# Spring 5 course : Udemy - Unit 2

[toc]

## Unit 2: Building a Spring Boot Web App

*Quick overview of Spring in a very productive way.*

Generate html with dynamic content.

Disclaimer: how to use this but not going fully in details in this chapter.

- Spring Boot
- Spring MVC
- Spring Data JPA (Hibernate)
- H2 database



## Spring Initializr

Back in time you needed to create you own project with maven. Spring Initializr does this job for you (maven or gradle).

https://github.com/spring-projects/spring-boot/tree/main/spring-boot-project/spring-boot-starters



Create a simple webapp with: https://start.spring.io/

- Spring Web (Spring mvc)
- Spring Data JPA (abstraction for hibernate)
- H2 Database (our in memory database)



### Open the project in IntelliJ

For a maven project: ***From Existing source > Select the pom.xml*** file at the root of the project

Look at currated dependencies in the pom.xml by ctrl+click on the `parent.artifactId`

From the currated dependancies you can omit the version when you add them to your pom.xml because they are references in `spring-boot-parent-2.x.x.RELEASE.pom`



Session 3 - 28/10/2022 - ended here

<hr>
## Github Workflow

[Starts from here](https://sparkers.udemy.com/course/spring-framework-5-beginner-to-guru/learn/lecture/17789252#overview) Github workflow.

- starting source
- end source

1- fork the project and clone the repo to local

2- co fork start with starting source

3- use compare feature of git with relevant branch



Compare to source (not fork)

1st- >Copy the cloning url from original project

```
git remote add sfgRepo <protocol:originalrepo/url>
git fetch sfgRepo
```

**Then in the GUI:** git > compare with branch.



## JPA Entities

*Java Persistance API - api for Hibernate.*

Modeling the data.

### Creating two POJOs

**Book**

- title
- isbn
- authors (`as Set<Author>`)

**Author**

- firstName
- lastName
- books (`as Set<Book>`)

***NOTE: JPA requires a 0 args construcor***

Tips: Bring up the menu with `alt+insert` for constructors, getters and setters



Now we are going to make them official JPA entities that can be persisted.

***Leakage*** - object leaking up in an object database.

### Assign JPA Id's

```java
@Entity
public class Book {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    ...
```



### JPA Relationships

*Many to many relationships.* (there will be a dedicated section in the framework course).

```
@ManyToMany(mappedBy = 'authors')
```

```
@ManyToMany
@JoinTable(name= 'author_book', joinColumns = @JoinColumn(name= 'book_id'), inverseJoinColumns = @JoinColumn(name= 'author_id'))
```



Session 4 - 30/10/2022 : ended here

<hr>



***Session 5 - 31/10/2022 : [Starts from here](https://sparkers.udemy.com/course/spring-framework-5-beginner-to-guru/learn/lecture/17792132#notes) Equality in hibernate***