Creating a Repository Interface
Spring’s CrudRepository interface provides all the methods like findById() and save() to fetch from the database or to update the database. All we need to do is define a specialized interface to extend the CrudRepository. Spring Data will generate implementations for interfaces that extend CrudRepository.
If we were writing in Java, we’d write something like:
| | //Java code only for comparison purpose |
| | package com.agiledeveloper.todo; |
| | |
| | import org.springframework.data.repository.CrudRepository; |
| | |
| | interface TaskRepository extends CrudRepository<Task, Long> { |
| | } |
The Kotlin code isn’t too different from that: there’s no need for ; or {}, and we replaced extends with :. Let’s write the Kotlin equivalent of the interface by creating a file, todo/src/main/kotlin/com/agiledeveloper/todo/TaskRepository.kt, with the following content:
| | package com.agiledeveloper.todo |
| | |
| | import org.springframework.data.repository.CrudRepository |
| | |
| | interface TaskRepository : CrudRepository<Task, Long> |
The interface TaskRepository extends from CrudRepository<Task, Long>, where the first parametric type Task specifies the type of the entity, and the second parametric type Long specifies the type of the primary key.
We’re all set to perform CRUD operations, but we need a service to make the calls from. Let’s write that next.