What query should be created for this case

Question

Here are those classes:
Folder{
    String name;
    @ManyToOne
    Subject owner;
Subject {
    String name;
}What query should I create in order to: find out if there is an actual Folder for a Subject with the name X in the database ?
Actually, the question is kinda stupid, but im not experienced with queries....

Answer 1

javaUserMuser wrote:
Here are those classes:
Folder{
String name;
@ManyToOne
Subject owner;
Subject {
String name;
}What query should I create in order to: find out if there is an actual Folder for a Subject with the name X in the database ?Can't tell based on the info you posted. These are Java objects, and queries deal with relational tables.
Your naming is confusing. Subject and owner are two very different things.
If I had two tables like this:
CREATE TABLE IF NOT EXISTS owners
    owner_id bigint not null auto_increment,
    name varchar(80),
    primary key(owner_id)
CREATE TABLE IF NOT EXISTS folders
    folder_id bigint not null auto_increment,
    name varchar(80),
    owner_id bigint   
    primary key(folder_id),
    foreign key(owner_id) references(owners)
);I'd write the JOIN query this way:
SELECT f.name, o.name
FROM folders as f, owners as o
WHERE o.owner_id = ?
AND o.owner_id = f.owner_idYou realize, of course, that if you're using EJB3 as the annotations suggest, that you don't write any SQL. EJB3 generates it dynamically for you.
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