I'm using JPA from SPRING and I'm having trouble creating this relationship for a social network.
I was a little confused.
can someone help me with this relationship?
#Entity(name = "tbl_user")
public class User {
#Id
private String id;
#ManyToMany
private List<User> friends;
}
#Entity(name = "tbl_friendship")
public class Friendship {
#Id
private String id;
#ManyToMany
private User source;
#ManyToMany
private User target;
}
Related
I am trying to save a JPA entity which has ManytoMany Relationship (Consumer and Product table) and OnetoOne relation with ConsumerDetailstable.Below are my entities
#JsonInclude(JsonInclude.Include.NON_NULL)
#JsonIgnoreProperties(ignoreUnknown = true)
#JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class)
#Entity
public class Consumer {
#Id
#GeneratedValue
private Long id;
private String firstName;
private String lastName;
#JsonManagedReference
#OnToMany(mappedBy = "consumer")
private Set<ConsumerProduct> consumerProducts;
#OneToOne
private CustomerDetails consumerDetails;
}
#Entity
public class Product {
#Id
#GeneratedValue
private Long productId;
private String productCode;
#OneToMany(mappedBy = "product")
private Set<ConsumerProduct> consumerProducts;
}
#JsonInclude(JsonInclude.Include.NON_NULL)
#JsonIgnoreProperties(ignoreUnknown = true)
#JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class)
#Entity(the join table)
public class ConsumerProduct {
#EmbeddedId
ConsumerProductKey id;
#JsonBackReference
#ManyToOne
#MapsId("id")
#JoinColumn(name = "id")
private Consumer consumer;
#ManyToOne
#MapsId("productId")
#JoinColumn(name = "product_id")
private Product product;
}
#Embeddable (forgein keys combined as embeded id)
public class ConsumerProductKey implements Serializable {
#Column(name="id")
private Long id;
#Column(name = "product_id")
private Long productId;
}
#Enitity (one to one relation table)
public class CustomerDetails {
#Id
#GeneratedValue
private Long consumerDtlId;
#OneToOne
private Consumer consumer;
private String city;
private String state;
private String country;
}
To save the entity am have just extended JPARepository and called save method
public class ConsumerRepository<Consumer> Implements JPARepository<Consumer, Long> {
#Override
public Consumer S save(Consumer entity) {
return save(entity);
};
}
I get java.lang.StackOverFlowError at save method.
Anything wrong with my Mappings ?
Question: Since this will be save operation and since Consumer Id is yet to be generated how do I assign to below Entities
ConsumerProduct.ConsumerProductKey (how do i assign Id of consumer table once it is inserted to join table ? will JPA take care of it)
CustomerDetails (how do i assign Id of consumer table once it is inserted to join table ? will JPA take care of it)
EDIT: I have updated the entity with JsonManagedReference and JsonBackedReference but still i have am facing stackoverflow error
It is due to Consumer trying to access ConsumerProduct and ConsumerProduct trying to access consumer entity and end up with StackOverflow error.
You should use #JsonManagedReference and #JsonBackReference annotation in consumer and ConsumerProduct respectivly.
Interestingly, I can't find any solution for a seemingly common scenario! So I'm asking here to learn from experienced professionals in Spring Data JPA. I'll consider using Lombok to make the sample codes more concise.
Consider a simple IMDB example web application. I've defined two simple entities as below:
#Data
#Entity
public class Movie {
#Id
#GeneratedValue
private long id;
private String title;
private int year;
private int rating;
}
#Data
#Entity
public class Actor {
#Id
#GeneratedValue
private long id;
private String firstName;
private String lastName;
private Date birthday;
private String gender;
}
Now we need a join-table to link these two entities; but this is not just a simple join-table. Other than the actor and movie columns, this table has some additional attributes. We didn't want to waste storage by adding an ID column here, instead we used a composite-key consisting of actor and movie:
#Data
#Embeddable
public class MovieActorId implements Serializable {
private Actor actor;
private Movie movie;
}
#Data
#Entity
public class MovieActor {
#EmbeddedId
private MovieActorId id;
private int salary;
private String characterName;
}
There are two Many-to-One relations here: MovieActor >-- Actor and MovieActor >-- Movie.
Now my main question is: "Assuming the above design, how should I define the #ManyToOne relationships in this design?"
