I have two class
Class Item
{
private Auction CorrespondingAuction;
}
Class Auction
{
private Item CurrentItem;
}
Can someone tell how to set this one to one mapping in XML, it must be bidirectional
Bookmark this cheat sheet.This shows simple examples of all the mappings supported by Hibernate.
In Auction XML FILE:
<many-to-one name="CurrentItem" class="com.BiddingSystem.Models.Item" fetch="join"
not-null="true" cascade="all" unique="true" lazy="false">
<column name="CURRENTITEM" />
</many-to-one>
In Item XML File:
<one-to-one name="auction" class="com.BiddingSystem.Models.Auction" property-ref="CurrentItem"/>
property-ref refers to the name of the variable corresponding to class item in the auction class
You need to have PK in common:
Class Item {
#Id
Long id;
#OneToOne
private Auction CorrespondingAuction;
}
Class Auction {
#Id
Long id;
private Item CurrentItem;
}
The ID for Auction is taken from the ID already generated for Item
Related
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 am using NHibernate 3.1.0.4000 and AutoMapper 2.0.0.0 in a WCF. I have a parent-child relationship I want to maintain from the "many" end. I have no problems maintaining the objects if I do it from the "one" end but in this case that does not make sense. My issue is no matter how I change my mappings, POCOs, etc. the parent object when I attempt to add a child is null in the child causing the insert to fail. What am I missing to get the parent property in the child to populate?
I have a parent-child relationship defined in the following tables:
Create Table Attribute (AttributeUID uniqueidentifier, LongName varchar(20))
Create Table AnswerOption (AnswerOptionID int, AttributeUID uniqueidentifier)
I want the Attribute (parent) to be the owner so I declare the relationship in that mapping file and not in the AnswerOption (child). Though, I have tried with having the relationship bidirectional as well and that has not changed any behaviors in my tests. My mappings apear as follows. Attribute:
<class name="RCAttribute" table="rcs.tblAttribute">
<cache usage="read-write"/>
<id name="ID">
<column name="AttributeUID" />
<generator class="guid" />
</id>
<property name="LongName" type="string" not-null="true" length="200" column="LongName" />
<bag name="AnswerOptions" lazy="true" inverse="true" cascade="all">
<key column="AttributeUID"/>
<one-to-many class="AnswerOption" />
</bag>
</class>
AnswerOption:
<class name="AnswerOption" table="rcs.tblAnswerOption" lazy="true">
<cache usage="read-write"/>
<id name="ID">
<column name="AnswerOptionID" />
<generator class="native" />
</id>
</class>
Attribute Class:
[Serializable]
public class RCAttribute
{
public virtual Guid ID { get; set; }
public virtual string LongName { get; set; }
public virtual ICollection<AnswerOption> AnswerOptions { get; set; }
public RCAttribute() { ID = new Guid("00000000-0000-0000-0000-000000000000"); }
}
AnswerOption Class:
[Serializable]
public class AnswerOption
{
public virtual int ID { get; set; }
public AnswerOption() { ID = 0; }
}
My test procedure looks like this;
public void CreateAnswerOption()
{
AnswerOption newOpt = new AnswerOption();
Attribute.AnswerOptions.Add(newOpt);
Attribute = rc.RCAttributeSave(Attribute);
}
When it goes to create this the Attribute property of the AnswerOption is null so it cannot insert since the parent cannot be null in the child in this case. What am I missing to get it to populate the parent property on the child and be able to insert?
Mapping the collection as inverse without mapping the many-to-one on the other side makes no sense.
You have three options:
Use a bidirectional mapping with inverse="true" on the collection side and set the many-to-one propery (parent reference) in your code before saving the child (yes, I read that you don't want to do it that way).
Only map the collection side (not inverse). NHibernate will then first insert the child with NULL as parent reference, but will update it with the correct parent ID in the same transaction. So you can't have a not null constraint on the parent ID column in the child table (at least it must be deferrable).
(This option only works with NHibernate 3.2.0 or newer) Same as option 2, but add not-null="true" to the key tag in the collection mapping. Then NHibernate will insert the child with the parent ID already set.
