Hello,

I'm trying to add attachments to various objects without having to create a join table for each object. For example, to add a set of attachments to BR, I created a join table called ATTACHMENT_BR and added the relationship to the hibernate mapping file.

<set name="attachments"
cascade="all, delete-orphan"
lazy="true"
table="ATTACHMENT_BR">
<key column="BR_ID" />
<many-to-many class="com.foo.bar.vo.Attachment" column="ATTACHMENT_ID" not-found="ignore"/>
</set>

CREATE TABLE ATTACHMENT_BR
(
BR_ID INTEGER NOT NULL,
ATTACHMENT_ID INTEGER NOT NULL
)

I'm trying to keep the Attachment object clean without adding a column and foreign key each time I relate it to another object.

However, adding attachments using join tables means if I add a set of attachments to a dozen objects, it requires a dozen join tables. Is there a way to relate one table to many others without having to create a separate join table for each one or add many columns to the table?

I think I have made something similar and I solved by introducing an intermediate entity. In your case it would be called something like AttachementSet. The solution introduces an extra column in the tables of those objects that you want to add attachments to. Here are some example mappings which may help you. There may be some error and you need to add options for cascading, lazy loading, etc.

For any entity that needs association to attachments:



In AttachmentSet.hbm.xml:




This should create one table (ATTACHMENT_SETS) with just a single column (attachmentset_id) and one join table (ATTACHMENT_JOINS) with two columns (attachmentset_id and attachment_id).

Another possible solution may be to use the <many-to-any> mapping but this probably needs to be done from the Attachment side. I am not very familiar with this so the examples below are just guesses. As I understand it though you get an extra column in the join table that holds the entity name. Eg something like:




The inverse mapping may need a "where" to filter on the ENTITY_NAME column, but I don't know if something like this works or not.