I have a ManyToMany relationship that is broken down into 2 OneToMany relation. A Book can belong to multiple Categories and a Category can have many Books.
When I query for Book, the categories list just get empty. How can I get a list of all Categories that a Book belong to ? Am I missing something ?
#Entity
public class Book {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private Integer id;
#NotBlank(message = "Please input book title")
private String title;
private Integer publishYear;
private String publisher;
private String language;
private Integer numberOfPages;
private String avatarUrl;
#OneToMany(targetEntity = BookCategory.class, cascade = CascadeType.ALL)
#JoinColumn(name = "category", nullable = false, insertable = false, updatable = false)
private Set<BookCategory> categories = new LinkedHashSet<>();
}
#Entity
public class Category {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private Integer id;
#Column(nullable = false)
#NotBlank(message = "Please input category name")
private String name;
}
#Entity
public class BookCategory {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private Integer id;
#ManyToOne
#JoinColumn(name = "book", nullable = false)
private Book book;
#ManyToOne
#JoinColumn(name = "category", nullable = false)
private Category category;
}
Try using mappedBy attribute with #OneTOMany annotation on the 'One' side of the OneToMany relation.
Or you can also try using the following:
#ManyToMany
#JoinTable(
name = “book”_category,
joinColumns = #JoinColumn(name = “book_id”),
inverseJoinColumns = #JoinColumn(name = “category_id))
Read more:
https://vladmihalcea.com/the-best-way-to-use-the-manytomany-annotation-with-jpa-and-hibernate/
Related
I made 2 one-to-one relationships with 2 foreign keys, but I can't make a constraint or how could I make the 2 unique keys be a unique key in the new table?
#Table(name = "cart")
public class Cart {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "id", nullable = false)
private Long id;
private int quantity;
#OneToOne(cascade = CascadeType.ALL)
#JoinColumn(name = "product_id")
private Product products;
#OneToOne(cascade = CascadeType.ALL)
#JoinColumn(name = "user_id")
private User users;
}
#Entity
#Table(name = "Products")
public class Product {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
private String name;
private int quantity;
private Double price;
private String image;
It spells my 2 keys correctly, for example
user_id = 2 , product_id =2 would be ok
but if I enter another user_id=2, product_id=2 should not work, but for me it is entered in the database
You can use #PrimaryKeyJoinColumn in the #OneToOne relation:
#OneToOne(cascade = CascadeType.ALL)
#PrimaryKeyJoinColumn(name = "product_id", referencedColumnName = "id")
private Product products;
I have two table user(id,name) and user_mails(id,email,user_id) user to user_mails have one to many relation.
I have created following entity in spring boot
User
#Entity
#Table(name = "user")
public class User {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
#Column(name = "id")
private int id;
#Column(name = "name", nullable = false)
private String name;
#OneToMany(mappedBy = "user", cascade = CascadeType.ALL)
private Set<UserMail> userMails =new HashSet<UserMail>(0);
//Getter setter and constructor
}
UserMail
#Entity
#Table(name = "user_mails")
public class UserMail {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private int id;
#Column(name = "email", nullable = false)
private String name;
#ManyToOne(fetch = FetchType.LAZY, optional = false)
#JoinColumn(name = "user_id")
private User user;
It is showing following output on calling controller
[{"id":1,"name":"Ram","userMails":[{"id":2,"name":"ram#b.com","user":{"id":1,"name":"Ram","userMails":[{"id":2,"name":"ram#b.com","user":{"id":1,"name":"Ram","userMails":[{"id":2,"name":"ram#b.com","user":{"id":1,"name":"Ram","userMails":[{"id":2,"name":"ram#b.com","user":{"id":1,"name":"Ram","userMails":[{"id":2,"name":"ram#b.com","user":{"id":1,"name":"Ram","userMails":[{"id":2,"name":"ram#b.com","user":{"id":1,"name":"Ram","userMails":
and more
I want to access all users with all mail ids also want to acces mail id with user details
What changes should I do to get proper result
Simple Fetch Problem I'm facing in a straight-forward OneToMany Relationship: One Author Many Books.
