Question

I have the following tables:

1. Application
2. Component
3. Position

An Application can have 1 to many Components
An Application can have 1 to many Positions.

When I try to run a join using NHibernate like this:

IEnumerable<Application> applications = Session.Query<Application>()
    .FetchMany(r => r.Components)
    .FetchMany(r => r.Positions)

and I look at the positions list it has duplicate positions. This goes away if I remove the first FetchMany():

IEnumerable<Application> applications = Session.Query<Application>()
    .FetchMany(r=>r.Positions)

I thought NHibernate takes care of normalizing your collections when doing multiple 1 to many joins but it doesn’t seem to be working.

Any suggestions or workarounds on how to allow me to do multiple 1 to many joins using NHibernate LINQ without getting these duplicate records?

Answer 1

This is not a solution, but a workaround that performs better than a solution.

Seperate queries will probably perform better than one big query because they retrieve less data. You can execute the separate queries at once by using .Future()

One large result set with 2 Apps with 2 components and 2 positions = 24 elements

ApplicationColumns ComponentColumns PositionColumns
AppA               ColA             PosA
AppA               ColB             PosA
AppA               ColA             PosB
AppA               ColB             PosB   
AppB               ColC             PosC
AppB               ColD             PosC
AppB               ColC             PosD
AppB               ColD             PosD  

Three small result sets with 2 Apps with 2 components and 2 positions = 10 elements

ApplicationColumns
AppB
AppB

ComponentColumns
ColA
ColB
ColC
ColD

PositionColumns
PosA
PosB
PosC
PosD

Select N+1 and outer join are not the only choice.