I'm having trouble with a joined-subclass mapping within my domain
model using NHibernate.
I have an abstract class "ProjectMedia" with some properties, and 2
concrete classes that inherit from this class, "ProjectImage" and
"ProjectVideo". These map to tables ProjectMedia, ProjectImage and
ProjectVideo, respectively, in the database.
I am using the "Table per subclass" mapping scenario, where the 3
tables have a shared primary/foreign key so that they can be joined to
get the concrete data for each object.
Along with this, I have a "Project" class, which has a list of images
and videos, which map to ProjectImage and ProjectVideo. Here are my
mappings:
For the Project class:
<class name="Project" table="Projects" lazy="true">
<id name="ProjectId">
<generator class="native" />
</id>
<property name="ProjectDate" not-null="true" />
...
<property name="PDF" not-null="false" />
<bag name="Images" table="ProjectMedia"
cascade="all-delete-orphan"
inverse="true">
<key column="ProjectId" />
<one-to-many class="ProjectImage" />
</bag>
<bag name="Videos" table="ProjectMedia"
cascade="all-delete-orphan"
inverse="true">
<key column="ProjectId" />
<one-to-many class="ProjectVideo" />
</bag>
</class>
For the ProjectMedia/ProjectVideo/ProjectImage classes:
<class name="ProjectMedia" table="ProjectMedia" lazy="true">
<id name="ProjectMediaId">
<generator class="native" />
</id>
<property name="MediaPath" />
<property name="ThumbnailPath" />
<many-to-one name="Project" column="ProjectId"
class="IdMedia.Data.Domain.Project, IdMedia.Data" not-null="true" />
<joined-subclass
extends="ProjectMedia"
name="ProjectImage"
table="ProjectImage">
<key column="ProjectImageId" />
<property name="ImageCredit" />
<property name="ImageCaption" />
</joined-subclass>
<joined-subclass
extends="ProjectMedia"
name="ProjectVideo"
table="ProjectVideo">
<key column="ProjectVideoId" />
<property name="CreditLine" />
</joined-subclass>
</class>
Saving and loading of the project work fine with images and videos
added to the collection.
However, when I try to access either the Image or Video collections, I
get this error:
NHibernate.Exceptions.GenericADOException : could not initialize a
collection: [IdMedia.Data.Domain.Project.Images#163][SQL: SELECT
images0_.ProjectId as ProjectId1_, images0_.ProjectImageId as
ProjectI1_1_, images0_.ProjectImageId as ProjectM1_1_0_,
images0_1_.MediaPath as MediaPath1_0_, images0_1_.ThumbnailPath as
Thumbnai3_1_0_, images0_1_.ProjectId as ProjectId1_0_,
images0_.ImageCredit as ImageCre2_2_0_, images0_.ImageCaption as
ImageCap3_2_0_ FROM ProjectImage images0_ inner join ProjectMedia
images0_1_ on images0_.ProjectImageId=images0_1_.ProjectMediaId WHERE
images0_.ProjectId=?]
----> System.Data.SqlClient.SqlException : Invalid column name
'ProjectId'.
Invalid column name 'ProjectId'.
It seems that NHibernate is setting up the join for the joined-
subclasses fine, but it has the tables in the join specified in the
wrong order, therefore, ProjectId (the foreign key to the Projects
table) is being referenced incorrectly.
Can anyone help with this? I cannot see a reason why this will not
work the way I have defined the mappings. I have searched everywhere,
but cannot find an answer. This method was even taken from the book
"NHibernate in Action", so I cannot understand why it is not working.
I know I can get around it using 1 table per concrete class, but I
would prefer to do it using joined subclasses, as this saves from data
repetition.
Thanks,
Dan.
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