Java 插入查询的空指针异常

我有我的表格国家和指标的E bean模型。 指标模型如下所示

public class Indicators extends Model {

private static final long serialVersionUID = 1L;

@Id
public Long id;

@OneToMany(mappedBy = "indicator")
public HashSet<Indicators> transactions;

@ManyToOne
@JoinColumn(name = "countryid")
public Countries country;
}

    public class Countries extends Model {
          private static final long serialVersionUID = 1L;

           @Id
          @Column(name = "COUNTRYID")
          public Long countryId;

          @OneToMany(mappedBy = "country")
          public HashSet<Countries> indicators;
             }

但是，indObj.country.countryId会导致空指针异常

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感谢您的帮助。谢谢：

默认情况下，实例变量设置为null，并且由于您尚未初始化对象指示符的国家/地区变量，因此它将为null。因此，在null对象上设置countryId将导致NullPointerException

您还需要初始化Indicators对象的country属性：

Indicators indObj = new Indicators();
indObj.country = new Countries();
indObj.country.countryId = 542L;
indObj.save();

Indicators indObj = new Indicators();
indObj.country = new Countries();
indObj.country.countryId = 542L;
indObj.save();