I ve got the following setup:
public class ParentEntity
{
public ICollection<ChildEntity> {get; set; }
}
public class ChildEntity
{
// do i need to the parent here?
}
I managed to save the ParentEntity and cascaded the save to the added child entities which were saved as well. But in the db table the ParentId reference of the child was set to allow NULL. When setting it to NOT NULL the save failes since the ParentId in the child table is NULL.
What's happening there? ;)
When
You should map both sides of the relationship normally, and when you add a child to the parent's collection, you should also set the parent property on the child. Normally you would achieve this by writing a method like this:
public void AddChild(ChildEntity child)
{
this.Children.Add(child);
child.Parent = this;
}
NHibernate persists the ParentId column in the Child table based on the mapped property in the ChildEntity class. The definition of the one-to-many relationship merely allows NHibernate to load the collection from the database based on values in this column
I am having the same issue and need this to either have nHibernate expose the foreign key column, or do it in class via collection.
Problem: nHibernate creates the collection object (IList, for example) and you can not override the or listen to the add events of basic collections.
This becomes an issue only because it is required by the WCF RIA Services framework.
Related
I have two objects - ContentPage, which has a collection of ChildLinks.
ContentPage
-----------
ID
Title
ChildLink
----------
ID
ParentPageID [ContentPage]
ChildPageID [ContentPage]
Priority
The ContentPage.ChildLinks property utilises the 2nd level cache. I am using Fluent NH to configure Nhibernate, and using Nhibernate 3.1. Cache is set as 'Read-Write' both for the collection, and the 'ChildLink' class.
I've noticed that whenever I delete a ChildLink, the collection cache is not being invalidated. Thus, when I call the ContentPage.ChildLinks, I get an error:
no row with the given identifier exists
I've turned off the cache, and it works well. Shouldn't the cache be automatically invalidated? I am using SysCache as the cache provider, and MySQL as the database.
Thanks in advance!
I had the same problem and I can across the following article which solved my problem:
Inverse Mapped Collections and NHibernate's Second-Level Cache
Basically if you have mapped your collections as inverse, when you delete the child item you also have to make sure to explicitly remove it from the parent collection or the cache state will be invalid after you delete the child. The first thing to check is if the relationship really needs to be inverse.
Assuming inverse is necessary or desired, and using your example:
Instead of only something like:
Session.Delete(ChildLink);
You have to do:
ContentPage.ChildLinks.Remove(ChildLink);
ChildLink.ParentPage = null;
Session.Delete(ChildLink);
You also might need to explicitly save your ContentPage object at this point as well, it depends on your Session flush settings.
I use methods on my entities for managing such inverse relationships, for example:
public ChildLink
{
public ContentPage ParentPage {get;set;}
public void AddToPage(ContentPage addTo)
{
addTo.ChildLinks.Add(this);
this.ParentPage = addTo;
}
public void RemoveFromPage()
{
ParentPage.ChildLinks.Remove(this);
this.ParentPage = null;
}
}
And then when deleting a child object:
ChildLink.RemoveFromPage();
Session.Delete(ChildLink);
I have a database with a ProbateCases table and a Properties table. The Properties table has a foreign key to the ProbateCases table called ProbateCaseId, so the relationship between ProbateCases and Properties is one-to-many.
My domain layer has a ProbateCase class and a Property class. The ProbateCase class has a collection of Properties defined as follows:
private IList<Property> _properties = new List<Property>();
public virtual IEnumerable<Property> Properties { get { return _properties; } }
public virtual Property AddProperty()
{
Property property = new Property();
_properties.Add(property);
return property;
}
The corresponding part of the Fluent NHibernate mapping looks like this:
HasMany(x => x.Properties).Where("Deleted = 0").KeyColumn("ProbateCaseId").Cascade.All().Access.CamelCaseField(Prefix.Underscore);
Note that the association is unidirectional - the ProbateCase class has a collection of Properties, but the Property class does not have a ProbateCase member.
I'm finding that querying works fine - NHibernate is creating the appropriate SQL to get Properties with the appropriate ProbateCaseId value.
However, when I save a ProbateCase to which I have added a new Property, the INSERT SQL does NOT contain a value for the foreign key field - so I get a SQL Exception complaining of a NULL value in the foreign key:
INSERT INTO AdminOverview.Properties (PropertyName) VALUES ('Name of property') -- Where the hell is the ProbateCaseId field value???
Should I be expecting NHibernate to populate the foreign key value itself, or is there something else I should be doing?
