Databases and ORM

Question 1

What is java database connectivity(JDBC)

Answer 1

JDBC uses classes and attributes to manipulate the database, but the
content of the database is not manipulated as objects and attribute

Question 2

What are the pros of java database connectivity

Answer 2

o database accessible from Java
o handle errors with Exception handling

Question 3

What are the cons of java database connectivity

Answer 3

o SQL statements in the code
o complexify the program
o mapping between object and tables needs to be specified and
maintained

Question 4

What is Object-Relational Impedance Mismatch

Answer 4

Object-Relational Impedance Mismatch’ is just a fancy way of saying that
object models and relational models do not work very well together.
RDBMSs represent data in a tabular format , whereas object-oriented
languages, such as Java, represent it as an interconnected graph of objects.
Loading and storing graphs of objects using a tabular relational database
exposes us to […] mismatch problems.

Question 5

What is object relational mapping(ORM)

Answer 5

ORM = a task
- converting OO concepts to relational databases concepts
- input: a domain model (class diagram)
- output: relational schema

Question 6

How do we specify and use our mapping in our java application?

Answer 6

By use of Jakarta and hibernate

Question 7

what is jakarta persistemce API(JPA)

Answer 7

▪ specification (not a tool -> guidelines)
▪ removes the burden of thinking relationally in Java code

Question 8

What is hibernate

Answer 8

It’s the implementation of JPA (= JPA provider)
It rely on ORM to simplify the persistence layer
▪ e.g., manipulating data as objects, without JDBC or SQ

Question 9

What is the purpose of JPA (Jakarta Persistence API)?

Answer 9

JPA simplifies the persistence layer by allowing developers to manage relational data as Java objects using annotations, an EntityManager API, and JPQL (object-based query language)

Question 10

Is JPA a tool or a specification?

Answer 10

JPA is a specification (guidelines). Tools like Hibernate provide its implementation

Question 11

What is Hibernate in relation to JPA?

Answer 11

Hibernate is a JPA provider (implementation). It manages ORM and allows data to be manipulated as Java objects, removing the need for JDBC/SQL code

Question 12

What annotation makes a class persistable in JPA?

Answer 12

@Entity

Question 13

How do you mark the primary key in JPA?

Answer 13

With @Id. Optionally, use @GeneratedValue to auto-generate unique primary keys

Question 14

Which JPA annotations handle associations?

Answer 14

One-to-Many: @OneToMany / @ManyToOne

Many-to-Many: @ManyToMany

Question 15

What is the EntityManager API in JPA?

Answer 15

An API that provides CRUD operations (Create, Read, Update, Delete) without writing JDBC or SQL code

Question 16

What is JPQL, and how does it differ from SQL?

Answer 16

JPQL (Java Persistence Query Language) is like SQL but operates on objects, attributes, and relationships, not on tables and columns

Question 17

Give an example JPQL query.

Answer 17

SELECT s.name FROM Student s
SELECT o FROM Offering o WHERE o.courseID = “ECSE321”

Question 18

What are the main steps of using JPA persistence?

Answer 18

1.Annotate classes for persistence (@Entity, @Id, etc.).
2.Manage data with EntityManager (CRUD).
3.Query with JPQL

Question 19

What is Spring Data JPA?

Answer 19

A framework built on top of JPA that reduces boilerplate by providing repositories and auto-generated query methods

Question 20

What does CrudRepository provide in Spring Data JPA?

Answer 20

Standard CRUD methods: save, findOne, findAll, count, delete, exists

Question 21

What are the two ways to define query methods in Spring Data JPA?

Answer 21

1.With @Query annotation (using JPQL).
2.Automatically derived from method names (e.g., findByLastOrFirst)

Question 22

Give an example of a custom query with @Query.

Answer 22

@Query(“SELECT o FROM Offering o JOIN o.course c WHERE c.courseId = ?1”)
Collection<Offering> findAllOfferingOfCourse(String courseId);</Offering>

Question 23

What problem does ORM (and JPA/Hibernate) solve compared to JDBC?

Answer 23

It solves the object-relational impedance mismatch: the difficulty of mapping object-oriented models (Java) to relational models (tables)