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".
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 the below two classes:
public class Project
{
public virtual int ProjectId { get; set; }
public virtual string ProjectName { get; set; }
public virtual LegalEntity LegalEntity { get; set; }
}
and
public class LegalEntity
{
public virtual int LegalEntId { get; set; }
public virtual string Name { get; set; }
}
with mappings as:
<class name="Project" table="Project" dynamic-update="true">
<id name="ProjectId">
<generator class="native"/>
</id>
<property name="ProjectName" />
<many-to-one name="LegalEntity" column="LegalEntId" fetch="join" cascade="all-delete-orphan" />
</class>
and
<class name="LegalEntity" table="LegalEnt" dynamic-update="true">
<id name="LegalEntId">
<generator class="native"/>
</id>
<property name="Name" />
</class>
In database, Project table has a FK to LegalEntity's PK column. One Project will have only one legal entity. Different projects can have same legal entity. So thats the reason I have gone for many-to-one. Not sure if this is correct though.
Insert and update is working fine. But if I update a legal entity id in a project and that legal entity becomes orphan, I want it to be deleted. But its not happening. Am I wrong in understanding delete-all-orphan? If yes, how can I achieve this behaviour?
The many-to-one cascade does not support all-delete-orphan, see:
5.1.10. many-to-one
<many-to-one
...
cascade="all|none|save-update|delete" (4)
...
Also, it would be almost impossible to handle this feature by NHibernate's session. Because it does not have to be clear, that the referenced many-to-one is really orphan. There should be some farther checks in DB... there could be other places referencing this table row...
Suggestion: do it in your code as a part of the DAO or Business Facade implementation. Check if there are really no dependencies, and then issue explicit Delete()
EXTEND: Here is a QueryOver syntax to get a list of all "orphan" LegalEntity
// subquery
var subquery = QueryOver.Of<Project>()
.Select(x => x.LegalEntity.LegalEntId);
// just these legal entities, which are NOT used
var query = session.QueryOver<LegalEntity>()
.WithSubquery
.WhereProperty(y => y.LegalEntId)
.NotIn(subquery)
;
// orphans
var list = query
.List<LegalEntity>();
Now all-delete-orphan and delete-orphan have been implemented for many-to-one as you can see in this commit from Nov 19, 2014.
Those were not supported when the OP asked the questions or when Radim Köhler wrote his answer, but I think future visitors will appretiate the update.
The documentation is also updated and now says:
cascade="all|none|save-update|delete|delete-orphan|all-delete-orphan"
But the documentation is confusing now, because it still has the following note:
The cascade attribute permits the following values: all, save-update, delete, none.
So I've created a defect to fix that last part of the documentation.
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>
I'm looking to create a many to many relationship using NHibernate. I'm not sure how to map these in the XML files. I have not created the classes yet, but they will just be basic POCOs.
Tables
Person
personId
name
Competency
competencyId
title
Person_x_Competency
personId
competencyId
Would I essentially create a List in each POCO for the other class? Then map those somehow using the NHibernate configuration files?
You can put the many-to-many relation to either class, or even to both. This is up to your domain model. If you map it to both, one of them is inverse.
class Person
{
// id ...
IList<Competency> Competencies { get; private set; }
// you domain model is responsible to manage bidirectional dependencies.
// of course this is not a complete implementation
public void AddCompetency(Competency competency)
{
Competencies.Add(competency);
competency.AddPerson(this);
}
}
class Competency
{
// id ...
IList<Person> Persons { get; private set; }
}
Mapping:
<class name="Person">
<id ....>
<bag name="Competencies" table="Person_x_Competency">
<key column="personId"/>
<many-to-many class="Competency" column="competencyId"/>
</bag>
</class>
<class name="Competency">
<id ....>
<bag name="Persons" table="Person_x_Competency" inverse="true">
<key column="competencyId"/>
<many-to-many class="Person" column="personId"/>
</bag>
</class>
Only make it bidirectional if you really need it.
By the way: it is much better to write the classes first and create the database design afterwards. The database can be exported from the mapping files. This is very useful.
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