I have an nhibernate issue where I am projecting the sql Coalesce function.
I am comparing two string properties having the same name, from two different entities. In the resulting sql, the same property from only the first entity is being compared thus:
var list = Projections.ProjectionList();
list.Add(
Projections.SqlFunction("Coalesce",
NHibernateUtil.String,
Projections.Property<TranslatedText>(tt => tt.ItemText),
Projections.Property<TextItem>(ti => ti.ItemText)));
var q = Session.QueryOver<TextItem>()
.Left.JoinQueryOver(ti => ti.TranslatedItems);
Evaluating q results in this sql
coalesce(this_.ItemText, this_.ItemText)
the this_ in the RHS needs to be an aliased table
I can use Projections.Alias(Projections.Property<TranslatedText>(tt => tt.ItemText), "ttAlias") but am not sure how to map "ttAlias" in the JoinQueryOver.
I can create an alias there too, but can't see how to name it.
TranslatedText ttAlias = null;
...
JoinQueryOver(ti => ti.TranslatedItems, () => ttAlias)
Aliases are variables in QueryOver, like you showed in the JoinQueryOver call. Alias names (strings) should not be needed in QueryOver, they are for Criteria queries.
To the problem itself: I can't test it right now, but I think this should work:
Projections.Property(() => ttAlias.ItemText)
I used this topic as a resource while writing a unit test. This QueryOver works well and may help others with similar issues. QueryOver still struggles with property mapping to transformers using expressions. It's technically possible to remove "Id" but IMHO it hinders clarity.
The complete example is on GitHub
String LocalizedName = "LocalizedName";
//Build a set of columns with a coalese
ProjectionList plColumns = Projections.ProjectionList();
plColumns.Add(Projections.Property<Entity>(x => x.Id), "Id");
plColumns.Add(Projections.SqlFunction("coalesce",
NHibernateUtil.String,
Projections.Property<Entity>(x => x.EnglishName),
Projections.Property<Entity>(x => x.GermanName))
.WithAlias(() => LocalizedName));
ProjectionList plDistinct = Projections.ProjectionList();
plDistinct.Add(Projections.Distinct(plColumns));
//Make sure we parse and run without error
Assert.DoesNotThrow(() => session.QueryOver<Entity>()
.Select(plDistinct)
.TransformUsing(Transformers.AliasToBean<LocalizedEntity>())
.OrderByAlias(() => LocalizedName).Asc
.Skip(10)
.Take(20)
.List<LocalizedEntity>());
Related
how can I do this with queryover and a subquery?
FakturaObjektGutschrift fog = null;
int[] idS = Session.QueryOver(() => fog)
.SelectList( list => list
.SelectMax(() => fog.Id)
.SelectGroup(() => fog.SammelKontierung)
).List<object[]>().Select(x => (int)x[0]).ToArray();
And using the ids in another query
IQueryOver<Beleg, Beleg> sdfsd = Session.QueryOver(() => bGut)
.AndRestrictionOn(() => fog.Id).IsIn(idS); //iDs is a list of int.
I would like do this with a subquery because there is a limitation on the number of parameters for a SQL query. How do I do this?
How do I write the first query, but without selecting the SelectGroup()? This is exactly where I got stuck.
Group by without projection in QueryOver API is currently not supported link.
You can use LINQ to create the projection in a subquery:
var subquery = Session.Query<FakturaObjektGutschrift>()
.GroupBy(x => x.SammelKontierung)
.Select(x => x.Max(y => y.Id));
var query = Session.Query<Beleg>()
.Where(x => subquery.Contains(x.Id));
If you really needs QueryOver to create more complex queries check this solution link.
I'm struggling with using QueryOver.OrderBy with strings for property names on child entities. e.g. the following works but I am hardcoding the OrderBy field.
Customer custAlias = null;
session.QueryOver<Campaign>()
.JoinAlias(x => x.Customer, () => custAlias)
.OrderBy(() => custAlias.Name).Desc() // want to use string property name
.List();
I can specify the OrderBy using a string with something like:
.OrderBy(Projections.Property("DOB")).Desc();
But this is looking for "DOB" on the Campaign entity, not the child Customer entity. Is it possible to retrieve the alias used by NH and then set the path to the property e.g.
