using spring data, I created User 1:N UserDog N:1 Dog relation. Both 1:N relations are unidirectional #ManyToOne with UserDog being the custom relation table.
User entity:
#Entity
public class User {
#Id
#GeneratedValue
private long id;
#Column(nullable = false)
private String name;
}
Dog entity:
#Entity
public class Dog {
#Id
#GeneratedValue
private long id;
#Column(nullable = false)
private String name;
}
User dog relation table:
#Entity
public class UserDog {
#Id
#GeneratedValue
private long id;
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn
#OnDelete(action = OnDeleteAction.CASCADE)
private User user;
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn
#OnDelete(action = OnDeleteAction.CASCADE)
private Dog dog;
#Column(nullable = false)
private Instant createdOn = Instant.now();
#Column
private Instant disabledOn;
}
Use case
Use case is to store history of User-Dog bindings, where the concrete Dog can be bound only to one User at the time. That's why I added createdOn and disabledOn columns to UserDog. disabledOn being null indicates that the relation is active and the Dog can't be assigned another User. If disabledOn is not null, then the record is stored only for evidence purposes and the Dog can be assigned to the same or another User again.
Question
How to ensure that the combination of Dog's id and disabledOn being null is unique in UserDog table?
In pseudo code I want something like this:
#Entity
#UniqueConstraint({#UniqueConstraint(this.dog.id), #NullConstraint(this.disabledOn)})
public class UserDog {...}
You can simply create a unique constraint for dogId and disabledOn.
It does add the limitation that no two relationships may end at the same time but this seems to fit your use case.
Related
I have one to many relation ship between a User and UserRole.
public class User {
#Id
#GeneratedValue
private long id;
#Column(unique = true)
private String username;
private String password;
#OneToMany(fetch=FetchType.EAGER)
#JoinTable(
name = "user_roles",
joinColumns = {#JoinColumn(name="userId")},
inverseJoinColumns = {#JoinColumn(name="roleId")}
)
private Collection<UserRole> roles;
}
and
public class UserRole {
#Id
#GeneratedValue
private long id;
#Column(unique = true)
private String roleName;
}
I am able to save a user at first. But when I try to save another user it rejects with an exception of duplicated entry on the junction table
One thing I noticed is when we have One-to-Many association the many side foreign key will be a primary key on the junction table. So, I need to make the relation Many-to-Many. So that the combination of both foreign keys will serve as a composite key.
Let's se we have Hibernate entity User with basic fields such as username, password, roles etc..
Now we have an entity such as Car.
User has a OneToOne relationship with Car, cause he can own a car. But he also has besides this a OneToMany relationship to Car, because he also owns the cars of his children. But in the frontend I want to know which cars he owns for himself and which cars he owns for his children. The same applies to the relationship between User and motorbike (his own, his childrens, etc...)
How would the User entity class look like? Is it good to have the relationships mapped in an "Helper" entity such as UserData:
#Entity
#Data
#Table( name = "users",
uniqueConstraints = {
#UniqueConstraint(columnNames = "username")
})
public class User {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#NotBlank
#Size(max = 150)
private String username;
#NotBlank
#Size(max = 120)
private String password;
#OneToOne(cascade = {CascadeType.ALL}, fetch = FetchType.EAGER)
#JoinColumn(name = "USER_DATA_ID")
private UserData userData;
UserData:
#Entity
#Data
#Table( name = "user_data")
public class UserData {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#OneToOne(cascade = {CascadeType.ALL}, fetch = FetchType.EAGER)
#JoinColumn(name = "OWN_CAR_ID")
private Car ownCar;
#OneToOne(cascade = {CascadeType.ALL}, fetch = FetchType.EAGER)
#JoinColumn(name = "PARTNER_CAR_ID")
private Car partnerCar;
#ManyToMany(fetch = FetchType.LAZY)
#JoinTable( name = "user_children_cars",
joinColumns = #JoinColumn(name = "user_data_id"),
inverseJoinColumns = #JoinColumn(name = "car_id"))
private Set<Car> childrenCars = new HashSet<>();
public boolean addToChildrenCarSet(Car c) {
return childrenCars.add(c);
}
public UserData() {
}
}
As you ask for an opinion, I would say it gets unnecessary complicated if you use the intermediate entity user_data. :-) There is no real drawback to add more fields and keys into the user class - performance is probably also better then using the EAGER fetching. If performance is an issue, better optimize querys later on then splitting the table now.
