I have been trying to work with DDD style for my e-commerce application. Most of my business logic are implemented using fake repositories. Now, I would like to use NHibernate to hook my Domain Model to a real database.
I have a class Order which contains a list of OrderLines object
public IList<OrderLine> OrderLines{ ... } //line 1
In my OrderLine class I have a reference to the parent Order as follows
2. public Order Order { set; get;} // line 2
According to my understanding, OrderLine is a Value class instead of an Entity class, so I will use the composite-element to do the mapping.
<bag name="OrderLines" table="OrderLines" lazy="true">
<key column="Order_ID"/> <!--This is where I got confused. line 3-->
<composite-element class="OrderLine">
<!-- class attribute required -->
<many-to-one name="Order" class="Order" column="Order_ID"/> <!--Do I need this? line 4-->
...
</composite-element>
</bag>
Note that in line 3, I created a key element for the mapping(syntax requires this). But since I have defined a reference to Order class in my OrderLine class(line 2), do I also need to create a mapping at line 4?
You don't need line#4.
You can find a great explanation on the subject in another thread at stackoverflow here: Nhibernate , collections and compositeid
Related
I have recently inherited a project at work that contains NHibernate. I am extremely new to it and have to make a modification to one of the mappings. I've read through the documentation here and I'm still not sure how to do this or if my understanding/terminology is even correct.
So given the following table structure I need a bag that will get me the ProjectName:
User
UserID (PK)
ProjectUser
UserID (PK, FK User.UserID)
ProjectID (PK, FK Project.ProjectID)
Project
ProjectID (PK)
ProjectName
Here is the existing bag mapping and it correctly returns the ProjectID, but now I'm trying to understand how I need to modify it to return both the ProjectID and the ProjectName:
<bag name="Projects" table="ProjectUser" lazy="true" inverse="true" cascade="save-update">
<key column="UserId"></key>
<many-to-many class="Project" column="ProjectID"></many-to-many>
</bag>
Well, your mapping seems to be correct, i.e. already returning the ProjectName. To be sure please, check that the object Project is mapped like this:
<class name="Project" table="Project">
<id name="Id" column="ProjectID" generator class="native"/>
<!-- above as the Id we have mapping for column ProjectId
below the C# Name will contain the column ProjectName -->
<property name="Name" column="ProjectName" />
<!-- related Users to this Project -->
<bag name="Users" table="ProjectUser" lazy="true" >
<key column="ProjectID"></key>
<many-to-many class="User" column="UserID" />
</bag>
</class>
And the Project would be like this
public class Project
{
public virtual int Id { get; set;}
public virtual string Name { get; set;}
public virtual IList<User> Users { get; set;}
...
So, having this in place, we should be able to use the User:
public class User
{
public virtual IList<Project> Projects { get; set;}
...
mapped and loaded by NHibernate like this
user = session.Get<User>(x) // id of searched user
foreach(var project in user.Projects)
{
var name = project.Name;
var id = project.Id;
...
}
NOTES:
In case of many-to-many there obviously could/should be <bag> mapping on both sides - Project and User. But only one of them can have inverse="true". So in this case Project.Users does not have that.
The cascade setting on many-to-many is doing (most likely) different thing than one would expect. It is not related to the pairing table but to the second end of that mapping.
Cascading of the pairing object is done out of the box. It does not have to be mapped, in fact it cannot be mapped or turned off... Other words I would suggest to remove that cascade, unless you really want to change the Project in persistence, if you are working with some User.
Check also:
23.2. Author/Work
How to do it without many-to-many ... with explicit pairing object as a mapped Entity: Nhibernate: How to represent Many-To-Many relationships with One-to-Many relationships? or Am I doing many to many incorrectly when using fluent nhibernate?
My many-to-many relationship does not involve the standard "joining-table" approach, in which a table stores the "FK1-to-FK2" relationships.
