Eager load while using Linq in NHibernate 3 - nhibernate

I need help with eager loading in with Linq in NHibernate 3 trunk version.
I have a many-to-many relationship like this:
public class Post
{
public int Id {get;set;}
public IList<Tag> Tags { get;set;}
.
.
.
}
Now I have the following mapping in Fluent NHibernate
public class PostMap:ClassMap<Post>
{
public PostMap()
{
Table("Posts");
Id(x => x.Id);
.
.
HasManyToMany(x => x.Tags)
.Table("PostsTags")
.ParentKeyColumn("PostId")
.ChildKeyColumn("TagId")
.Not.LazyLoad(); // this is not working..
}
}
Now while fetching the posts, I need the Tags also to eager load. I know that it is possible with Criteria API and HQL and the SetFetchMode is what I should use. But is there are way to use SetFetchMode when using Linq?

Support for this went into the trunk sometime ago; the syntax is be something like
var query = session.Query<Post>().Where(bla bla).Fetch(p => p.Tags);
If Tags in turn had another relationship, you can do:
var query = session.Query<Post>().Where(bla bla).Fetch(p => p.Tags).ThenFetch(t => t.SomethingElse);

For me this thread solve problem.
Linq for NHibernate - filtering on <many-to-one> foreign key causes extra lookup
var linqsession = session.Linq<FeedItem>();
linqsession.QueryOptions.RegisterCustomAction(c => c.SetResultTransformer(new DistinctRootEntityResultTransformer()));
var feedItemQuery = from ad in linqsession.Expand("Ads")
where ad.Id == Id
select ad

Related

Pulling a property up to the parent object level

Take the following NHibernate scenario:
I have two tables:
Header
HeaderID (int),
ForeignKey1 (int),
ForeignKey2 (int)
Child
ForeignKey1 (int),
ForeignKey2 (int)
Description (varchar)
...
Metric Shed Ton Of Other Columns That Im Not InterestedIn(various types)
I'm using Fluent NHibernate - I'd like to project the value of Description on the Child object into the parent (is that the correct terminology?!) - but obviously Child contains a lot of data in its columns - I don't want all that extra data, just the description...how do I get NH to produce the equivalent of the following query:
select
Header.*, Child.Description
from
Header
inner join
Child ON Header.ForeignKey1 = Child.ForeignKey1 AND Header.ForeignKey2 = Child.ForeignKey2
The only way I've got this working up to now is to use a Reference mapping to reference the child from the Header entity and then just created a non-mapped property on Header which pointed to Child.Description. Obviously this means that NH fetches the whole child object before it can query the value of Description
(I don't think the composite key is a problem here, the join seems to work fine - it's just how to get the data without getting all the non-interesting data)
At the moment my header entity looks like this:
public virtual int HeaderID { get; set; }
public virtual int KeyColumn1 { get; set; }
public virtual int KeyColumn2 { get; set; }
public virtual Child Child { get; set; }
public virtual string Description { get { return Child.Description; } }
The mappings for it:
Id(x => x.HeaderID);
Map(x => x.KeyColumn1);
Map(x => x.KeyColumn2);
References<Child>(x => x.Child).Fetch.Join().Columns("KeyColumn1", "KeyColumn2").ReadOnly();
Basically, I can't change the schema, I'm not interested in the rest of the data in the Child table, and I can't create views (can't change schema)
Anyone have any ideas if this is possible? I'm going to be querying a big list of Header objects, and I need that field from Child but I don't want the query to take forever!
Is this something I would have to do at the query level instead using hql or crit API?
Edit:
Trying to get this working using query API
Header.Session.QueryOver<Header>(() => parent)
.Where(h => h.HeaderID == 1)
.Inner.JoinQueryOver(x => x.Child, () => child)
.Select(x => x.HeaderID, x => x.ForeignKey1, x => x.ForeignKey2, x => child.Description);
Checking the SQL shows the query is exactly what I want - but I get an exception System.Object[] is not of type Header and cannot be used in this generic collection
I assume this is because what I'm getting is just an array of values from the Select() - any idea how I can transform this into a Header object?
Edit: I ended up with
Header.Session.QueryOver<Header>(() => parent)
.Where(h => h.HeaderID == 1)
.Inner.JoinQueryOver(x => x.Child, () => child)
.Select(x => x.HeaderID, x => x.ForeignKey1, x => x.ForeignKey2, x => child.Description)
.TransformUsing(new GenericResultTransformer(typeof(Header), "HeaderID", "ForeignKey1", "ForeignKey2", "Description"));
Which works just how I want it - if anyone has a better suggestion I'm open to it, but like I said, I can't touch the schema at all
There is the concept of lazy properties, but that is really for the opposite situation, i.e. there is a small number of properties that you want to exclude.
If this is for a presentation scenario, use can use any of NHibernate's query methods, to project just the columns you like - the query result need not be a complete entity. See for instance the select clause in HQL and LINQ, and the SetProjection() family in Criteria/QueryOver.

