休眠从两个表中选择数据

Question

I have two tables: authors and books

Author:

 @Entity
 @Table (name="authors")
 public class Author implements  java.io.Serializable {

private Integer id;
private String name;
private String lastName;
/*book list*/
private Set<Book> books= new HashSet<Book>(0);

public Author() {
}

public Author(String name, String lastName) {
    this.name = name;
    this.lastName = lastName;
}

public Author(String name, String lastName, Set<Book> books) {
    this.name = name;
    this.lastName = lastName;
    this.books = books;
}
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "AUTHOR_ID", unique = true, nullable = false)
public Integer getId() {
    return id;
}
public void setId(Integer id) {
    this.id = id;
}

@Column(name = "AUTHOR_NAME", unique = true, nullable = false, length = 10)
public String getName() {
    return name;
}
public void setName(String name) {
    this.name = name;
}

@Column(name = "AUTHOR_LASTNAME", unique = true, nullable = false, length = 10)
public String getLastName() {
    return lastName;
}

public void setLastName(String lastName) {
    this.lastName = lastName;
}


@OneToMany(fetch = FetchType.LAZY, mappedBy = "author")
public Set<Book> getBooks() {
    return books;
}

public void setBooks(Set<Book> books) {
    this.books = books;
}
}

Book:

import javax.persistence.*;

@Entity
@Table(name = "books")
public class Book implements  java.io.Serializable {
private Integer id;
private String name;
private Author author;
public Book() {
}
public Book(String name) {
    this.name = name;
}

public Book(String name, Author author) {
    this.name = name;
    this.author = author;
}
@Id
@Column(name = "BOOK_ID")
@GeneratedValue(strategy = GenerationType.IDENTITY)
public Integer getId() {
    return id;
}

public void setId(Integer id) {
    this.id = id;
}

@Column(name = "BOOK_NAME")
public String getName() {
    return name;
}

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

@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "AUTHOR_ID",nullable = false)
public Author getAuthor() {
    return author;
}
public void setAuthor(Author author) {
    this.author = author;
}
}

In my book's table I have field with id author . How can I get all books from one author? How Can I solve it? Must I use HQL or other methods? I am beginner in this.

Answer 1

I wont help you with the code here but the logic.. The very first thing you need to do is build a relationship between Author and Books using the annotations @OneToMany or @ManyToOne depending on your structure.

Next use the Author Class Object to retrive the list of Books.

Answer 2

first you need to the mapping between two entities.

Author class

@OneToMany(mappedBy="author")
private Set<Book> books= new HashSet<Book>(0);

Book class

@ManyToOne
private Author author;

after that you can use a simple criteria query to retrieve the relevant records.