I am creating a survey application where I have a survey which has a collection of pages. Each page will have a collection of questions and each question will have a collection of answer options. My class structure looks like:
public class Survey : Entity {
public IList<Page> Pages { get; set; }
}
public class Page : Entity {
public IList<Question> Questions { get;set; }
}
public class Question : Entity {
public IList<Option> Options { get; set; }
}
public class Option : Entity {}
The mapping for each class is:
<!-- mapping for ID and other properties excluded -->
<class name="Survey">
<bag name="Pages" generic="true" inverse="true">
<key column="SurveyId" />
<one-to-many class="Page" />
</bag>
<bag name="Questions" access="none">
<key column="SurveyId" />
<one-to-many class="Question" />
</bag>
</class>
<class name="Page">
<many-to-one name="Survey" column="SurveyId" />
<bag name="Questions" generic="true" inverse="true">
<key column="PageId" />
<one-to-many class="Question" />
</bag>
</class>
<class name="Question">
<many-to-one name="Page" column="PageId" />
<many-to-one name="Survey" column="SurveyId" />
<bag name="Options" generic="true" inverse="true">
<key column="QuestionId" />
<one-to-many class="Option" />
</bag>
</class>
<class name="AnswerOption">
<many-to-one name="Question" column="QuestionId" />
</class>
I need to display all the questions on a page so I start with the survey object and loop through the pages, items and options. This causes NHibernate to execute many queries and I would like to optimize this. How can I get the survey object with the nested collections in the best possible way without executing too many queries?
This is the code I have at the moment but it still executes many queries:
var result = Session.CreateMultiQuery()
.Add(Session.CreateQuery("from Survey s inner join fetch s.Pages where s.Id = :id"))
.Add(Session.CreateQuery("from Survey s inner join fetch s.Question where s.Id = :id"))
.SetInt32("id", id)
.List();
IList list = (IList)result[0];
return list[0] as Survey;
I have also tried Future queries but they don't help to reduce the number of queries.
Any ideas?
If I understood correctly, you can achieve this with the following HQL (of course the same idea can be used with ICriteria)
from Survey s
inner join fetch s.Pages p
inner join fetch p.Questions q
inner join fetch q.Options
where s.Id = :id
If you also want to fetch survey.Questions then the best option is to fetch those in separate qyery and used Futures to avoid cartesian product.
Also, if I remember correctly HQL queries ignores fetch's defined in mappings. If the collection is mapped with lazy="false" fetch="join" then it is fetch when used ICriteria but not when using HQL.
You could try adding
lazy="false" fetch="join"
to your bag declarations. That way you can be sure the bag will be fetched using one query.
A solution I'm using is reversing relation between entities. With this you can be sure when a record of Survey is loaded, no record of Page is loaded unless you call LoadAll method. LoadAll is a method in each class that search all related records. Consider following code:
public class Survey : Entity {
Survey[] LoadAll {
string hql = "from Page page where page.SurveyID =" + this.ID;
//....
}
}
public class Page : Entity {
public Survey { get;set; }
}
public class Question : Entity {
public Page Page { get; set; }
}
public class Option : Entity {
public Question Question {set; get;}
}
I have a tree where every node is a Resource class:
public abstract class Resource
{
public virtual Guid Id { get; set; }
public virtual Resource Parent { get; set; }
public virtual IList<Resource> ChildResources { get; set; }
}
as you can see this class is abstract and there are many different derived classes from Resource (3 at the moment, more to come).
In my database i have a table for Resource, and a table for each class which
derives from Resource. These are mapped together with <joined-subclass>.
I've read this:
http://ayende.com/Blog/archive/2009/08/28/nhibernate-tips-amp-tricks-efficiently-selecting-a-tree.aspx
and i have the same code as Ayende to load my tree:
var resource = UnitOfWork.Current.Session
.CreateQuery("from Resource r join fetch r.ChildResources")
.SetResultTransformer(new DistinctRootEntityResultTransformer())
.SetReadOnly(true)
.List<Resource>();
which is all working fine (all Resources are returned with a single select) However, I'm seeing extra selects occurring as I enumerate a Resource's ChildResources list.
Is that because of this?:
http://ayende.com/Blog/archive/2009/09/03/answer-the-lazy-loaded-inheritance-many-to-one-association-orm.aspx
Either way, how do I prevent this from happening?
Here's the part of the mappings for the relationships (class names
trimmed for clarity):
<bag cascade="save-update" fetch="join" lazy="false" inverse="true" name="ChildResources">
<key>
<column name="Parent_Id" />
</key>
<one-to-many class="Resource" />
</bag>
<many-to-one class="Resource" name="Parent">
<column name="Parent_Id" />
</many-to-one>
Thanks
UPDATE
Slight oversight, its only issuing extra selects when enumerating the child collections of the leaf nodes in the tree...
Either do this:
<bag ... lazy="false">
to eager fetch the items always, or do this (in HQL):
var resources = session.CreateQuery("from Resource r join fetch r.ChildResources");
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