I was using Fluent NHibernate and I had these two entities:
public class Location
{
public virtual int Id { get; protected set; }
public virtual string Name { get; set; }
private Stack<Place> _places;
public virtual IList<Place> Places
{
get { return _places.ToList(); }
set { _places = new Stack<Place>(value); }
}
public virtual void AddPlace(Place place)
{
_places.Push(place);
place.LocationReference = this;
}
}
public class Place
{
public virtual int Id { get; protected set; }
public virtual Location LocationReference { get; set; }
}
mapped as follow:
class LocationMap : ClassMap<Location>
{
public LocationMap()
{
Id(x => x.Id);
Map(x => x.Name)
.Not.Nullable()
.Unique();
HasMany(x => x.Places)
.Cascade.All()
.Inverse();
}
}
class PlaceMap : ClassMap<Place>
{
public PlaceMap()
{
Id(x => x.Id);
References(x => x.LocationReference);
}
}
I was using SQLite as RDBMS and I was saving only the Location, relying on Cascade() for managing Places insertion.
The two entities were successfully inserted in the DB, but when I tried to read a Location back and to access its list of Places, the list was empty.
After removing Inverse(), the code seemed to properly work. But when I inspected the DB, I found two columns within the Place table, while I expected only one of them: Location_id (that was empty) and LocationReference_id (that was set).
After one whole day of desperate googling, I noticed that everyone was naming the reference property as the class itself. So, I renamed it from LocationReference to Location, I added back the Inverse() call and everything worked fine. Only the column Location_id was in the DB, of course.
Does anyone know why this happened? Thanks.
Related
I have a "Group" class and a "GroupSummaryLevel" class, codes are given below. There is a one-to-one relation between these entities in DB. I need the "GroupSummaryLevel" as a property in Groups class. It is supposed to be a very simple join like
(SELECT g.Id FROM GroupSummaryLevel g WHERE g.AcctGroup = GroupID)
Unfortunately, I wasn't able to figure this out how to do with NHibernate. The many answers I saw here is no help to me. I would appreaciate any inputs from the more experienced NHibernate users out there. Thanks in advance.
public class Group : DomainEntity
{
public virtual string GroupId { get; set; }
public virtual string GroupName { get; set; }
public virtual GroupSummaryLevel GroupSummaryLevel { get; set; }
}
public class GroupSummaryLevel : DomainEntity
{
public virtual int Id { get; set; }
public virtual string AcctGroup { get; set; }
public virtual GroupSummaryLevel Parent { get; set; }
public virtual IList<GroupSummaryLevel> Children { get; set; }
public GroupSummaryLevel()
{
Children = new List<GroupSummaryLevel>();
}
}
The mapping I have done did not work so far. My mapping codes are as below:
public GroupMap()
{
Table("Groups");
LazyLoad();
Id(x => x.GroupId).GeneratedBy.Assigned().Column("GroupID").CustomType<TrimmedString>();
Map(x => x.GroupName).Column("GroupName").CustomType<TrimmedString>().Not.Nullable();
HasOne(x => x.GroupSummaryLevel).Cascade.None().ForeignKey("AcctGroup");
}
public GroupSummaryLevelMap()
{
Table("GroupSummaryLevel");
LazyLoad();
Id(x => x.Id).GeneratedBy.Identity().Column("Id");
Map(x => x.AcctGroup).Column("AcctGroup").CustomType<TrimmedString>().Not.Nullable();
//References(x => x.Parent).Column("ParentId");
//HasMany(x => x.Children).Cascade.All().KeyColumn("ParentId");
}
Note: I also need to do a self-join for GroupSummaryLevel, and no success with that either. Any recommendations for that will also be appreciated :)
I would say, that your one-to-one is not driven by primary/foreign keys, but by property-ref. So the Group should map the summary by saying something like this:
...if you want to find related SummaryLevel, pass my <id> into column mapped as AcctGroup
public GroupMap()
{
...
HasOne(x => x.GroupSummaryLevel)
.Cascade.None()
//.ForeignKey("AcctGroup")
.PropertyRef(gsl => gsl.AcctGroup)
;
}
public GroupSummaryLevelMap()
{
...
//References(x => x.Parent).Column("ParentId");
//HasMany(x => x.Children).Cascade.All().KeyColumn("ParentId");
References(x => x.Parent, "AcctGroup");
}
NOTEs for completeness, as discussed in comments:
In this scenario, when the "child" has reference to parent - it really calls for one-to-many/.HasMany() mapping.
