JPA Map mapping

问题:

How can I map a Map in JPA without using Hibernate's classes?

回答1:

Does not the following work for you?

@ManyToMany(cascade = CascadeType.ALL)
Map<String,EntityType> entitytMap = new HashMap<String, EntityType>();

EntityType could be any entity type, including a String.

回答2:

Although answer given by Subhendu Mahanta is correct. But @CollectionOfElements is deprecated. You can use @ElementCollection instead:

@ElementCollection
@JoinTable(name="ATTRIBUTE_VALUE_RANGE", joinColumns=@JoinColumn(name="ID"))
@MapKeyColumn (name="RANGE_ID")
@Column(name="VALUE")
private Map<String, String> attributeValueRange = new HashMap<String, String>();

There is no need to create a separate Entity class for the Map field. It will be done automatically.

回答3:

Suppose I have an entity named Book which is having a Map of chapters:

import java.io.Serializable;
import java.util.Map;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;    
import org.hibernate.annotations.CollectionOfElements;
import org.hibernate.annotations.MapKey;
@Entity
public class Book implements Serializable{
@Column(name="BOOK_ID")
@Id
@GeneratedValue(strategy=GenerationType.AUTO)
private Long bookId;    

@CollectionOfElements(targetElement=java.lang.String.class)
@JoinTable(name="BOOK_CHAPTER",
        joinColumns=@JoinColumn(name="BOOK_ID"))
@MapKey (columns=@Column(name="CHAPTER_KEY"))
@Column(name="CHAPTER")
private Map<String,String> chapters;
public Long getBookId() {
    return bookId;
}
public void setBookId(Long bookId) {
    this.bookId = bookId;
}
public Map<String,String> getChapters() {
    return chapters;
}
public void setChapters(Map<String,String> chapters) {
    this.chapters = chapters;
}               

}

It works for me.

回答4:

A working example:

@ElementCollection(fetch=FetchType.EAGER)
@CollectionTable(name = "TABLENAME")
@MapKeyColumn(name = "KEY")
@Column(name = "VALUE")
public Map<String, String> getMap() {
    return _map;
}