Question

I am trying to setup a 1to0..1 (zero or one) relationship, but am running into issues.

Now my assumption is to use the @OneToMany, and not @OneToOne.

Basically I want my “child” table to hold the foreign key to the “parent” (I use child and parent very loosely). I never need to load “children” standalone

This is the basic table structure I want to achieve

ITEM {
  ID
  RELATED_ITEM_ID
}

INVOICE {
  ID
}
CATALOGUE {
  ID
}

Reprsented as Java classes like the following

class Item {
...
}

class Invoice {
  @OneToMany(fetch=FetchType.EAGER, orphanRemoval = true, cascade = { javax.persistence.CascadeType.ALL })
  @Fetch(FetchMode.JOIN)
  @JoinColumn(name="RELATED_ITEM_ID", nullable=false)
  Set<Item> items;
}

class Catalogue {
  @OneToMany(fetch=FetchType.EAGER, orphanRemoval = true, cascade = { javax.persistence.CascadeType.ALL })
  @Fetch(FetchMode.JOIN)
  @JoinColumn(name="RELATED_ITEM_ID", nullable=false)
  Set<Item> items;
}

The above code, if I only have Invoice or Catalogue registered in hibernate will create the tables as I want, and work perfectly. However, as soon as I have both Invoice and Catalogue registered, hibernate throws me the error

org.hibernate.MappingException: Duplicate property mapping of _itemsBackref found in package.name.Item

Answer 1

I sort of ended up cheating to get this to work how I want. I dont ideally want a hierachy like that, but I need to get this working, and I feel this is a compromise with working around hibernate.

ITEM {
  ID
  RELATED_ITEM_ID
  DTYPE
}

INVOICE {
  ID
}

CATALOGUE {
  ID
}

Reprsented as Java classes like the following

@Entity
@Table(name="RECIPIENTS")
abstract class Item {
  ...
}

@Entity
  public class InvoiceItem extends Item {
}

@Entity
  public class CatalogueItem extends Item {
}


class Invoice {
  @OneToMany(fetch=FetchType.EAGER, orphanRemoval = true, cascade = { javax.persistence.CascadeType.ALL })
  @Fetch(FetchMode.JOIN)
  @JoinColumn(name="RELATED_ITEM_ID", nullable=false)
  Set<InvoiceItem> items;
}

class Catalogue {
  @OneToMany(fetch=FetchType.EAGER, orphanRemoval = true, cascade = { javax.persistence.CascadeType.ALL })
  @Fetch(FetchMode.JOIN)
  @JoinColumn(name="RELATED_ITEM_ID", nullable=false)
  Set<CatalogueItem> items;
}