NHibernate Linq - how to create a where statement with IS NOT NULL - nhibernate

how can i achieve this query with Nhibernate Linq?
var l = session.CreateQuery("from Auswahl a where a.Returnkey is not null").List<Auswahl>();
i tried this but it always returns an empty list.
var l = session.Linq<Auswahl>()
.Where(item => !String.IsNullOrEmpty(item.Returnkey))
.Select(item => item)
.ToList();

Have you tried:
var l = session.Linq<Auswahl>()
.Where(item => item.Returnkey != null && item.Returnkey != "")
.Select(item => item)
.ToList();
I'm not sure that using String.IsNullOrEmpty would work, also it checks for two conditions - if it's NULL and if it's a blank empty string, how would that get translated into SQL? Might be worth having a look at SQL Profiler to see the raw SQL query it generates.

Related

Selecting an object from the GroupBy key

I'm accustomed to GroupBy() being more of an art than a science, but maybe someone can help me with a very specific problem:
Given the following code
var results = session.Query<MyClass>()
.GroupBy(c => c.OtherPersistentObject)
.Select(group => new
{
key = group.Key,
count = group.Count()
})
.ToList();
The generated query comes out like this:
/* [expression] */select
otherclass_.ID as col_0_0_,
cast(count(*) as INT) as col_1_0_,
otherclass_.ID as id1_1_,
otherclass_.START_DATE as start2_1_,
otherclass_.END_DATE as end3_1_,
otherclass_.Zone as zone9_1_
from
mytable mytable0_
left outer join
otherclass otherclass_
on mytable0_.otherID=otherclass_.ID
group by
mytable0_.otherID
which gives me the SQL error "Column 'otherclass .ID' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause"
Is there a way to get the Select to do what I want?
TIA
It's a known NHibernate issue NH-3027.
As a workaround you can use last approach described in this answer (rewrite GroupBy part as sub-query). So your query can be rewritten to something like:
var results = session.Query<MyClass>()
.Where(c => c == session.Query<MyClass>().First(cs => cs.OtherPersistentObject == c.OtherPersistentObject))
.Select(x => new
{
key = x.OtherPersistentObject,
count = session.Query<MyClass>().Count(cs => cs.OtherPersistentObject == x.OtherPersistentObject)
}).ToList();
Try this:
var results = session
.Query<MyClass>()
.GroupBy(c => c.OtherPersistentObject)
.Select(group => new
{
key = group.Key.Id,
count = group.Count()
})
.ToList();
Here you can find the reason for the error.

query did not return a unique result: 2 . Issue with Nhibernate Query

I am current having an issue with getting records from database using nhibernate.
My 'publicstring' column is having two values, one with lower case and the other with upper case.
I am trying to fetch one of them depending on what is typed.
Below is my query
private string _publicId;
var _mediaFileShare = this.Session.QueryOver<MediaFileShare>()
.Where(q => q.Publicsting == _publicstring)
.SingleOrDefault();
Answers would be appreciated..
A naive solution is:
var _mediaFileShare = this.Session.QueryOver<MediaFileShare>()
.Where(q => q.PublicString == _publicString)
.List()
.SingleOrDefault(r => string.Compare(r.PublicString, _publicString, StringComparison.Ordinal) == 0);
If you're confident that the query will always return two rows then performance should be very acceptable. Alternatively you could use a dynamic order by, something like:
var query = this.Session.QueryOver<MediaFileShare>()
.Where(q => q.PublicString == _publicString);
query = _publicString == _publicString.ToLower()
? query.OrderBy(q => q.PublicString)
: query.OrderByDescending(q => q.PublicString);
var _mediaFileShare = query.Take(1).SingleOrDefault();
The results using an order by will be dependent on your database and its collation setting.

