I have a simple hierarchy of classes mapped with the "subclass + join"
strategy:
<class name="A" abstract="true">
<id name="Id" column="a_id">
<generator class="native" />
</id>
<discriminator column="a_type" type="string" />
<property name="FieldA" column="a_field_a" />
<subclass name="B" discriminator-value="B">
<join table="B">
<key column="b_id" />
<property name="FieldB" column="b_field_b" />
<many-to-one name="C" column="c_id" not-null="true" />
</join>
</subclass>
</class>
and another entity is supposed to contain a collection of the subclass
B:
<class name="C">
<id name="Id" column="c_id">
<generator class="native" />
</id>
<set name="B" inverse="true" cascade="all-delete-orphan">
<key column="c_id" />
<one-to-many class="B" />
</set>
</class>
I thought that NH would see that the foreign key of the collection
belonged to the joined table B and would join tables B and C. But
unfortunately NH didn't. The second try was to use may-to-many element
with the intermediate table:
<set name="B" table="B" inverse="true" cascade="all-delete-orphan">
<key column="c_id" />
<many-to-many class="B" column="b_id" unique="true" />
</set>
It works but when loading the collection NH joins table B twice: first
time to load an instance of class B and second time because of using
many-to-may element.
/* load collection NHTest.Model.C.B */ SELECT
b0_.c_id as c3_1_,
b0_.b_id as b1_1_,
b1_.a_id as a1_3_0_,
b1_.a_field_a as a3_3_0_,
b1_1_.b_field_b as b2_4_0_,
b1_1_.c_id as c3_4_0_
FROM
B b0_
left outer join
A b1_
on b0_.b_id=b1_.a_id
left outer join
B b1_1_
on b1_.a_id=b1_1_.b_id
WHERE
b0_.c_...@p0;
@p0 = 1
Besides of using many-to-many element, is there another way to point
out NH that it should look for a foreign key of the collection in the
joined table?
Thank you.
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