Insert new NHibernate entity and immediately assign to parent

I have parent and child objects BOOKLET and DEMOGRAPHICS_INFO in my Oracle database mapped as follows in my data layer:
public BookletMapping()
{
Table("BOOKLET");
Id(x => x.Id, m => m.Column("ID");
...
ManyToOne(x => x.DemographicsInfo, m => m.Column("DEMOGRAPHICS_INFO_ID"));
}
public DemographicsInfoMapping()
{
Table("DEMOGRAPHICS_INFO");
Id(x => x.Id, m => m.Column("ID");
...
}
I have intentionally left out the DemographicsInfo relationship to the Booklet because I don't need to traverse my entities that direction. The ManyToOne relationship will actually be a one-to-one.
I have written a test to ensure I can create a DemographicsInfo and immediately assign it to its parent Booklet, and that looks like this:
[Test]
public void ShouldSaveCorrectEntity()
{
var booklet = _unitOfWork.Get<Booklet>(4);
var demInfo = new DemographicsInfo();
_unitOfWork.Insert(demInfo);
booklet.DemographicsInfo = demInfo;
_unitOfWork.Save();
demInfo.Id.ShouldNotEqual(0);
}
When I call Save(), I get the following exception:
{"ORA-02291: integrity constraint (<schema>.BOOKLET_DEMOGRAPHICS_INFO_FK1) violated - parent key not found\n"}
This is because the demInfo object is not given an Id upon Insert(). My Insert implementation looks like this:
public void Insert<T>(T entity)
{
using (var transaction = _session.BeginTransaction())
{
_session.Save(objectToSave);
_session.Flush();
transaction.Commit();
}
}
Where _session is an NHibernate ISession. Because I have both Saved the new entity (it persists successfully) and Flushed my session, I would expect my demInfo variable to have an Id, but it remains 0, which is a foreign key violation when I try to save my parent object. Am I overlooking a step here? Should I rethink my pattern for adding a new child to an existing parent?
I have solved my issue. As it turns out, the Oracle convention of using Sequences for Id column values and populating them using Triggers on row insert disallows NHibernate from learning the Id upon persisting an entity. I added a Sequence Generator to my Id maps and Insert() now updates the Id on my transient entity upon save so I can assign the DemographicsInfo to my Booklet.DemographicsInfo.
Id(x => x.Id, m =>
{
m.Column("ID");
m.Generator(Generators.Sequence, a => a.Params(new { sequence = "SEQ_TABLE_ID" }));
});
Now my test passes with no exceptions.

How do you work with detached QueryOver instances?

This NHibernate blog entry notes how detached QueryOver queries (analogous to DetachedCriteria) can be created (using QueryOver.Of<T>()). However, looking this over, it doesn't look analogous to me at all.
With DetachedCriteria, I would create my instance and set it up however I need, and afterwards call GetExecutableCriteria() to then assign the session and execute the query. With the "detached" QueryOver, most of the API is unavailable (ie, to add restrictions, joins, ordering, etc...) until I call GetExecutableQueryOver, which requires takes an ISession or IStatelessSession, at which point you are no longer disconnected.
How do you work with detached QueryOver instances?
EDIT:
Actual problem was related to how I'm storing the detached QueryOver instance:
public class CriteriaQuery<T>
{
internal protected QueryOver<T> _QueryOver { get; set; }
public CriteriaQuery()
{
_QueryOver = QueryOver.Of<T>();
}
// Snip
}
It should be a QueryOver<T, T>.
I'm using NHibernate 3.1.0.4000. The following code compiles successfully:
Employee salesRepAlias = null;
var query = QueryOver.Of<Customer>()
.JoinAlias(x => x.SalesRep, () => salesRepAlias)
.Where(x => x.LastName == "Smith")
.Where(() => salesRepAlias.Office.Id == 23)
.OrderBy(x => x.LastName).Asc
.ThenBy(x => x.FirstName).Asc;
return query.GetExecutableQueryOver(session)
.List();
This illustrates using restrictions, joins, and ordering on a detached QueryOver just like you would with a regular one.
Could you please post the code that demonstrates the API features that are unavailable?

