如何解决JPA加入2个基于1个公共实体的实体
我有3个表-国家,地区和国家/地区。
- 国家-countryId(PK),countryName
- 地区-regionId(PK),regionName
- CountryRegion-countryId(FK),regionId(FK)
我想在获取地区时获取国家列表。就像:
*
{
regionId:11
regionName:"abc"
countries: [
{countryId:"67",countryName:"us"
},{...}
]
}
不需要CountryRegion表,但可以使用旧版数据库。
我已经实现了:
package com.example.demo.model;
import javax.persistence.*;
import java.util.ArrayList;
import java.util.List;
@Entity
@Table(name = "country")
public class Country {
@Id
@Column(name = "countryid")
private int countryId;
@Column(name = "countryname")
private String countryName;
@OneToMany(fetch = FetchType.EAGER,mappedBy = "country")
private List<CountryRegion> regions = new ArrayList<>();
public int getCountryId() {
return countryId;
}
public void setCountryId(int countryId) {
this.countryId = countryId;
}
public String getCountryName() {
return countryName;
}
public void setCountryName(String countryName) {
this.countryName = countryName;
}
public List<CountryRegion> getRegions() {
return regions;
}
public void setRegions(List<CountryRegion> regions) {
this.regions = regions;
}
}
package com.example.demo.model;
import com.fasterxml.jackson.annotation.JsonIgnore;
import javax.persistence.*;
import java.util.ArrayList;
import java.util.List;
@Entity
@Table(name = "region")
public class Region {
@Id
@Column(name = "regionid")
private int regionId;
@Column(name = "regionname")
private String regionName;
@OneToMany(mappedBy = "region")
private List<CountryRegion> countries = new ArrayList<>();
public int getRegionId() {
return regionId;
}
public void setRegionId(int regionId) {
this.regionId = regionId;
}
public String getRegionName() {
return regionName;
}
public void setRegionName(String regionName) {
this.regionName = regionName;
}
public List<CountryRegion> getCountries() {
return countries;
}
public void setCountries(List<CountryRegion> countries) {
this.countries = countries;
}
}
package com.example.demo.model;
import com.fasterxml.jackson.annotation.JsonBackReference;
import com.fasterxml.jackson.annotation.JsonIgnore;
import javax.persistence.*;
import java.io.Serializable;
import java.util.List;
@Entity
@Table(name = "countryregion1")
public class CountryRegion implements Serializable {
@Id @ManyToOne
@JoinColumn(name = "regionid",referencedColumnName = "regionId")
private Region region;
@Id @ManyToOne
@JoinColumn(name = "countryid",referencedColumnName = "countryId")
private Country country;
public Region getRegion() {
return this.region;
}
public void setRegion(Region region) {
this.region = null;
}
public Country getCountry() {
return this.country;
}
public void setCountry(Country country) {
this.country = country;
}
}
package com.example.demo.dao;
import com.example.demo.model.Country;
import org.springframework.data.repository.CrudRepository;
import org.springframework.stereotype.Repository;
import java.util.List;
@Repository
public interface CountryRepository extends CrudRepository<Country,Integer> {
@Override
List<Country> findAll();
}
package com.example.demo.dao;
import com.example.demo.model.Country;
import com.example.demo.model.Region;
import org.springframework.data.repository.CrudRepository;
import org.springframework.stereotype.Repository;
import java.util.List;
@Repository
public interface RegionRepository extends CrudRepository<Region,Integer> {
@Override
List<Region> findAll();
}
- 公开API以获得数据的控制器和服务。
上面的代码有问题,因为我只想获取国家(或地区)列表
此代码在JSON中导致无限循环。尝试过Json忽略等。但是在那种情况下,我在列表中没有任何价值。
TIA !!
解决方法
首先,您应该指定国家和地区之间的关系。我认为您不需要定义CountryRegion类。如果关系是ManyToMany,则可以在Region类中使用以下代码:
ycbcr1 = cv2.imread(Ycbcr_new.jpg)
ycbcr1 == x
,如果是OneToMany,则在Region类中实现的等级就足够了。但我认为您想要与您的愿望相对应的ManyToMany
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