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From Frank Schwarz <frank.schw...@gmx.de>
Subject One-sided one-to-many - how to map?
Date Thu, 15 May 2008 13:20:30 GMT
Hi,

my apologies if this question has been asked recently. However my search 
did not reveal an appropriate answer.

How do I map a unidirectional one-to-many relationship between a master 
and a detail such that a column "master_id" in table "detail" is used 
for joining both tables?

According to [1], it should be like:

@Entity
public class Person {
    @OneToMany
    @ElementJoinColumn(name="Person_id")
    private Set<Address> addresses = new HashSet<Address>();
}

@Entity
public class Address {
}

However, this is causing two issues:
1.) I have to do the schema creation on my own as the OpenJPA mapping 
tool creates a join-table database mapping, i.e.
    CREATE TABLE Address (id NUMBER NOT NULL, ..., PRIMARY KEY (id));
    CREATE TABLE Person (id NUMBER NOT NULL, ..., PRIMARY KEY (id));
    CREATE TABLE Person_Address (Person_id NUMBER, addresses_id NUMBER);

2.) I cannot transfer an address-object from one person to another:

    Address address = person1.getAddresses().iterator().next();
    person1.getAddresses().remove(address);
    person2.getAddresses().add(address);

This raises an InvalidStateException: Attempt to set column 
"Address.Person_id" to two different values: (null)"null", (class 
java.lang.Long)"2".

Is the mapping correct? And if so, how can I get the mapping tool to 
create the correct table definitions?

Kind regards,
Frank

[1] 
http://openjpa.apache.org/builds/1.0.2/apache-openjpa-1.0.2/docs/manual/manual.html#ref_guide_mapping_jpa_onemany

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