Unable to implement hierarchical persistence as described in docs

Simple Reference Project Documentation Version: 4.0 Corda Version: 4.0

In the docs a child token is tied to the parent token via:

 @Entity
 @CordaSerializable
 @Table(name = "child_data")
 class PersistentChildToken(
         @Id
         var Id: UUID = UUID.randomUUID(),

         // code for other columns

         @ManyToOne(targetEntity = PersistentParentToken::class)
         var persistentParentToken: TokenState

 ) : PersistentState()

but whenever i annotate a child with @Id i receive the following error:

net.corda.nodeapi.internal.persistence.HibernateConfigException: Could not create Hibernate configuration: net.corda.core.schemas.PersistentStateRef must not have @Id properties when used as an @EmbeddedId

i’ve looked through the source code and saw that a PersistentState is defined as the following:

@KeepForDJVM
@MappedSuperclass
@CordaSerializable
class PersistentState(@EmbeddedId override var stateRef: PersistentStateRef? = null) : DirectStatePersistable

so i guess i understand where the error is coming from, PersistentChildToken implements PersistentState which already has @EmbeddedId. but if i remove the @Id field i get the following error:

javax.persistence.PersistenceException: org.hibernate.id.IdentifierGenerationException: null id generated for:class

it seems like i can’t use the @Id annotation because PersistentState is already annotated with EmbeddedId, but I also need the @Id annotation or else an id will not be properly generated.

there are further errors i have run into while trying to implement the hierarchal relationship which were eventually solved by adding a @OneToMany annotation above @JoinColumns. In the context of the docs it would be:

@OneToMany(
  cascade = [CascadeType.ALL],
  targetEntity = PersistentChildToken::class
)

the project i am attempting implement the hierarchical relationships is more complex than the simple reference project, but the core of the workflows, table creation, and relationship mapping is there.

any help implementing a one to many relationship would be greatly appreciated, thank you.

[nargas-ritu]

Internal ticket - CORDA-4212

[jrosmith]

@amolpednekar you are absolutely correct about the added overhead and i share your frustration with not being able to use Corda’s built in querying apis to handle the situation. unfortunately this approach was the best option available given the circumstances of our use case. if anyone else has found another solution to make this work using the querying api’s, i would be interested in hearing it

@SweeXordious some pseudo-code to get you started - note that this logic does not handle consumed/unconsumed states

 fun getParentAndChildren(parentLinearId: UUID)  {
   val nativeQuery = getNativeQuery(linearId)
   val session= serviceHub.jdbcSession()
   val rs = session.prepareStatement(nativeQuery).executeQuery()
   
   while (rs.next()) {
     // business logic
    }
 }
 
 fun getNativeQuery(linearId: UUID) : String {
    return """
      select 
        *
      from
        parent_table as p
      join
        child_table as c
      on
        c.parent_linear_id = '$linear_id'::uuid
      where
         p.linear_id = '$linear_id'::uuid
    """.trimIndent()
 }