# 3.1 Accessing databases in SpringBoot
The Jakarta Persistence API (JPA) defines a standard interface to manage data over relational databases;
There are several frameworks that implement the JPA specification, such as the Hibernate framework.
JPA offers a specification for ORM (object-relational mapping).
Spring Data uses and enhances the JPA. When you use Spring Data your Java code is independent from the specific database implementation.
## Spring boot CRUD[^1] application with Thymeleaf
For this part of the lab we are following this tutorial: [Spring Boot CRUD Application](https://www.baeldung.com/spring-boot-crud-thymeleaf)
[^1]: CRUD = Create, read, update and delete
The dependencies for the tutorial can be automatically imported via Spring Initializr (same procedure as last lab) with the following dependencies:
- Spring Web
- Thymeleaf
- Spring Data JPA
- H2 database
- Validation
While following the tutorial I still managed to find some annoying errors, to see them please refer to [Errors encountered](#errors-encountered)
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## Lab questions (b)
**- The “UserController” class gets an instance of “UserRepository” through its constructor; how is this new repository instantiated?**
In UserController we use the annotation @Autowired, while referencing the UserRepository class.
The Autowiring feature of spring framework enables you to inject the object dependency implicitly.
**- List the methods invoked in the “UserRepository” object by the “UserController”. Where are these methods defined?**
The methods invoked in the CrudRepository, (class extended by UserRepository) are:
- findAll(),
- findById(),
- save(),
- delete().
**-Where is the data being saved?**
The data is being saved by the H2 database (added to the project as a dependency, in pom.xml), as it has an in memory database.
**-Where is the rule for the “not empty” email address defined?**
The "not empty" rule is defined in the User, with the annotation ```@NotBlank``` when we declare the email attribute.
## Errors Encountered
- ```the Javax imports weren't loading```
- **Solution**: As I knew they were included in the spring-boot starter data jpa dependency, it couldnt be a code-sided error so even though I tried many commands and restarts to get them to work, I ended up just deleting the project and remaking it the same way. The true engineer way!
- ```The import org.springframework.stereotype.Repository conflicts with a type defined in the same file```
- **Solution**: It turned out that I named my file Repository.java which conflicted with the annotation Controller
- ```Error executing DDL "drop table if exists user cascade" via JDBC Statement```
- **Solution**: ```user``` is a reserved word in PostgreSQL, make sure you name the User entity as users or any other name using ```@Entity(name="users")``` on the file User.java