Hibernate insert with foreign key

Question

Ι have the following database:

    SET SQL_MODE = "NO_AUTO_VALUE_ON_ZERO";
    SET time_zone = "+00:00";

    CREATE TABLE IF NOT EXISTS `Authors` (
           `AutID` int(11) NOT NULL,
            `Name` varchar(50) NOT NULL 
    ) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=latin1;


    INSERT INTO `Authors` (`AutID`, `Name`) VALUES
    (1, 'Tolkien');

      CREATE TABLE IF NOT EXISTS `Books` (
         `BookID` int(11) NOT NULL,
         `AutID` int(11) NOT NULL,
          `Name` varchar(50) NOT NULL
          ) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=latin1;


   ALTER TABLE `Authors`
    ADD PRIMARY KEY (`AutID`);

   ALTER TABLE `Books`
        ADD PRIMARY KEY (`BookID`), ADD KEY `AutID` (`AutID`);

  ALTER TABLE `Authors`
         MODIFY `AutID` int(11) NOT NULL AUTO_INCREMENT,AUTO_INCREMENT=2;

   ALTER TABLE `Books`
        MODIFY `BookID` int(11) NOT NULL AUTO_INCREMENT,AUTO_INCREMENT=2;

    ALTER TABLE `Books`
       ADD CONSTRAINT `fkautid` FOREIGN KEY (`AutID`) REFERENCES                    `Authors` (`AutID`) ON DELETE NO ACTION ON UPDATE NO ACTION;

and the following classes:

@Entity
@Table(name="Books"
,catalog="Autor"
)
public class Books  implements java.io.Serializable {


 private Integer bookId;
 private Authors authors;
 private String name;

public Books() {
}

public Books(Authors authors, String name) {
   this.authors = authors;
   this.name = name;
}

 @Id @GeneratedValue(strategy=IDENTITY)


@Column(name="BookID", unique=true, nullable=false)
public Integer getBookId() {
    return this.bookId;
}

public void setBookId(Integer bookId) {
    this.bookId = bookId;
}

@ManyToOne
@JoinColumn(name="AutID", nullable=false,insertable =  false, updatable = false)
public Authors getAuthors() {
    return this.authors;
}

public void setAuthors(Authors authors) {
    this.authors = authors;
}


@Column(name="Name", nullable=false, length=50)
public String getName() {
    return this.name;
}

public void setName(String name) {
    this.name = name;
}




}




@Entity   
@Table(name="Authors"
 ,catalog="Autor"
)
public class Authors  implements java.io.Serializable {


  private Integer autId;
  private String name;
  private Set<Books> bookses = new HashSet<Books>(0);

public Authors() {
}


public Authors(String name) {
    this.name = name;
}
public Authors(String name, Set<Books> bookses) {
   this.name = name;
   this.bookses = bookses;
}

 @Id @GeneratedValue(strategy=IDENTITY)


@Column(name="AutID", unique=true, nullable=false)
public Integer getAutId() {
    return this.autId;
}

public void setAutId(Integer autId) {
    this.autId = autId;
}


@Column(name="Name", nullable=false, length=50)
public String getName() {
    return this.name;
}

public void setName(String name) {
    this.name = name;
}

@OneToMany(fetch=FetchType.LAZY, mappedBy="authors")
public Set<Books> getBookses() {
    return this.bookses;
}

public void setBookses(Set<Books> bookses) {
    this.bookses = bookses;
}




}

I want to insert into the DB books written by Tolkien. I am doing this using the following snippet:

  public static void main(String[] args) {


    try {

        BufferedReader br=new BufferedReader(new InputStreamReader (System.in));

        System.out.println("Book Name");
        String NamesnsBook=br.readLine();


        HibernateUtil myHiber=new HibernateUtil();

        SessionFactory sessFabrika=myHiber.getSessionFactory();

        Session s = sessFabrika.openSession();
        s.beginTransaction();


        //get author
        Query q=s.createQuery("FROM Authors Where Name=:n");
        q.setParameter("n", "Tolkien");
        Authors Auth=(Authors) q.list().get(0);

        Books b=new Books();
        b.setAuthors(Auth);
        b.setName(NamesnsBook);


        s.save(b);
        s.getTransaction().commit();
        s.close();

        System.out.println("OK");

    }

    catch (Exception ex) {
        ex.printStackTrace();
    }
}

}

Is this the optimal way of inserting books of authors that already exist in the db? I mean, do I have to query the db every time in order to get the foreign key object (the Authors instance Auth in this case)?

Answer 1

Always use singular names for entities. It's Book, not Books; and Author, not Authors.

Always get the ID. Get the surrogate key, not the business key, from the UI.

You can use Session.load to set up foreign key relations without querying the DB.

void addBook(int authorId, String bookName) {
    Session session = //...get a session

    Author author = session.load(Author.class, authorId);

    Book book = new Book(author, bookName);

    s.save(b);
}