Also the #ManyToMany I would avoid - better create the intermediate table and relations yourself. You can check out https://bootify.io and create your database schema there. There is no EAGER fetching and also no CascadeType.ALL (both only good ideas in special cases), you would probably add more problems with that then actual helping in any way.
So the addToChildrenCarSet method would end up in a #Service class, in a method with #Transactional, in my proposal.
I have a table structure like this
Good Assignments Entity
#Embeddable
public class GoodAssignmentId {
String clientId,
String assignmentNumber;
LocalDate effectiveDate;
// Getters and setters
}
#Entity
#IdClass(GoodAssignmentId.class)
class GoodAssignment {
#id
String clientId;
#Id
String assignmentNumber;
#Id
LocalDate effectiveDate;
#OneToMany(mappedBy = "parentKey")
Set<GoodTasks> children;
String description;
// getters and setters goes below
}
Bad Assignments Entity
#Entity
#IdClass(BadAssignmentId.class)
class BadAssignment {
#id
String clientId;
#Id
String assignementNumber;
#Id
LocalDate effectiveDate;
String description;
// Getters and setters goes below
}
Child entities
#Entity
#IdClass(ParentTasksId.class)
#DiscriminatorColumn(name = "fieldD", discriminatorType = DiscriminatorType.STRING)
class ParentTasks {
#Id
String clientId;
#Id
String assignmentNumber;
#Id
String taskNumber;
}
#Entity
#DiscriminatorValue("G")
class GoodTasks extends ParentTasks {
#ManyToOne
#JoinColumns({
#JoinColumn(name = "clientId", referencedColumName = "clientId"),
#JoinColumn(name = "assignmentNumber", referencedColumName = "assignmentNumber")
})
GoodAssignments parentKey;
other fields....
}
This shows the error referencedColumnNames(fieldA, fieldB) of .... not mapped to a single property.
Unfortunately I cannot change the table structure. TableA has 3 columns as primary key, but only two of them forms the primary key in table B along with another field (fieldD via #DiscriminatorValue used by multiple classes). How can I map this relationship to get list of TableB items in TableA?
Example Class Diagram:
Effective date in the assignments tables is not part of tasks. So this is not a perfect relationship in JPA terms. It's a legacy design which cannot be changed for some reasons.
I have SpringBoot 2.1.3 and Java 8 application. Building DB with JPA I have 3 table in one to one relationship. Suppose the tables is the follows:
#Entity
#Data //lombok
#Table(name = "users")
public class User {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
#Column(name = "id")
private Long id;
#OneToOne(mappedBy = "user", cascade = CascadeType.ALL)
private Address address;
}
And then:
#Entity
#Data
#Table(name = "address")
public class Address {
#Id
#Column(name = "id")
private Long id;
#OneToOne
#MapsId
private User user;
}
That's works.. and it is the best way to do (this exactly example is taken from documentation).
If I start the application the DB is created and if I tried to add entities all works well. The model created follows:
Now I want to add a Country object to my address Entities (for example) and I modified the Entities as follows:
#Entity
#Data
#Table(name = "address")
public class Address {
#Id
#Column(name = "id")
private Long id;
#OneToOne
#MapsId
private User user;
#OneToOne
#MapsId
private Country country;
}
And Country Entities:
#Entity
#Data
#Table(name = "country")
public class Country {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
#Column(name = "id")
private Long id;
#OneToOne(mappedBy = "country", cascade = CascadeType.ALL)
private Address address;
}
The application still starts, the DB is created and the model follows:
But if I try to save a User as follows:
User user = new User();
Address address = new Address();
Country country = new Country();
user.setAddress(address);
address.setUser(user);
address.setCountry(country);
country.setAddress(address);
userRepository.save(user);
I obtain the error:
java.sql.SQLException: Field 'country_id' doesn't have a default value
Anyway I solve the issue removing #MapsId and added #JoinColumn but I would like to understand what's wrong.
P.S.: I'm using MySQL 5.7 with InnoDB dialect (setting on application.properties)
Thanks all
It works only with one #MapsId annotation. Using two is causing that country id is not inserted:
insert into Country (id) values (?)
insert into Users (id) values (?)
insert into Address (user_id) values (?)
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).