以前已经回答了一个类似的问题和另一个问题。我使用Hibernate建立了双向@ManyToMany关系。数据持久存储到单独的实体表中，但映射到实体表的id列为空。我在Empty Join Table resulting from JPA ManyToMany，ManyToMany relationship, deleting records from relationship table和Hibernate Many-to-many association: left hand side collection contains elements, but right hand side collection is empty中尝试了这些建议，但到目前为止还没有取得成功。下面是我的完整性代码（我还在学习java和spring框架，所以我提前为任何菜鸟错误道歉）：
CaseStudy Class
@Entity
public class CaseStudy {
@Id
@GeneratedValue (strategy = GenerationType.AUTO)
private Long caseStudyId;
private String location;
private String equipment;
private String issue;
private String solution;
private String benefit;
private float upper_dissolved_Oxygen;
private float lower_dissolved_Oxygen;
private float upper_pH;
private float lower_pH;
private float upper_temp;
private float lower_temp;
private float upper_conductivity;
private float lower_conductivity;
@CreationTimestamp
private Date created;
@ManyToOne
@JsonBackReference
private User user;
private int likes;
@ManyToMany(mappedBy="casestudyList", fetch = FetchType.EAGER)
private List<WaterQuality> waterQualityList = new List<WaterQuality>();
@OneToMany(mappedBy = "casestudy", fetch = FetchType.EAGER)
private List<Comment> commentList;
public Long getCaseStudyId() {
return caseStudyId;
}
public void setCaseStudyId(Long caseStudyId) {
this.caseStudyId = caseStudyId;
}
public String getLocation() {
return location;
}
public void setLocation(String location) {
this.location = location;
}
public String getIssue() {
return issue;
}
public void setIssue(String issue) {
this.issue = issue;
}
public String getSolution() {
return solution;
}
public void setSolution(String solution) {
this.solution = solution;
}
public String getBenefit() {
return benefit;
}
public void setBenefit(String benefit) {
this.benefit = benefit;
}
public Date getCreated() {
return created;
}
public void setCreated(Date created) {
this.created = created;
}
public User getUser() {
return user;
}
public void setUser(User user) {
this.user = user;
}
public int getLikes() {
return likes;
}
public void setLikes(int likes) {
this.likes = likes;
}
public List<Comment> getCommentList() {
return commentList;
}
public void setCommentList(List<Comment> commentList) {
this.commentList = commentList;
}
public String getEquipment() {
return equipment;
}
public void setEquipment(String equipment) {
this.equipment = equipment;
}
public float getUpper_dissolved_Oxygen() {
return upper_dissolved_Oxygen;
}
public void setUpper_dissolved_Oxygen(float upper_dissolved_Oxygen) {
this.upper_dissolved_Oxygen = upper_dissolved_Oxygen;
}
public float getLower_dissolved_Oxygen() {
return lower_dissolved_Oxygen;
}
public void setLower_dissolved_Oxygen(float lower_dissolved_Oxygen) {
this.lower_dissolved_Oxygen = lower_dissolved_Oxygen;
}
public float getUpper_pH() {
return upper_pH;
}
public void setUpper_pH(float upper_pH) {
this.upper_pH = upper_pH;
}
public float getLower_pH() {
return lower_pH;
}
public void setLower_pH(float lower_pH) {
this.lower_pH = lower_pH;
}
public float getUpper_temp() {
return upper_temp;
}
public void setUpper_temp(float upper_temp) {
this.upper_temp = upper_temp;
}
public float getLower_temp() {
return lower_temp;
}
public void setLower_temp(float lower_temp) {
this.lower_temp = lower_temp;
}
public float getUpper_conductivity() {
return upper_conductivity;
}
public void setUpper_conductivity(float upper_conductivity) {
this.upper_conductivity = upper_conductivity;
}
public float getLower_conductivity() {
return lower_conductivity;
}
public void setLower_conductivity(float lower_conductivity) {
this.lower_conductivity = lower_conductivity;
}
public List<WaterQuality> getWaterQualityList() {
return waterQualityList;
}
public void setWaterQualityList(List<WaterQuality> waterQualityList) {
