Imagine a library. The library contains books. Each book is a separate entity. There are readers (peoples) in the library. When a person takes a book to read, I indicate that this book was read by people.
The subject area has been redesigned for the question, don't swear off the logic
I can't understand how to make a Criteria query to see if Set<People> peoples contains people of a certain People
#Entity
#Table(name = "book")
public class Book{
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
Long id;
#Column
#NotEmpty
String title;
#ManyToMany(cascade = {
CascadeType.PERSIST,
CascadeType.MERGE
})
#JoinTable(name = "people_read",
joinColumns = #JoinColumn(name = "id_people"),
inverseJoinColumns = #JoinColumn(name = "id_book"))
Set<People> peoples = new HashSet<>();
}
#Getter
#Setter
#Entity
#Table(name = "people")
public class People {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
Long id;
#Column
#NotEmpty
String name;
#ManyToMany(mappedBy = "peoples")
Set<Book> books = new HashSet<>();
}
What I'm trying to do:
Path<Object> peoples = root.get("peoples");
(Predicate) query.where(peoples .get("id").in(cb.parameter(Set.class, "3"))); //3 is for example the id of people whom I want to know if they have read the book
I don't know how to write this query checking the Id only, but if you have an Instance of People the query would look like this
query.where(cb.isMember(peopleInstance, root.get("peoples"))
Related
I am working on a springboot application. I have 2 entity classes, Group and User. I also have #ManyToMany relationship defined in the Group class (Owning entity), and also in the User class, so that I can fetch all the groups a user belongs to. Unfortunately, I can't create a new group or a new user due to the following error;
{
"timestamp": "2022-09-09T20:29:22.606+00:00",
"status": 415,
"error": "Unsupported Media Type",
"message": "Content type 'application/json;charset=UTF-8' not supported"
}
When I try to fetch all groups a user belongs to by calling user.get().getGroups(); I get a a stack overflow error
Note: Currently I have #JsonManagedReference and #JsonBackReference in Group and User classes respectively. I also tried adding #JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, property = "id") on both classes, but this did not work either. Adding value parameter to #JsonManagedReference and #JsonBackReference as demonstrated below did not work either. What am I doing wrong? What am I missing?
This is my Group entity class
#Table(name = "`group`") // <- group is a reserved keyword in SQL
public class Group {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
#JsonView(Views.Public.class)
private String name;
private Integer maximumMembers;
#ManyToMany(fetch = FetchType.LAZY, cascade = {CascadeType.ALL})
#JoinTable(name = "group_user", joinColumns = #JoinColumn(name = "group_id"), inverseJoinColumns = #JoinColumn(name = "user_id"))
#JsonView(Views.Public.class)
#JsonManagedReference(value = "group-member")
private Set<User> groupMembers;
}
This is my User entity class
public class User {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
#JsonView(Views.Public.class)
private Long id;
#JsonView(Views.Public.class)
private String nickname;
#JsonView(Views.Public.class)
private String username; // <- Unique user's phone number
private String password;
#ElementCollection(targetClass = ApplicationUserRole.class)
#CollectionTable(name = "user_role", joinColumns = #JoinColumn(name = "user_id"))
#Enumerated(EnumType.STRING)
#Column(name = "role")
private Set<ApplicationUserRole> roles;
#ManyToMany(mappedBy = "groupMembers", fetch = FetchType.LAZY, targetEntity = Group.class)
#JsonBackReference(value = "user-group")
private Set<Group> groups;
}
Minimal, Reproducible Example https://github.com/Java-Techie-jt/JPA-ManyToMany
I found a permanent solution for this problem. For anyone else facing a similar problem, This is what I found. First, my entity classes had #Data Lombok annotation. I removed this because the #Data annotation has a tendency of almost always loading collections even if you have FetchType.LAZY.
You can read more about why you should't annotate your entity class with #Data here https://www.jpa-buddy.com/blog/lombok-and-jpa-what-may-go-wrong/
After removing this annotation, I removed #JsonManagedReference and #JsonBackReference from both sides of the relationship(both entities). I then added #Jsonignore to the referencing side only(User class). This solves 2 things
Creating a group with a list of users works fine
Adding a list of users to a group works fine.
After this, we are left with one last problem. When we try to read a user from the api, we get a user without the associated list of groups they belong to, because we have #JsonIgnore on the user list. To solve this, I made the controller return a new object. So after fetching the user from my service, I map it to a new data transfer object, the I return this object in the controller.