How to construct a proper WHERE clause with RavenDb

I have experimented with 2 forms of the call, this one
products = DocumentSession.Query<Product>()
.Statistics(out stats)
.Where(p => p.INFO2.StartsWith(term1))
.Where(p => p.INFO2.StartsWith(term2))
.Where(p => p.INFO2.StartsWith(term3))
.OrderByField(columnToSortBy, columnToSortByAsc)
.Skip(pageIndex * pageSize)
.Take(pageSize)
.ToList()
;
and this way
products = DocumentSession.Query<Product>()
.Statistics(out stats)
.Where(p => p.INFO2.StartsWith(term1) & p.INFO2.StartsWith(term2) & p.INFO2.StartsWith(term3))
.OrderByField(columnToSortBy, columnToSortByAsc)
.Skip(pageIndex * pageSize)
.Take(pageSize)
.ToList()
;
The first one returns records that are more in-line with my expectations, while the seconds seems to return ALL documents of type Product. What are the differences between the 2 from a LINQ expression point of view, and have I overlooked anything that might negate what I am trying to accomplish, which is a 3 term query and each term being AND'd together.
EDIT: revised code per Russ.
string t1 = terms[0];
string t2 = terms[1];
string t3 = terms[2];
products = DocumentSession.Query<Product>()
.Statistics(out stats)
.Where(p => p.INFO2.StartsWith(t1) && p.INFO2.StartsWith(t2) && p.INFO2.StartsWith(t3))
.OrderByField(columnToSortBy, columnToSortByAsc)
.Skip(pageIndex * pageSize)
.Take(pageSize)
.ToList()
;
EDIT 2: This is where you smash your face down on the keyboard, or any other solid object for that matter... Gotta get back to the basic here with standard C# And and Or
Thank you,
Stephen
In the second block you're doing an & instead of an && so instead of being an AND comparison, it's trying to do a bitwise operation.
Edit: in the 2nd case, you can change this:
.Where(p => p.INFO2.StartsWith(terms[0]) & p.INFO2.StartsWith(terms[1]) & p.INFO2.StartsWith(terms[2]))
to this:
.Where(p => p.INFO2.StartsWith(terms[0]) && p.INFO2.StartsWith(terms[1]) && p.INFO2.StartsWith(terms[2]))
Which makes it proper AND clause.
2nd edit: If this is meant to be an AND operation, then you don't need 3 terms - you need a single term, otherwise you'll be comparing against 3 instances of the same string.
terms[0] = "test";
terms[1] = "test";
terms[2] = "test";
.Where(p => p.INFO2.StartsWith(terms[0]) && p.INFO2.StartsWith(terms[1]) && p.INFO2.StartsWith(terms[2]))
Is the same as
string term = "test";
.Where(p => p.INFO2.StartsWith(term) && p.INFO2.StartsWith(term) && p.INFO2.StartsWith(term))
Just mentioning this as this may make your code harder to maintain in the future.

QueryOver fails with could not resolve property:

I am using NHibernate 3.0 and was comparing Query and QueryOver
var p = _prepo.Query<Party>()
.Where(c => c.Person.LastName == "Bobby")
.FirstOrDefault();
The above works, I get proxy class for p.Person if I view the object graph.
var p = _prepo.QueryOver<Party>()
.Where(c => c.Person.LastName == "Bobby")
.FirstOrDefault();
This one fails with error ==> could not resolve property: Person.LastName of:
Why?
I'm not familiar with the Linq provider but when using QueryOver you have to use a join to do a query like that:
Example 1
IQueryOver<Cat,Kitten> catQuery =
session.QueryOver<Cat>()
.JoinQueryOver(c => c.Kittens)
.Where(k => k.Name == "Tiddles");
Example 2
Cat catAlias = null;
Kitten kittenAlias = null;
IQueryOver<Cat,Cat> catQuery =
session.QueryOver<Cat>(() => catAlias)
.JoinAlias(() => catAlias.Kittens, () => kittenAlias)
.Where(() => catAlias.Age > 5)
.And(() => kittenAlias.Name == "Tiddles");
It works when you use Linq in this case because the filtering is being done on the client, not in the database. So it is actually the IEnumerable version of Where that is running which is not related to NHibernate.
The QueryOver uses Expression<Func<T,object>> which NHibernate tries to translate to SQL but fails. For reasons unknown to me you must explicitly join using JoinQueryOver or JoinAlias.
Some more info on QueryOver here:
http://nhibernate.info/blog/2009/12/17/queryover-in-nh-3-0.html

Duplicated and unnecessary joins when using Linq in NHibernate

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