Fluent Nhibernate generating incorrect query resulting in Cartesian product instead of single row - nhibernate

Question

After trying numerous things, I am still unable to figure out the right way to query the following relationship using Fluent NHibernate.
This would otherwise have been an easier task if I had to write SQL queries. Hope to get some better advice to avoid N+1 issue and unoptimized auto-generated SQL queries.
I have the following relationship which goes something as below :
Tags can have media content (Images of various predefined sizes, videos, documents etc.) associated with it.
- 1 Tags can have multiple Media Items mapped to it (Lets's say images with dimension 32x32, 64x64, 600x100, 0 or more Videos)
- Every media item is mapped to a media description which helps in identifying the size and type of the media
- The same media item can be used by a different tag. Example, having a generic image for all tags which do not have any icons.
Entities:
Media
public class Media:IEntity
{
private ICollection<TagMedia> _tagMedia;
public virtual int Id { get; set; }
public virtual string FilePath { get; set; }
public virtual MediaType MediaType { get; set; }
public virtual ICollection<TagMedia> TagMedia
{
get { return _tagMedia?? (_tagMedia= new List<TagMedia>()); }
protected set { _tagMedia= value; }
}
}
Tag
public class Tag:IEntity
{
private ICollection<TagMedia> _tagMedia;
public virtual int Id { get; set; }
public virtual string Name { get; set; }
public virtual ICollection<TagMedia> TagMedia
{
get { return _tagMedia?? (_tagMedia= new List<TagMedia>()); }
set { _tagMedia= value; }
}
}
TagMedia
public class TagMedia :IEntity
{
public virtual int Id { get; set; }
public virtual Media Media { get; set; }
public virtual Tag Tag { get; set; }
public virtual DateTime AddedOn { get; set; }
}
MediaType
public class MediaType:IEntity
{
public virtual int Id { get; set; }
public virtual string Description { get; set; }
}
Mappings
MediaMapping
public class MediaMapping : IAutoMappingOverride<Media>
{
public void Override(AutoMapping<Media> mapping)
{
mapping.Map(c => c.FileName).CustomSqlType("varchar(60)").Not.Nullable();
}
}
TagMapping
public class TagMapping : IAutoMappingOverride<Tag>
{
public void Override(AutoMapping<Tag> mapping)
{
mapping.HasMany<TagMedia>(c => c.TagMedia)
.KeyColumn("TagId")
.Cascade.SaveUpdate()
.BatchSize(25);
mapping.BatchSize(25);
mapping.DynamicUpdate();
mapping.DynamicInsert();
}
}
TagMediaMapping
public class TagMediaMapping : IAutoMappingOverride<TagMedia>
{
public void Override(AutoMapping<TagMedia> mapping)
{
mapping.Map(c=>c.AddedOn);
}
}
Query:
The following query gets the cartesian product of all media mapped to the tag and does not eliminate records other than "Icon-16x16". I expect the ORM to return no more than one row.
Any help would be highly appreciated.
_session.Query<Tag>()
.FetchMany(x => x.TagMedia)
.ThenFetch(x => x.Media)
.ThenFetch(x=>x.MediaType)
.Where(c => c.Id == id
&& c.TaxonomyMedia.Any(x=>x.Media.MediaType.Description== "Icon-16x16"))
.SingleOrDefault();
Generated SQL:
exec sp_executesql N'select *
from [Tag] Tag0_ left outer join [TagMedia] Tagme1_ on Tag0_.TagId=Tagme1_.TagId
left outer join [Media] media2_ on Tagme1_.MediaId=media2_.MediaId
left outer join [MediaType] mediatype3_ on media2_.MediaTypeId=mediatype3_.MediaTypeId
where Tag0_.TagId=#p0
and (exists (select Tagme4_.TagMediaId
from [TagMedia] Tagme4_ inner join [Media] media5_ on Tagme4_.MediaId=media5_.MediaId inner join [MediaType] mediatype6_ on media5_.MediaTypeId=mediatype6_.MediaTypeId where Tag0_.TagId=Tagme4_.TagId and mediatype6_.MediaTypeDescription=#p1))',N'#p0 int,#p1 nvarchar(4000)',#p0=102,#p1=N'Icon-16x16'
go

Answer 1

the SingleOrDefault function is a LINQ function and not implemented by NHibernate. Use .Take(1)
I think the solution is:
_session.Query<Tag>()
.FetchMany(x => x.TagMedia)
.ThenFetch(x => x.Media)
.ThenFetch(x=>x.MediaType)
.Where(c => c.Id == id
&& c.TaxonomyMedia.Any(x=>x.Media.MediaType.Description== "Icon-16x16"))
.Take(1)
.SingleOrDefault();