I have 'Course' and 'Student' entities. They have many-to-many relation. So, i have COURSE_STUDENT(contains 'student_id' and 'course_id' columns) table. I want to register students to courses with a button.(For example; a student lists courses and click Register button to register a specific course).
When i want to create new courses, i use courseRepository and courseMapper which comes from JHipster by default.
But i don't have repository and mapper files for COURSE_STUDENT. Because it is not actually a main entity. It is created for many-to-many relation.
How can i register students to courses?
Git repo:https://github.com/canberkizgi/monolithic-mucs
My course entity:
#Entity
#Table(name = "course")
#Cache(usage = CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)
public class Course implements Serializable {
private static final long serialVersionUID = 1L;
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#NotNull
#Column(name = "title", nullable = false)
private String title;
#Column(name = "description")
private String description;
#ManyToOne
private Instructor instructor;
#ManyToMany(fetch = FetchType.EAGER)
#Cache(usage = CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)
#JoinTable(name = "course_student",
joinColumns = #JoinColumn(name="courses_id", referencedColumnName="id"),
inverseJoinColumns = #JoinColumn(name="students_id", referencedColumnName="id"))
private Set<Student> students = new HashSet<>();
Student entity:
#Entity
#Table(name = "student")
#Cache(usage = CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)
public class Student implements Serializable {
private static final long serialVersionUID = 1L;
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#OneToOne
#JoinColumn(unique = true)
private User user;
#ManyToMany(fetch = FetchType.EAGER,mappedBy = "students")
#JsonIgnore
#Cache(usage = CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)
private Set<Course> courses = new HashSet<>();
For example; Createcourse function with Mapper and Repository
#PostMapping("/courses")
#Timed
public ResponseEntity<CourseDTO> createCourse(#Valid #RequestBody CourseDTO courseDTO) throws URISyntaxException {
log.debug("REST request to save Course : {}", courseDTO);
if (courseDTO.getId() != null) {
return ResponseEntity.badRequest().headers(HeaderUtil.createFailureAlert(ENTITY_NAME, "idexists", "A new course cannot already have an ID")).body(null);
}
Course course = courseMapper.toEntity(courseDTO);
course = courseRepository.save(course);
CourseDTO result = courseMapper.toDto(course);
return ResponseEntity.created(new URI("/api/courses/" + result.getId()))
.headers(HeaderUtil.createEntityCreationAlert(ENTITY_NAME, result.getId().toString()))
.body(result);
}
The relationship is owned by the course entity. Thats because on the student side the #ManyToMany annotation has a mappedBy attribute. This means, that the database will reflect the set in the course. You need to add students to that set to save the relationship. That change needs to be done within a transaction.
That being said it would probably be best to follow DDD here. I would create a registerTo method in the student class that would take the course as a parameter. I would then call this.courses.add(course) and course.getStudents().add(this) in that method.
Related
I'm using Spring JPA and MySQL as the database. I have trouble with self-referencing its own entity.
I know the code below would do self-referencing, but it actually creates a new table to do so.
#Getter
#Entity
#NoArgsConstructor(access = AccessLevel.PROTECTED)
public class Member extends BaseTimeEntity {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "member_id")
private Long id;
#ManyToMany
#JoinColumn(name = "followings_id")
private List<Member> followings = new ArrayList<Member>();
#ManyToMany
#JoinColumn(name = "followers_id")
private List<Member> followers = new ArrayList<Member>();
#ManyToMany
#JoinColumn(name = "blocked_id")
private List<Member> blocked = new ArrayList<Member>();
...
}
Question: I'm wondering if I can do this in a single table(which would be the member table) without creating a new table to do many-to-many self-referencing.
