I'm in the process of learning Fluent nHibernate. I'm having trouble with building a query thats not quite the same as the classic examples I've found online. Typically I've found this example:
IQueryOver<Cat,Cat> catQuery =
session.QueryOver<Cat>(() => catAlias)
.JoinAlias(() => catAlias.Kittens, () => kittenAlias)
.Where(() => catAlias.Age > 5)
.And(() => kittenAlias.Name == "Tiddles");
So from what I understand in this example a Cat object is being returned after being joined on Kittens and then filtered using the kittens name and the cat's age. And the join works because the Cat object has a property called Kittens.
An example of what I'm trying to do would look like this:
Forest f = null;
Tree t = null;
ForestsFound = session.QueryOver<Forest>(() => f)
.JoinAlias(() => t.Forest, () => f)
.Where(() => t.NumberOfTrees > 1000)
.List<Forest>()
.ToList<Forest>();
A forest is essentially a lookup table, it's the Tree that has a link to what forest the tree is in but I want to return a distinct list of forests. So in regular sql it would look like:
select f.*
from Forest f
inner join Tree t
on t.Forest_id = f.ID
where t.NumberOfTrees > 1000
If you have a relationship from Forest -> Trees then you can do this:
Forest f = null;
Tree t = null;
ForestsFound = session.QueryOver<Forest>(() => f)
.JoinAlias(() => f.Trees, () => t)
.Where(() => t.NumberOfTrees > 1000)
.List<Forest>();
Related
I try to run query like this with Nhibernate v.4:
Select o.Number, c.Address
From Order o join Client c on o.ClientId = c.Id
Where c.Name = "John"
Tried many ways to do that with JoinQueryOver and JoinAlias but nothing helps, endup with error "could not resolve property: Address of Order"
Session.QueryOver<Order>()
.JoinQueryOver(s => s.Client)
.Where(() => c.Name == "John")
.SelectList(x => .Select(Projections.Property<Order>(o => o.Number)
.SelectList(x => .Select(Projections.Property<Order>(o => o.Client.Address))
or like this
...
.SelectList(x => .Select(Projections.Property<Order>(o => o.Number)
.SelectList(x => .Select(Projections.Property<Client>(c => c.Address))
What is the right way to build the query or something very similar? Problem with 'Select' operator, 'Where' part works fine. I can also build non-join queries by this 2 entities separate from each other and it works well, but no idea how to join them
Finally I've figured out how to make it work:
Client client = null;
OrderClientDto dto = null;
var result = Session.QueryOver<Order>()
.JoinAlias(o => o.Client, () => client)
.Where(() => c.Name == "John")
.SelectList(x => x
.Select(o => o.Number).WithAlias(() => dto.Number)
.Select(() => o.Client.Address).WithAlias(() => dto.Address))
.TransformUsing(Transformers.AliasToBean<OrderClientDto>())
.List<OrderClientDto>();
Nhb is far from being intuitive and convenient. Same query is much easier to write in EF.
I have some QueryOver with several joins and the result I get is OK in terms of the returned objects. This is the code>
var l = session.QueryOver<Discount>(() => discount)
.JoinQueryOver<ConPrdGrp>(r => r.ConPrdGrps)
.JoinQueryOver<PrdGroupTree>(k => k.PrdGroupTree)
.JoinQueryOver<Product>(g => g.Products)
.Where(p => p.ProductID == Product.ProductID)
.And(() => discount.FomDato <= DateTime.Now && discount.TomDato >= DateTime.Now).List();
But if I look at the SQL statement, I can see that the generated query selects ALL columns from all joined tables although the result only returns a list of Discount objects. I can get some properties of Discount using projections and the query will be much smaller. But how I can instruct NHibernate to get just columns from the Discount table and not from all joined tables?
As far as I know there is NOT a simple way like: .Select(Projections.Properties<Discount>()). Check this a bit outdated question (NHIbernate: Shortcut for projecting all properties?)
What you can do is explicitly name the columns you would like to see:
... // the QueryOver you have
.SelectList (l => l
.Select(() => discount.ID).WithAlias(() => discount.ID)
.Select(() => discount.Code).WithAlias(() => discount.Code)
...
)
.TransformUsing(Transformers.AliasToBean<Discount>())
...
