[英]Cycle in Hibernate OneToMany relation
我使用休眠和
有两个具有OneToMany关系的实体(城市和区域)。
首先:
@Entity
@Table(name = "p_region")
public class Region implements Serializable{
@OneToMany(mappedBy = "region",fetch= FetchType.LAZY, cascade = CascadeType.MERGE)
private List<City> citys;
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer id;
private String name;
//++++++++++++++++++++ GETSET
public List<City> getCitys() {
return citys;
}
public void setCitys(List<City> citys) {
this.citys = citys;
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
第二个:
@Entity
@Table(name = "p_city")
public class City implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer id;
@NotEmpty(message = "Название не должно быть пустым")
@Length(max = 10, min = 2, message = "Название должно быть менее 2 символов и не
более 100")
private String cityName;
@NotEmpty(message = "Код города не должно быть пустым")
private String cityCode;
@Column(name = "zone")
private Integer zone;
@Basic(optional = true)
@Temporal(javax.persistence.TemporalType.TIMESTAMP)
private Date entryDate = Calendar.getInstance().getTime();
@ManyToOne()
private Region region;
@Basic(optional = true)
private String zip_code;
// GET SET ::::::::::::::::::::::::::::::::::
public Integer getZone() {
return zone;
}
public void setZone(Integer zone) {
this.zone = zone;
}
public Region getRegion() {
return region;
}
public void setRegion(Region region) {
this.region = region;
}
public void delete() {
System.out.println("QQQQQQQQQQQQQQQQQQQQQQ");
}
public String getCityCode() {
return cityCode;
}
public void setCityCode(String cityCode) {
this.cityCode = cityCode;
}
public String getCityName() {
return cityName;
}
public void setCityName(String cityName) {
this.cityName = cityName;
}
public Date getEntryDate() {
return entryDate;
}
public void setEntryDate(Date entryDate) {
this.entryDate = entryDate;
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getZip_code() {
return zip_code;
}
public void setZip_code(String zip_code) {
this.zip_code = zip_code;
}
}
当我尝试使用JSON获取简单的Object(City)时,它返回循环:
{"id":577,"region":{"name":"нет региона","id":15,"citys":[{"id":577,"region":
{"name":"нет региона","id":15,"citys":[{"id":577,"region":{"name":"нет
региона","id":15,"citys":[{"id":577,"region":{"name":"нет
региона","id":15,"citys":[{"id":577,"region":{"name":"нет
региона","id":15,"citys":[{"id":577,"region":{"name":"нет
региона","id":15,"citys":[{"id":577,"region":{"name":"нет......so on.
这个问题有解决方案吗?
在转换为JSON之前,您需要打破实体之间的双向关系。
我认为有两种选择:
迭代子集合,例如Region中的citys
,并将Region
设置为null。 这样,循环依赖将被打破。 你是我想添加一个名字映射属性regionId
在City
,这样的关系的信息仍然是可用的。
创建另一组没有循环依赖性的POJO
对象,从Entity Objects复制值,然后使用POJO对象获取JSON。
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