Fluent Nhibernate many-to-many where table has multiple columns - nhibernate

I am trying to to map a many to many relationship using Fluent NHibernate.
I have a table User and a second table Organization. The association table is UserOrganization which contains the UserId and OrganizationId. The UserOrganization table also contains a few other fields (YearBegan, YearEnd).
How would I go ahead and map those using fluent mapping.
Thanks

You should probably make UserOrganization its own entity that contains those fields. That also gives you more flexibility in terms of cascading updates and deletes.
public class UserOrganization {
public virtual User User { get; set; }
public virtual Organization Organization { get; set; }
public virtual DateTime YearBegan { get; set; }
public virtual DateTime YearEnd { get; set; }
}

Related

Fluent Nhibernate Cascade.None() results in HasOne foreign key relationship not being persisted

I'm having issues with Nhibernate persisting a HasOne Relationship for one of my entities with Cascade.None() in effect. My domain model involves 4 classes listed below.
public class Project
{
public virtual int Id {get;set;}
public virtual IList<ProjectRole> Team { get; protected set; }
}
public class ProjectRole
{
public virtual int Id { get; set; }
public virtual User User { get; set; }
public virtual Role Role { get; set; }
}
public class Role
{
public virtual int Id { get; set; }
public virtual string Value { get; set; }
}
public class User
{
public virtual int Id { get; protected set; }
public virtual string LoginName { get; set; }
}
So basically we have projects, which have a list of ProjectRoles available from the Team property. Each ProjectRole links a User to the specific Role they play on that project.
I'm trying to setup the following cascade relationships for these entities.
project.HasMany<ProjectRoles>(p=> p.Team).Cascade.All()
projectRole.HasOne<Role>(r => r.Role).Cascade.None()
projectRole.HasOne<User>(r => r.User).Cascade.SaveUpdate()
I've used fluent nhibernate overrides to setup the cascades as above, but I'm finding that the line
projectRole.HasOne<Role>(r => r.Role).Cascade.None()
is resulting in the ProjectRole.Role property not being saved to the database. I've diagnosed this be looking at the SQL Generated by Nhibernate and I can see that the "Role_id" column in the ProjectRoles table is never set on update or insert.
I've also tried using
projectRole.HasOne<Role>(r => r.Role).Cascade.SaveUpdate()
but that fails as well. Unfortunately leaving it Cascade.All() is not an option as that results in the system deleting the Role objects when I try to delete a project role.
Any idea how to setup Cascade.None() for the ProjectRole-> Role relationship with out breaking persistence.
HasOne is for a one-to-one relationship which are rare. You want to use References to declare the one side of a one-to-many relationship. Making some assumptions about your domain model, the mapping should look like:
project.HasMany<ProjectRoles>(p=> p.Team).Inverse().Cascade.AllDeleteOrphan()
projectRole.References<Role>(r => r.Role);
projectRole.References<User>(r => r.User);
See also this question about the difference between HasOne and References.

NHibernate (Fluent) Lazy Loading Not Working

I am attempting to use NHibernate to generate a model for a very odd database. The tables themselves have primary keys for show only, all the actual relationships are on unique columns. For example, a product table with a product id primary key and a unique product name column. Another table, demand, has a product name column and that defines the relationship. I know this situation isn't ideal but it's out of my control.
At any rate, I was able to use Fluent NHibrenate to map product to demand, but I cannot seem to get the entity to lazy-load.
public class Demand
{
public virtual DemandId { get; set; }
public virtual Product { get; set; }
}
public class DemandMap : ClassMap<Demand>
{
public DemandMap()
{
this.Table("Demand");
this.LazyLoad();
this.Id(x => x.DemandId);
this.References(x => x.Product).PropertyRef(x => x.ProductName).LazyLoad();
}
}
Does anyone have any insight into why lazy loading is not working? I know it is not because I can see the product being fetched along with the demand in the SQL profiler.
My idea (Maybe you can try use "HasMany" there is example but you can read something about this):
First class
public class Demand
{
public virtual int DemandId { get; set; }
public virtual int Product { get; set; }
public virtual IEnumerable<NewClass> Name {get; set;}
}
this.HasMany(x=> x.Product).Column("Product_id").not.nullable;
Second class
public class NewClass
{
public virtual Demand Product_id {get; set;}
}
this.References(x => x.Product).Column("product_id).not.nullable

Fluent Nhibernate Many to Many association to multiple classes

Fluent Nhibernate Many to Many association to multiple classes
We use Nhibernate and up to now we have been able use the auto mapping. But I think this is about to change.
We have a Code class that has a many to many relation with several other classes.
I’m thinking something along these lines:
public class Code
{
public virtual Guid Id { get; set; }
public virtual ICollection<CodeUsage> Usage { get; set; }
}
class CodeUsage
{
public virtual Guid Id { get; set; }
public virtual Code Code { get; set; }
// Class, [Property,] Id for "ANY" mapping to A & B
}
class A
{
public virtual Guid Id { get; set; }
public virtual ICollection<CodeUsage> Codes { get; set; }
}
class B
{
public virtual Guid Id { get; set; }
public virtual ICollection<CodeUsage> Codes { get; set; }
}
Many to Many will lead to the creation of a linking table, in the linking table their needs come a mapping to the classes using codes. In the documentation it is referred to as a “Any” mapping.
But I have no idea how get fluent to create one.
Thoughts anyone? or even better: a solution <);o)}{
You can't map <many-to-any> in Fluent NHibernate - it's not supported.
I think it may be a good reason to move to mapping-by-code, that supports it well.