From http://nhibernate.info/doc/nh/en/index.html#collections-onetomany:
Very Important Note: If the column of a association is declared NOT NULL, NHibernate may cause constraint violations when it creates or updates the association. To prevent this problem, you must use a bidirectional association with the many valued end (the set or bag) marked as inverse="true". See the discussion of bidirectional associations later in this chapter.
I'm wondering what the best design would be for persisteing a new child entity with NHibernate without accidentally overwriting the parent in the database.
The problem I have is that the child entity will look something like this:
class Child
{
Parent Parent;
// other fields
}
My problem is that the child has been supplied from the UI layer along with the ID of the parent, and that means that the Parent ref is basically uninitialized: It will have the ID populated but everything else null - because the only way to populate its fields would be an extra round trip to the database to read them.
Now if I call Session.SaveOrUpdate(child) on NHibernate, what's going to happen with the parent. I don't want NHibernate to cascade save the uninitialized parent since that would just destroy the data in the database. How would people approach this problem? Any best practices?
You must use the session.Load(parentid) to get the aggregate root. In contrast to the session.Get() method, this does not actually fetch any data from the database, it just instantiates a Parent proxy object used to add Child objects to the correct Parent in the DB (eg. get the foreign key correctly).
Your code would probably look something like:
// Set the Parent to a nhibernate proxy of the Parent using the ParentId supplied from the UI
childFromUI.Parent = Session.Load<Parent>(childFromUI.Parent.Id);
Session.Save(childFromUI);
This article explains Get/Load and the nhibernate caches really well
You should probably be working with the aggregate root (probably the Parent) when doing Saves (or SaveOrUpdates etc).
Why not just:
Fetch the parent object using the parent id you have in the child from the UI layer
Add the child to the parents 'children' collection
I think you have to overview your mapping configuration for nhibernate. If you have defined on the reference by the child to the parent that hi has to Cascade all, it will update it!
So if you say Cascade.None he will do nothing. All other are bad ideas. Because you allready has the information of this parent. So why read from db agane?!
If your models looks like this
class Parent
{
}
class Child
{
Parent myParent;
}
and you are trying to set the parent and save the child without having a full parent object, just the ID.
You could try this:
session.Lock(child.myParent, LockMode.None);
before saving, this should tell nhibernate that there are no changes to the parent object to persist and it should only look at the object for the Id to persist the association between Parent and Child
Instead of getting into code, I have a simple question. Default behavior for a simple one-to-many is that it inserts the child record then updates the foreign key column with the parent key.
Has anyone ever had a one-to-many where the child object gets inserted but not updated resulting in a row in my table with a null in the foreign key column?
I want the default behaviour for a standard one-to-many. I don't want to have to add the parent as a property to the child.
Thanks.
This would happen if you didn't have cascade="save-update" on your set/bag
or if you set your session's FlushMode to 'None' or 'Commit'
and saved the child using your childRepository and neglected to save the object containing the collection using its repository.
I think you have to set parent reference in child item.
class Parent {
public virtual IList<Child> Children;
}
class Child {
public virtual Parent Parent;
}
Parent p = new Parent();
Child c = new Child();
c.Parent = p;
p.Children = new List<Child>();
p.Children.Add(c);
Now when you save this transient object p you will have the right foreign key in the child table.
I'm having some trouble getting NH to persist my object graph.
I have (something like) this:
/*Tables*/
TABLE Parent
ParentID PK
LastEventID NULL
TABLE Event
EventID PK
ParentID FK NOT NULL
//Model Classes
public class Parent
{
public List<Event> Events; //Inverse
//Denormalized bit
public Event LastEvent; //not inverse
}
public class Event
{
public Parent Parent; //Makes the association up there Inverse
}
I'm creating a new Parent, creating a new Event, adding the new Event
to Parent.Events and setting Parent.LastEvent to the new Event.
When I tell NH to save the Parent I get an error about a transient
object needing to be saved first. I assume its because the association
between Parent and Event is not clear.
The way the SQL needs to go is to insert the Parent with a null
LastEvent, then insert the Event, then update Parent.LastEvent.
So how do I get NH to do this?
Without seeing your mapping schema, I'll have to guess.
Are you cascading your updates? From the reference:
To save or update all objects in a graph of associated objects, you must either
Save(), SaveOrUpdate() or Update() each individual object OR
map associated objects using cascade="all" or cascade="save-update".
Assuming you don't already have this, does adding cascade="all" or cascade="save-update" to the side marked inverse="true" fix the problem?