It is possible,
Instead of using the #ManyToMany annotation, you can use the #OneToMany and #ManyToOne annotations to create the self-referencing relationship
#Getter
#Entity
#NoArgsConstructor(access = AccessLevel.PROTECTED)
public class Member extends BaseTimeEntity {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "member_id")
private Long id;
#OneToMany(mappedBy = "follower")
private List<Follow> followings = new ArrayList<>();
#OneToMany(mappedBy = "following")
private List<Follow> followers = new ArrayList<>();
#OneToMany(mappedBy = "blocker")
private List<Block> blocked = new ArrayList<>();
}
#Entity
#Getter
#NoArgsConstructor(access = AccessLevel.PROTECTED)
public class Follow {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#ManyToOne
#JoinColumn(name = "follower_id")
private Member follower;
#ManyToOne
#JoinColumn(name = "following_id")
private Member following;
}
#Entity
#Getter
#NoArgsConstructor(access = AccessLevel.PROTECTED)
public class Block {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#ManyToOne
#JoinColumn(name = "blocker_id")
private Member blocker;
#ManyToOne
#JoinColumn(name = "blocked_id")
private Member blocked;
}
Now Follow and Block entities represent the many-to-many relationships between Member entities and follower and following properties in the Follow entity represent the two sides of the many-to-many relationship, and the same is for blocked and blocker.
I have two entities with one-to-mane relationship:
#Entity
public class User implements Serializable {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "id", nullable = false)
private Long id;
#OneToMany(mappedBy = "user", cascade = CascadeType.ALL)
#JsonManagedReference
private List<RealEstate> realEstates = new ArrayList<>();
#Entity
public class RealEstate implements Serializable {
#Id
#GeneratedValue(strategy = GenerationType.SEQUENCE)
private Long id;
private String name;
#ManyToOne(cascade = CascadeType.ALL)
#JoinColumn(name = "user_id")
#JsonBackReference
private User user;
I try to save realEstate entity with this code:
realEstate.setUser(user);
realEstateService.saveRealEstate(realEstate);
And this response:
[
{
"id": 1,
"name" : "Bueno",
"user" : 1
}
]
By all I have is creating new record in user table and relation with this new ID.
What I do wrong? What I need to read about this?
You first need to save User entity record and then RealEstate entity record.
Please read this article to implement One To Many relationship. I am sure your issue will be resolved.
https://attacomsian.com/blog/spring-data-jpa-one-to-many-mapping
I have a Spring Boot project (with JHipster) with 2 JPA Entities : User and Film.
I've created an unidirectionnal ManyToMany relationship between them.
User is the owner of the relationship.
I would like to add films into favorite list of films of user (property 'favorites' in User entity).
But when I try to add a film into favorites list, nothing is persisted into table 'user_film_favorite' (join table between the 2 entities).
The mapping seems ok because when I manually enter data in this join table, I'm able to retrieve the list of films for a user.
I've looked for a lot of similar issues here but can't find where the problem is.
Entity User :
#Entity
#Table(name = "jhi_user")
#Cache(usage = CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)
public class User extends AbstractAuditingEntity implements Serializable {
private static final long serialVersionUID = 1L;
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
// Other properties
#ManyToMany(cascade = CascadeType.PERSIST)
#JoinTable(
name = "user_film_favorite",
joinColumns = { #JoinColumn(name = "user_id", referencedColumnName = "id") },
inverseJoinColumns = { #JoinColumn(name = "movie_id", referencedColumnName = "id") }
)
#Cache(usage = CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)
#BatchSize(size = 20)
private List<Film> favorites = new ArrayList<>();
Entity Film :
#Entity
#Table(name = "film")
#Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
public class Film implements Serializable {
private static final long serialVersionUID = 1L;
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "id")
private Long id;
#NotNull
#Column(name = "title", nullable = false)
private String title;
#Column(name = "plot")
private String plot;
#Column(name = "rating")
private Float rating;
FilmService :
/**
* Add one film to current user favorites.
*
* #param id the id of the film.
* #return the film saved into user favorites.
*/
#Transactional(readOnly = true)
public Optional<FilmDTO> addToFavorites(Long id) {
log.debug("Request to get Film : {}", id);
Optional<Film> filmOpt = filmRepository.findById(id);
// Get current logged user with his favorites
Optional<User> userOpt = userService.getUserWithFavorites();
if (filmOpt.isPresent() && userOpt.isPresent()) {
User user = userOpt.get();
user.getFavorites().add(filmOpt.get());
userService.save(user);
}
return filmOpt.map(filmMapper::toDto);
}
UserService :
/**
* Save a user.
