Multiple PK, one from joined column

Question

Hi all,
I have this situation:
2 entities, country and state
country has code and name as fields, code is PK
state has code, name and country_code (linked to country code field) as fields, code is PK and country_code should too.
@Entity @Table(name="country")
class Country implements Serializable{
@Id @Column(name="code",length=2)
private String code;
@Column(name="name",length=50)
private String name;
//setters and getters here
}     then
@Entity @Table(name="state")
class State implements Serializable{
@Id @Column(name="code",length=2)
private String state;
@Column(length=50)
private String name;
@ManyToOne
@JoinColumn(name = "countryCode", nullable = false)
private Country country; //<-- should be PK too!!!
//setters and getters here
}     Can someone help me to understand this?
Thank you all in advance

Answer 1

Hi,
Don't use wm_concat. It's undocumented, so it could disappear in the next version of Oracle, or it could do something slightly different, which you might not notice until you've gotten wrong results for months.
If you like wm_concat, then install and use STRAGG, which you can copy from
http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:2196162600402
Stragg seems to do the same thing as wm_concat. (Since wm_concat is undocumented, we can only guess at what it actually does. We can be sure what stragg dioes, and that it will keep doing exactly the same thing if we change versions.)
Either way, you're calling an aggregate fucntion, so everyhting in your SELECT clause has to be one of the GROUP BY expressions or an aggregate.
You could make a really big GROUP BY clause, but if you're joining tables, it may be simpler and more efficient to compute stragg in a sub-query, which just uses one table, and then join the results to the other tables.
I hope this answers your question.
If not, post a little sample data (CREATE TABLE and INSERT statements, relevant columns only) for all tables, and also post the results you want from that data.
Explain, using specific examples, how you get those results from that data.
Simplify the question as much as possible. I'll be you could get a good example of your problem using no more than 5 columns from 2 tables. (If you used scott.emp and scott.dept to illustrate the problem, you wouldn't even have to post sample data.)
Always say which version of Oracle you're using.