Hi I am new to Hibernate and trying to build a Rest APP.
I have 3 tables in the database as shown in the above image.
USERS table has ManyToMany relation with GROUPS table and USER_GROUP is an association table.
I am using ORM, Hibernate and CurdRepository.
I am able to insert into users table and group table with save() method of CurdRepository.
Now I am trying to add a row in GROUPS table and USER_GROUP table only. Can anyone lead me to the right direction?
For example:
I want to add an groupid to GROUPS table and then associate it with an user id
Let's say I want to insert (10) groupid in GROUPS and (14,10) in USER_GROUP table.
Is it doable with ORM, if yes how?
Thanks in advance
To use existing connecting table, USE_GROUP, User entity will be like following .
#Entity
public class Users {
#Id
private Integer userid;
private String password;
#ManyToMany(cascade = { CascadeType.MERGE, CascadeType.PERSIST })
#JoinTable(name = "USER_GROUP", joinColumns = { #JoinColumn(name = "USERID") },
inverseJoinColumns = { #JoinColumn(name = "GROUPID") })
private Set<Groups> groups;
// Getter, Setter
}
And then client code, add new User and Group, will be something like below.
User user = new User()
// set password , etc
Set<Groups> groups = new HashSet<>();
Group group = new Group();
// set
groups.add(group);
user.setGroups(groups);
userRepository.save(user);
There are many articles online about exactly this model to showcase how to use Hibernate. Here is one article I quickly found by googling for "hibernate user group example": https://www.codejava.net/frameworks/hibernate/hibernate-many-to-many-association-annotations-example
Related
The Problem
I have a 1:n relation, but the n side shouldnt rely on constraints. So i actually wanna insert a EntityPojo via its future id, when its not saved yet ( Lets ignore that its a bad practice ). This looks kinda like this.
var relation = new RelationshipPojo();
.
.
.
relation.targets.add(session.getReference(futureID, EntityPojo.class));
session.save(relation);
// A few frames later
session.save(theEntityPojoWithTheSpecificId);
Cascading is not possible here, i only have its future ID, not a reference to the object i wanna save. Only its id it will have in the future.
#Entity
#Table(name = "relationship")
#Access(AccessType.FIELD)
public class RelationshipPojo {
.
.
.
#ManyToMany(cascade = {}, fetch = FetchType.EAGER)
public Set<EntityPojo> targets = new LinkedHashSet<>();
}
Question
How do we tell hibernate that it should ignore the constraints for this 1:n "target" relation ? It should just insert the given ID into the database, ignoring if that EntityPojo really exists yet.
Glad for any help on this topic, thanks !
For a much simpler solution, see the EDIT below
If the goal is to insert rows into the join table, without affecting the ENTITY_POJO table, you could model the many-to-many association as an entity itself:
#Entity
#Table(name = "relationship")
#Access(AccessType.FIELD)
public class RelationshipPojo {
#OneToMany(cascade = PERSIST, fetch = EAGER, mappedBy = "relationship")
public Set<RelationShipEntityPojo> targets = new LinkedHashSet<>();
}
#Entity
public class RelationShipEntityPojo {
#Column(name = "entity_id")
private Long entityId;
#ManyToOne
private RelationshipPojo relationship;
#ManyToOne
#NotFound(action = IGNORE)
#JoinColumn(insertable = false, updatable = false)
private EntityPojo entity;
}
This way, you'll be able to set a value to the entityId property to a non-existent id, and if an EntityPojo by that id is later inserted, Hibernate will know how to populate relationship properly. The caveat is a more complicated domain model, and the fact that you will need to control the association between RelationshipEntityPojo and EntityPojo using the entityId property, not entity.
EDIT Actually, disregard the above answer, it's overly complicated. Turing85 is right in that you should simply remove the constraint. You can prevent Hibernate from generating it in the first place using:
#ManyToMany(cascade = CascadeType.PERSIST, fetch = FetchType.EAGER)
#JoinTable(inverseJoinColumns = #JoinColumn(name = "target_id", foreignKey = #ForeignKey(name = "none", value = ConstraintMode.NO_CONSTRAINT)))
public Set<EntityPojo> targets = new LinkedHashSet<>();
The only caveat is that when you try to load RelationshipPojo.targets before inserting the missing EntityPojo, Hibernate will complain about the missing entity, as apparently #NotFound is ignored for #ManyToMany.
So I have 2 tables. A users table and a finished_exams table. The finished_exams table has a user_id as foreign key and is related as OneToOne with the users table.
