Spring JPA Saving Parent Object is not Saving Child Object-CodePudding

I have a csv file that has a list of employees and projects information (each employee having multiple projects). I upload the file, parse the csv and build a parent-child relationship -> Employee and Projects respectively and save it to Database.

Below is my Employee Entity class (I tried the commented part but no luck)

@Entity
@Table(name = "employees")
@Data
@NoArgsConstructor
@AllArgsConstructor
public class Employee {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private long id;
    @NotNull
    private String name;
    @NotNull
    private String empId;
    @NotNull
    private String department;

    //@OneToMany(fetch = FetchType.LAZY, mappedBy = "transcript", cascade = CascadeType.ALL) //tried didn't work
    @OneToMany(fetch = FetchType.LAZY, cascade = CascadeType.ALL, mappedBy = "employee", orphanRemoval = true)
    private List<Project> projects;

    public Employee(String name, String empId, String department) {
        this.name = name;
        this.empId = empId;
        this.department = department;
    }
}

Below is my Project Entity class

@Entity
@Table(name = "projects")
@Data
@NoArgsConstructor
@AllArgsConstructor
public class Project {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private long id;

    private String projectName;
    private String projectCode;
        private Instant projectStartDate;

    @ManyToOne(fetch = FetchType.EAGER, cascade = CascadeType.PERSIST)
    @JoinColumn(name = "employee_id", nullable = false)
    @JsonBackReference
    private Employee employee;

    public Project(String name, String code, Instant time) {
        this.projectName = name;
        this.projectCode = code;
        this.projectStartDate = time;
    }
}

This is where I am trying to save my Employee object:

@Transactional
    public void uploadEmployees(MultipartFile file) {
        try {
//calls csv helper that does all the parsing and brings into Employee model object format
            Set<Employess> employees = CSVHelper.csvToEmployess(file.getInputStream(), "2");
            employeeRepository.saveAll(employees);
            System.out.println("I processed all the records of cdv into java");
        } catch (IOException e) {
            throw new RuntimeException(e);
        }catch (Exception e ){
            throw new RuntimeException(e.getMessage());
        }
    }

This above method throws :

2022-09-11T22:30:08.438-05:00 ERROR 63321 --- [nio-8086-exec-5] o.h.engine.jdbc.spi.SqlExceptionHelper   : ERROR: null value in column "employee_id" of relation "projects" violates not-null constraint
  Detail: Failing row contains (6, p1, 123, 0184-06-08T01:07:47Z, null).

If I change the id generation type to @GeneratedValue(strategy = GenerationType.AUTO) : I get the below exception:

2022-09-12T00:55:09.465-05:00  WARN 73014 --- [nio-8086-exec-1] o.h.engine.jdbc.spi.SqlExceptionHelper   : SQL Error: 0, SQLState: 42P01
2022-09-12T00:55:09.465-05:00 ERROR 73014 --- [nio-8086-exec-1] o.h.engine.jdbc.spi.SqlExceptionHelper   : ERROR: relation "hibernate_sequence" does not exist
  Position: 17
org.springframework.dao.InvalidDataAccessResourceUsageException: could not extract ResultSet; SQL [n/a]; nested exception is org.hibernate.exception.SQLGrammarException: could not extract ResultSet
    at org.springframework.orm.jpa.vendor.HibernateJpaDialect.convertHibernateAccessException(HibernateJpaDialect.java:259)
    at org.springframework.orm.jpa.vendor.HibernateJpaDialect.translateExceptionIfPossible(HibernateJpaDialect.java:233)
    at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.translateExceptionIfPossible(AbstractEntityManagerFactoryBean.java:551)
    at org.springframework.dao.support.ChainedPersistenceExceptionTranslator.translateExceptionIfPossible(ChainedPersistenceExceptionTranslator.java:61)
    at org.springframework.dao.support.DataAccessUtils.translateIfNecessary(DataAccessUtils.java:242)
    at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:152)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
    at org.springframework.data.jpa.repository.support.CrudMethodMetadataPostProcessor$CrudMethodMetadataPopulatingMethodInterceptor.invoke(CrudMethodMetadataPostProcessor.java:174)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
    at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:97)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
    at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:215)
    at jdk.proxy2/jdk.proxy2.$Proxy133.saveAll(Unknown Source)

Just before executing saveAll method,I tried looking how my employees list looks like using debugger and it looks as below :

  Employee(id=0, name="test", empId="4511504557911789", department="JJ967W"
        projects=[
                Project(id=0, projectName="p1", projectCode="123", projectStartDate="0184-06-08T01:07:47Z", employee=null),
                Project(id=0, projectName="p2", projectCode="345", projectStartDate="0184-06-08T01:07:47Z", employee=null)
                ]
        )

I am thinking employee=null makes sense because it was not saved to DB yet.

Please help me out in what I am missing here that is causing this to break. Thank you very much for taking time in providng help.

CodePudding user response：

Further to comment by @M.Deinum - declare a method like this in your Employee class and use it to add a project to an employee ensuring the bidirectional relationship is kept in sync

    public void addProject(Project project) {
        if (projects == null) {
            projects = new ArrayList<>();
        }
        project.setEmployee(this);
        projects.add(project);
    }

CodePudding user response：

I am thinking employee=null makes sense because it was not saved to DB yet.

This is wrong. If you save an item with bi-directional relationship then you cannot have a case when an orphan Project exists without an Employee. So before calling any CrudRepository.save*() you must make sure that all projects reference some Employee.

Often in such cases when you add projects to employee you do it like:

// method of Employee class
public void addAll(Projects projects) {
  for (Project : projects) {
    project.setEmployee(this);
  }
  this.projects.addAll(projects);
}