From here I used #JsonView to filter my responses.
This is how my classes look, notice there is no #Data in annotations.
Group
#Builder
#Entity
#NoArgsConstructor
#AllArgsConstructor
#ToString
#Getter
#Setter
#Table(name = "`group`") // <- group is a reserved keyword in SQL
public class Group {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
private String name;
private Integer maximumMembers;
#ManyToMany(fetch = FetchType.EAGER,
cascade = {CascadeType.MERGE, CascadeType.MERGE, CascadeType.PERSIST, CascadeType.REFRESH})
#JoinTable(name = "group_user",
joinColumns = #JoinColumn(name = "group_id"),
inverseJoinColumns = #JoinColumn(name = "user_id"))
#JsonView(UserViews.PublicUserDetails.class)
private Set<User> groupMembers = new HashSet<>();
}
User
#Builder
#Entity
#NoArgsConstructor
#AllArgsConstructor
#ToString
#Getter
#Setter
public class User {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
#JsonView(UserViews.PublicUserDetails.class)
private Long id;
#JsonView(UserViews.PublicUserDetails.class)
private String nickname;
#JsonView(UserViews.PublicUserDetails.class)
private String username; // <- Unique user's phone number
private String password;
#ElementCollection(targetClass = ApplicationUserRole.class)
#CollectionTable(name = "user_role", joinColumns = #JoinColumn(name = "user_id"))
#Enumerated(EnumType.STRING)
#Column(name = "role")
#JsonView(UserViews.PublicUserDetails.class)
private Set<ApplicationUserRole> roles;
#JsonIgnore
#ManyToMany(mappedBy = "groupMembers", fetch = FetchType.LAZY, targetEntity = Group.class)
private Set<Group> groups = new HashSet<>();
}
Method fetching user in user controller
#GetMapping("/get-groups")
public ResponseEntity<UserRequestResponseDTO> getWithGroups(#RequestParam(name = "userId") Long userId) {
User user = userService.getWithGroups(userId);
UserRequestResponseDTO response = UserRequestResponseDTO.builder()
.nickname(user.getNickname())
.username(user.getUsername())
.groups(user.getGroups())
.build();
return ResponseEntity.ok().body(response);
}
Hopefully this helps someone💁
I am new in Hibernate and just look at several examples and started to make some practice.
Here in the 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;
}
My questions are:
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 know only basics of DB and JPA/Hibernate. I have to manage a User table, where a user can have many roles. The roles are contained in a catalog table which in my User formulary i do not pretend to manage/modify, i just need the catalog values as a reference to add or delete to my user.
I think the best approach would be to create a relationship table between User and Role to hold the users and their roles 'User_Roles' (unless there is a more efficient approach).
I am not allowed to modify the Role entity since it is used for different purposes in a lot of other areas of my app that are independent of the User table.
I've seen a lot of examples but I still do not know which one exactly aplies to my specific needs. How can I map my User and its roles in a sigle Entity with JPA and Hibernate?
Maybe the next image describes better what I want:
Thank you very much in advance for your answers.
In your case you have to use #ManyToMany to associate both tables.
That should look at this:
#Entity
#Table(name = "User")
public class User {
...
#ManyToMany
#JoinTable(name = "User_Roles", joinColumn = "id_person")
private Set<Role> roles = new HashSet<>;
}
#Entity
#Table(name = "Role")
public class Role {
...
#ManyToMany(mappedBy = "roles")
private Set<User> users = new HashSet<>;
}
What you're describing is a one-to-many relationship but it's between User and the joining table - User_Roles. Since there is not much you can do to avoid the joining table, the best thing would be to use #ManyToMany with #JoinTable annotations to map the relationship. Remember to use Set instead of List. You don't need an entity for the joinint table then.
You can find a discussion about this topic in this blog post.
As per your above screen, what I understood user can be assigned more than 1 role.
i.e. 1 user can be mapped to multiple role and 1 role can be mapped to multiple users.
