I'm building an ecommerce site using S#arp Architecture.
I'm trying to map a hierachy of categories and retrieve the top level categories.
I'm using NHibernate.Linq for this.
I have the following entity:
public class Category : Entity
{
#region Properties
[DomainSignature]
[NotNullNotEmpty]
public virtual string Name { get; set; }
public virtual string Description { get; set; }
public virtual int ListOrder { get; set; }
public virtual IList<Product> Products { get; set; }
public virtual IList<Category> ParentCategories { get; set; }
public virtual IList<Category> ChildCategories { get; set; }
#endregion
public Category()
{
Products = new List<Product>();
ParentCategories = new List<Category>();
ChildCategories = new List<Category>();
}
}
with the following Fluent NHibernate mapping:
public class CategoryMap : ClassMap<Category>
{
public CategoryMap()
{
Id(x => x.Id);
Map(x => x.Name);
HasManyToMany(p => p.Products)
.Cascade.All()
.Table("CategoryProduct");
HasManyToMany(c => c.ParentCategories)
.Table("CategoryHierarchy")
.ParentKeyColumn("Child")
.ChildKeyColumn("Parent")
.Cascade.SaveUpdate()
.AsBag();
HasManyToMany(c => c.ChildCategories)
.Table("CategoryHierarchy")
.ParentKeyColumn("Parent")
.ChildKeyColumn("Child")
.Cascade.SaveUpdate()
.Inverse()
.LazyLoad()
.AsBag();
}
}
I want to retrieve the root categories. I know I have eight in my db so here's my test:
[Test]
public void Can_get_root_categories()
{
// Arrange
var repository = new CategoryRepository();
// Act
var rootCategories = repository.GetRootCategories();
// Assert
Assert.IsNotNull(rootCategories);
Assert.AreEqual(8, rootCategories.Count());
}
I figure I just get all Categories where the ParentCategories list is empty (initialized in the ctor of Category). So here's my repository method:
public IQueryable<Category> GetRootCategories()
{
var session = NHibernateSession.Current;
// using NHibernate.Linq here
var categories = from c in session.Linq<Category>()
where c.ParentCategories.Count == 0
select c;
return categories;
}
When I run my test I get "NHibernate.QueryException : could not resolve property: ParentCategories.Id of: MyStore.Core.Category"
What am I doing wrong?
Here are related questions, but didn't quite solve my problem:
Fluent nHibernate: Need help with ManyToMany Self-referencing mapping
Querying a self referencing join with NHibernate Linq
Fluent NHibernate: ManyToMany Self-referencing mapping
Edit:
I think the problem lies with the .count in the Linq expression. This post related to this, but I'm not sure how to progress...
Got it. The problem was in the linq expression. It didn't like .Count for some reason. This might be a bug in NHibernate.Linq (NH2), but I hear NH3 linq is rock solid now.
Anyway, my solution is to use a Criteria instead:
var categories = session.CreateCriteria(typeof (Category))
.Add(Restrictions.IsEmpty("ParentCategories"))
.List();
Thanks to a blog post by nixsolutions.com for getting me on the right track. All green again.
You should be using the Count() extension method instead of the Count property. This works fine in NHibernate 2.
Regards
Jon
Related
I'm having a problem with NHibernate querying the database way too many times. I just realized it likely relates to the n+1 problem but I can't figure out how to change my mappings to solve the problem.
As you will see, my attempts involve specifying not to lazy load other objects, but it doesn't seem to do the trick.
This is the query:
public IQueryable<Report> ReadAll(DateTime since)
{
return m_session.QueryOver<Report>()
.JoinQueryOver(r => r.Mail)
.Where(m => m.Received >= since)
.List()
.AsQueryable();
}
Thanks in advance for any response! If you need any more information about my objects or mappings, please let me know.