Instead, I'm "loosely" joining to a legacy read-only view as follows:
Appointment class (based on the Appointment table)
int AppointmentId (PK)
int OrderId
List<LegacyOrder> LegacyOrders
LegacyOrder class (based on the LEGACY_ORDERS_VIEW view in our legacy system)
int OrderId (composite PK)
int VersionNumber (composite PK)
An Appointment can have many (versions of a) LegacyOrder.
A LegacyOrder can have many Appointments, but this relationship is not important in our application.
I want to populate the LegacyOrders property with all LegacyOrders for the specified OrderId.
My attempt at mapping is as follows:
<class name="Appointment" table="Appointments" lazy="true">
<bag name="Orders" table="LEGACY_ORDERS_VIEW" inverse="true">
<key column="OrderId" />
<many-to-many class="LegacyOrder" column="ORDER_ID" />
</bag>
</class>
....but I'm getting "could not execute query" exceptions due to invalid SQL.
I think the table referred to in the <bag> mapping should be the "joining table".... but I don't have one.
I'm fairly sure my mapping approach is fundamentally wrong.... what's the right way to go about it?
Edit:
Thanks Radim: perhaps a better name for LegacyOrder would be LegacyOrderVersion: each record in that view corresponds to a "version" of an order, rather than an order.
i.e. An order may be for 100 units, then when say 20 units are collected, another record is written with the same OrderId but for 80 units. (I did warn you it was legacy :)
If an Appointment (in the new system) can retrieve all related LegacyOrderVersions, then it can derive useful properties such as CurrentLegacyOrderVersion and OriginalLegacyOrderVersion.
FWIW: this works great for me:
<class name="Appointment" table="Appointments" lazy="true">
<bag name="Orders" inverse="true">
<key property-ref="OrderId" column="ORDER_ID" />
<one-to-many class="LegacyOrder" />
</bag>
</class>
One way how to solve this a bit challenging DB structure, could be with the property-ref feature. See more details here: 5.1.10. many-to-one, working even for our many-to-many scenario.
So firstly we have to map the property, which we will use as a reference:
<class name="Appointment" table="Appointments" lazy="true">
...
// the column name is coming from the Appointment table
<property name="OrderId" column="ORDER_ID" />
So, now we have mapped the OrderId - the property (column) - which we will use to map the <bag>.
Well, honestly, now I am not sure what your thoughts were. In case that LegacyOrder would have one column mapped as key (the Order_ID) we can do it like this.
<bag name="Orders" table="LEGACY_ORDERS_VIEW" inverse="true">
<key column="ORDER_ID" property-ref="OrderId" />
<many-to-many class="LegacyOrder" formula="ORDER_ID" />
</bag>
But that's not reasonable, because the Order_Id is not unique. In fact the LegacyOrder view, does not seem to be the entity at all. It could be some real intermediate structure.
I would say, that what the pairing view Legacy_orders_view represents, is the map (dictionary) saying: The Order with ID == X, had these Versions.
This information, the int Version numbers, is the only thing/information I can find out as really interesting. The OrderId is representing still the same Order
Anyhow, with the proeprty-ref and more detailed knowledge what you need to achieve we can at the end have:
// I. Map
public virtual IDictionary<int, Order> OrderMap { get; set; }
above the Version will play the role of the Key, the Order is questinable, because it will be the same Order as the OrderId says
// II. Version collection
public virtual IList<int> OrderVersions { get; set; }
in this case we will get set of int numbers related to the OrderId. Seems to be the only interesting message we can get.
III. There must be more information, about your entity/DB model. Why does the Legacy_orders_view exists at all? What would we like to get from that "relation" at the end?
I have customer and BankAccount tables. CustomerID is a foreign key in the BankAccount table. Here we have to do with one to many relationship. I have done mapping for CustomerInfo and BankAccountInfo. I have attached with the question post.
Here we want to do with collection using Iesi.collections. Does anyone have ideas on how to do this in Nhibernate?