The down side is, that child is represented as a colleciton of children: IList<GroupSummaryLevel>. It is not as straighforward to use, but we can create some virtual property, returning the .FirstOrDefault(). The benefit we get - is lazy loading (not in place with one-to-one).
I have small problem with nHibernate (fluent) I have two objects, one contains another - a parent and a child (predefined objects, readonly).
mappings:
public class ParentClass
{
public virtual int Id { get; set; }
public virtual ChildClass Metoda { get; set; }
}
public ParentClassMap() {
Table("Wyceny");
Id(x => x.Id).Column("Id").GeneratedBy.TriggerIdentity();
References(x => x.Metoda).Column("RMW_ID");
}
public ChildClass
{
public virtual int Id { get; set; }
public virtual string Nazwa { get; set; }
}
public ChildClassMap()
{
Table("Metody");
Id(x => x.Id).Column("Id");
Map(x => x.Nazwa).Column("Nazwa_met");
}
Everything works perfectly until I chose child object with id = 0, reading still works for id=0, but when I'm trying to save or update Parent with correct ChildObject(readed previously from db through nHibernate), nHibernate stores null instead of value.
Any suggestions?
nHibernate 3.3.1.4000
fluent 1.4.0.0
The issue here would be the unsaved-value. NHibernate must decide if operations with object will be insert or update. This decision comes from unsaved-value setting, which is by default for int set to 0.
Try to extend your mapping of a ChildClass:
public ChildClassMap()
{
Table("Metody");
Id(x => x.Id)
.Column("Id")
.UnsavedValue(-1);
...
See 5.1.4. id, cite:
unsaved-value (optional - defaults to a "sensible" value): An identifier property value that indicates that an instance is newly instantiated (unsaved), distinguishing it from transient instances that were saved or loaded in a previous session.
And here is nice Id mapping overview by Adam Bar (the second half of the article)
I would like to be able to add a collection of Notes to any of my main entities in my NHibernate application. I can see how you could do this with a seperate junction table per entity. However, I would like to be able to avoid this and only have one junction table - if this is possible.
Below is the code so far, however this will result in all Notes being loaded for every Entity and I only want to load the notes for that particular entity. What are the alternative approaches I need to take?
public class Entity
{
public virtual int Id { get; set; }
}
public class EntityType1 : Entity
{
public EntityType1()
{
Notes = new List<Note>();
}
public virtual string EntityTypeName { get; set; }
public virtual IList<Note> Notes {get;set;}
}
public class EntityType2 : Entity
{
public EntityType2()
{
Notes = new List<Note>();
}
public virtual string EntityType2Name { get; set; }
public virtual IList<Note> Notes { get; set; }
}
public class Note
{
public virtual int Id { get; set; }
public virtual IList<Entity> Entities { get; set; }
public virtual string NoteText { get; set; }
}
}
namespace FluentNHib.Mappings
{
public class EntityMap : ClassMap<Entity>
{
public EntityMap()
{
Id(m => m.Id);
}
}
public class EntityType1Map : ClassMap<EntityType1>
{
public EntityType1Map()
{
Id(m => m.Id);
Map(m => m.EntityTypeName1);
HasManyToMany(m => m.Notes).Table("EntityToNotes")
.ParentKeyColumn("EntityId")
.ChildKeyColumn("NoteId")
.LazyLoad()
.Cascade.SaveUpdate();
}
}
public class EntityType2Map : ClassMap<EntityType2>
{
public EntityType2Map()
{
Id(m => m.Id);
Map(m => m.EntityType2ame);
HasManyToMany(m => m.Notes).Table("EntityToNotes")
.ParentKeyColumn("EntityId")
.ChildKeyColumn("NoteId")
.LazyLoad()
.Cascade.SaveUpdate();
}
}
public class NoteMap : ClassMap<Note>
{
public NoteMap()
{
Id(m => m.Id);
Map(m => m.NoteText);
}
}
I am not sure what the real issue is:
...however this will result in all Notes being loaded for every Entity and I only want to load the notes for that particular entity...
Is the issue in lazy loading? or in fact that Entity1 and Entity2 can have same ID, therefore the references are mixed? (I expect that and this should be part of the answer below)
Anyhow, I would say that we can achieve what you need: map the Note with just one table EntityToNotes. And that is good.
But, in general, I would descourage you from using the many-to-many. It is just my own feeling, experience. Below are some links with more explanation:
Am I doing many to many incorrectly when using fluent nhibernate?
NHibernate how do you map a crossreference table to a bag?
Nhibernate: How to represent Many-To-Many relationships with One-to-Many relationships?