NHibernate Search Index poco object throws TransientObjectException

When calling Index method on FullTextSession with plain poco object throws the error below, works fine with proxied object.
Stacktrace:
[TransientObjectException: the instance was not associated with this session]
NHibernate.Impl.SessionImpl.GetIdentifier(Object obj) +500
I'm trying to squeeze the performance out of the nhibernate select method I've got the following code:
public virtual IList<T> LoadSearch()
{
return Adapater.Session.QueryOver<T>()
.SelectList(e =>
{
e.Select(x => x.Id);
e.Select(x => x.Title);
e.Select(x => x.Description);
return e;
}).List<object[]>()
.Select(props => new T
{
Id = (Guid)props[0],
Title = (string)props[1],
Description = (string)props[2]
}).ToList();
}
Is there way to return a proxied result? or some how adapt the list to a proxied list?
I think you can only index objects that are associated with a session, i.e. proxied entities.
The plain POCOs you are returning didn't come from NH - so aren't associated with a NH session.
You could try using ISession.Lock(instance, NHibernate.LockMode.None); on each entity to associate it with the session, but I really don't know if that'd work.

How to update a specific fields of class in Fluent NHibernate with out updating the whole object? [duplicate]

This question already has answers here:
NHibernate update on single property updates all properties in sql
(2 answers)
Closed 5 years ago.
I am using Fluent NHibernate to do my NHibernate mappings, but now I have come to a problem that I am not sure how to solve. A simplified version of the problem follows.
I have a user class:
public class User {
public virtual int Id { get; set; }
public virtual string FirstName { get; set; }
public virtual string LastName { get; set; }
}
This is the associated Fluent NHibernate Class Map
public class UserMap : ClassMap<User> {
public UserMap() {
Id(x => x.Id);
Map(x => x.FirstName);
Map(x => x.LastName);
}
}
I have two web forms. One form allows me to change the users first name, and the second form allows me to change the users last name. What I am trying to achieve is a simple SQL statement like this:
For the first form:
UPDATE [users] SET firstname='new first name' WHERE id=1
For the second form:
UPDATE [users] SET lastname='new last name' WHERE id=1
Currently NHibernate performs the following SQL on my database:
UPDATE [users] SET firstname=null, lastname='new last name' WHERE id=1
The problem in the real world application, is that there are too many properties to update on some big objects (as well as access restrictions), and it seems pointless to update the whole object, when all I want / am allowed to do is update a single property.
I am hoping that someone can provide some advice as to how I can realise this, or point me in the right direction to solve this.
Hibernate's doing the right thing, but your problem indicates that your schema needs some normalization.
Ok, that works, Thanks for the help and tips Queen3!
here is how I sovled it:
using (var sf = Repository.CreateSessionFactory()) {
using (var s = sf.OpenSession()) {
using (var t = session.BeginTransaction()) {
var existingUser = s.Get<User>(editedUser.Id);
existingUser.LastName = editedUser.LastName;
s.SaveOrUpdate(existingUser);
t.Commit();
}
}
}
Although this does work, it requires that I retrieve the User from the database first and work within the same session. The good thing is that the sql statement that is generated just updates the dirty LastName field. :-)
I am unable to get it to work with a detached instance of the user, this is similar to how I was doing it before, which resulted in every field of the user being updated.
using (var sf = Repository.CreateSessionFactory()) {
using (var s = sf.OpenSession()) {
using (var t = session.BeginTransaction()) {
s.SaveOrUpdate(editedUser);
t.Commit();
}
}
}