*
* #param user the entity to save.
* #return the persisted entity.
*/
public User save(User user) {
log.debug("Request to save User : {}", user);
return userRepository.save(user);
}
If anyone could help me that would be really cool ! Thanks in advance :)
You are reading the User from the database so calling save will call EntityManger.merge. Therefor you also need to add
CascadeType.MERGE
to the ManyToMany mapping.
I have 2 entities that relate to one another. These 2 entities should map to each other in a Many-To-Many relationship, however, I need to also have a timestamp of their respective relationship (when it happened), so I am trying to map them using an intermediary table.
Initially, the relationship was One-To-Many, but I realized that I actually need a Many-To-Many as the business logic requires this. The structure is still the same, as in there is a Parent-Child relationship, but this time, a child should have multiple parents as well.
My BaseEntity is an abstract class that contains the fields present in all the other entities:
#Data
#MappedSuperclass
public abstract class BaseEntity {
#Id
#Min(100)
#Max(Integer.MAX_VALUE)
#GeneratedValue(strategy = GenerationType.IDENTITY)
protected Long id;
#CreationTimestamp
#Column(name = "Created_At", updatable = false)
protected ZonedDateTime createdDate;
#UpdateTimestamp
#Column(name = "Updated_At")
protected ZonedDateTime updatedDate;
#NotNull
#Column(name = "Is_Active")
protected Boolean active = true;
}
Then I have my 2 entities that should relate in a Many-To-Many style. This is my first entity and should be the parent:
#Data
#Entity
#NoArgsConstructor
#AllArgsConstructor
#Table(name = "User")
#EqualsAndHashCode(callSuper = true)
#TypeDefs( {
#TypeDef(name = "json", typeClass = JsonStringType.class),
#TypeDef(name = "jsonb", typeClass = JsonBinaryType.class)
})
public class UserEntity extends BaseEntity {
#NotBlank
#Column(name = "User_Name", columnDefinition = "varchar(255) default 'N/A'")
private String userName;
#Nullable
#JoinColumn(name = "User_Id")
#OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY)
private List<UserRole> roleList = new ArrayList<>();
}
My second entity is considered the child entity:
#Data
#Entity
#NoArgsConstructor
#AllArgsConstructor
#Table(name = "Role")
#Where(clause = "is_active = true")
#EqualsAndHashCode(callSuper = true)
public class RoleEntity extends BaseEntity {
#NotBlank
#Column(name = "Name")
private String name;
#JsonIgnore
#JoinColumn(name = "Role_Id")
#OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY)
private List<UserRole> userList = new ArrayList<>();
}
I also have my intermediary entity:
#Data
#Entity
#Getter
#NoArgsConstructor
#AllArgsConstructor
#Where(clause = "is_active = true")
#EqualsAndHashCode(callSuper = true)
#Table(name = "User_Role", uniqueConstraints= #UniqueConstraint(columnNames={"User_Id", "Role_Id"}))
public class UserRole extends BaseEntity {
// Adding #JsonIgnore here will only cause an error
#JoinColumn(name = "User_Id")
#ManyToOne(cascade = CascadeType.ALL, fetch = FetchType.LAZY, optional = false, targetEntity = UserEntity.class)
private UserEntity user;
#JoinColumn(name = "Role_Id")
#ManyToOne(cascade = CascadeType.ALL, fetch = FetchType.LAZY, optional = false, targetEntity = RoleEntity.class)
private RoleEntity role;
}
Problem now is that when I try to get my UserEntity, I get infinite recursion.
So far I've tried using #JsonIgnore, #JsonManagedReference, #JsonBackReference and it did not work or I simply don't know where or how to use them properly.
Recap:
2 entities mapped by Many-To-Many relationship;
Many-To-Many implemented using an intermediary entity and One-To-Many + Many-To-One associations;
Getting recursion when showing my UserEntity;
Update: I managed to get this fixed using a different approach described in my answer to this question.
