I have the following class
public class Person
{
private IList<Person> _children;
public IEnumerable<Person> Children { get; }
public void AddChild(Person child)
{
// Some business logic and adding to the internal list
}
}
What changes would I have to make for NHibenrate to be able to persist the Child collection (apart from making everything virtual, I know that one).
Do I have to add a setter to the children property which does something like a _children.Clear(); _children.AddRange(value). Currently the model expresses my intent quite nicely but I'm not sure how much alteration is need for NH to be able to help me out with persistence.
NHibernate is able to map private fields. Access and naming strategies are discussed in the property section of the reference documentation.
Making your public members virtual is required for proxies to work. These will usually be runtime-generated subclasses of your entity classes.
In this example mapping the field _children will be Children in HQL and Criteria queries.
<class name="Person" table="person">
<bag name="Children" access="field.camelcase-underscore">
<key column="parentid" />
<one-to-many class="Person" />
</bag>
</class>
Related
I have two objects, Case and Note. A Case can have gobs of Notes, like, in the thousands. We are trying to load them asynchronously, in batches, and stream them to the UI so there is no delay waiting for them all to load.
The class/mappings are
public class Case
{
public virtual IList<Note> Notes { get; protected set; }
}
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="SCMS.TAMS.BusinessEntities" namespace="SCMS.TAMS.BusinessEntities">
<class name="Case" table="Cases">
<bag name="Notes" inverse="true" cascade="all" lazy="true">
<key column="CaseID" />
<one-to-many class="Note" />
</bag>
</class>
</hibernate-mapping>
public class Note
{
public virtual Case Case {get; set;}
public virtual long CaseId {get; set;}
}
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="SCMS.TAMS.BusinessEntities" namespace="SCMS.TAMS.BusinessEntities" default-lazy="true">
<class name="Note" table="CaseNotes">
<many-to-one name="Case" column="CaseID"/>
<property name="CaseId" column="CaseID" />
</class>
</hibernate-mapping>
Now, when I call
NHibernateSession.Query<Note>().Where(n => n.CaseId == 123).Skip(0).Take(10).ToList();
to load the first 10 Notes for Case 123, the thing loads the Case object, which takes about 30 seconds because there's lots of other things on it, and other logic when it gets loaded, etc., none of which I need/want at this time. All I want/need are the 10 Notes.
I've tried all sorts of variations on this mapping and none of them have worked. What am I doing wrong here?
How are you using this query? is it some thing for the UI? liking showing in a grid or something? or are you performing business logic in a component?
Either way you want to project into another object. Your query right now returns a list of notes which is then going to load that parent object per the mappings.
So if you are using this query to send the information to the UI of an asp.net mvc application, project directly into your view model
NHibernateSession.Query<Note>().Where(n => n.CaseId == 123).Select(n => new SomeViewModel { Prop1 = n.Prop1, Prop2 = n.Prop2 ...}).Skip(0).Take(10).ToList();
or create an anonymous object
NHibernateSession.Query<Note>().Where(n => n.CaseId == 123).Select n => new { n.Prop1, n.Prop2, ...}).Skip(0).Take(10).ToList();
This will keep the parent object from loading. It also has the added benefit that you are only querying the information you need because the query be limited to the data you are projecting.
Important to know is that if all above is true...
this is the real mapping (which is not it is just an obvious extract)
<class name="Note" table="CaseNotes">
<many-to-one name="Case" column="CaseID"/>
...
this is the class (again extract without ID)
public class Note
{
public virtual Case Case {get; set;}
public virtual long CaseId {get; set;}
}
and that would be a UNIT TEST statement to load notes:
var list = NHibernateSession
.Query<Note>()
.Where(n => n.CaseId == 123)
.Skip(0).Take(10)
.ToList();
then NHibernate will NEVER load the Case object. Never. Because:
NHibernate is lazy, just live with it
The reason, the trigger to load related reference (Case property) must be something explicit.
Mostly:
there is usage of the Case object somewhere. E.g. in override of the GetHashCode() the Case.ID is used
Or:
there is a serialization or DTO conversion which does touch the Case property
In those case, NHibernate must load that...
So, create few unit tests with basic queries and assure that your the is really as shown above. Then it will work as expected
i have old legacy DB which has dead links in their tables. I have class mapped in nhibernate like this:
<class name="Visible" table="table_visible">
<composite-id>
<key-many-to-one column="object_id" name="ObjectA" />
<key-many-to-one column="sub_object_id" name="SubObject" />
</composite-id>
<property column="visible" name="VisibleRow" />
</class>
and:
public class Visible
{
public virtual ObjectAClass ObjectA { get; set; }
public virtual SubObjectClass SubObject { get; set; }
public virtual bool VisibleRow { get; set; }
public override bool Equals(object obj)
{
var other = ((Visible)obj);
return this.ObjectA.Equals(other.ObjectA) && this.SubObject.Equals(other.SubObject);
}
public override int GetHashCode()
{
return this.ObjectA.GetHashCode() + (this.SubObject != null? this.SubObject.GetHashCode(): 0);
}
}
Now all works fine when all joins in database are correct, but when i find such sub_object_id which doesnt have entity, nhibernate throws me error
No row with the given identifier exists:[SubObject#123]
Is there a way to map composite key so that when its subentity is not found, the whole entity wouldnt be loaded (like with inner join)?
NHibernate v2.0.50727
Following Daniel Schilling idea of fetch Visible entities with a where exists sub-query, found that there is loader element available in mappings.
<class name="ObjectA" table="table_object">
.........
