I have the following model:
(...)
#IdClass(BetID.class) //Primary Key, composite = userID+gameID
public class Bet {
(...)
//Primary Key
#ManyToOne
#Id
private User user; //Composite key:userID
#ManyToOne
#Id
private Game game; //Composite key:gameID
In which, of course, has the following Composite key:
public class BetID implements Serializable {
#OneToOne
private User user;
#OneToOne
private Game game;
Here, User and Game are foreign keys, but also entities. Problem is when I'm trying to handle, so I can't set/get the key as easy as having a normal key like:
#EmbeddedId BetID bet id because the id has to refer 2 attributes from Bet. So using #Getter and #Setter (with lombok) is not possible.
So, how can I handle this? Is even possible to have a key like this?
You can add a setter with two arguments:
public void setBetID(User user, Game game) {
this.betId = new BetID(user, game);
}
Related
I am new using Hibernate and I am trying to know if is possible to change the primary key of a child component with a composite key. This is my parent component:
public class Person{
#Id
#Column(name = "id", unique = true)
private String id;
private String name;
private String surname;
}
This is my child component:
public class User extends Person {
private String email;
private String password;
}
I would like to identify my user with id+email key. Is that possible?
If your inherited entities share the same table, it wouldn't be possible, as in the database there can be only one primary key logic per table.
However if you have a inheritance strategy using joins, it would be possible I guess - check out Hibernate - Foreign and primary keys in inheritance
I've a question about One to One unidirectional Mapping in Spring Boot.
I've a Customer class with a One to One unidirectional mapping to an Address class.
But when I try to associate a new customer with an existing Address, the database is updated.
So two Customers are now associated with the one Address.
As I understand it only one Customer should be associated with one unique Address. Do I understand the concept correctly, or am I doing something wrong in Spring Boot/ Spring Data JPA/ Hibernate?
Customer
#Entity
public class Customer {
#Id
private Long cId;
private String cName;
#OneToOne(cascade = CascadeType.ALL)
#JoinColumn(name="aid")
private Address cAddr;
:
}
Address
#Entity
public class Address {
#Id
private Long aid;
private String town;
private String county;
:
}
data.sql
insert into address values (100, "New York", "NY");
insert into customer values (1, "John Smith", 100);
Application.java
#Override
public void run(String... args) throws Exception {
Customer c1 = new Customer((long)5, "Mr. Men");
Optional<Address> a100 = ar.findById((long)100);
c1.setcAddr(a100.get());
cr.save(c1);
}
Database
There are 2 options on how to make #OneToOne relation: unidirectional and bidirectional: see hibernate doc.
When you scroll down a little bit you will find the following:
When using a bidirectional #OneToOne association, Hibernate enforces the unique constraint upon fetching the child-side. If there are more than one children associated with the same parent, Hibernate will throw a org.hibernate.exception.ConstraintViolationException
It means that you'll have the exception only on fetching and when you have a bidirectional association. Because Hibernate will make an additional query to find the dependent entities, will find 2 of them, which doesn't fit #OneToOne relation and will have to throw an exception.
One way to "fix" uniqueness for your entities, is to make cAddr unique:
#OneToOne(cascade = CascadeType.ALL)
#JoinColumn(name="aid", unique=true)
private Address cAddr;
If you create your db tables, by setting hbm2ddl property this will add a unique constraint to the aid column.
I really recommend to read the following:
#OneToOne javadoc itself provides examples of how to do everything correctly (for you Examples 1 and 2 are the most useful)
Check Vlad's blog about #OneToOne. It must be the best you can find. At least jump to the chapter "The most efficient mapping" and implement it bidirectional and sharing the PK, using #MapsId.
Also maybe you will come up to the idea to use #ManyToOne option (at least i can imagine that customer can have multiple addresses)
This is not One-to-Many relation. It's One-to-Many as One object has multiple related objects. Checkout this article.
Example:
Post.java
#Getter
#Setter
#AllArgsConstructor
#NoArgsConstructor
#Entity
#Table
public class Post {
#Id
#GeneratedValue
#Column(name = "post_id")
private Long id;
#Column
private String postHeader;
#OneToMany(
cascade = CascadeType.ALL,
orphanRemoval = true
)
private List<Comment> comments = new ArrayList<>();
public void addComment(Comment comment) {
comments.add(comment);
}
public void removeComment(Comment comment) {
comments.remove(comment);
}
// equals() and hashCode()
}
Comment:
#Getter
#Setter
#AllArgsConstructor
#NoArgsConstructor
#Entity
#Table
public class Comment {
#Id
#GeneratedValue
#Column(name = "postcom_id")
private Long id;
#Column
private String text;
// equals() and hashCode()
}
Check out step "3. Uni-directional one-to-one mapping demonstration" at this site basically carbon copy of what you're trying to do.
