3. what is Repository class

In the context of a Spring Boot application, a repository class serves as an interface between the application’s business logic and the underlying data storage mechanism, typically a database. Here’s a more detailed explanation:

1. Responsibilities:

   • Data access: The primary responsibility of a repository class is to provide methods for performing CRUD (Create, Read, Update, Delete) operations on domain objects (entities) stored in a database.
   • Encapsulation of database interactions: Repository classes encapsulate the details of database interactions, such as SQL queries or MongoDB commands, behind a higher-level interface. This allows the rest of the application to work with domain objects without needing to understand the specifics of how data is stored or retrieved.
   • Query methods: Repository classes often include methods for executing custom queries to retrieve data based on specific criteria. These queries can be defined using method naming conventions or by using query annotations like @Query.
   • Transaction management: Repository methods may be annotated with transactional annotations like @Transactional to define transactional boundaries for database operations. This ensures that multiple database operations are executed atomically and consistently.

2. Examples of Repository Methods:

   • save: Method for saving or updating an entity in the database.
   • findById: Method for retrieving an entity by its unique identifier.
   • findAll: Method for retrieving all entities of a certain type.
   • Custom query methods: Methods for executing custom database queries based on specific criteria, such as finding users by their username or retrieving orders by their status.

3. Repository Layer in the Application Architecture:

   • Repository classes are part of the repository layer in the application architecture, which sits between the service layer (responsible for business logic) and the data storage layer (e.g., database).
   • The repository layer helps to abstract away the details of database interactions and promotes a modular, maintainable design by providing a clean separation of concerns.
   • Repository classes are typically interfaces that extend Spring Data interfaces like CrudRepository or MongoRepository. Spring Data provides implementations for these interfaces at runtime, based on the data storage technology used (e.g., Hibernate for relational databases or Spring Data MongoDB for MongoDB).

4. Usage of Repository Classes:

   • Repository classes are typically defined as interfaces annotated with @Repository or @Component to indicate their role in the application.
   • These interfaces define methods for data access operations, which are implemented by Spring Data at runtime based on the method signatures.
   • Repository instances are typically injected into service classes using dependency injection, allowing service methods to interact with the database through the repository interface.

In summary, repository classes in a Spring Boot application serve as an abstraction layer for data access, providing a clean and consistent interface for interacting with the underlying database. They help to separate concerns, promote modularity, and simplify database interactions within the application.