Here's Author :
#Entity
#Table(name = "authors")
public class AuthorEntity {
#Id
#GeneratedValue
private UUID id;
#Column(name = "first_name")
private String firstName;
#Column(name = "last_name")
private String lastName;
#OneToMany(
mappedBy = "author",
orphanRemoval = true,
fetch = FetchType.EAGER
)
private List<BookEntity> books; // Getters and Setters
}
Here's Book:
#Entity
#Table(name = "books")
public class BookEntity {
#Id
#Column(name = "id")
#GeneratedValue
private UUID id;
#Column(name = "title")
private String title;
#ManyToOne(optional = false)
#JoinColumn(
name = "author_id",
referencedColumnName = "id"
)
private AuthorEntity author;
// Getters and Setters
}
I saved an author and a book through their respective repositories and I checked everything is fine, and here's my query to fetch the author :
SELECT a FROM AuthorEntity a JOIN a.books WHERE a.id = :authorId
Now when I try to access author.getBooks() it says it is null, why doesn't it fetch ? Why do I always have to fetch the books separately ? What's the right query ?
I am getting StackOverflow recursion error when I run query in Postman or Browser .
When i run says:
.w.s.m.s.DefaultHandlerExceptionResolver : Could not write JSON: Infinite recursion (StackOverflowError); nested exception is com.fasterxml.jackson.databind.JsonMappingException: Infinite recursion (StackOverflowError)
Here is the model classes :
#Entity
public class Product {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#NotNull
private String title;
#NotNull
private String description;
#NotNull
private double price;
#OneToOne(fetch = FetchType.LAZY, optional = false)
#JoinColumn(name = "category_id", nullable = false)
private Category category;
private boolean isSealed;
#OneToOne(fetch = FetchType.LAZY, optional = false)
#JoinColumn(name = "currency_id", nullable = false)
private Currency currency;
#OneToOne(fetch = FetchType.LAZY, optional = false)
#JoinColumn(name = "user_id", nullable = false)
private User user;
#Nullable
#OneToMany(mappedBy = "product",
cascade = CascadeType.ALL, orphanRemoval = true)
private List<Images> images;
private Date createdDate = new Date();
#OneToOne(fetch = FetchType.LAZY,
cascade = CascadeType.ALL,
mappedBy = "product")
private View view;
#OneToOne(fetch = FetchType.LAZY,cascade=CascadeType.ALL)
#JoinColumn(name="type_id")
private Type type;
private Long viewCount; }
#Entity public class Images{
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String imagePath;
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "product_id")
private Product product; }
#Entity public class User implements UserDetails, Serializable {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#NotEmpty
private String fullName;
#NotEmpty
#Email
#Column(unique = true)
private String email;
#NotNull
#Column(unique = true)
private int phoneNumber;
#NotEmpty
#Size(min = 5)
private String password;
private Date createAt = new Date();
#Nullable
private String picPath;
#Nullable
private String token;
#ManyToMany
#JoinTable(name = "user_roles", joinColumns = {#JoinColumn(
name = "user_id")},
inverseJoinColumns = {#JoinColumn(name = "role_id")})
private List<Role> roles;
#OneToOne(fetch = FetchType.LAZY,
cascade = CascadeType.ALL,
mappedBy = "user")
private Product product;
#OneToOne(fetch = FetchType.LAZY,
cascade = CascadeType.ALL,
mappedBy = "user")
private View view; }
#Entity
public class Currency{
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String code;
private String currency;
private String region_country;
#OneToOne(mappedBy = "currency", cascade = CascadeType.ALL, fetch = FetchType.LAZY)
private Product product; }
#Entity
public class Category {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String name;
private String imagePath;
#OneToOne(cascade = CascadeType.ALL, fetch = FetchType.LAZY,
mappedBy = "category")
private Product product;
#OneToMany(mappedBy = "category", fetch = FetchType.LAZY,
cascade = CascadeType.ALL)
private Set<Brand> brands; }
#Entity public class Brand {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String name;
#ManyToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
#JoinColumn(name = "category_id", nullable = false)
private Category category; }
#Entity public class View {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#OneToOne(fetch = FetchType.LAZY, optional = false)
#JoinColumn(name = "user_id", nullable = false)
private User user;
#OneToOne(fetch = FetchType.LAZY, optional = false)
#JoinColumn(name = "product_id", nullable = false)
private Product product; }
#Entity public class Type {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#NotNull
private String name;
#OneToOne(fetch = FetchType.LAZY,
cascade = CascadeType.ALL,
mappedBy = "type")
private Product product; }
#Id
private String role;
#ManyToMany(mappedBy = "roles")
private List<User> users;
}
More than one of your entities have each other in themselves.