I made the relation in Users model like this:
#OneToOne(fetch = FetchType.EAGER, mappedBy = "user")
private FinishedExam finishedExam;
And in the FinishedExams model like this:
#OneToOne(fetch = FetchType.EAGER)
#JoinColumn(name = "user_id")
private User user;
When I call all finished exams like this in the controller:
#GetMapping("/all")
public Iterable<FinishedExam> getAllFinishedExams()
{
return finishedExamRepository.findAll();
}
I get all Finishedexams linked with the users which is good.
My question is, is it possible to get ALL users with their finishedExam if they have it and without if they don't (So basically a LEFT JOIN)
Is this possible in Hibernate?
EDIT:
I just tried this but it only returns all users without the exams.
#GetMapping("/allUsersWithExams")
#Fetch(FetchMode.SELECT)
public Iterable<User> getAllUsersWithTheirExams()
{
return userRepository.findAll();
}
First of all sure is possible, you just have to write the query yourself:
"Select u from Users u LEFT JOIN u.finishedExam"
simple enough.
But what's stopping you to just select all user and get all their finished exam?
public Iterable<Users> getAllUsers()
{
return UsersRepository.findAll();
}
It will give you a list of all Users independently from having or not any finishedExam
I have problem with hibernate and #ManyToMany annotation. Please look at two entities classes:
Company entity:
#ManyToMany
#JoinTable(name="company_user_tab",
joinColumns={#JoinColumn(name="company_id")},
inverseJoinColumns={#JoinColumn(name="user_id")})
private Set<User> users = new HashSet<User>();
... getters and setters
User entity:
#ManyToMany(mappedBy="users")
private Set<Company> companies = new HashSet<Company>();
... getters and setters
Scenario:
I created first user and first company and connect them correctly.
Problem occured when I create new user and try update existing company with new user. I receive database error on company_user_tab: "duplicate key value violates unique constraint"
It's look like hibernate insert again to join table first user witch is correctly associated with company.
How I update object?
entityManager.merge(object);
Of course I add before user to company and company to user for example:
user.getCompanies().add(company);
company.getUsers().add(user);
Thanks for advice.
try this code:
#ManyToMany(cascade= {CaseCadeType.ALL})
#JoinTable(
name = "company_user_tab",
joinColumns = { #JoinColumn(name="company_id") },
inverseJoinColumns = { #JoinColumn(name="user_id") }
)
private Set<User> users = new HashSet<User>();
// setters and getters
I have two entities, User and Event. Each event can have multiple users associated with it, so its a one to many between Event and User.
The way its being stored in the database, is that I have 3 tables, user, event, and event_user. event_user contains 3 fields, id, eventId, userId. So I can do a query like select userId from event_user where eventId = ? to get all the users which are associated with the event.
My question is, how can I map this relationship between the events and users in Hibernate, to get it to auto save/load the users associated with the event? I want to have the following field in the Event class:
Set<User> users = new HashSet<>();
and have hibernate auto load / save the users to this set.
How can I map this (using annotations)?
Use the #ManyToMany annotation.
class Event{
#ManyToMany(cascade=CascadeType.ALL)
#JoinTable(name = "EVENT_USER",
joinColumns = { #JoinColumn(name = "EVENT_ID") },
inverseJoinColumns = { #JoinColumn(name = "USER_ID") })
private Set<Users> users = new HashSet<Users>();
}
For more information on many to many associations in JPA check out this video tutorial at my blog.
Hibernate doc on the Bidirectional mapping using annotations should help
Basically you need to do something like this
#Entity
public class User implements Serializable {
#ManyToMany(
targetEntity=org.hibernate.test.metadata.manytomany.Event.class,
cascade={CascadeType.ALL}
)
#JoinTable(
name="USER_EVENT",
joinColumns=#JoinColumn(name="USER_ID"),
inverseJoinColumns=#JoinColumn(name="EVENT_ID")
)
public Set<Event> getEvents() {
return events;
}
...
}
#Entity
public class Event implements Serializable {
#ManyToMany(
cascade = {CascadeType.ALL},
mappedBy = "events",
targetEntity = User.class
)
public Set<User> getUsers() {
return users;
}
}
I have User class and Country class with respective tables. Country table data is fixed.
I make a mapping table User_Country(userid, countryid) and following mapping in User class
#OneToMany(fetch=FetchType.EAGER)
#JoinTable(name = "User_Country", joinColumns ={
#JoinColumn(name = "userid")
}, inverseJoinColumns = {
#JoinColumn(name = "COUNTRYID")
})
private Set<Country> country;
When i persist User class it successfully persist user data and insert data in mapping table(user_country). This is exactly i want but when i find User by using hql('from user where userid=?') and then try to get country maaping (which is stored in mapping tableuser_country). I didn't get any data from user_country. How can i write annotation so that it gets data from user_country. If i put cascade then it update country table(which is fixed) which i don't want.
I am not too sure but, try with inverse="false", as that might help.