deleteById() 方法不适用于 ManyToMany 映射：Spring Boot 和 JPA

Question

我有一个场景，其中策略和县实体表之间有一个多对多映射。这是实体代码-InsurancePolicy.java-

@Entity
@Table(name = "insurance_policy")

public class InsurancePolicy {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name="policy_id")
    private long policyId;

    @Column(name="policy_name",nullable = false,unique = true)
    private String policyName;

    //Short description
    @Column(name="policy_description",nullable = false)
    private String policyDescription;

    //Long description
    @Column(name="choose_description",nullable = false)
    private String chooseDescription;


    //many policies can belong to one category
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "company_id", nullable = false)
    private Company company;

    //many policies can belong to one category
    @ManyToOne(fetch=FetchType.LAZY)
    @JoinColumn(name="category_id",nullable=false)
    private Category category;

    @ManyToMany(mappedBy = "queriedPolices",fetch = FetchType.LAZY,cascade = {CascadeType.DETACH, CascadeType.MERGE, CascadeType.PERSIST, CascadeType.REFRESH})
    private Set<User> usersQueried=new HashSet<>();

    @OneToMany(mappedBy = "policy", cascade = {CascadeType.MERGE,CascadeType.PERSIST,CascadeType.REMOVE},fetch = FetchType.LAZY)
    private Set<PolicyCounty> policyCounties = new HashSet<>();

PolicyCounty.java-（关系表）

@Data
@Entity
@Table(name="policy_county")
public class PolicyCounty {


    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name="policy_county_id")
    private long policyStateId;

    @ManyToOne
    @JoinColumn(name="policy_id")
    private InsurancePolicy policy;


    @ManyToOne
    @JoinColumn(name = "county_id")
    private County county;

    @Column(name="cost",nullable = false)
    private double cost;
}

County.java-

@Entity
@Data
@Table(name="county")
public class County {

    @Id
    @Column(name="countyid")
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long countyId;

    @Column(name="countyname",nullable = false,unique = true)
    private String countyName;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "adminId", nullable = false)
    private Admin admin;

    @OneToMany(mappedBy = "county", cascade = {CascadeType.MERGE,CascadeType.PERSIST},fetch = FetchType.LAZY)
    private Set<PolicyCounty> policyStates = new HashSet<>();

}

问题 -
我想删除InsurancePolicy实体，并删除 PolicyCounty 表中的相应实体。为此，我编写了删除方法 -

@Override
    public long deletePolicy(long policyId) {
        boolean isPresent=insurancePolicyRepository.existsById(policyId);
        if(isPresent){
            insurancePolicyRepository.deleteById(policyId);
            return insurancePolicyRepository.count();
        }
        throw new ResourceNotFoundException("Policy with id "+policyId+" not found");
    }

现在，当我尝试删除时，实体不会从表中删除。在此操作过程中我没有遇到任何异常。我怀疑问题出在与实体一起使用的级联类型上。请帮助我理解这一点。

Answer 1

在您的代码中，您应该在 InsurancePolicy 中提交一个链接到县的文件

    @ManyToMany(fetch = FetchType.LAZY, cascade = CascadeType.REMOVE)
@JoinTable(name = "policy_county",
        joinColumns = @JoinColumn(name = "insurance_policy_id"),
        inverseJoinColumns = @JoinColumn(name = "county_id"))
private Set<County> counties= new HashSet<>();

你应该像这样在县提交申请

 @ManyToMany(mappedBy = "insurance_policy", fetch = FetchType.LAZY)
private Set<InsurancePolicy > students = new HashSet<>();

如果没有的话，hibernate 现在不会有多对多关系。

但是如果你的连接表中有额外的字段，比如成本字段，当你删除一个实体时，Hibernate不会自动从连接表中删除相应的条目。相反，您需要使用本机 SQL 查询或 Hibernate 的 Criteria API 手动删除连接表中的条目。

另一种选择是将多对多关系转换为 2 个一对多关系，如下所示：

public class Student {

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;

@Column(name = "name")
private String name;

@OneToMany(mappedBy = "student", cascade = CascadeType.ALL, orphanRemoval = true)
private Set<Enrollment> enrollments = new HashSet<>();}

public class Course {

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;

@Column(name = "name")
private String name;

@OneToMany(mappedBy = "course", cascade = CascadeType.ALL, orphanRemoval = true)
private Set<Enrollment> enrollments = new HashSet<>();}


public class Enrollment {

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;

@ManyToOne(fetch = FetchType.LAZY)
private Student student;

@ManyToOne(fetch = FetchType.LAZY)
private Course course;

@Column(name = "cost")
private BigDecimal cost;}

在上面的示例中，“学生”实体与“入学”实体具有一对多关系，“课程”实体也与“入学”实体具有一对多关系。这两种关系都使用 CascadeType.ALL 选项设置级联删除，这将导致在删除“学生”或“课程”实体时自动删除关联的“注册”实体。orphanRemoval 属性设置为 true，这将删除不再与“学生”或“课程”实体关联的任何“注册”实体。

设置级联删除后，您可以删除“学生”或“课程”实体，并且所有关联的“注册”实体将自动删除：