Problem with eager load polymorphic associations using Linq and NHibernate
- by Voislav
Is it possible to eagerly load polymorphic association using Linq and NH?
For example: Company is base class, Department is inherited from Company, and Company has association Employees to the User (one-to-many) and also association to the Country (many-to-one).
Here is mapping part related to inherited class (without User and Country classes):
<class name="Company" discriminator-value="Company">
<id name="Id" type="int" unsaved-value="0" access="nosetter.camelcase-underscore">
<generator class="native"></generator>
</id>
<discriminator column="OrganizationUnit" type="string" length="10" not-null="true"/>
<property name="Name" type="string" length="50" not-null="true"/>
<many-to-one name="Country" class="Country" column="CountryId" not-null ="false" foreign-key="FK_Company_CountryId" access="field.camelcase-underscore" />
<set name="Departments" inverse="true" lazy="true" access="field.camelcase-underscore">
<key column="DepartmentParentId" not-null="false" foreign-key="FK_Department_DepartmentParentId"></key>
<one-to-many class="Department"></one-to-many>
</set>
<set name="Employees" inverse="true" lazy="true" access="field.camelcase-underscore">
<key column="CompanyId" not-null="false" foreign-key="FK_User_CompanyId"></key>
<one-to-many class="User"></one-to-many>
</set>
<subclass name="Department" extends="Company" discriminator-value="Department">
<many-to-one name="DepartmentParent" class="Company" column="DepartmentParentId" not-null ="false" foreign-key="FK_Department_DepartmentParentId" access="field.camelcase-underscore" />
</subclass>
</class>
I do not have problem to eagerly load any of the association on the Company:
Session.Query<Company>().Where(c => c.Name == "Main Company").Fetch(c => c.Country).Single();
Session.Query<Company>().Where(c => c.Name == "Main Company").FetchMany(c => c.Employees).Single();
Also, I could eagerly load not-polymorphic association on the department:
Session.Query<Department>().Where(d => d.Name == "Department 1").Fetch(d => d.DepartmentParent).Single();
But I get NullReferenceException when I try to eagerly load any of the polymorphic association (from the Department):
Assert.Throws<NullReferenceException>(() => Session.Query<Department>().Where(d => d.Name == "Department 1").Fetch(d => d.Country).Single());
Assert.Throws<NullReferenceException>(() => Session.Query<Department>().Where(d => d.Name == "Department 1").FetchMany(d => d.Employees).Single());
Am I doing something wrong or this is not supported yet?
