How to map m2m tables with properties in the joining table

[Michael W Powell]

Hello,

I want to map a joining table between A and B. I have a sense how to map the A and B sides of the relationship, one of which I think should be .Inverse(), yes?

I am not hundred percent positive, but I may need to attach additional properties than just linking A to B and vice versa.

So I need to introduce a map for the joining table C as well. But, personally, I'm not quite sure how that would work.

Any insights?

Best, thank you...

Michael W. Powell

[Michael W Powell]

Getting some errors after mapping the joining table. It is for whatever reason looking for a column i.e. vehiclereg0_.vehicleregistration_id, vreg being object 'table'. The base model Id property should be this:

Id(x => x.Id)
    .Column(nameof(ModelBase.Id))
    .Not.Nullable()
    .GeneratedBy.GuidComb();

Not sure why the joining is trying to label it "vehicleregistration_id" that is definitely incorrect.

How to persuade NH? Fluent NH? How to map it correctly?

The only columns that should really be mapped otherwise are:

References(x => x.Owner)
    .Not.Nullable();

References(x => x.Vehicle)
    .Not.Nullable();

TBD what level of inverse relationship there should be.

Note, vehicle can only be registered to one player at a time, so perhaps M2M is overkill.

Thoughts?

Thank you...

[Michael W Powell]

Also it's not the only columns which are misidentified, or that I have not trained the ORM how to identify, YET... Which is what I'd like to puzzle through if it is even possible, vehiclereg0_.Player_id.

Honestly I'm not even sure how this SQL is being formed, unless perhaps I have a relationship or reference inversion incorrect perhaps.

SELECT vehiclereg0_.Player_id as player4_5_9_, vehiclereg0_.VehicleRegistration_id as vehicleregistration5_5_9_, vehiclereg1_.Id as id1_5_0_, vehiclereg1_.PlayerId as playerid2_5_0_, vehiclereg1_.VehicleId as vehicleid3_5_0_, player2_.Id as id1_4_1_, player2_.ServerProfileId as serverprofileid2_4_1_ ...  left outer join public.efcore_wbe_serverprofile serverprof9_ on motorvehic6_.ServerProfileId=serverprof9_.Id WHERE vehiclereg0_.Player_id=?

The example SQL above, not even sure how the majority of all this is even necessary, seems like extraneous junk happening somehow, because I am mapping a joining table? Is there a better base mapping class for that, perhaps? I'm not sure...

[Michael W Powell]

Perhaps I am not mapping it quite right either side of the relationship.

From the player:

HasManyToMany(x => x.VehicleRegistrations)
    .Cascade.AllDeleteOrphan()
    .Table(JoinNames([TableNames.efcore, TableNames.wbe, nameof(VehicleRegistration).ToLower()]));

From the vehicle:

HasManyToMany(x => x.VehicleRegistrations)
    .Cascade.AllDeleteOrphan()
    .Inverse()
    .Table(JoinNames([TableNames.efcore, TableNames.wbe, nameof(VehicleRegistration).ToLower()]));

Whereas this somewhat dated example:

https://belter.io/manytomany-fluentnhibernate not mentioning any joining object whatsoever, which is a bit interesting to me.

Question though, in my joining table, what happens if I want to identify additional bits in that part of the model? i.e. is not just "joining two tables, with two FK references" and so forth.

If I go by the example, it appears to me the map drills right through that would-be entity.

Anyone?

Thanks...

[Michael W Powell]

Trying a slightly different tact, instead of M2M joining table, there is no reason for the Owner to be more than a column or property, since Vehicle can have only one Owner. However, in this approach, Vehicle effectively has one and a half parents. One parent a Not Nullable, MotorVehicleDivision. The other parent, a Nullable, Player Owner.

See discussion: https://github.com/nhibernate/fluent-nhibernate/discussions/762

Open to suggestions how to persuade the relationship to behave properly. On the Owner side, I've tried Refresh Cascade, same sort of effect, does not work. Also None Cascade.