From: "Walter Lo Nigro" <webobjects-dev@wocommunity.org>
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Subject: Very stupid question re: One-to-many, single table inheritance in D2W
 ERModernLook
Message-Id: <D4FAAA7E-EEF6-4311-9006-64299A99BDDA@lonigro.net>
Date: Tue, 6 Jul 2021 15:37:54 +0200
To: WebObjects & WOnder Development <webobjects-dev@wocommunity.org>

Hi everybody,

I just resolved to write to the list, obviouly risking any sort of =
ominously nefast/sarcastic comments=E2=80=A6 (please be kind).

I am struggling with a very simple situation, and I=E2=80=99m sure I=E2=80=
=99m missing something basic. I apologize for that.

I have a generic entity =E2=80=98Utente=E2=80=99, and another one =
=E2=80=98Studente=E2=80=99 which inherits from the first one via =
single-table inheritance.=20
I set up a further entity =E2=80=98Qualifica=E2=80=99 with just one =
column =E2=80=99tipo', and I populate it with some values (just =
=E2=80=9Cstudente=E2=80=9D for a start), and use it merely as a lookup =
table for Utente and Studente via a One-to-many relationship:

Utente.qualifica.tipo << - > Qualifica.tipo

Utente has also a key =E2=80=98tipo=E2=80=99 which is the flattened =
relationship between Utente and Qualifica.
Obviously same for Studente, which also have a qualifier: tipo =3D =
=E2=80=9Cstudente=E2=80=9D.

For Studente I have added something to preset value of tipo =3D =
=E2=80=9Cstudente=E2=80=9D, here is the extended class definition (which =
inherits from _Studente, which of course inherits from _Utente base =
class):

public class Studente extends _Studente {
	@SuppressWarnings("unused")
	private static final Logger log =3D =
LoggerFactory.getLogger(Studente.class);

	public void awakeFromInsertion(EOEditingContext eo) {
		super.awakeFromInsertion(eo);
		Qualifica qual =3D new Qualifica();
		eo.insertObject(qual);
		qual.setTipo("studente");
		this.setQualifica(qual);
		this.setTipo(qual.tipo());
	}

	public static Studente createStudente(EOEditingContext =
editingContext, String nome, your.app.model.Qualifica qualifica) {
		Studente eo =3D (Studente) =
EOUtilities.createAndInsertInstance(editingContext, =
_Studente.ENTITY_NAME);
		eo.setNome(nome); // (n.b. the only other attribute in =
Utente/Studente)
		eo.setQualificaRelationship(qualifica);
		return eo;
	}
}

Everything seems ok but, when I try and create a new Studente object =
(having already inserted a =E2=80=9Cstudente=E2=80=9D row into =
Qualifica), I get the following error:

com.webobjects.eoaccess.EOGeneralAdaptorException: EvaluateExpression =
failed: <com.webobjects.jdbcadaptor.PostgresqlExpression: "INSERT INTO =
Qualifica(id, tipo) VALUES (?::int4, ?::varchar(50))" withBindings: =
1:4(id), 2:"studente"(tipo)>: Next exception:SQL State:23505 -- error =
code: 0 -- msg: ERROR: duplicate key value violates unique constraint =
"qualifica_pk" Dettaglio: Key (id)=3D(4) already exists.

In Properties I have:
# EOF
er.extensions.ERXEC.safeLocking=3Dtrue
er.extensions.ERXEC.useSharedEditingContext=3Dfalse
=
er.extensions.ERXEnterpriseObject.applyRestrictingQualifierOnInsert=3Dfals=
e
er.extensions.ERXEnterpriseObject.updateInverseRelationships=3Dfalse

Which is the best method to avoid the database server trying to update =
BOTH sides of relationship? I am using Postgresql.

Please help (and have mercy on me). Thank you.


***  Walter Lo Nigro, Trieste, Italy  -  http://www.wln.it  ***
***  Choral Activities, "G. Tartini" Conservatory, Trieste  ***
***  Freelance conductor, RiscOS/ROOL registered developer  ***