this.waterQualityList = waterQualityList;
}
}
WaterQuality Class
@Entity
public class WaterQuality {
@Id
@GeneratedValue(strategy=GenerationType.AUTO)
private Long waterQualityId;
private String description;
private String status;
private float dissolved_Oxygen;
private float pH;
private float temp;
private float conductivity;
@CreationTimestamp
private Date publishDate;
@ManyToOne
@JsonBackReference
private User user;
@ManyToMany(targetEntity = CaseStudy.class, cascade = {CascadeType.ALL})
@JoinTable(
joinColumns = {@JoinColumn(name="water_quality_id")},
inverseJoinColumns = {@JoinColumn(name="case_study_id")})
private Set<CaseStudy> casestudyList = new HashSet<CaseStudy>();
public Long getWaterQualityId() {
return waterQualityId;
}
public void setWaterQualityId(Long waterQualityId) {
this.waterQualityId = waterQualityId;
}
public String getDescription() {
return description;
}
public void setDescription(String description) {
this.description = description;
}
public String getStatus() {
return status;
}
public void setStatus(String status) {
this.status = status;
}
public float getDissolved_Oxygen() {
return dissolved_Oxygen;
}
public void setDissolved_Oxygen(float dissolved_Oxygen) {
this.dissolved_Oxygen = dissolved_Oxygen;
}
public float getpH() {
return pH;
}
public void setpH(float pH) {
this.pH = pH;
}
public float getTemp() {
return temp;
}
public void setTemp(float temp) {
this.temp = temp;
}
public float getConductivity() {
return conductivity;
}
public void setConductivity(float conductivity) {
this.conductivity = conductivity;
}
public Date getPublishDate() {
return publishDate;
}
public void setPublishDate(Date publishDate) {
this.publishDate = publishDate;
}
public User getUser() {
return user;
}
public void setUser(User user) {
this.user = user;
}
public Set<CaseStudy> getCasestudyList() {
return casestudyList;
}
public void setCasestudyList(Set<CaseStudy> casestudyList) {
this.casestudyList = casestudyList;
}
public List<CaseStudy> getDissolvedOxygenalert() {
List<CaseStudy> dissolvedOxygenalert = casestudyList.stream() //convert list to stream
.filter(casestudy -> casestudy.getUpper_dissolved_Oxygen() < getDissolved_Oxygen() || casestudy.getLower_dissolved_Oxygen() > getDissolved_Oxygen())
.collect(Collectors.toList()); //collect the output and convert streams to a List
System.out.print(dissolvedOxygenalert);
return dissolvedOxygenalert;
}
}
我已经尝试删除数据库并再次创建它，但到目前为止还没有解决问题。
以下是将数据保存到数据库的代码 ++++++++++++++++++++++++++++++++++++++++++++++++++ +++++++++++++++++++++++++++++
CaseStudy服务实施
import java.util.List;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import com.scrunch.data.dao.CaseStudyDao;
import com.scrunch.data.model.CaseStudy;
import com.scrunch.data.model.User;
import com.scrunch.data.service.CaseStudyService;
@Service
public class CaseStudyServiceImpl implements CaseStudyService{
@Autowired
private CaseStudyDao casestudyDao;
public CaseStudy save(CaseStudy casestudy) {
return casestudyDao.save(casestudy);
}
public Set<CaseStudy> findByUser(User user) {
return casestudyDao.findByUser(user);
}
public CaseStudy findByCaseStudyId(Long caseStudyId) {
return casestudyDao.findByCaseStudyId(caseStudyId);
}
public Set<CaseStudy> findAll() {
return casestudyDao.findAll();
}
}
WaterQuality服务实施
import java.util.Date;
import java.util.List;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import com.scrunch.data.dao.WaterQualityDao;
import com.scrunch.data.model.User;
import com.scrunch.data.model.WaterQuality;
import com.scrunch.data.service.WaterQualityService;
@Service
public class WaterQualityServiceImpl implements WaterQualityService{
// private static final Logger LOGGER = LoggerFactory.getLogger(WaterQualityServiceImpl.class);
@Autowired
private WaterQualityDao waterQualityDao;