To do Collection mapping start reading this documentation: Chapter 6. Collection Mapping
In case that you will use the Iesi collections, most suitable could be ISet<>, which is designed to allow only unqiue values to be inserted:
public class Customer
{
public virtual Iesi.Collections.Generic.ISet<BankAccount> BankAccounts { get; set; }
}
And the mapping could be like this
<set name="BankAccounts" inverse="true" lazy="true" table="BankAccount"
cascade="all" batch-size="25" >
<key column="CustomerId" />
<one-to-many class="BankAccount" />
</set>
Notes: This mapping has some redundant attributes, which can help to do smarter loading. E.g. batch-size will avoid 1+N loads, while doing 1 + N/25... cascade will implicitly solve the persistence of added items... read more in doc.
The complete ISet description: http://ayende.com/blog/3943/nhibernate-mapping-set
I'm having an entity object called Patient and this entity is having a property called Visits which is of type VisitsCollection.
VisitsCollections is a child class of IList<Visit> but it also adds some custom logic to the collection (like auto ordering, some validation, notifications, etc..).
I need to use the custom collection type as it adds some data to the entities that are added to the collection and performs some other paperwork transparently.
Now I want to map that in NHibernate, so I've created:
<list name="Visits" lazy="true" fetch="select">
<key foreign-key="PatientId" />
<index column="Timestamp" />
<one-to-many class="Visit" not-found="ignore"/>
</list>
I'm getting an exception:
Unable to cast object of type 'NHibernate.Collection.PersistentList' to type '...VisitsCollection'
Whenever I'm accessing the visits property.
I've also tried to map it this way:
<list name="Visits" lazy="true" fetch="select" collection-type="VisitsCollection">
<key foreign-key="PatientId" />
<index column="Timestamp" />
<one-to-many class="Visit" not-found="ignore"/>
</list>
but still, I'm getting this exception:
Custom type does not implement UserCollectionType: .....VisitsCollection
I don't want to inherit my VisitsCollection from any NHibernate type as the collection class is part of a framework that I want it to be DAL-agnostic (as it will be used in many scenarios - not only with a database).
Any ideas on how to map this, preserving the structure of my code?
Thanks in advance.
I never use custom collection types, mainly because I'm lazy. NHibernate wants you to use a IUserCollectionType I believe, which requires a bit of plumbing.
Rather than that, my first stop would be to look at using extension methods as discussed by Billly McCafferty. But you have code written so...
Alternatively, you could map your collection as a component as discussed here by Colin Jack. This might be easier for your scenario?
Also check this SO thread.
I also vote up not to use custom collections. Anyway, you can do it via component.
<component name="Warehouses" class="Core.Domain.Collections.EntitySet`1[Core.Domain.OrgStructure.IWarehouseEntity,Core],Core">
<set name="_internalCollection" table="`WAREHOUSE`" cascade="save-update" access="field" generic="true" lazy="true" >
<key column="`WarehouseOrgId`" foreign-key="FK_OrgWarehouse" />
<!--This is used to set the type of the collection items-->
<one-to-many class="Domain.Model.OrgStructure.WarehouseEntity,Domain"/>
</set>
How to map NHibernate custom collection with fluentNHibernate?
Just for reference, here is how you could do it using FluentNHibernate
Whether we should or should not create a custom collection type is a separate topic IMHO
public class PatientOverride : IAutoMappingOverride<Patient>
{
public void Override(AutoMapping<Patient> mapping)
{
mapping.Component(
x => x.Visits,
part =>
{
part.HasMany(Reveal.Member<VisitsCollection, IEnumerable<Visit>>("backingFieldName")) // this is the backing field name for collection inside the VisitsCollection class
.KeyColumn("PatientId")
.Inverse(); // depends on your use case whether you need it or not
});
}
}
Nhibernate users, professionals, gurus and developers are expected. Please help !!!
I want to realise a n:m relation between two classes. A student attends in more courses and a course consists of more students as members. I do a bidirectional association many-to-many with bag to get the both lists from each site.