<set name="VisibleList" cascade="all" lazy="false" inverse="true">
<key column="object_id" />
<one-to-many class="Visible" />
<loader query-ref="valid_entities"/>
</set>
</class>
<sql-query name="valid_entities">
<load-collection alias="v" role="ObjectA.VisibleList"/>
SELECT {v.*}
FROM table_visible v
INNER JOIN table_sub_entities e ON e.sub_entity_id=v.sub_entity_id
WHERE v.object_id=?
</sql-query>
And nothing else needed to be changed.
<key-many-to-one column="sub_object_id" name="SubObject" not-found="ignore" />
... may be helpful. From the NHibernate Documentation...
ignore will treat a missing row as a null association
Please be aware of the performance penalty associated with using this option. Whenever NHibernate fetches a Visible entity, it will also have to fetch SubObject. If you don't go ahead and fetch it in your query, this means that NHibernate will be issuing lots of lazy loads.
This doesn't meet your "when its sub-entity is not found, the whole entity wouldn't be loaded" goal. Instead NHibernate would give you an entity with a null sub-entity. If you want that inner-join-like behavior, then I think you would need to fetch your Visible entities with a where exists sub-query to make sure the SubObject actually exists.
The best option would be to fix the data in the database and add a foreign key constraint.
I just ran across this: Relations with not-found="ignore". I promise I'm not copying Ricci's content - I'm writing this from my own experience.
I've got this relationship between a ReportRow (parent) and a Mark (child)
<class name="ReportRow">
<bag name="Marks" cascade="save-update" inverse="true">
<key column="ReportRowId"/>
<one-to-many class="Mark"/>
</bag>
</class>
// C# code
public virtual IList<Mark> Marks { get; set; }
But it's not being saved (in the Mark table, ReportRowId is always null).
I know these relationships always have to be bidirectional because of the NHibernate 'quirk' so for my Mark class I have:
<many-to-one name="ReportRow" class="ReportRow" column="ReportRowId" />
// C#
public virtual ReportRow ReportRow { get; set; }
I've even got some other examples of this kind of relationship working elsewhere in my project, but this one isn't working and I can't see any difference apart from...
... both Mark and ReportRow both have subclasses (e.g. ModuleMark and ModuleReportRow), which I'm using the joined-subclass strategy to implement the inheritance.
Would that have something to do with it? For both ends of the relationship, the mappings are defined in the parent class mapping rather than nested inside the <joined-subclass> mappings.
Thanks
How are you adding Marks to the collection? Because the collection is the inverse side of the relationship, you need to set the reference to the parent object on the child when adding it to the collection. A common approach is to use methods in the parent object to maintain the relationship, e.g.:
public void AddMark(Mark mark)
{
mark.ReportRow = this;
Marks.Add(mark); // better yet map the collection as a private field
}
I think of "inverse" as "who wears the pants in this relationship".
I have a bidirectional relationship in NHibernate:
<class name="Child" table="Children">
<many-to-one name="Parent" column="ParentId" not-null="true" />
</class>
<class name="Parent">
<set name="Children" lazy="true" table="Children" cascade="all">
<key column="ParentId" not-null="true" />
<one-to-many class="Child" />
</set>
</class>
How do I save it without setting inverse="true" and setting Parent property on Child?
I do not want to do this because it does not make much sense from the POCO perspective.
Alternatively, is it possible to intercept Add called on NHibernate proxy collection (Children)?
In that case, I would just put the Parent setting logic here.
Unless you're willing to make the foreign key nullable and accept an insert followed by an update, that's the way bidirectional one-to-many works in NHibernate.
I do have a generic implementation of this pattern that you can use... it's a proof of concept; it can be useful or not, depending on how you look at it, as it kinda breaks the POCO approach, but... well, here it is:
public interface IHaveParent<T>
{
T Parent { get; set; }
}
public interface IHaveMany<T>
{
ICollection<T> Children { get; }
}
public static class OneToManyHelper
{
public static void AddChild<TParent, TChild>(this TParent parent,
TChild child)
where TChild : IHaveParent<TParent>
where TParent : IHaveMany<TChild>
{
parent.Children.Add(child);
child.Parent = parent;
}
}
With this, you can all AddChild on any parent.
The problem with intercepting Add calls is that you'd always need to instantiate your collections using a special method (which, again, is not POCO).
My class has a field of type Dictionary<string, List<string>>. What's the best way to map it with NHibernate? I'd better leave it as a field, don't want to expose it.
Thanks a lot!
ulu
You can't directly map it. There are two rules to consider:
Always use interfaces for collections (eg. IList<T>, IDictionary<K,V>)
NH does not support nested collections. I've never seen an application for it before
and never heard someone requesting it.
Put your list of string into a class and use interfaces:
class StringList
{
IList<string> Strings { get; private set; }
}
class Entity
{
private IDictionary<string, StringList> stringDict;
}
You might even see some advantages of having such a class.
Mapping:
<class name="Entity">
...
<map name="stringDict" table="Entity_StringDict" access="field">
<key column="Entity_FK"/>
<index column="Key" type="System.String"/>
<composite-element class="StringList">
<bag name="Strings" table="Entity_StringDict_Strings">
<key column="Entity_StringDict_FK"/>
<element type="System.String" column="String"/>
</bag>
</composite-element>
</map>
</class>
Maps to three Tables:
Table Entity
Table Entity_StringDict
Column Entity_FK
Column Key
Table Entity_StringDict_Strings
Column Entity_StringDict_FK
Column String