.OrderBy(Projections.Property("cust.DOB")).Desc(); // where "cust" is the alias
Any ideas?
The alias used is the name of the variable. So
Projections.Property("custAlias.DOB")
(can't test now, but if I remember corretly it works)
Interestingly, it isn't the variable, in itself, that is used as the alias, but its name. What does it means?
QueryOver<Campaign> query;
{
Customer custAlias = null;
query = session.QueryOver<Campaign>()
.JoinAlias(x => x.Customer, () => custAlias)
}
{
Customer custAlias = null;
var result = query.OrderBy(() => custAlias.Name).Desc() // want to use string property name
.List()
}
Two different custAlias, but it still works :-)
(useful if you want to split pieces of a query in multiple methods... The only important thing is that they use the same naming for the aliases)
I am trying to select a distinct list of values from a table whilst ordering on another column.
The only thing working for me so far uses magic strings and an object array. Any better (type-safe) way?
var projectionList = Projections.ProjectionList();
projectionList.Add(Projections.Property("FolderName"));
projectionList.Add(Projections.Property("FolderOrder"));
var list = Session.QueryOver<T>()
.Where(d => d.Company.Id == SharePointContextHelper.Current.CurrentCompanyId)
.OrderBy(t => t.FolderOrder).Asc
.Select(Projections.Distinct(projectionList))
.List<object[]>()
.ToList();
return list.Select(l => new Folder((string)l[0])).ToList();
btw, doing it with linq won't work, you must select FolderOrder otherwise you'll get a sql error (ORDER BY items must appear in the select list if SELECT DISTINCT is specified.
)
and then doing that gives a known error : Expression type 'NhDistinctExpression' is not supported by this SelectClauseVisitor. regarding using anonymous types with distinct
var q = Session.Query<T>()
.Where(d => d.Company.Id == SharePointContextHelper.Current.CurrentCompanyId)
.OrderBy(d => d.FolderOrder)
.Select(d => new {d.FolderName, d.FolderOrder})
.Distinct();
return q.ToList().Select(f => new Folder(f));
All seems a lot of hoops and complexity to do some sql basics....
To resolve the type-safety issue, the syntax is:
var projectionList = Projections.ProjectionList();
projectionList.Add(Projections.Property<T>(d => d.FolderName));
projectionList.Add(Projections.Property<T>(d => d.FolderOrder));
the object [] thing is unavoidable, unless you define a special class / struct to hold just FolderName and FolderOrder.
see this great introduction to QueryOver for type-saftey, which is most certainly supported.
best of luck.
I have Entity 'Content'. Each Content has a 'Placement' property. Placement has a many-to-many relationship width 'AdType' entity (Placement has IList<\AdType> property mapped).
I need to load all Placements that are used at least in one Content and associated width specified AdType.
My DAL function looks like this:
public IList<Placement> Load(AdType adType)
{
return NHibernateSession.QueryOver<Content>()
.JoinQueryOver(content => content.Placement)
.JoinQueryOver<AdType>(placement => placement.AdTypes)
.Where(_adType => _adType.Id == adType.Id)
.Select(x => x.Placement).List<Placement>();
}
This works fine but when I look to the SQL log i see:
SELECT this_.PlacementId as y0_ FROM AdManager.dbo.[Content] this_ inner join AdManager.dbo.[Placement] placement1_ on this_.PlacementId=placement1_.PlacementId inner join AdManager.dbo.AdTypeToPlacement adtypes5_ on placement1_.PlacementId=adtypes5_.PlacementId inner join AdManager.dbo.[AdType] adtype2_ on adtypes5_.AdTypeId=adtype2_.AdTypeId WHERE adtype2_.AdTypeId = #p0
SELECT placement0_.PlacementId as Placemen1_26_0_, placement0_.Name as Name26_0_ FROM AdManager.dbo.[Placement] placement0_ WHERE placement0_.PlacementId=#p0
SELECT placement0_.PlacementId as Placemen1_26_0_, placement0_.Name as Name26_0_ FROM AdManager.dbo.[Placement] placement0_ WHERE placement0_.PlacementId=#p0
This means that NHibernate takes all placements Id in first query and then queries all fields from Placement table by Id.