The two Student and Course classes:
public class Student {
// Attributes........
[XmlIgnore]
public virtual IList MyCourses { get; set; }
// Add Method
public virtual void AddCourse(Course c)
{
if (MyCourses == null)
MyCourses = new List<Course>();
if (!MyCourses.Contains(c))
MyCourses.Add(c);
if (c.Members== null)
c.Members= new List<Student>();
if (!c.Members.Contains(this))
c.Members.Add(this);
}
public virtual void RemoveCourse(Course c)
{
if (MyCourses != null)
MyCourses.Remove(c);
if (c.Members!= null)
c.Members.Remove(this);
}
}
public class Course {
// Attributes........
[XmlIgnore]
public virtual IList Members { get; set; }
}
In database there are two tables t_Student, t_Course and a relation table tr_StudentCourse(id, student_id, course_id).
<class name="Student" table="t_Student" polymorphism="explicit">
.....
<bag name="MyCourses" table="tr_StudentCourse">
<key column="student_id" />
<many-to-many class="Course" column="course_id" not-found="ignore" />
</bag>
</class>
<class name="Course" table="t_Course" polymorphism="explicit">
.....
<bag name="Members" table="tr_StudentCourse" inverse="true">
<key column="course_id" />
<many-to-many class="Student" column="student_id" not-found="ignore" />
</bag>
</class>
Course was chosen as inverse in the bidirectional association. I did the same as example (Categorie, Item) in section 6.8 of nhibernate documentation. So I saved the student object after inserting a course in the list MyCourses by calling the Add/Remove-method.
Student st1 = new Student();
Course c1 = new Course();
Course c2 = new Course();
st1.AddCourse(c1);
st1.AddCourse(c2);
session.saveOrUpdate(st1);
That works fine, the st1, c1 and their relation (st1,c1) can be find in the database. The relation datasets are (id=1, st1.id, c1.id) and (id=2, st1.id, c2.id).
Then I add more courses to the object st1.
Course c3 = new Course();
st1.AddCourse(c3);
session.saveOrUpdate(st1);
I can see the 3 relation datasets, but the two old relations were deleted and new three were created with another new id. (id=3, st1.id, c1.id), (id=4, st1.id, c2.id) and (id=5, st1.id, c3.id). There are not dataset with id=1 and 2 more in relation table.
The same by deleting if I remove a course from student.MyCourse and then save the student object. All collection was also deleted and recreated a new list which less one deleted element. That problem makes the id in the relation table increates very fast and a have troble by doing a backup of relation.
I have looked some days in internet, documentation and forums to find out why the whole old collection was deleted and a new as created by each changing, but I was not successful. It is a bug from nhibernate mapping or did I do any wrong?
I am very very grateful to your help and answer.
Nhibernate documentation http://nhforge.org/doc/nh/en/index.htm
NHibernate can't create, delete or
update rows individually, because
there is no key that may be used to
identify an individual row.
By note from "6.2. Mapping a Collection"
As soon as you have id in tr_StudentCourse you can try using indexed collections, i.e. replace <bag> with <map> or similar and add <index> element to the mapping:
<index
column="id"
type="int"
/>
or even create a special entity for the relation table to use with <index-many-to-many>.
This is what I've found on the NHibernate website:
Hibernate is deleting my entire
collection and recreating it instead
of updating the table.
This generally happens when NHibernate
can't figure out which items changed
in the collection. Common causes are:
replacing a persistent collection
entirely with a new collection
instance passing NHibernate a manually
constructed object and calling Update
on it.
serializing/deserializing a
persistent collection apparently also
causes this problem.
updating a
with inverse="false" - in this case,
NHibernate can't construct SQL to
update an individual collection item.
Thus, to avoid the problem:
pass the same collection instance that
you got from NHibernate back to it
(not necessarily in the same session),
try using some other collection
instead of <bag> (<idbag> or <set>),
or try using inverse="true" attribute
for <bag>.