I have an existing database modeled the following way:
Student - SchoolId(PK), StudentId(PK), StudentName
Teacher - SchoolId(PK), TeacherId(PK), TeacherName
Student_Teacher - SchoolId(PK), StudentId(PK), TeacherId(PK)
Foreign key references exist from Student_Teacher to respective entities.
Now I am creating hibernate entities for this existing database. And I am running into weird issues creating Many-to-Many mapping from Student to Teacher.
#Entity
#Table(name = "Student")
public class Student {
#EmbeddableId
private StudentPK itemId;
#Column(name="StudentName")
private String studentName;
#ManyToMany(cascade = CascadeType.ALL)
#JoinTable(name="Student_Teacher", joinColumns={#JoinColumn(name="SchoolId", referencedColumnName="SchoolId"),#JoinColumn(name="StudentId", referencedColumnName="StudentId")}, inverseJoinColumns={#JoinColumn(name="SchoolId", referencedColumnName="SchoolId"),#JoinColumn(name="TeacherId", referencedColumnName="TeacherId")})
private List<Teacher> attachments=new ArrayList<Teacher>();
}
The above code compains about some duplicate SchoolId reference.
Any ideas?
As I see that there is an issue in your mapping of entities, It should be as follows
school - school_id(PK), school_name
student - student_id(PK) , student_name, fk_school_id(FK),
teacher - teacher_id(PK), teacher_name , fk_school_id(FK)
*student_teacher* - student_teacher_id(PK), fk_student_id(FK), fk_teacher_id(FK)
and Entity clasess as follows
School Entity
#Entity
#Table(name = "school")
public class School {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column (name = "school_id")
private int Id;
#Column(name="school_name")
private String schoolName;
#OneToMany(fetch = FetchType.LAZY, mappedBy = "school")
private Set<Student> students = new HashSet<Student>
#OneToMany(fetch = FetchType.LAZY, mappedBy = "school")
private Set<Teacher> teachers = new HashSet<Teacher>
}
Student Entity
#Entity
#Table(name = "student")
public class Student {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column (name = "student_id")
private int Id;
#Column(name="student_name")
private String studentName;
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "school_id", nullable = false)
private School school;
#ManyToMany(cascade = CascadeType.ALL)
#JoinTable(name = "student_teacher", joinColumns = {#JoinColumn(name = "fk_student_id") }, inverseJoinColumns = { #JoinColumn(name = "fk_teacher_id") })
private List<Teacher> teachers = new ArrayList<Teacher>();
}
Teacher Entity
#Entity
#Table(name = "teacher")
public class Teacher {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column (name = "teacher_id")
private int Id;
#Column(name="teacher_name")
private String name;
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "school_id", nullable = false)
private School school;
#ManyToMany(cascade = CascadeType.ALL)
#JoinTable(name = "student_teacher", joinColumns = {#JoinColumn(name = "fk_teacher_id") }, inverseJoinColumns = { #JoinColumn(name = "fk_student_id") })
private List<Student> students =new ArrayList<Student>();
}
hope this will solve this problem..
as you have declare 'SchoolId' as PK in Student_Teacher table it will not allow you to add duplicate entry for SchoolId field for Student_Teacher table and this is not the case. thus the above relationship will gives duplicate SchoolId reference. when you are going to add two different students from same school into Student_Teacher table..
Did you define the various PKs per entity as compound keys, as i note that you use multiple PKs per entity. Is there any constraint why you can't use a sole PK per entity and just use a relation table to bind the 2 entities?
Related
I have two Entities in my Spring-Boot mongoDb Application:
Course.java
#Entity
#Table(name = "students")
public class Course {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
Long id;
String title;
#Enumerated(EnumType.STRING)
OptionCourse optionCourse;
private double fee;
#ManyToMany(fetch = FetchType.LAZY,
cascade = {
CascadeType.PERSIST,
CascadeType.MERGE
},
mappedBy = "courses")
private Set<Student> student = new HashSet<>();
}
and
Student.java
Entity
#Table(name = "students")
public class Student {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
Long id;
int age;
String department;
#ManyToMany(fetch = FetchType.LAZY,
cascade = {
CascadeType.PERSIST,
CascadeType.MERGE
})
#JoinTable(name = "student_courses",
joinColumns = { #JoinColumn(name = "student_id") },
inverseJoinColumns = { #JoinColumn(name = "course_id") })
private Set<Course> courses = new HashSet<>();
}
for my mongoDb database:
I want to realise a Many-to-Many-Relationship between both Entities. Every courses should be able to assign multiple student.
