....either use different sessions OR as a quick fix, I have added "session.Clear()" in the method "InitializeDatabase()" of "DatabaseSetUpHelper". Clearing the session clears first level cache and force NH to fetch data from DB again and the resulting entities have their graph set up properly.
public static ISession InitializeDatabase()
{
NHibernateSessionHolder.CreateSessionFactory();
session = NHibernateSessionHolder.OpenSession();
CreateBaseEntries();
session.Clear(); // notice this!!! this clears first level cache of session, thus forcing fetching of data from DB
return session;
}
Note: My quick-fix is not final solution, it is there just show how session behaves. In proper solution, you must use different sessions.