Hibernate Interview Questions - Part 1

TYPE OF ASSOCIATION	OPTIONS/ USAGE
One-to-one	Either end can be made the owner, but one (and only one) of them should be; if you don’t specify this, you will end up with a circular dependency.
One-to-many	The many end must be made the owner of the association.
Many-to-one	This is the same as the one-to-many relationship viewed from the opposite perspective, so the same rule applies: the many end must be made the owner of the association.
Many-to-many	Either end of the association can be made the owner.

https://stackoverflow.com/questions/33096466/generationtype-auto-vs-generationtype-identity-in-hibernate


Hibernate Basic Configuration with spring boot

Open application.properties file and add the following properties to it.


## Spring DATASOURCE (DataSourceAutoConfiguration & DataSourceProperties)
spring.datasource.url = jdbc:mysql://localhost:3306/notes_app?useSSL=false
spring.datasource.username = root
spring.datasource.password = root


## Hibernate Properties
# The SQL dialect makes Hibernate generate better SQL for the chosen database
spring.jpa.properties.hibernate.dialect = org.hibernate.dialect.MySQL5InnoDBDialect

# Hibernate ddl auto (create, create-drop, validate, update)
spring.jpa.hibernate.ddl-auto = update

Mappings :

Hibernate one to one mapping with foreign key association

EmployeeEntity.java
@OneToOne
@JoinColumn(name="ACCOUNT_ID")
private AccountEntity account;

AccountEntity.java
@OneToOne(mappedBy="account")
private EmployeeEntity employee;

In a bidirectional relationship, one of the sides (and only one) has to be the owner. The owner is responsible for the association column(s) update. To declare a side as not responsible for the relationship, the attribute mappedBy is used. ‘mappedBy’ refers to the property name of the association on the owner side.

Hibernate one to many mapping annotation example

1. Hibernate one to many mapping with foreign key association



EmployeeEntity.java
@OneToMany(cascade=CascadeType.ALL)
@JoinColumn(name="EMPLOYEE_ID")

private Set<AccountEntity> accounts;


AccountEntity.java
@ManyToOne
 private EmployeeEntity employee;


2. Hibernate one to many mapping with join table



EmployeeEntity.java
@OneToMany(cascade=CascadeType.ALL)
    @JoinTable(name="EMPLOYEE_ACCOUNT", joinColumns={@JoinColumn(name="EMPLOYEE_ID", referencedColumnName="ID")}
    , inverseJoinColumns={@JoinColumn(name="ACCOUNT_ID", referencedColumnName="ID")})
    private Set<AccountEntity> accounts;

AccountEntity.java
No changes required


Hibernate many to many mapping annotation example



ReaderEntity.java
  @ManyToMany(cascade=CascadeType.ALL)
    @JoinTable(name="READER_SUBSCRIPTIONS", joinColumns={@JoinColumn(referencedColumnName="ID")}
                                        , inverseJoinColumns={@JoinColumn(referencedColumnName="ID")})
    private Set<SubscriptionEntity> subscriptions;


SubscriptionEntity.java
 @ManyToMany(mappedBy="subscriptions")
    private Set<ReaderEntity> readers;




Useful Link

https://javarevisited.blogspot.com/2013/05/10-hibernate-interview-questions-answers-java-j2ee-senior.html




Ehcache - Second level caching

https://dzone.com/articles/spring-hibernate-ehcache-caching

https://www.devglan.com/spring-mvc/spring-ehcache-cacheable-example-javaconfig]

https://www.devglan.com/spring-mvc/spring-ehcache-cacheable-example-javaconfig


N+1 problem solution

https://dzone.com/articles/how-identify-and-resilve-n1

https://www.javacodemonk.com/what-is-n-1-problem-in-hibernate-how-will-you-identify-and-solve-it-894097b9