Hibernate Tutorial

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https://www.geeksforgeeks.org/java/hibernate-tutorial/
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Batch Insert/Update

spring.jpa.properties.hibernate.jdbc.batch_size=5
spring.jpa.properties.hibernate.order_inserts=true
spring.jpa.properties.hibernate.order_updates=true
spring.jpa.properties.hibernate.batch_versioned_data=true

https://www.baeldung.com/jpa-hibernate-batch-insert-update

@PersistenceContext
    private EntityManager entityManager;

entityManager.persist(employee)
entityManager.flush()
entityManager.clear()
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public interface ProductRepository extends PagingAndSortingRepository<Product, Integer> {

    List<Product> findAllByPrice(double price, Pageable pageable);
}
Pageable firstPageWithTwoElements = PageRequest.of(0, 2);
Pageable secondPageWithFiveElements = PageRequest.of(1, 5);
productRepository.findAll(Sort.by("name"));
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By default, data.sql scripts get executed before the Hibernate is initialized. 
spring.jpa.defer-datasource-initialization=true
spring.sql.init.mode=always

schema.sql File
spring.jpa.hibernate.ddl-auto=none

https://www.baeldung.com/spring-boot-data-sql-and-schema-sql
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@OneToOne(cascade = CascadeType.ALL)
    @JoinColumn(name = "student_gfg_detail_id")
    private StudentGfgDetail studentGfgDetail;

@OneToOne(mappedBy = "studentGfgDetail",
              cascade = CascadeType.ALL)
    private Student student;
mappedBy = "studentGfgDetail" tells Hibernate to look for a field named studentGfgDetail in the Student class and link that particular instance to the current student object. 
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// A manufacturer can have many models
    @OneToMany(mappedBy = "manufacturer")
    private List<Model> models;

// A model belongs to one manufacturer
      // Foreign key referencing the manufacturer table
    @ManyToOne
    @JoinColumn(name = "manufacture_id")
    private Manufactures manufacturer;
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@ManyToMany
@JoinTable(
  name = "course_like", 
  joinColumns = @JoinColumn(name = "student_id"), 
  inverseJoinColumns = @JoinColumn(name = "course_id"))
Set<Course> likedCourses;

@ManyToMany(mappedBy = "likedCourses")
Set<Student> likes;

new Attribute to the relation table
@Embeddable
class CourseRatingKey implements Serializable {
    @Column(name = "student_id")
    Long studentId;
    @Column(name = "course_id")
    Long courseId;
    // standard constructors, getters, and setters
    // hashcode and equals implementation
}


@Entity
class CourseRating {
    @EmbeddedId
    CourseRatingKey id;

    @ManyToOne
    @MapsId("studentId")
    @JoinColumn(name = "student_id")
    Student student;

    @ManyToOne
    @MapsId("courseId")
    @JoinColumn(name = "course_id")
    Course course;

    int rating;
    // standard constructors, getters, and setters
}

class Student {
    // ...
    @OneToMany(mappedBy = "student")
    Set<CourseRating> ratings;
    // ...
}

class Course {
    // ...
    @OneToMany(mappedBy = "course")
    Set<CourseRating> ratings;
    // ...
}

https://www.baeldung.com/jpa-many-to-many
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Interview question - 
Lazy loading in oneToMany relationship
  Used Hibernate.initialize(user.getContracts()) - this should be called within transaction

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