From: "Ralf Schuchardt" <webobjects-dev@wocommunity.org>
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To: "WebObjects & WOnder Development" <webobjects-dev@wocommunity.org>
Subject: Re: [WO-DEV] Very stupid question re: One-to-many, single table  inheritance in D2W ERModernLook
Date: Tue, 06 Jul 2021 17:55:04 +0200
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Hi Walter,

maybe I can explain the problem you are seeing.

In `awakeFromInsertion` you create a new Qualifica object.

		Qualifica qual =3D new Qualifica();
		eo.insertObject(qual);

This Qualifica object has an `id` attribute probably of type `serial` or =
maybe an `int4` with an attached sequence. EOF uses the sequence (or an i=
nternal table) to assign the new primary key for this new object.
But as you have already inserted some values to Qualifica the sequence ge=
neration is probably out of sync with the already inserted values. Theref=
ore you get a duplicate key error when using the sequence values in the n=
ew object.
To solve this you may need to update the Qualifica sequence (if used by E=
OF) with the greatest id value already used in Qualifica.

But I don=E2=80=99t know, why you even create a new Qualifica object in `=
awakeFromInsertion`, as setting the qualifica relationship already assign=
s one in `createStudente`.
If you want to insert it as a default value, it may be better to fetch th=
e existing one:

public void awakeFromInsertion(EOEditingContext ec) {
	super.awakeFromInsertion(ec);
	Qualifica qual =3D Qualifica.fetchRequiredQualifica(ec, Qualifica.TIPO.e=
q("studente=E2=80=9C));
	this.setQualificaRelationship(qual);
}

If you are using Wonder you may also want to use the init(EOEditingContex=
t) method instead of awakeFormInsertion.

Ralf

On 6 Jul 2021, at 15:37, Walter Lo Nigro wrote:

> Hi everybody,
>
> I just resolved to write to the list, obviouly risking any sort of omin=
ously 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 i=
nheritance.
> I set up a further entity =E2=80=98Qualifica=E2=80=99 with just one col=
umn =E2=80=99tipo', and I populate it with some values (just =E2=80=9Cstu=
dente=E2=80=9D for a start), and use it merely as a lookup table for Uten=
te 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 rel=
ationship 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=9C=
studente=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.c=
lass);
>
> 	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(editin=
gContext, _Studente.ENTITY_NAME);
> 		eo.setNome(nome); // (n.b. the only other attribute in Utente/Student=
e)
> 		eo.setQualificaRelationship(qualifica);
> 		return eo;
> 	}
> }
>
> Everything seems ok but, when I try and create a new Studente object (h=
aving already inserted a =E2=80=9Cstudente=E2=80=9D row into Qualifica), =
I get the following error:
>
> com.webobjects.eoaccess.EOGeneralAdaptorException: EvaluateExpression f=
ailed: <com.webobjects.jdbcadaptor.PostgresqlExpression: "INSERT INTO Qua=
lifica(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=3Df=
alse
> 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  ***
>
>
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