NOTE: I believe if we add an additional ID column to the MovieActor join-table instead of the composite/embedded MovieActorId, the JPA code will become fairly straight-forward. But suppose we have some sort of limitation, and we need to stick to this design as much as possible.
You need to use #MapsId which provides the mapping for an EmbeddedId primary key in #ManyToOne relation
#Data
#Embeddable
public class MovieActorId implements Serializable {
private long actorId;
private long movieId;
// constructor, setter, etc
}
#Data
#Entity
public class MovieActor {
#EmbeddedId
private MovieActorId id;
#ManyToOne(cascade = CascadeType.ALL)
#MapsId("actorId")
private Actor actor;
#ManyToOne(cascade = CascadeType.ALL)
#MapsId("movieId")
private Movie movie;
...
}
I am working a very small application which contains 3 entity classes.
1.Category.
2.Products.
3.User
Relationships:-
a. OneToMany between User and Products.
b. OneToMany and ManyToOne between category and products i.e. a category can have multiple products and multiple products can belong to same category.
Entity Classes are shown below:-
User Entity:-
#Entity
public class User {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private int id;
private String username;
private String lastname;
private String email;
private String password;
#OneToMany(cascade = {CascadeType.PERSIST, CascadeType.MERGE},
fetch = FetchType.EAGER)
private Set<Products> products;
//getter and setter
}
Products Entity:-
#Entity
public class Products {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private int id;
private String productname;
private String cost;
#ManyToOne(cascade = {CascadeType.MERGE,CascadeType.PERSIST},
fetch = FetchType.LAZY)
private Category category;
//getter and setters
}
Category Entity:-
#Entity
public class Category {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private int id;
private String name;
#OneToMany(mappedBy = "category",
cascade = {CascadeType.PERSIST, CascadeType.MERGE},
fetch = FetchType.EAGER)
private List<Products> products;
//getter and setters
}
Method to merge User with products in data base:-
#GetMapping("/cart")
public String Cart(Model model){
model.addAttribute("cart",productsSet);
System.out.println(productsSet);//At this stage in console I am able to see products added in set
User user = userRepository.findById(1);//hard coded for now.
user.setProducts(productsSet);
userService.saveUserProducts(user);//saveUserProducts() method in shown below.
productsSet.clear();
return "mycart";
}
saveUserProducts() :-
#Override
#Transactional
public void saveUserProducts(User user) {
entityManager.merge(user);
}
But when I am running the program I see the following exception in console:-
java.lang.IllegalStateException: Multiple representations of the same entity [com.demo.shopping.com.Entity.Products#2] are being merged. Detached: [Products{id=2, productname='p2', cost='200'}]; Detached: [Products{id=2, productname='p2', cost='200'}]
I found an article on stack-overflow but it was not fit in my situation.(java.lang.IllegalStateException: Multiple representations of the same entity with #ManyToMany 3 entities).Except this I don't get any relevant thing.
Please help me to let me know how to deal with this situation. Hope someone will help.
Thanks in advance.
Remove CascadeType.MERGE user class because in my program I am not adding new products also except this I am creating relation between existing user and products.
First of all hello everybody, it's my first post here.
I'm very new at spring and have bit trouble to grasp mapping object to database. To be more specific, there is an article:
OneToMany
In given example there are 2 clases:
#Entity
public class Employee {
#Id
#Column(name="EMP_ID")
private long id;
...
#OneToMany(mappedBy="owner")
private List<Phone> phones;
...
}
#Entity
public class Phone {
#Id
private long id;
...
#ManyToOne(fetch=FetchType.LAZY)
#JoinColumn(name="OWNER_ID")
private Employee owner;
...
}
Can I place some annotation to make the table Employee have a column with list of phones?
I apparently doing something wrong in the configuration of a jdbcRealm. But I don't know what exactly.
This is my configuration:
What else is needed to help me?
#Entity
#Table(name = "gebruiker")
public class User implements Serializable {
#Id #Column(name="User_NAME")
private String name;
#ManyToOne
#JoinTable(name = "groep_gebruiker")
private Role rol;
#Entity
#Table(name = "groep")
public class Role implements Serializable {
#Id
private String rol;
#OneToMany(mappedBy = "rol")
private Collection<User> gebruikers = new ArrayList();
Obviously this is because you did not create a JDBC realm user /Hans/