Simplified objects graph (some omitted):
public class Report : EntityBase
{
public virtual Product Product { get; set; }
public virtual StackTrace StackTrace { get; set; }
public virtual Mail Mail { get; set; }
public virtual IList<ClientUser> ReadBy { get; set; }
}
-
public class Product : EntityBase
{
public virtual string Name { get; set; }
public virtual Version Version { get; set; }
public virtual IList<Report> Reports { get; set; }
public virtual IList<StackTrace> StackTraces { get; set; }
}
-
public class StackTrace : EntityBase
{
public virtual IList<StackTraceEntry> Entries { get; set; }
public virtual IList<Report> Reports { get; set; }
public virtual Product Product { get; set; }
}
Mapping examples:
public class ReportMap : ClassMap<Report>
{
public ReportMap()
{
Table("Report");
References(x => x.User)
.Column("EndUserId")
.Not.LazyLoad();
References(x => x.Product)
.Column("ProductId")
.Not.LazyLoad();
References(x => x.StackTrace)
.Column("StackTraceId")
.Not.LazyLoad();
HasManyToMany(x => x.ReadBy)
.Cascade.SaveUpdate()
.Table("ClientUserRead")
.ParentKeyColumn("ReportId")
.ChildKeyColumn("ClientUserId")
.Not.LazyLoad().BatchSize(200);
}
}
-
public class StackTraceMap : ClassMap<StackTrace>
{
public StackTraceMap()
{
Table("StackTrace");
References(x => x.Product)
.Column("ProductId");
HasMany(x => x.Entries)
.KeyColumn("StackTraceId")
.Not.LazyLoad()
.Cascade
.All().BatchSize(500);
HasMany(x => x.Reports)
.KeyColumn("StackTraceId")
.Inverse().BatchSize(100);
}
}
The way to go is to use batch fetching. Read more about it here:
How to Eager Load Associations without duplication in NHibernate?
On every entity mapping apply BatchSize (for many-to-one relation - avoiding 1 + N)
public ReportMap()
{
Table(...)
BatchSize(25);
...
And on every collection (solves issue with one-to-many 1 + N)
HasMany(x => x.Reports)
.KeyColumn("StackTraceId")
.BatchSize(25)
...
You can specify fetch paths in the query. For example, this fetch path can tell the query to eagerly join product and main objects, as well as an imaginary association on the collection of clients:
public IQueryable<Report> ReadAll(DateTime since)
{
return m_session.QueryOver<Report>()
.JoinQueryOver(r => r.Mail)
.Where(m => m.Received >= since)
.Fetch(x => x.Product).Eager
.Fetch(x => x.Mail).Eager
.Fetch(x => x.ReadBy.First().SomeProp).Eager
.List()
.AsQueryable();
}
If you want that always to happen, try using .Fetch.Join() instead of .Not.LazyLoad() for the assocations. But I would not recommend that because it can cause simple queries to become huge. Batching or subqueries can help too.
I have read this in order to compile NH spatial for Nhibernate 3.1
http://build-failed.blogspot.it/2012/02/nhibernate-spatial-part-2.html
I have also read this
NHibernate.Spatial and Sql 2008 Geography type - How to configure
but the same code for me don't compile... I have this
using NetTopologySuite.Geometries;
namespace Core
{
public class District
{
public virtual int Id { get; set; }
public virtual Polygon Area { get; set; }
public virtual string Name { get; set; }
}
}
using Core;
using FluentNHibernate.Mapping;
namespace TestNHSpatial
{
public class DistrictMap : ClassMap<District>
{
public DistrictMap()
{
ImportType<NetTopologySuite.Geometries.Point>();
Id(x => x.Id);
Map(x => x.Name);
Map(x => x.Area).CustomType<Wgs84GeographyType>();
}
}
}
and this
[Serializable]
public class Wgs84GeographyType : MsSql2008GeographyType
{
protected override void SetDefaultSRID(GeoAPI.Geometries.IGeometry geometry)
{
geometry.SRID = 4326;
}
}
finally
var cfg = new OrderingSystemConfiguration();
var configuration = Fluently.Configure()
.Database(MsSqlConfiguration.MsSql2008
.ConnectionString(connString)
.Dialect<MsSql2008GeographyDialect>())
.Mappings(m => m.AutoMappings.Add(
AutoMap.AssemblyOf<District>(cfg)))
.BuildConfiguration();
var exporter = new SchemaExport(configuration);
exporter.Drop(false, true);
exporter.Create(true, true);
i have this error...