I have read about the use of #MapsId and #PrimaryKeyJoinColumn annotations, which sounds like a great options. I have two tables (UserList and UserInformation) which have a child, parent relationship, respectively; both classes below are abbreviated to just include the relevant columns. UserInformation's primary key value is always null and does not take the value of its parent column.
User Class
#Entity
#Data
#Table(name = "user_list")
public class UserList {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer id;
// List of foreign keys connecting different entities
#OneToOne(mappedBy = "user")
#MapsId("id")
private UserInformation userInfo;
}
UserInformation Class
#Entity
#Data
#Table(name = "user_information")
public class UserInformation implements Serializable {
#Id
private Integer userId;
#OneToOne
private UserList user;
}
I would prefer to not use an intermediary class if possible. I'm not tied to MapsId or even this implementation if there is a better solution.
Thanks!
The question is not very clear to me, but I think you could improve the following in the modeling of the entity:
The #column annotation can only be omitted when the class parameter is called exactly the same as the database column, taking into account the table name nomenclature, could it be that the column is user_id ?, if so the id parameter should be :
#Id
#column(name="USER_ID")
private Integer userId;
In the user entity being id, it will match the DB ID field so the #column annotation is not necessary
I have two tables. I want to make between them relationship, but the thing is that the child table connects to an attribute in a parent node, which is not a PK. How can I assign a non-PK field as a FK for a table?
Here are the tables. User Information:
#Entity
#Table(name="user")
public class userinformation implements Serializable {
#Id
#GeneratedValue(strategy=GenerationType.IDENTITY)
#Column(name="USER_ID")
private int uID;
#Column(name="LIB_ID")
private String libID;
//Other attributes
}
Lib Information
#Entity
#Table(name="libinfo")
public class Auth {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name="AUTH_ID")
private int authID;
#Column(name="LIB_ID")
private String lib_ID;
//Other attributes
}
They both should be linked through libID (surely unique). Any idea how to implement it correctly?
Given:
class User {
#Column(name = "lib_id")
private String libID;
}
you must map the Auth entity as:
class Auth {
#JoinColumn(name = "lib_id", referencedColumnName = "lib_id")
#ManyToOne
private User user;
}
Basically, referencedColumnName is used to inform the JPA provider that it should use a column other than the primary key column of the referenced entity (which is used by default with #ManyToOne mappings).
Let's consider the following:
#Entity
#Table(name="person")
public class Person implements Serializable {
#Id
#GeneratedValue
#Column(name="id")
private int id;
#Column(name="firstName")
private String firstName;
#Column(name="lastName")
private String lastName;
...getters/setters...
}
and
#Entity
#Table(name="car")
public class Car implements Serializable {
#Id
#GeneratedValue
#Column(name="id")
private int id;
#Column(name="brand")
private String brand;
#Column(name="model")
private String model;
#Column(name="personId")
private String personId;
...getters/setters...
}
Let's imagine that a user is going to subscribe and enter his personal info, like first name, last name, the brand of his car, as well as the model of the car.
I do not want the personal info of the person to be stored in the same table than the car info.
I also would like to be able to retrieve the car information with the personId, this is why I have personId in the Car class.
Which annotations should I use to be able to accomplish this? Obviously I will need a constraint on the Car table and make personId a foreign key, right? What is the best way?
I have seen different things, what is the best?
In Car class, replace
#Column(name="personId")
private String personId;
with
#ManytoOne(fetch = FetchType.LAZY)
#CJoinColumn(name="person")
private Person person;
In Person class, add
#OneToMany(cascade = {CascadeType.MERGE, CascadeType.PERSIST, CascadeType.REMOVE})
private List<Car> cars;
You are now forming bi-directional one-to-many which means you can retrieve cars of person and person (ownder) of the car.
The cascade allows saving or updating of cars when person is saved. All cars are also deleted when person is removed.
It depends on your requirements.
If you want to use the same vehicle for multiple users, then you shall make it an entity, and use a many-to-many relationship.
If you don't want to change your entity structure at all, but just the database mapping then look at #SecondaryTable and #SecondaryTables annotations, they define more tables for an entity, and then you shall specify which table to use for each column (otherwise they are assigned to main table).