The second approach could be to create the Subquery, and then just QueryOver<Discount>() 16.8. Subqueries
QueryOver<Discount> subQuery =
QueryOver.Of<Discount>(() => innerDiscount)
.JoinQueryOver<ConPrdGrp>(r => r.ConPrdGrps)
.JoinQueryOver<PrdGroupTree>(k => k.PrdGroupTree)
.JoinQueryOver<Product>(g => g.Products)
.Where(p => p.ProductID == Product.ProductID)
.And(() => innerDiscount.FomDato <= DateTime.Now
&& innerDiscount.TomDato >= DateTime.Now).List()
.Select( Projections.Property(() => innerDiscount.ID))
;
var query = session.QueryOver<Discount>(() => discount)
.Where(Subqueries.PropertyIn("ID", subQuery.DetachedCriteria))
;
Basically I crossed the same problem of Linq provider in this linq-to-nhibernate-produces-unnecessary-joins
List<Competitions> dtoCompetitions;
dtoCompetitions = (from compset in session.Query<FWBCompetitionSet>()
where compset.HeadLine == true
&& compset.A.B.CurrentSeason == true
select (new Competitions
{
CompetitionSetID = compset.CompetitionSetID,
Name = compset.Name,
Description = compset.Description,
Area = compset.Area,
Type = compset.Type,
CurrentSeason = compset.A.B.CurrentSeason,
StartDate = compset.StartDate
}
)).ToList();
Which leads to duplicated join in its generated SQL
SELECT fwbcompeti0_.competitionsetid AS col_0_0_,
fwbcompeti0_.name AS col_1_0_,
fwbcompeti0_.DESCRIPTION AS col_2_0_,
fwbcompeti0_.area AS col_3_0_,
fwbcompeti0_.TYPE AS col_4_0_,
fwbseason3_.currentseason AS col_5_0_,
fwbcompeti0_.startdate AS col_6_0_
FROM fwbcompetitionset fwbcompeti0_
INNER JOIN A fwbcompeti1_
ON fwbcompeti0_.competitionseasonid = fwbcompeti1_.competitionseasonid
INNER JOIN A fwbcompeti2_
ON fwbcompeti0_.competitionseasonid = fwbcompeti2_.competitionseasonid
INNER JOIN B fwbseason3_
ON fwbcompeti2_.seasonid = fwbseason3_.seasonid
WHERE fwbcompeti0_.headline = #p0
AND fwbseason3_.currentseason = #p1
Notice these joins, which are totally duplicated and also affect my SQL Server's performence.
INNER JOIN A fwbcompeti1_
ON fwbcompeti0_.competitionseasonid = fwbcompeti1_.competitionseasonid
INNER JOIN A fwbcompeti2_
ON fwbcompeti0_.competitionseasonid = fwbcompeti2_.competitionseasonid
Update1
In the NHibernate 3.2, this LiNQ bug is still valid, and I could not find a simple and reasonable Linq solution.
So I used QueryOver + JoinAlias + TransformUsing finishing the job, workds perfect to me.
FWBCompetitionSet compset = null;
FWBCompetitionSeason compseason = null;
FWBSeason season = null;
IList<Competitions> dtoCompetitions;
dtoCompetitions = session.QueryOver<FWBCompetitionSet>(() => compset)
.JoinAlias(() => compset.FWBCompetitionSeason, () => compseason)
.JoinAlias(() => compseason.FWBSeason, () => season)
.Where(() => compset.HeadLine == true)
.And(() => season.CurrentSeason == true)
.SelectList(
list => list
.Select(c => c.CompetitionSetID).WithAlias(() => compset.CompetitionSetID)
.Select(c => c.Name).WithAlias(() => compset.Name)
.Select(c => c.Description).WithAlias(() => compset.Description)
.Select(c => c.Area).WithAlias(() => compset.Area)
.Select(c => c.Type).WithAlias(() => compset.Type)
.Select(c => season.CurrentSeason).WithAlias(() => season.CurrentSeason)
.Select(c => c.StartDate).WithAlias(() => compset.StartDate)
)
.TransformUsing(Transformers.AliasToBean<Competitions>())
.List<Competitions>();
Yet Another Edit:
I think I finally found out what's going on. It seems that the LINQ to NHibernate provider has trouble navigating associations from the target to the source table and generates a separate join each time it encounters such an association.
Since you don't provide your mapping, I used the mapping from linq-to-nhibernate-produces-unnecessary-joins. This model has a Document with one Job and many TranslationUnits. Each TranslationUnit has many Translation entities.
When you try to find a Translation based on a Job, you are traversing the associations in the reverse order and the LINQ provider generates multiple joins: one for Translation -> TranslationUnit and one for TranslationUnit to Document.
This query will generate redundant joins:
session.Query<TmTranslation>()
.Where(x => x.TranslationUnit.Document.Job == job)
.OrderBy(x => x.Id)
.ToList();
If you reverse the navigation order to Document -> TranslationUnit -> Translation, you get a query that doesn't produce any redundant joins:
var items=(from doc in session.Query<Document>()
from tu in doc.TranslationUnits
from translation in tu.Translations
where doc.Job ==job
orderby translation.Id
select translation).ToList();
Given this quirkiness, QueryOver seems like a better option.