NHibernate.MappingException : An association from the table District refers to an unmapped class: NetTopologySuite.Geometries.Polygon
can anyone help me?
thanks
UPDATE:
The code has some issues, namely:
You're using AutoMappings. You need to use custom mappings
You're using the wrong assembly when searching for the mappings
The export schema code is incorrect.
I'm the author of the blog post that you refer.
Change the type from Polygon (from NetTopologySuite) to IPolygon(from GeoAPI).
Should be something like this:
using GeoAPI.Geometries;
public class District
{
public virtual int Id { get; set; }
public virtual IPolygon Area { get; set; }
public virtual string Name { get; set; }
}
Anyway, if this doesn't work, send me a zip with a test project and I'll check it out.
Hopefully the title of this question makes sense, if not, here is my elaboration.
With two entities, Brand and Affiliate and a many-to-may relationship between them i would like to be able to use a query to find the Affiliates where the BrandName is a variable value.
Here is the Affiliate class and Affiliate MapClass (simplified of course)
public class Affiliate
{
public virtual int Id { get; private set; }
public virtual DateTime DateReceived { get; set; }
public virtual IList<Brand> Brands { get; set; }
public Affiliate()
{
Brands = new List<Brand>();
}
}
public class AffiliateApplicationRecordMap : ClassMap<Affiliate>
{
public AffiliateApplicationRecordMap()
{
Id(x => x.Id).GeneratedBy.Identity();
Map(x => x.DateReceived, "TimeStampCreated");
HasManyToMany(x => x.Brands)
.Cascade.All()
.ParentKeyColumn("AffiliateID")
.ChildKeyColumn("BrandID")
.Table("AffiliateBrand");
}
}
There is a mapping table called AffiliateBrand which provides the many to many mapping.
Here is the Brand class and ClassMap
public class Brand
{
public virtual int ID { get; private set; }
public virtual string Name { get; set; }
public virtual IList<Affiliate> Affiliates{ get; set; }
public Brand()
{
Affiliates = new List<Affiliate>();
}
public virtual void AddAffiliateApplication(Affiliate affiliate)
{
affiliate.Brands.Add(this);
Brands.Add(affiliate);
}
}
public class BrandMap : ClassMap<Brand>
{
public BrandMap()
{
Id(x => x.ID).GeneratedBy.Identity();
Map(x => x.Name);
HasManyToMany(x => x.Affiliates)
.Cascade.All()
.Inverse()
.ParentKeyColumn("BrandID")
.ChildKeyColumn("PartnerID")
.Table("AffiliateBrand");
}
}
Now i'm tyring to write this query with NHibernate:
var result = session
.CreateCriteria(typeof(Partner))
.AddOrder(Order.Asc("DateReceived"))
.Add(Restrictions.Eq("Brands.Name", brandName))
.SetMaxResults(10)
.List<Partner>();
Now clearly this isn't working and i didn't really think it would. What i'm trying to do is get all Affiliates back where the Brand has a specific name. How do i write this query?
You need to add a join to your criteria using CreateAlias
var result = session
.CreateCriteria(typeof(Partner))
.AddOrder(Order.Asc("DateReceived"))
.CreateAlias("Brands", "brand")
.Add(Restrictions.Eq("brand.Name", brandName))
.SetMaxResults(10)
.List<Partner>();
I am new to NHibernate.
I am using Fluent Nhibernate and when I run a simple query I get null results.
Here is my configuration:
Fluent Configuration:
Fluently.Configure().Database(MsSqlConfiguration.MsSql2008
.ShowSql()
.ConnectionString(c => c
.FromConnectionStringWithKey("MY_DB")))
.Mappings(m =>m.FluentMappings.AddFromAssemblyOf<CsrDAL.Mappings.CsrRegistrationMap>())
.BuildSessionFactory();
Entity Class
public class Industry
{
public virtual int Id { get; private set; }
public virtual string Name { get; set; }
public virtual IList<CsrRegistration> ReferencedRegistrations { get; set; }
}
Map Class
public class IndustryMap : ClassMap<Industry>
{
public IndustryMap()
{
Table("industries");
Id(x => x.Id. "id");
Map(x => x.Name, "name");
}
}
Repository Fetch Method
public static IList<Industry> getData(CsrRegistration registration)
{
using (var session = CsrDalHelper.OpenSession())
{
using (var transaction = session.BeginTransaction())
{
try
{
IQuery q = session.CreateQuery("from Industry ind where ind.Id=1");
IList<Industry> inds =
q.List<Industry>();
return inds; // <-- This is null
}
}
}
}
Thank you in advance!