How can i replace my annotations (#Entity, #Table,#Id, #Enumerated(EnumType.STRING) and #ManyToMany(fetch = FetchType.LAZY,...)) in my entities. I use spring-boot-starter-data-mongodb in my maven dependencies
I have this many-many relationship between students and courses as in following JPA models
#Entity(name = "course_result")
public class CourseResult {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private BigInteger id;
#ManyToOne(targetEntity = Student.class, cascade = CascadeType.ALL)
#JoinColumn(name = "student_id")
private Student student;
#ManyToOne(targetEntity = Course.class, cascade = CascadeType.ALL)
#JoinColumn(name = "course_id", referencedColumnName = "id")
private Course course;
private float grade;
}
#Entity
public class Course {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private BigInteger id;
private String courseName;
private String description;
#OneToMany(mappedBy = "course", fetch = FetchType.EAGER)
private Set<CourseResult> courseResult;
}
#Entity
public class Student {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private BigInteger id;
private String studentName;
private String studentClass;
#OneToMany(mappedBy = "student", fetch = FetchType.EAGER)
private Set<CourseResult> courseResult;
}
When persisting a CourseResult, I want a new course/student would be created if it not yet exists otherwise they'll be updated only. That's why I set the cascade type to ALL. T
However, it always throws an exception when I try to persist a new CourseResult with existing Student and Course, say both with Id = 1
Student student = studentRepo.findById(BigInteger.ONE).get();
Course course = courseRepo.findById(BigInteger.ONE).get();
CourseResult courseResult = new CourseResult()
.setCourse(course)
.setStudent(student)
.setGrade(1.5F);
courseResultRepository.save(courseResult);
org.springframework.dao.InvalidDataAccessApiUsageException: detached entity passed to persist: org.example.domain.Course; nested exception is org.hibernate.PersistentObjectException: detached entity passed to persist: org.example.domain.Course
Do you have any idea why?
TIA,
There are a couple of approaches you could try
Is there a Transaction around your Code ? It is not shown in your example. Ensure that the import is using the spring Transaction.
Try adding the courseResult to the other enities
Student student = studentRepo.findById(BigInteger.ONE).get();
Course course = courseRepo.findById(BigInteger.ONE).get();
student.getCourseResult().add()
CourseResult courseResult = new CourseResult()
.setGrade(1.5F);
student.getCourseResult().add(courseResult);
course.getCourseResult().add(courseResult);
Try saving the CourseResult before adding it to the Objects. That way it might then be recognized by Hibernate as a managed entity
Student student = studentRepo.findById(BigInteger.ONE).get();
Course course = courseRepo.findById(BigInteger.ONE).get();
student.getCourseResult().add()
CourseResult courseResult = new CourseResult()
.setGrade(1.5F);
courseResultRepository.save(courseResult);
courseResult.setStudent(student);
courseResult.setCourse(course);
courseResultRepository.save(courseResult);
Try adding
cascade = CascadeType.ALL
to
#OneToMany(mappedBy = "course", fetch = FetchType.EAGER, cascade = CascadeType.ALL)
private Set<CourseResult> courseResult;
and
#OneToMany(mappedBy = "student", fetch = FetchType.EAGER, cascade = CascadeType.ALL)
private Set<CourseResult> courseResult;
Try using cascade= CascadeTyp.Mergeinsdead of cascade= CascadeTyp.ALL (PersistentObjectException: detached entity passed to persist thrown by JPA and Hibernate)
In the following example, there are 3 entities which have relations e.g. #ManyToMany, #OneToMany and #ManyToOne:
Student:
#Entity
#Data
public class Student {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
Long id;
private String name;
#JsonIgnore
#ManyToMany(mappedBy = "students")
private Set<Subject> subjects = new HashSet<>();
}
Subject:
#Entity
#Data
public class Subject {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
Long id;
private String name;
#ManyToMany
#JoinTable(
name = "subject_student",
joinColumns = #JoinColumn(name = "subject_id"),
inverseJoinColumns = #JoinColumn(name = "student_id")
)
Set<Student> students = new HashSet<>();
#ManyToOne(cascade = CascadeType.ALL)
#JoinColumn(name = "teacher_id", referencedColumnName = "id")
private Teacher teacher;
}
Teacher:
#Entity
#Data
public class Teacher {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String name;
#JsonIgnore
#OneToMany(mappedBy = "teacher")
private Set<Subject> subjects;
}
1. In the subject entity, I tried to remove #JoinColumn and the related entities are connected as the example above:
#ManyToMany
#JoinTable(name="subject_student")
public Set<Student> students = new HashSet<>();
#ManyToOne(cascade = CascadeType.ALL)
private Teacher teacher;
So, if we want to use subject_id - student_id pair in subject_student table and use teacher_id in subject table as it is created in the example, can I use my simplified notation by removing #JoinColumn? Because, if there is not a special case, I think it is redundant to verbose notation of relations.
2. When I use the second approach, the columns are created as plural e.g. subjects_id - students_id in subject_student. So, can I prevent this and create them as in the previous example by using my approach?