@Override
public List<WaterQuality> listAllWaterQualityByUserAndDescription(
User user, String description) {
return waterQualityDao.findAllWaterQualityByUserAndDescriptionContaining(user, description);
}
@Override
public WaterQuality save(WaterQuality waterQuality) {
return waterQualityDao.save(waterQuality);
}
@Override
public List<WaterQuality> findByUser(User user) {
return waterQualityDao.findByUser(user);
}
@Override
public WaterQuality findWaterQualityById(Long waterQualityId) {
return waterQualityDao.findByWaterQualityId(waterQualityId);
}
@Override
public List<WaterQuality> findAll() {
return waterQualityDao.findAll();
}
}
WaterQuality Controller
import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;
import com.fasterxml.jackson.annotation.JsonIgnore;
import com.scrunch.data.model.CaseStudy;
import com.scrunch.data.model.User;
import com.scrunch.data.model.WaterQuality;
import com.scrunch.data.service.WaterQualityService;
@RestController
@RequestMapping("/rest")
public class WaterQualityResource {
private String location;
private String equipment;
private String issue;
private String solution;
private String benefit;
private float upper_dissolved_Oxygen;
private float lower_dissolved_Oxygen;
private int likes;
@Autowired
private WaterQualityService waterQualityService;
@RequestMapping(value="/waterquality/add", method=RequestMethod.POST)
public WaterQuality addWaterQuality(@RequestBody WaterQuality waterQuality) {
waterQuality.setCasestudyList(new HashSet<CaseStudy>());
CaseStudy casestudy = new CaseStudy();
casestudy.setLocation(location);
casestudy.setEquipment(equipment);
casestudy.setIssue(issue);
casestudy.setSolution(solution);
casestudy.setBenefit(benefit);
casestudy.setUpper_dissolved_Oxygen(upper_dissolved_Oxygen);
casestudy.setLower_dissolved_Oxygen(lower_dissolved_Oxygen);
waterQuality.getCasestudyList().add(casestudy);
return waterQualityService.save(waterQuality);
}
获取所有水质响应返回的请求以及相同结果的无限循环。
[{"waterQualityId":1,"description":"sdfdsf","status":"dsfdsf","dissolved_Oxygen":5.0,"pH":7.0,"temp":72.0,"conductivity":500.0,"publishDate":1472784062000,"dissolvedOxygenalert":[{"caseStudyId":2,"location":null,"equipment":null,"issue":null,"solution":null,"benefit":null,"upper_dissolved_Oxygen":0.0,"lower_dissolved_Oxygen":0.0,"upper_pH":0.0,"lower_pH":0.0,"upper_temp":0.0,"lower_temp":0.0,"upper_conductivity":0.0,"lower_conductivity":0.0,"created":1472784062000,"likes":0,"waterQualityList":[{"waterQualityId":1,"description":"sdfdsf","status":"dsfdsf","dissolved_Oxygen":5.0,"pH":7.0,"temp":72.0,"conductivity":500.0,"publishDate":1472784062000,"dissolvedOxygenalert":[{"caseStudyId":2,"location":null,"equipment":null,"issue":null,"solution":null,"benefit":null,"upper_dissolved_Oxygen":0.0,"lower_dissolved_Oxygen":0.0,"upper_pH":0.0,"lower_pH":0.0,"upper_temp":0.0,"lower_temp":0.0,"upper_conductivity":0.0,"lower_conductivity":0.0,"created":1472784062000,"likes":0,"waterQualityList":
我能够将数据填充到连接表中，但它似乎无休止地填充。它会在添加水质数据时发生。
答案 0 :(得分：1)
在发布的代码中不清楚您是如何尝试保存关联实体的。你应该坚持这样......
WaterQuality waterQuality = new WaterQuality();
//Set other fields too
CaseStudy caseStudy1 = new CaseStudy();
CaseStudy caseStudy2 = new CaseStudy();
CaseStudy caseStudy3 = new CaseStudy();
CaseStudy caseStudy4 = new CaseStudy();
//Set other fileds of case study too
List<CaseStudy> caseStudyList = waterQuality.getCaseStudyList();
caseStudyList.add(caseStudy1);
caseStudyList.add(caseStudy2);
caseStudyList.add(caseStudy3);
caseStudyList.add(caseStudy4);
waterQualityService.save(waterQuality);
如果您将WaterQuality对象分配给CaseStudy实体并保存CaseStudy，则不会在JoinTable中填充关联。
还有一个重要的事情，使用Set而不是List for Collection。如果是List，假设，你已经有100个关于waterQuality的案例研究，如果你想删除其中一个，那么它将首先删除整个案例研究然后再次添加所有案例研究，除了已删除的案例。如果您的集合不包含重复项，请使用Set。如果您的集合也包含重复项，那么请使用List with index。