Dimitris
The problem was in session management, somewhere else in my code.
I was wrongly adding collection items to an entity outside the NH session.
As a newcomer to nhibernate, I am now studying the docs in more details.
Thank you
I am trying to figure out what I thought was just a simple one to many mapping using fluent Nhibernate. I hoping someone can point me to the right directory to achieve this one to many relations
I have an articles table and a categories table
Many Articles can only belong to one Category
Now my Categores table has 4 Categories and Articles has one article associated with cateory1
here is my setup.
using FluentNHibernate.Mapping;
using System.Collections;
using System.Collections.Generic;
namespace FluentMapping
{
public class Article
{
public virtual int Id { get; private set; }
public virtual string Title { get; set; }
public virtual Category Category{get;set;}
}
public class Category
{
public virtual int Id { get; private set; }
public virtual string Description { get; set; }
public virtual IList<Article> Articles { get; set; }
public Category()
{
Articles=new List<Article>();
}
public virtual void AddArticle(Article article)
{
article.Category = this;
Articles.Add(article);
}
public virtual void RemoveArticle(Article article)
{
Articles.Remove(article);
}
}
public class ArticleMap:ClassMap<Article>
{
public ArticleMap()
{
Table("Articles");
Id(x => x.Id).GeneratedBy.Identity();
Map(x => x.Title);
References(x => x.Category).Column("CategoryId").LazyLoad();
}
public class CategoryMap:ClassMap<Category>
{
public CategoryMap()
{
Table("Categories");
Id(x => x.Id).GeneratedBy.Identity();
Map(x => x.Description);
HasMany(x => x.Articles).KeyColumn("CategoryId").Fetch.Join();
}
}
}
}
if I run this test
[Fact]
public void Can_Get_Categories()
{
using (var session = SessionManager.Instance.Current)
{
using (var transaction = session.BeginTransaction())
{
var categories = session.CreateCriteria(typeof(Category))
//.CreateCriteria("Articles").Add(NHibernate.Criterion.Restrictions.EqProperty("Category", "Id"))
.AddOrder(Order.Asc("Description"))
.List<Category>();
}
}
}
I am getting 7 Categories due to Left outer join used by Nhibernate
any idea what I am doing wrong in here?
Thanks
[Solution]
After a couple of hours reading nhibernate docs I here is what I came up with
var criteria = session.CreateCriteria(typeof (Category));
criteria.AddOrder(Order.Asc("Description"));
criteria.SetResultTransformer(new DistinctRootEntityResultTransformer());
var cats1 = criteria.List<Category>();
Using Nhibernate linq provider
var linq = session.Linq<Category>();
linq.QueryOptions.RegisterCustomAction(c => c.SetResultTransformer(new DistinctRootEntityResultTransformer()));
var cats2 = linq.ToList();
I don't really know what's the problem, because I don't know how you save the categories, but it might be caused by using the wrong cascade setting in the mapping?
Using Join on a HasMany is unusual; it's typically used on References, the many side of a one-to-many relationship. Instead of the solution you came up with, you should lazy load the collection or use Fetch.Select. Both will cause NH to issue two selects, one to load the Category and another to load its associated Articles.
Addendum:
The error you're getting is pretty straight-forward: the collection can't be loaded because the ISession that was used to load the parent is out of scope (or its connection was closed). Setting the fetch mode to Select will resolve this (I think, I haven't tried it). So your collection mapping would be:
HasMany(x => x.Articles).KeyColumn("CategoryId").Fetch.Select();
If you can keep the ISession open I would recommend lazy loading:
HasMany(x => x.Articles).KeyColumn("CategoryId").LazyLoad();
It's unusual to use Join on a collection mapping due to the problem you ran into. Issuing a join from the one side will return a parent object for each object in the collection, just as it would in SQL.