Default FetchMode is Join for many-to-one

Seems like the same as

this was a hard one (at least for me)

setting use-many-to-one="false" on the filter-def fixed it.

and this seems to be the cause:

enabledFiltersForManyToOne.Count = 1, although there is no filter for the manytoone but for the list/one-to-many.

JoinWalker -> MergeOuterJoins:

// NH Different behavior : NH1179 and NH1293
// Apply filters in Many-To-One association
if (enabledFiltersForManyToOne.Count > 0)
{
string manyToOneFilterFragment = oj.Joinable.FilterFragment(oj.RHSAlias, enabledFiltersForManyToOne);
bool joinClauseDoesNotContainsFilterAlready =
outerjoin.ToFromFragmentString.IndexOfCaseInsensitive(manyToOneFilterFragment) == -1;
if (joinClauseDoesNotContainsFilterAlready)
{
outerjoin.AddCondition(manyToOneFilterFragment);
}
}

ok its not "that" easy...
what causes this behaviour is a filter inside a collection.

<class name="A">
<many-to-one name="B" />
<many-to-one name="C1" />
<list name="ListOfD" cascade="all-delete-orphan" lazy="false">
<key column="itemid"/>
<index column="itemdetailindex"/>
<one-to-many class="D"/>
<filter name="FilterForD" condition="arameter&lt;=somevalue OR somevalue IS NULL"/>
</list>
...
</class>

activating the filter will produce the sql as described above.

turns out that the default has been join before too BUT in 3.2 the where clause for the many-to-one's is included which means that the left outer joins actually become inner joins.
having a where defined in the mapping for the many-to-one entity or using subclassing with discriminators will generate those where-clauses.

<class name="A">
<many-to-one name="B" />
<many-to-one name="C1" />
</class>

<class name="B" where="somefield=1">
</class>

<class name="C" abstract="true">
<discriminator column="type" type="String"/>
<subclass name="C1" discriminator-value="test"/>
</class>

will result in a query like:

select fields from A
left outer join B on A.refB = B.id
left outer join C1 on A.refC = C1.id
where B.somefield = 1 and C1.type = 'test'

so having null values in one of those references will actually end up with no results beeing returned.