I fixed this by implementing a Composite Key structure and just using the #JsonIgnore annotation:
#Getter
#Setter
#Embeddable
#EqualsAndHashCode
#NoArgsConstructor
#AllArgsConstructor
public class UserRoleKey implements Serializable {
#Column(name = "User_Id")
Long userId;
#Column(name = "Role_Id")
Long roleId;
}
This gets to be used in the intermediary entity, which now doesn't use my BaseEntity anymore.
#Data
#Entity
#NoArgsConstructor
#AllArgsConstructor
#Table(name = "User_Role", uniqueConstraints= #UniqueConstraint(columnNames={"User_Id", "Role_Id"}))
public class UserRole {
#JsonIgnore
#EmbeddedId
private UserRoleKey id;
#JsonIgnore
#MapsId("userId")
#JoinColumn(name = "User_Id")
#ManyToOne(optional = false, targetEntity = UserEntity.class)
private UserEntity user;
#MapsId("roleId")
#JoinColumn(name = "Role_Id")
#ManyToOne(optional = false, targetEntity = RoleEntity.class)
private RoleEntity role;
#CreationTimestamp
#Column(name = "Created_At", updatable = false)
private ZonedDateTime createdDate;
}
Now, for my two entities, I have this definition:
UserEntity class (definition of the role):
#Nullable
#OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY, mappedBy = "user", orphanRemoval = true)
private List<UserRole> roleList = new ArrayList<>();
RoleEntity class (definition of the user)
#Nullable
#JsonIgnore
#OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY, mappedBy = "role", orphanRemoval = true)
private List<UserRole> userList = new ArrayList<>();
This seems to be working and no longer returns an infinite JSON recursion.
Hibernate lazy loading is not working in my code. It loads the entire data even it is specified as FetchType LAZY
#Transactional(propagation = Propagation.NEVER)
public OrderItem getItem(String itemId) throws Exception {
OrderItem item = itemDao.find(OrderItem.class, Integer.parseInt(itemId));
if (item == null) {
throw new Exception(502, "We are unable to load item for #" + itemId);
}
return item;
}
#NotFound(action = NotFoundAction.IGNORE)
#OneToMany(cascade={CascadeType.PERSIST, CascadeType.MERGE}, fetch = FetchType.LAZY)
#JoinColumn(name = "id_order_detail")
#Fetch(value= FetchMode.JOIN)
#JsonManagedReference
private Set<OrderItemStateChangeEntry> itemStateHistory;
I could not able to lazy load the contents. There is no foreign key constraint set in the db. And its not possible to set as the many parent data not present in the system.
Can somebody help me on this
Update
Added my class and reference. But lazy load work
#Entity
#Table(name = "ps_orders")
#AttributeOverrides({
#AttributeOverride(name="id",column=#Column(name="id_order")),
#AttributeOverride(name="createTime",column=#Column(name="date_add")),
#AttributeOverride(name="updateTime",column=#Column(name="date_upd"))
})
public class Order extends BaseEntity{
#Column(name = "id_carrier")
private Integer carrier = 0;
#NotFound(action = NotFoundAction.IGNORE)
#OneToMany(fetch = FetchType.LAZY,cascade={CascadeType.PERSIST, CascadeType.MERGE}, mappedBy="order")
#Fetch(FetchMode.SELECT)
#JsonManagedReference
private Set<OrderStateChangeEntry> orderHistory;
//Getters and Setters
}
#Entity
#Table(name = "ps_order_history")
#EnableBouncerProfile
public class OrderStateChangeEntry implements java.io.Serializable{
public OrderStateChangeEntry(){}
public OrderStateChangeEntry(Order order){
this.order = order;
}
#Id
#Column(name = "id_order_history")
#GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
#ManyToOne(fetch = FetchType.EAGER)
#JoinColumn(name="id_order", nullable=false)
#JsonBackReference
private Order order;
//Getters and Setters
}
It is because of your
#Fetch(value= FetchMode.JOIN)
it disables the lazy loading ...
As you specify the fetch mode in your #OnetoMany relationship, i would say that you can simply remove that line above.