My question is: Does enyone know how to modify QueryOver method to force NHibernate load data in one query?
it seems NHibernate does think there might be something in the where which maybe filters out data which is needed tro initialize the placement. You can go with a subquery:
public IList<Placement> Load(AdType adType)
{
var subquery = QueryOver.For<Content>()
.JoinQueryOver(content => content.Placement)
.JoinQueryOver<AdType>(placement => placement.AdTypes)
.Where(_adType => _adType.Id == adType.Id)
.Select(x => x.Id);
return NHibernateSession.QueryOver<Content>()
.WithSubquery.Where(content => content.Id).IsIn(subquery))
//.Fetch(x => x.Placement).Eager try with and without
.Select(x => x.Placement).List<Placement>();
}
or SQL (has the disadvantage that it just fills the new Placement but doest track it)
public IList<Placement> Load(AdType adType)
{
return NHibernateSession.CreateSQLQuery("SELECT p.Name as Name, ... FROM content c join placement p...")
.SetResultTransformer(Transformers.AliastoBean<Placement>())
.List<Placement>();
}
I'm trying to load all the collections eagerly, using NHibernate 3 alpha 1. I'm wondering if this the right way of using ThenFetch()?
Properties with plural names are collections. The others are just a single object.
IQueryable<T> milestoneInstances = Db.Find<T, IQueryable<T>>(db =>
from mi in db
where mi.RunDate == runDate
select mi).Fetch(mi => mi.Milestone)
.ThenFetch(m => m.PrimaryOwners)
.Fetch(mi => mi.Milestone)
.ThenFetch(m => m.SecondaryOwners)
.Fetch(mi => mi.Milestone)
.ThenFetch(m => m.Predecessors)
.Fetch(mi => mi.Milestone)
.ThenFetch(m => m.Function)
.Fetch(mi => mi.Milestone)
.ThenFetchMany(m => m.Jobs)
.ThenFetch(j => j.Source)
;
I thought of asking this in the NHibernate forums but unfortunately access to google groups is forbidden from where I am. I know Fabio is here, so maybe the guys from the NHibernate team can shed some light on this?
Thanks
Apparently, there's no "right" way to use ThenFetch in such a case. Your example works fine but SQL produced contains many joins to Milestone, which isn't that right.
Using IQueryOver instead of IQueryable allows you to use complex syntax in Fetch:
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)
So in your case it would be:
query // = session.QueryOver<X>()
.Fetch(mi => mi.Milestone).Eager
.Fetch(mi => mi.Milestone.PrimaryOwners).Eager
.Fetch(mi => mi.Milestone.SecondaryOwners).Eager
.Fetch(mi => mi.Milestone.Predecessors).Eager
.Fetch(mi => mi.Milestone.Function).Eager
.Fetch(mi => mi.Milestone.Jobs).Eager
.Fetch(mi => mi.Milestone.Jobs.First().Source).Eager
The one thing you are missing is that you should use FetchMany() and ThenFetchMany() is the child property is a collection.
IQueryable<T> milestoneInstances = Db.Find<T, IQueryable<T>>(db =>
from mi in db
where mi.RunDate == runDate
select mi);
var fetch = milestoneInstances.Fetch(f => f.Milestone);
fetch.ThenFetch(f => f.PrimaryOwners);
fetch.ThenFetch(f => f.SecondaryOwners);
//...
As leora said, make sure when fetching children collections that you use
FetchMany()
ThenFetchMany()
A new Fetch, should pick up from the root, but this does not always happen. Sometimes you need to create them as separate queries or use Criteria Futures to batch up a multiple fetch.