Draft of the SOLUTION:
So, firstly we have to extend the table "EntityToNotes" with two columns
EntityToNoteId column - we need a primary key for new pairing object
Discriminator column
The Discriminator column will be used for (almost like a standard inheritance)
inserting Discriminator value during creation
filtering te IList<Notes> per Entity
These could be the pairing Entity (with an abstract base gathering the common stuff)
public abstract class EntityToNote<TEntity>
{
public abstract string Discriminator { get; set; }
public virtual TEntity Entity {get;set;}
public virtual Note Note {get;set;}
}
// the pairing objects
public class EntityType1ToNote : EntityToNote<EntityType1>
{
string _discriminator = "EntityType1"; // here we set the discriminator
public virtual string Discriminator
{
get { return _discriminator; }
set { _discriminator = value; }
}
...
// Similar for other pairing objects
The Entities will now be referencing lists of pairing objects
public class EntityType1 : Entity
{
public virtual IList<EntityType1ToNote> Notes {get;set;}
...
public class EntityType2 : Entity
{
public virtual IList<EntityType2ToNote> Notes { get; set; }
...
Here is snippet of the mapping (all other Entities will have usual mapping, including ClassMaps for EntityType1ToNote, EntityType2ToNote...)
public class EntityType1Map : ClassMap<EntityType1>
{
public EntityType1Map()
{
Id(m => m.Id);
Map(m => m.EntityTypeName1);
HasMany(m => m.Notes)
// this "table" setting is redundant, it will come from EntityType1ToNote
//.Table("EntityToNotes")
.KeyColumn("EntityId")
// here is the trick, that only related rows will be selected
.Where("Discriminator = 'EntityType1'")
.Cascade.AllDeleteOrphan();
}
}
As I tried to explain in the links provided, we gained this way a lot. Mostly the ability to use more columns on the pairing table - e.g. Discriminator (later we can have more columns like SortBy...) and we are able to use powerful searching with subqueries - see Query on HasMany reference
Also, in fact, the pairing could be mapped via the real inheritance... But the main point here is: Instead of many-to-many we introduced the pairing object and gained a lot
I have a model that looks like this:
public class ComponentAttributeDto
{
public virtual long ComponentAttributeId { get; set; }
public virtual ComponentAttributeDto ParentComponentAttributeDto { get; set; }
public virtual string ComponentAttributeName { get; set; }
public virtual string Value { get; set; }
public virtual DataType DataType { get; set; }
public virtual IList<ComponentAttributeDto> ChildComponentAttributes { get; set; }
}
With a mapping file of:
public class ComponentAttributeMapping : ClassMap<ComponentAttributeDto>
{
public ComponentAttributeMapping()
{
Table("ComponentAttributes");
Id(x => x.ComponentAttributeId)
.GeneratedBy.Identity();
References(x => x.ParentComponentAttributeDto)
.Column("ParentComponentAttributeId");
HasMany(x => x.ChildComponentAttributes)
.Fetch.Select()
.Inverse()
.Cascade.AllDeleteOrphan()
.KeyColumn("ParentComponentAttributeId");
Map(x => x.ComponentAttributeName)
.Length(50);
Map(x => x.Value)
.Length(1500);
Map(x => x.DataType)
.Length(20);
}
}
When loading this with a large dataset that goes about 4 levels deep the performance is terrible. When running profiler I noticed that is it executing a select statement for every single value in the table for the data I want to lookup. Is there a way I can improve the performance to do some type of join on the table or something else?
You could use batch-size to pre-fetch instances, which reduces the number of queries considerably.
mapping (not sure if it is supported by Fluent in the meanwhile):
HasMany(x => x.ChildComponentAttributes)
.Fetch.Select()
.SetAttribute("batch-size", "20")
.Inverse()
.Cascade.AllDeleteOrphan()
.KeyColumn("ParentComponentAttributeId");
If you had a Root property, you could make a query for the whole tree at once.
public class ComponentAttributeDto
{
public virtual ComponentAttributeDto ParentComponentAttributeDto { get; private set; }
public virtual ComponentAttributeDto Root
{
get
{
if (ParentComponentAttributeDto == null)
{
return this;
}
else
{
return ParentComponentAttributeDto.Root;
}
}
private set
{ /* just for NH to call it */ }
}
// ....
}
HasMany(x => x.Children).AsSet().SetAttribute("batch-size", "20")
the query
session.CreateQuery(
#"from ComponentAttributeDto
where Root = :root"
.SetEntity(root);
should actually result in only a single query. Not sure if NH doesn't actually perform queries for the lists (ChildComponentAttributes), but it is worth a try.
