Hi guys,
The way I understand it with Bags is that NHbernate cannot fire
PreCollectionUpdateEvents for these as it has to delete the whole
collection (as one large delete) and then add each row individually
afterwards as per the docs:
'Bags are the worst case. Since a bag permits duplicate element values and
has no index column, no primary key may be defined. NHibernate has no way
of distinguishing between duplicate rows. NHibernate resolves this problem
by completely removing (in a single DELETE) and recreating the collection
whenever it changes. This might be very inefficient.'
This is the behaviour that I can see happening in these 2 maps. I am using
Fluent NHibernate to map which defaults to Bag for these HasMany types, I
can confirm that in the first two map cases it does delete (it actually
orphans without delete) and recreate the whole collection, without firing a
PreCollectionUpdateEvent.
So here are the first 2 maps which do not fire PreCollectionUpdateEvents,
only deletes and inserts on collection changes:
HasMany(x => x.Class1)
.Cascade.All()
.Access.BackingField();
HasMany(x => x.Class2)
.Table("Class2")
.KeyColumn("Parent_id")
.Inverse()
.Cascade.AllDeleteOrphan();
However, a second map that I have which to me appears to follow the same
(well, similar) format, but this fires a PreCollectionUpdateEvent and not a
delete followed by multiple inserts as I would expect. I can't see a common
difference between the three that I can see mattering...I can say that
Class1 and Class2 have maps of their own, and both reference the Parent,
but in the following case Class3 is of Type String, so needs no Map.
HasMany(x =>
x.Class3).Table("Class3").Element("Class3Elem").Cascade.All();
I wonder if anyone can throw some ideas out there as to why this might be?
I can provide more information if needed, I believe the table constraints
are irrelevant as since it's mapped as a bag NHibernate will not check? The
types of Class 1, 2 and 3 are all mapped to IList properties of their
respective Type.
Thanks,
Mike
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