Previous Edit:
I suspect the culprit is compset.A.B.CurrentSeason. The first joined table (fwbcompeti1_) returns A.B while the next two (fwbcompeti2_ and fwbseason3_) are used to return A.B. The LINQ to NHibernate provider doesn't seem to guess that A is not used anywhere else and fails to remove it from the generated statement.
Try to help the optimizer a little by replacing CurrentSeason = compset.A.B.CurrentSeason with CurrentSeason = true from the select, since your where statement returns only items with CurrentSeason == true.
EDIT: What I mean is to change the query like this:
List<Competitions> dtoCompetitions;
dtoCompetitions = (from compset in session.Query<FWBCompetitionSet>()
where compset.HeadLine == true
&& compset.A.B.CurrentSeason == true
select (new Competitions
{
CompetitionSetID = compset.CompetitionSetID,
Name = compset.Name,
Description = compset.Description,
Area = compset.Area,
Type = compset.Type,
CurrentSeason = true,
StartDate = compset.StartDate
}
)).ToList();
I simply replace the value compset.A.B.CurrentSeason with true
Object Structure:
A house has many rooms.
A room has many tables.
A table has many vases (on it).
House > Rooms > Tables > Vases.
I'd like to use JoinQueryOver to select all tables with vases that are red - in a particular house.
I thought to do this:
var v = session.QueryOver<House>()
.Where(x => x.ID == HouseID)
.JoinQueryOver<Room>(x => x.Rooms)
.JoinQueryOver<Table>(x => x.Tables)
.JoinQueryOver<Vase>(x => x.Vases)
.Where(x => x.Color == "Red")
.SingleOrDefault<House>();
This was an approach I tried (of the many that failed). I don't really want the House and Room info.
Ultimately, I'm looking for a List of Tables (in a particular house), with their collections of Vases (that are red) fetched.
Thanks for the help!
Edit
Something like this would be nice:
var v = session.QueryOver<Table>()
.Where(x => x.Room.House.ID == HouseID) // this Where won't work.
.JoinQueryOver<Vase>(x => x.Vases)
.Where(x => x.Color == "Red")
.List().ToList();
var v = session.QueryOver<Table>()
.JoinAlias(x => x.Room, () => room)
.Where(() => room.House.ID == HouseID)
.JoinQueryOver<Vase>(x => x.Vases)
.Where(x => x.Color == "Red")
.List();
I'm using NHibernate 3.0 with both the LINQ provider and QueryOver. Sometimes I want to eager load related data, and there comes the method "Fetch" to the rescue, both in LINQ and QueryOver. Now I have a special scenario where I want to eager load a property not directly on the second level, like:
Foo f = ...;
f.A.B.C
with LINQ there's no problem, as you can "chain" fetches with the method "ThenFetch", like:
var result = Session.Query<Foo>().Fetch(a => a.A).ThenFetch(b => b.B).ThenFetch(c => c.C).ToList();
In QueryOver there's no such method, so how can I achieve the same result?
Thanks in advance.
I actually managed to solve this problem using two different approaches:
Approach one:
Session.QueryOver<Foo>().Fetch(x => x.A).Fetch(x => x.A.B).Fetch(x => x.A.B.C)
Approach two:
A a = null;
B b = null;
C c = null;
Session.QueryOver<Foo>()
.JoinAlias(x => x.A, () => a)
.JoinAlias(() => a.B, () => b)
.JoinAlias(() => b.C, () => c)
Both work (altough I'm not exactly sure if one of them generated "inner" and the other one "outer" joins).
Just as a curiosity, I'll post the reply they gave me on the NHibernate Jira:
query
.Fetch(p => p.B)
.Fetch(p => p.B.C) // if B is not a collection ... or
.Fetch(p => p.B[0].C) // if B is a collection ... or
.Fetch(p => p.B.First().C) // if B is an IEnumerable (using .First() extension method)
I think you can do that with JoinQueryOver
IQueryOver<Relation> actual =
CreateTestQueryOver<Relation>()
.Inner.JoinQueryOver(r => r.Related1)
.Left.JoinQueryOver(r => r.Related2)
.Right.JoinQueryOver(r => r.Related3)
.Full.JoinQueryOver(r => r.Related4)
.JoinQueryOver(r => r.Collection1, () => collection1Alias)
.Left.JoinQueryOver(r => r.Collection2, () => collection2Alias)
.Right.JoinQueryOver(r => r.Collection3)
.Full.JoinQueryOver(r => r.People, () => personAlias);