5:33 p.m.
<one-to-one> should not generate Sets
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Key: HBX-1179
URL: http://opensource.atlassian.com/projects/hibernate/browse/HBX-1179
Project: Hibernate Tools
Issue Type: Bug
Components: reverse-engineer
Environment: Hibernate Tools version as reported by Eclipse:
3.3.0.v20101016-0359-H111-Beta1
Feel free to identify the matching release numbers, I can't :-/
Reporter: Joachim Durchholz
Hibernate tools does not always recognize one-to-one associations as such, even if
specified as <one-to-one> in hibernate.reveng.xml.
1. It should generally not silently fall back to one-to-many or many-to-one if it
determines that one-to-one is not possible; it should report an error instead. (This
allows programmers to correct the database and/or the hibernate.reveng.xml: if it's
really a one-to-many, they can move the association to the other table and make it
many-to-one; if it should be one-to-one, they can add the missing constraints, giving
Hibernate better information about the database schema actually in place.)
2. In the following test case, it does not recognize the relationship as one-to-one even
though it is, erroneously generating a Set for the <inverse-one-to-one> direction
instead of a backlink.
Workarounds:
A) Use <inverse-one-to-one exclude="true"/> to prevent Set creation. Works
if you don't need the backlink.
B) Have a backlink field in the target table. Create two one-to-one associations, one for
each direction, and use <inverse-one-to-one exclude="true"/>.
C) Do not reverse engineer the one-to-one association at all and use Criteria, HQL, or SQL
to navigate the link.
D) Subclass DefaultReverseEngineeringStrategy and override isOneToOne() for that
particular association.
Test case:
Table creation (Oracle 10g)
CREATE TABLE "HF_DI_BVKRIT" (
"BKID" NUMBER(27,0) NOT NULL ENABLE,
"VERSION" NUMBER(18,0) DEFAULT 0 NOT NULL ENABLE,
"BKNAME" VARCHAR2(40) NOT NULL ENABLE
) ;
ALTER TABLE "HF_DI_BVKRIT" ADD CONSTRAINT "HF_DI_BVKRIT_PK"
PRIMARY KEY ("BKID") ENABLE;
CREATE TABLE "HF_DI_BVKOPF" (
"BVID" NUMBER(10,0) NOT NULL ENABLE,
"VERSION" NUMBER(18,0) DEFAULT 0 NOT NULL ENABLE,
"BVBKID" NUMBER(27,0) NOT NULL ENABLE,
"BVGPRS" NUMBER(8,2)
) ;
ALTER TABLE "HF_DI_BVKOPF" ADD CONSTRAINT "HF_DI_BVKOPF_PK"
PRIMARY KEY ("BVID") ENABLE;
ALTER TABLE "HF_DI_BVKOPF" ADD CONSTRAINT "HF_DI_BVKOPF_UK"
UNIQUE ("BVBKID") ENABLE;
ALTER TABLE "HF_DI_BVKOPF" ADD CONSTRAINT "HF_DI_BVKOPF_FK_BVKRIT"
FOREIGN KEY ("BVBKID") REFERENCES "HF_DI_BVKRIT" ("BKID")
ENABLE;
Relevant hibernate.reveng.xml section:
<table name="HF_DI_BVKOPF">
<column name="VERSION" type="long"></column>
<foreign-key constraint-name="HF_DI_BVKOPF_FK_BVKRIT">
<one-to-one />
<inverse-one-to-one />
</foreign-key>
</table>
Generated Java classes:
public class HfDiBvkrit implements java.io.Serializable {
private BigInteger bkid;
private long version;
private String bkname;
private Set <HfDiBvkopf> hfDiBvkopfs = new HashSet <HfDiBvkopf> (0);
// The above line should have been generated as:
// private HfDiBvkopf hfDiBvkopf;
...
}
public class HfDiBvkopf implements java.io.Serializable {
private BigInteger bvid;
private long version;
private HfDiBvkrit hfDiBvkrit;
private BigDecimal bvgprs;
...
}
Reasoning why this should be a one-to-one association (hopefully I didn't make too
many errors reversing the roles of left and right table):
There is a unique key on BVKOPF.BVBKID.
I.e. a BVKRIT record can find at most one BVKOPF with a BVBKID that matches its
BVKRIT.BKID.
The BVKOPF-BVKRIT association hence must be one-to-*. (1)
There is a foreign key from BVKOPF.BVBKID to BVKRIT.BKID.
BKID is a unique key in BVKRIT (it also happens to be the primary key, but that's
irrelevant here).
I.e. a BVKOPF record can find at most one BVKRIT with a BKID that matches its
BVKOPF.BVBKID.
The BVKOPF-BVKRIT association hence must be *-to-one. (2)
Combining (1) and (2) gives "must be one-to-one", q.e.d.
See also https://forum.hibernate.org/viewtopic.php?f=6&t=1009989&start=0
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