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 ?
Related
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
Below are my entity classes Instructor and Courses having OnetoMany Relations, where all CRUD Operation is working but while fetching Instructor I don't want courses to be fetched. But when I execute GET instructor By Id, It also fetches courses in Postman. This should be avoided.
public class Instructor {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "id")
private Long id;
private String firstName;
private String lastName;
private String email;
#OneToMany(mappedBy = "instructor", cascade = {CascadeType.ALL})
#JsonManagedReference
private List < Course > courses;
}
public class Course {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String title;
#ManyToOne(fetch =FetchType.LAZY)
#JoinColumn(name = "instructor_id")
#JsonBackReference
private Instructor instructor;
}
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/
I want to query data from two tables,
location field in Translation is a foreign key from id field of Location
#Entity
#Table(name = "Translation")
#Data
public class Translation {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer id;
#NotNull private String language;
#NotNull private String name;
#NotNull private String description;
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "location", nullable = false, insertable = false, updatable = false)
#Fetch(FetchMode.JOIN)
private Location location;
}
#Entity
#Table(name = "Location")
#Data
public class Location {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer id;
#NotNull private String code;
#NotNull private String type;
private Double longitude;
private Double latitude;
#Column(name = "parent_id")
private Integer parentId;
#OneToMany(targetEntity = Translation.class, mappedBy="id", fetch = FetchType.EAGER)
private Set<Translation> translations;
}
————————————————————————————————————————
But when I use a query
#Query(
"SELECT new com.afkl.travel.exercise.model.RetrieveLocationResponse("
+ "loc.code, tran.name, loc.type, loc.latitude, loc.longitude, tran.description, loc.parentId)"
+ "FROM Location loc LEFT JOIN loc.translation tran")
List<RetrieveLocationResponse> fetchLeftJoin();
All the fields related to Translation is null, having no idea what happened
UPDATE
The following ones work for me.
#OneToMany(mappedBy = "location", cascade = CascadeType.ALL)
#JsonIgnore
private Set<Translation> translations;
#ManyToOne
#JoinColumn(name = "location")
private Location location;
try
#OneToMany(mappedBy = "location", cascade = CascadeType.ALL)
#JsonIgnore
private Set<Translation> translations;
#ManyToOne
#JoinColumn(name = "location")
private Location location;
I have a problem with the relationship oneToMany. I created tables in SQLite DB, this is my tables:
My CategoryModel:
#Entity
#Table(name = "Category")
#JsonIgnoreProperties({ "hibernateLazyInitializer", "handler" })
public class CategoryModel {
#Id
#Column(name = "id")
#GeneratedValue(strategy = GenerationType.AUTO)
private int id;
private String category_name;
private String category_description;
private String image_path;
#JsonIgnore
#OneToMany( mappedBy = "category")
private Set<ProductModel> category;
My ProducCategory:
#Entity
#Table(name = "Product_Category")
#JsonIgnoreProperties({ "hibernateLazyInitializer", "handler" })
public class ProductModel {
#Id
#Column(name = "id")
#GeneratedValue(strategy = GenerationType.AUTO)
private Long product_id;
private Long category_id;
private String name;
private String description;
private int numberOfProduct;
private String image;
private int price;
#ManyToOne
#JoinColumn(name = "country_id", nullable = false)
private CategoryModel category;
I can get data from the Category table well but when I call data from the Product_Category table I have the error:
SQL error or missing database (no such column: productmod0_.country_id)
country_id does not exist anywhere in your tables.
What you want is : #JoinColumn(name = "category_id", nullable = false)