For example, Product has an object of User, and User has an object of Product.
To solve this, you have to write
#JsonBackReference(value = "user-product")
private User user;
in the Product class,
and
#JsonManagedReference(value = "user-product")
private Product product;
In the user class.
Do it in every field and for every class that call each other.
Also, Check this out
JPA: Having lists on both ends without infinite loop
You have cycles in your data model. For example, Product holds Images and Images point back to Products.
This works in an object oriented world, because only pointer references are stored in those fields.
When serialized, however, the actual object is written out as json text. Your Product prints the Images object which in turn prints the Product object which again prints the Image object and so on.
You need to decide how you want to represent your json, map your database model into simple plain old java object and use this for serializations. These POJOs are often called View Model or Transport Objects.
I have three tables:
1) book: id (primary), name
2) shop: code (unique, not primary), name
3) book_shop: book_id, shop_id (code), price
I want to get shops in book like
book.getShop();
How to link this entities?
I tried:
#Data
#NoArgsConstructor
#Entity
#Table(name = "book", schema = "example")
#EntityListeners(AuditingEntityListener.class)
public class Book {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private int id;
private String name;
#OneToMany(mappedBy = "book", cascade = CascadeType.ALL, orphanRemoval = true)
private Set<BookShop> bookShop;
}
.
#Data
#NoArgsConstructor
#Entity
#Table(name = "shop", schema = "example")
#EntityListeners(AuditingEntityListener.class)
public class Shop {
#Id
private int code;
private String name;
#OneToMany(mappedBy = "shop", cascade = CascadeType.ALL, orphanRemoval = true)
private Set<BookShop> bookShop;
}
.
#Data
#NoArgsConstructor
#Entity
#Table(name = "book_shop", schema = "example")
public class BookShop implements Serializable {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private int id;
#Id
#ManyToOne
#JoinColumn(name = "book_id")
private Book book;
#Id
#ManyToOne
#JoinColumn(name = "shop_id")
private Shop shop;
#Column(name = "price")
private int fromDate;
}
This code return empty set: Book book = bookRepostiory.getById(1).get().getBookShop()
Try the many to many mapping implement like as below remove your book_shop table,
add this code to shop entity,
#ManyToMany(fetch = FetchType.EAGER, cascade = CascadeType.PERSIST)
#JoinTable(name = "book_shop",
joinColumns = {#JoinColumn(name = "book_id", nullable = false)},
inverseJoinColumns = {#JoinColumn(name = "shop_id", nullable = false)})
private Set<Book> bookList = null;
add this code to book entity,
#ManyToMany(fetch = FetchType.LAZY, cascade = CascadeType.ALL,
mappedBy ="bookList")
private Set<Shop> shopList=null;
if any issue inform!!
I would suggest, first - initialize the set in the entity
private Set<BookShop> bookShop = new HashSet<>();
Second, add fetch = FetchType.EAGER to your association, for e.g.
#OneToMany(fetch = FetchType.EAGER, mappedBy = "book", cascade = CascadeType.ALL)