Do you need the entire data structure all at once? Usually when I run into this problem I just take away the mapping handling from nHibernate and deal with it myself. Create a method for the class called getChildren() and have it run the query when called. If you want to add a child record then add another method called addChild() and have it instantiate with it's own parent ID.
You could eagerly fetch the hierarchy when you query. You can do this by using the eager fetch option in your query:
Session.QueryOver<ComponentAttributeDto>
.Fetch(a => a.ChildComponentAttributes).Eager
Down to the level you want to fetch.
If I use session-per-transaction and call:
session.SaveOrUpdate(entity) corrected:
session.SaveOrUpdateCopy(entity)
..and entity is a transient instance with identity-Id=0. Shall the above line automatically update the Id of the entity, and make the instance persistent? Or should it do so on transaction.Commit? Or do I have to somehow code that explicitly?
Obviously the Id of the database row (new, since transient) is autogenerated and saved as some number, but I'm talking about the actual parameter instance here. Which is the business logic instance.
EDIT - Follow-up, of related problem.
Mappings:
public class StoreMap : ClassMap<Store>
{
public StoreMap()
{
Id(x => x.Id).GeneratedBy.Identity();
Map(x => x.Name);
HasMany(x => x.Staff) // 1:m
.Cascade.All();
HasManyToMany(x => x.Products) // m:m
.Cascade.All()
.Table("StoreProduct");
}
}
public class EmployeeMap : ClassMap<Employee>
{
public EmployeeMap()
{
Id(x => x.Id).GeneratedBy.Identity();
Map(x => x.FirstName);
Map(x => x.LastName);
References(x => x.Store); // m:1
}
}
public class ProductMap : ClassMap<Product>
{
public ProductMap()
{
Id(x => x.Id).GeneratedBy.Identity();
Map(x => x.Name).Length(20);
Map(x => x.Price).CustomSqlType("decimal").Precision(9).Scale(2);
HasManyToMany(x => x.StoresStockedIn)
.Cascade.All()
.Inverse()
.Table("StoreProduct");
}
}
EDIT2
Class definitions:
public class Store
{
public int Id { get; private set; }
public string Name { get; set; }
public IList<Product> Products { get; set; }
public IList<Employee> Staff { get; set; }
public Store()
{
Products = new List<Product>();
Staff = new List<Employee>();
}
// AddProduct & AddEmployee is required. "NH needs you to set both sides before
// it will save correctly"
public void AddProduct(Product product)
{
product.StoresStockedIn.Add(this);
Products.Add(product);
}
public void AddEmployee(Employee employee)
{
employee.Store = this;
Staff.Add(employee);
}
}
public class Employee
{
public int Id { get; private set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public Store Store { get; set; }
}
public class Product
{
public int Id { get; private set; }
public string Name { get; set; }
public decimal Price { get; set; }
public IList<Store> StoresStockedIn { get; private set; }
}
As far as your question is concerned, whenever you flush your session is when your entity is persisted to the database. When saving your (new) entity, NHibernate generates the ID for you using the generator you provided.
Keep in mind that an Identity generator is not recommended (see this post by Ayende).
When you use an Identity generator, your new entity is persisted to the database when you save, even if you don't flush to the database. The reason this happens is because NHibernate needs to provide you with an ID for the entity, which it can't do without doing a roundtrip to the database.
A better solution would be to use something like a Guid generator, or HiLo if you want 'normal' values. This way you can save your entity without actually having to do a database roundtrip, which allows you to do a lot more performance wise (batching comes to mind).
I'm not sure I understand your question. The actual saving to the database occurs when the session is flushed (e.g. by committing the transaction). Calling SaveOrUpdate() doesn't itself save the entity, it just informs the session that the entity is due to be saved when the session is flushed.
Assuming that the ID of the entity maps to an identity field in the database and that your mapping tells NHibernate that identity is set by the database, then the ID set by the database will be set as the entity's ID when it is saved.
Nhibernate will set the ID property of your entity just after SaveOrUpdate call.
I noticed I saved by calling:
session.SaveOrUpdateCopy(entity);
..which does NOT update the Id. But by changing to:
session.SaveOrUpdate(entity);
..the Id's of transient entity will be updated.
I probably misunderstood the documentation (?).. Section 9.4.2 says:
SaveOrUpdateCopy(Object o)... If the given instance is unsaved or does not exist in the database, NHibernate will save it and return it as a newly persistent instance.
Is it just me, or does it not sound like a transient object (unsaved), will be "returned as persistent" ? Doesn't that mean with updated Id? Would appreciate a clarification how to interpret this sentence correctly (?)