I am using Hibernate/JPA, and have 3 tables:
Contact
pk contact_id
fk member_id
Employee
pk employee_id
fk member_id
Members
pk member_id
I have:
#Entity(name = "Contact" )
public class Contact implements Serializable {
#Id
#SequenceGenerator(allocationSize = 1, name = "contact_sequence", sequenceName = "contact_ids")
#GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "contact_sequence")
private java.lang.Long contact_id;
#OneToOne(cascade = CascadeType.ALL, targetEntity = Members.class)
#JoinColumn(name = "member_id")
private Members member;
#OneToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "member", referencedColumnName = "member")
private Employee employee;
and
#Entity(name = "Employee")
public class Employee implements Serializable {
#Id
#SequenceGenerator(allocationSize = 1, name = "employee_sequence", sequenceName = "employee_ids")
#GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "employee_sequence")
private java.lang.Long employee_id;
and
#Entity(name = "Members")
#Table(name = "Members")
public class Members implements Serializable {
#Id
#SequenceGenerator(allocationSize = 1, name = "members_sequence", sequenceName = "member_ids")
#GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "members_sequence")
private java.lang.Long member_id;
My problem is with the Contact entity private Employee employee;. When I start my Jboss server:
StartException in service jboss.persistenceunit.
Question
How do I annotate the private Employee employee; on the Contact entity?
Thank you
You are almost properly defining the private Members member;, so is there a reason for not doing the same for private Employee employee; ?
Like :
#OneToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "employee", referencedColumnName = "employee_id")
private Employee employee;
Also a simple link, just to cross-check the overall #JoinColumn functionality
===EDIT===
As it looks there is indeed a data structure issue as from the first place the relation is ManyToOne,
If you could try the below example :
//Employee
#ManyToOne(fetch = FetchType.EAGER)
#JoinColumn(name = "contact_id", referencedColumnName = "contact_id")
private Contact contact;
//Contact
#OneToMany(fetch = FetchType.LAZY, mappedBy = "employee_id")
private List<Employee> employees = new ArrayList<>();
Then by selecting the contact.getEmployees() should do the trick
I have two classes Student and Subject:
Student
#Entity
#Table(name = "students")
public class Student {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "id")
private int id;
#Column(name = "full_name")
private String fullName;
#ManyToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL, mappedBy = "students")
private Set<Subject> subject;
//Getters & setters
}
Subject
#Entity
#Table(name = "subjects")
public class Subject {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "id")
private int id;
#Column(name = "subject_name")
private String name;
#ManyToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
private Set<Student> students;
//Getters & setters
}
When I am trying to save a student registered with more than one subject, I am not getting any records in the JoinTable.
My code for saving the entiers:
Subject subject = new Subject();
subject.setName("JAVA");
Subject subject2 = new Subject();
subject2.setName("C");
Subject subject3 = new Subject();
subject3.setName("C++");
Student student = new Student();
student.setFullName("dibya");
Set<Subject> subjects = new HashSet<>();
subjects.add(subject2);
subjects.add(subject);
subjects.add(subject3);
student.setSubject(subjects);
session.saveOrUpdate(student);
Please tell me where am I doing wrong.
Found the solution to my problem.
It was not with the configuration. With just mappedBy attribute ManyToMany relationship can be accomplished.
In my program I have added session.saveOrUpdate(subject); after saving saving the students.
This solved my problem. :)
A many-to-many relationship is modeled as a join table. This is a table with 2 columns, both are foreign keys to the tables of the repationship (Student and Subject in your case).
In Hibernate if you use #ManyToMany you need to either #JoinTable or #JoinColumn to define the relationship. Once it's done your update will work.
See
http://docs.jboss.org/hibernate/orm/4.3/manual/en-US/html/ch07.html
and
http://www.dzone.com/tutorials/java/hibernate/hibernate-example/hibernate-mapping-many-to-many-using-annotations-1.html
EDIT:
Applied to your code it should look like (UNTESTED):
In Student:
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "student_id")
private int id;
....
#ManyToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
#JoinTable(name = "students_subject", joinColumns = { #JoinColumn(name = "student_id") }, inverseJoinColumns = { #JoinColumn(name = "subject_id") })
private Set<Subject> subject;
In Subject
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "subject_id")
private int id;
...
#ManyToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
#JoinTable(name = "students_subject", joinColumns = { #JoinColumn(name = "subject_id") }, inverseJoinColumns = { #JoinColumn(name = "student_id") })
private Set<Student> students;
Your case might be falling into mixing JPA and Hibernate cascading. Try annotate your #ManyToMany with additional
#Cascade({CascadeType.SAVE_UPDATE})
you can also consult this two links to check if this is really your case:
Confusion between JPA and Hibernate cascading
http://www.mkyong.com/hibernate/cascade-jpa-hibernate-annotation-common-mistake/