NHibernate mapping an entity without a primary key

Question

My Entity has no primary key for some reasons:

public partial class VehicleLocation
{
    public virtual string UserCode { get; set; }
    public virtual string DateTime { get; set; }
    public virtual string Device { get; set; }
    public virtual string Gps { get; set; }
    public virtual string GpsDateTime { get; set; }
    public virtual double Speed { get; set; }
}

The mapping:

class VehicleLoactionMap : ClassMap<VehicleLocation> 
{
    public VehicleLoactionMap()
    {
        Table("VEHICLE_LOCATION");
        LazyLoad();
        Map(x => x.UserCode).Column("USER_CODE");
        Map(x => x.DateTime).Column("DATE_TIME");
        Map(x => x.Device).Column("DEVICE");
        Map(x => x.Gps).Column("GPS");
        Map(x => x.GpsDateTime).Column("GPS_DATE_TIME");
        Map(x => x.Speed).Column("SPEED");
    }
}

I got this error:

The entity 'VehicleLocation' doesn't have an Id mapped...

How can I map my entity without using a primary key?

What is the reason for not having a PK? If it's simply a case of legacy database schema that you can't change, then you'll have to look at composite keys (though that will make things tricky). But otherwise, I can't see a good reason for not having a PK, even if it's only a surrogate key. Put one in, your NHibernate problem goes away. — Neil Hewitt, Apr 04 '13 at 10:08
Working with a pre-defined db schema that I can't change. I can't add/remove keys/fields.. in my db is this table without a PK and I'm trying to map it as you can see above in my sample code. — Stacked, Apr 04 '13 at 10:37
Alas, that's a bummer :-( I'd go with the composite key approaches suggested below, then. — Neil Hewitt, Apr 04 '13 at 11:08
Indeed, I'm using compo keys now and it's working fine. Thanks all — Stacked, Apr 04 '13 at 13:59

score 9 · Accepted Answer · edited May 23 '17 at 12:33

9

I had the same issue a while back, but after a lot of searching I found that it is not possible to have entities without an identifier field to be mapped in nHibernate.

But you can do this by having composite keys instead of unique identifiers. Although I haven't tried it myself.

Here is an answer to a similar question that might help you.

edited May 23 '17 at 12:33

Community

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answered Apr 04 '13 at 09:39

mridula

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mickfold · Answer 2 · 2013-10-24T15:32:01.117

2

There is no way of doing this as NHibernate requires a unique identifier for each entity. This is because NHibernate requires a way to tie a row of data in the database table to the entity. If it cannot do this then there is no way for it to perform any form of persistance on the entity data.

In situations where the table does not have a single primary key I have found two possible approaches to work.

Use a composite primary key.
If your DBMS supports you can use the physical row identifier. SQL Server 2008 has %%physloc%% and Oracle has ROWID.

But I would really not recommend option 2 in pretty much any scenario. This is because the DBMS makes no guarantees that the row id will stay the same over the lifetime of the row and is therefore a very un-reliable Primary Key.

edited Oct 24 '13 at 15:32

answered Apr 04 '13 at 10:04

mickfold

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`%%physloc%%` is undocumented and sounds like a generally dumb idea. 1) load entity with a given value of `%%physloc%%` 2) index maintenance runs 3) `%%physloc%%` now different. – ta.speot.is Oct 24 '13 at 01:25
@ta.speot.is I agree using %%physloc%% is a bad idea in 99.9% of scenarios. But sometimes when dealing with a legacy DB where it is not possible to change the schema it is the only option. You make a very good point though so I've updated my answer to reflect it – mickfold Oct 24 '13 at 15:16

score 1 · Answer 3 · edited Apr 29 '15 at 15:17

1

Easy to create a composite key. Code sample (VB):

Table("Table1")
CompositeId().KeyProperty(Function(x) x.Field1).KeyProperty(Function(x) x.Field2)

edited Apr 29 '15 at 15:17

alex.pulver

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answered Apr 29 '15 at 14:11

PaulG

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NHibernate mapping an entity without a primary key

3 Answers3