[英]Hibernate Entities Mapping NullPointerException
Hej Guys,這是我的問題。 我有一段Java代碼,不知道NullPointerException的原因是什么。 我認為這是由於錯誤的對象映射引起的,但我還沒有找到解決方案。
ArrayList<Auction> auctionList = auctionDAO.findAll(); /* Works correctly */
for(Auction auction : auctionList) {
System.out.println(auction.getOwner().getEmail()); /* NullPointerException */
}
/* -------------- ENTITIES --------------- */
@Entity
@Table(name="USERS")
public class User implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
private Integer id;
(other properties)
private String email;
@OneToMany(cascade=CascadeType.ALL, fetch=FetchType.EAGER, mappedBy="owner")
@JoinTable(
name="OWNER_AUCTION",
joinColumns = @JoinColumn(name="OWNER_ID"),
inverseJoinColumns = @JoinColumn(name="AUCTION_ID")
)
private Set<Auction> ownedAuctionList = new HashSet<Auction>();
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
(getters & setters)
}
@Entity
@Table(name="AUCTIONS")
public class Auction implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
private Integer id;
(other properties)
@ManyToOne(fetch=FetchType.EAGER)
private User owner;
(other properties & getters & setters)
}
沒有桌子,很難說。 但我想出於調試目的,您應該執行以下操作:
for(Auction auction : auctionList) {
if(auction.getOwner()==null){
System.out.println("Null Owner");
}
else if(auction.getOwner().getEmail()==null){
System.out.println("Null mail");
}
else
System.out.println(auction.getOwner().getEmail());
}
這應該可以幫助您找到問題
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