Fluent NHibernate one-to-many with intervening join table?

I'm having trouble getting the Fluent Nhibernate Automapper to create what I want. I have two entities, with a one-to-many relationship between them.
class Person
{
public string name;
IList<departments> worksIn;
}
class Department
{
public string name;
}
The above is obviously bare bones, but I would be expecting to generate the fleshed out schema of:
Person{id, name}
Department{id, name}
PersonDepartment{id(FK person), id(Fk Department)}
Unfortunately, I am instead getting:
Person{id, name}
Department{id, name, personid(FK)}
I don't want the FK for Person included on the department table, I want a separate join/lookup table (PersonDepartment above) which contains the primarykeys of both tables as a composite PK and also Fks.
I'm not sure if I am drawing up my initial classes wrong (perhaps should just be LIst workIn - representing ids, rather than List worksIn), or if I need to manually map this?
Can this be done?
The way the classes have been structured suggests a one-to-many relationship (and indeed that's how you describe it in your question), so it should not be a surprise that FNH opts to model the database relationship in that way.
It would be possible, as you suggest, to manually create a many-to-many table mapping. But, is this definitely what you want?
I tend to find that pure many-to-many relationships are quite rare, and there is usually a good case for introducing an intermediate entity and using two one-to-many relationships. This leaves open the possibility of adding extra information to the link (e.g. a person's "primary" department, or perhaps details of their office within each of their departments).
Some example "bare-bones" classes illustrating this kind of structure:
public class Person
{
public int Id { get; set;}
public string Name { get; set;}
public IList<PersonDepartment> Departments { get; set; }
}
public class PersonDepartment
{
public int Id { get; set; }
public Person Person { get; set; }
public Department Department { get; set; }
public bool IsPrimary { get; set; }
public string Office { get; set; }
}
public class Department
{
public int Id { get; set; }
public IList<PersonDepartment> Personnel { get; set; }
public string Name { get; set; }
}

Splitting Out a Table to Improve Performance

my user's table in the database is becoming increasingly larger (in terms of columns not rows) and as a consequence is slowing down various areas of my site. This is because it tries to grab every column from the user's table everytime it does a join against it.
I figured i would keep all the common fields in the user's table and then put the additional fields in seperate tables. For example, say i have the following tables in my database:
Users:
- UserID (PK, Identity)
- UserName
- Password
...
UsersActivity:
- UserID (PK, FK)
- LastActivityDate
- LastLoginDate
...
UsersPreferences:
- UserID (PK, FK)
- HtmlEmail
- HideEmail
...
With the following entities:
public class User {
public virtual int UserID { get; set; }
public virtual string UserName { get; set; }
public virtual string Password { get; set; }
public virtual UserActivity Activity { get; set; }
public virtual UserPreferences Preferences { get; set; }
}
public class UserActivity {
public virtual User User { get; set; }
public virtual DateTime LastActivityDate { get; set; }
public virtual DateTime LastLoginDate { get; set; }
}
public class UserPreferences {
public virtual User User { get; set; }
public virtual bool HtmlEmail { get; set; }
public virtual bool HideEmail { get; set; }
}
I was just wondering what is the best way to map this for optimum performance? I figured i could do a one-to-one mapping on the Activity and Performance properties in the User entity. However as far as i understand one-to-one mapping doesn't support lazy loading and this approach would end up being slower.
I also looked into component mapping and wasn't too sure whether i could map this into a seperate table (please correct me if it would be better to keep it in the same table) and whether components supported lazy loading.
Before i go about doing some heavy refactoring of my application i thought i would get the opinion of someone who might have done this. Really appreciate the help.
Thanks
Edit: I found that you could lazy load a one-to-one relationship as long as it is required/constrained. Which it is my case. Therefore i went ahead and carried out the instructions in the following article:
http://brunoreis.com/tech/fluent-nhibernate-hasone-how-implement-one-to-one-relationship/
The trouble now is that i get the error:
NHibernate.Id.IdentifierGenerationException: NHibernate.Id.IdentifierGenerationException: null id generated for: UserActivity.
In NHibernate 3.0 one-to-one relationship supports lazy loading.
And I think that it is better to use Component with combination of Lazy property. Then you will be able to leave all properties in one table and not load them all at once.
You should do some additional application profiling to determine why you're having a performance problem. It's unlikely that it's due to the number of columns in the select list. You probably have an N+1 select problem.
That said, there are many good reasons to use a lightweight object so you might want to look at implementing a DTO (data transfer object) for this.