Hence relationship between user and role is many to many.
many to many relationship can be achieved using third table which is called mapping table.
so , we have following tables in your example :-
user
user_roles
role
#Entity
#Table(name = "user")
#JsonInclude(JsonInclude.Include.NON_NULL)
public class User {
#Id
#SequenceGenerator(name = "USER_ID_GENERATOR", sequenceName = "USER_SEQ",
allocationSize = 1)
#GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "USER_ID_GENERATOR")
#Column(name = "user_id")
private Long userId;
#OneToOne
#JoinColumn(name = "persion_id")
private person person;`
enter code
here`
#Basic
#Column(name = "date")
private Date date;
#Basic
#Column(name = "observations")
private String observations;
#Basic
#Column(name = "text")
private String text;
#JsonIgnore
#OneToMany(mappedBy = "user", cascade = CascadeType.ALL)
private List<UserRoles> users = new ArrayList<>();
}
#Entity
#Table(name = "role")
#JsonInclude(JsonInclude.Include.NON_NULL)
public class Role {
#Id
#SequenceGenerator(name = "ROLE_ID_GENERATOR", sequenceName = "ROLE_SEQ",
allocationSize = 1)
#GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "ROLE_ID_GENERATOR")
#Column(name = "role_id")
private Long roleId;
#Basic
#Column(name = "id1")
private Long idOne;
#Basic
#Column(name = "id1")
private Long idTwo;
#Basic
#Column(name = "id1")
private Long idThree;
#Basic
#Column(name = "text")
private String text;
#JsonIgnore
#OneToMany(mappedBy = "role", cascade = CascadeType.ALL)
private List<UserRoles> users = new ArrayList<>();
}
#Entity
#Getter
#Setter
#Table(name = "user_roles")
#JsonInclude(JsonInclude.Include.NON_NULL)
#Audited
public class UserRoles {
private static final long serialVersionUID = 1L;
#EmbeddedId
UserRolesKey userRoleId;
#JsonIgnore
#ManyToOne(fetch = FetchType.LAZY)
#MapsId("role_id")
#JoinColumn(name = "role_id")
Roles role;
#JsonIgnore
#ManyToOne(fetch = FetchType.LAZY)
#MapsId("user_id")
#JoinColumn(user_id)
User user;
#PrePersist
private void prePersist() {
super.onPrePersist();
if (this.getId() == null) {
UserRolesKey mapKey = new UserRolesKey();
mapKey.setRoleId(this.getRole().getRoleId());
mapKey.setUserRoleId(this.getUser().getUserId());
this.setId(mapKey);
}
}
}
While saving you just need to populate user entity with all the uaerRoles mapping entity and persist it. jpa will save all the details.
while updating role assign to user you need to fetch the user entity and update the mapping by adding new userRoles entity and nullifying the while is going to be removed.
I'm writing an API using Spring Boot and Hibernate where my persisted entity objects are also used as DTOs sent to and from the client. This is a simplified version of a typical entity I use:
#Entity
#Table(name = "STUDENT")
public class Student {
#Id
#GeneratedValue
#Column(name = "ID")
private Long id;
#ElementCollection
#CollectionTable(name = "GROUP_STUDENT",
joinColumns = #JoinColumn(name = "GROUP_ID"))
#Column(name="STUDENT_ID")
private Set<Long> groupIds;
#JsonIgnore
#ManyToMany(fetch = FetchType.LAZY)
#JoinTable(name="GROUP_STUDENT",
joinColumns = #JoinColumn(name="GROUP_ID"),
inverseJoinColumns = #JoinColumn(name="STUDENT_ID")
)
private Set<Group> groups = new HashSet<>();
// getters and setters
}
and this is the associated class:
#Entity
#Table(name = "GROUP")
public class Group {
#Id
#GeneratedValue
#Column(name = "ID")
private Long id;
#JsonIgnore
#ManyToMany(fetch = FetchType.LAZY, mappedBy = "groups")
private Set<Student> students = new HashSet<>();
// getters and setters
}
As you can see, there is a #ManyToMany association between Student and Group.
Since I send objects like these to the client, I choose to send only the id's of the associations and not the associations themselves. I've solved this using this answer and it works as expected.
The problem is this. When hibernate tries to persist a Student object, it inserts the groups as expected, but it also tries to insert the groupIds into the mapping table GROUP_STUDENT. This will of course fail because of the unique constraint of the mapping table composite id. And it isn't possible to mark the groupIds as insertable = false since it is an #ElementCollection. And I don't think I can use #Formula since I require a Set and not a reduced value.
This can of course be solved by always emptying either the groups of the groupIds before saving or persisting such an entity, but this is extremely risky and easy to forget.
So what I want is basically a read only groupIds in the Student class that loads the data from the GROUP_STUDENT mapping table. Is this possible? I'm grateful for any suggestions and glad to ellaborate on the question if it seems unclear.
I've managed to solve this by making the id-collection #Transient and populating it using #PostLoad:
#Entity
#Table(name = "STUDENT")
public class Student {
#PostLoad
private void postLoad() {
groupIds = groups.stream().map(Group::getId).collect(Collectors.toSet());
}
#Id
#GeneratedValue
#Column(name = "ID")
private Long id;
#Transient
private Set<Long> groupIds;
#JsonIgnore
#ManyToMany(fetch = FetchType.LAZY)
#JoinTable(name="GROUP_STUDENT",
joinColumns = #JoinColumn(name="GROUP_ID"),
inverseJoinColumns = #JoinColumn(name="STUDENT_ID")
)
private Set<Group> groups = new HashSet<>();
// getters and setters
}
I'm trying to figure out what I'm doing wrong with this, but I'm learning hibernate annotations and creating a simple library system. Basically, a book gets checked out by a person, and eventually checked in. Here's how I have it configured:
#Entity
#Table
public class Book {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#Column(nullable = false, unique = true)
private long barcode;
#Column(nullable = false)
private String name;
#OneToMany
#JoinTable(name = "checkoutsession", joinColumns = { #JoinColumn(name = "book") }, inverseJoinColumns = { #JoinColumn(name = "id")})
private List<CheckOutSession> checkOutSessions;
}
#Entity
public class User {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private long id;
#Column(nullable = false, unique = true)
private long barcode;
#Column(name = "firstname")
private String firstName;
#Column(name = "lastname")
private String lastName;
#OneToMany
#JoinTable(name = "checkoutsession", joinColumns = { #JoinColumn(name = "user") }, inverseJoinColumns = { #JoinColumn(name = "id")})
private List<CheckOutSession> checkOutSessions;
}
#Entity
#Table(name = "checkoutsession", uniqueConstraints = {#UniqueConstraint(columnNames={"book", "checkIn"})})
public class CheckOutSession {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private long id;
#ManyToOne
#JoinColumn(name="book", nullable=false)
private Book book;
#ManyToOne
#JoinColumn(name="user", nullable=false)
private User user;
#Column(nullable = false)
private java.sql.Timestamp checkOut;
#Column
private java.sql.Timestamp checkIn;
}
I can't figure out for the life of me what I've got configured incorrectly.
[EDIT]
when I try to pull a book it is selecting everything from checkoutsession join checkoutsession join user and dies saying "Unknown column checkoutsess1_.check_in in 'field list';
[EDIT2]
A little more context, I have a BookDAO that extends JpaRepository and when I call findAll() is what's creating that query.
[EDIT3]
Rest Class:
#RestController
#RequestMapping("rest/books")
public class BookController {
#RequestMapping(method = RequestMethod.GET)
public List findBooks() {
return bookService.getAllBooks();
}
}
Service:
#Component
public class BookService {
private BookDao bookDao;
public List getAllBooks() {
return bookDao.findAll();
}
#Autowired
public void setBookDao(BookDao bookDao) {
this.bookDao = bookDao;
}
}
DAO:
public interface BookDao extends JpaRepository<Book, Long> {
}
Thanks for any help!
If I run your code and make JPA generate tables based on the entities it seems to work (at least, it does run).
However, your mappings appear to be odd to me, more specifically the #JoinTable annotation. The #JoinTable annotation is commonly used when you have a join table (eg. checkoutSession in your case), but you don't want to map it because it contains no useful information except the links between those two tables.
In that case, you use the #JoinTable annotation as following:
#ManyToMany
#JoinTable(
name = "checkoutsession", // Name of the join table
joinColumns = #JoinColumn(name = "book"), // The column name in checkoutsession that links to book
inverseJoinColumns = #JoinColumn(name = "user") // The column name in checkoutsession that links to user
)
private List<User> users;
So in this case, you can directly link the Book and User entity without having to create the CheckoutSession entity.
However, in your case your join table also contains two timestamps, if you need those in your application, then you don't have to use #JoinTable but simply use #JoinColumn to link them, for example:
#OneToMany(mappedBy = "book") // The field name in CheckoutSession that links to book
private List<CheckoutSession> checkOutSessions;
This is what you should have in your Book entity. Be aware that in this case we're talking about field names not about column names. You have to enter the name of the field in CheckoutSession that maps back to the Book entity.
For more information about the #JoinTable annotation I recommend you to read this answer: JPA "#JoinTable" annotation or this article.