Repositories

Now that we have a general idea of how to set up our entity classes and repositories, let’s take a deeper dive into how repositories are used to perform CRUD operations on a database.

CRUD Operations

Previously, we learned that we can create a repository to fetch rows of a table in a database. To do so, we need to create a corresponding controller.

When creating our controller, we add a variable of the repository type that has the annotation @Autowired.

Next, we will learn how to use some of the more common CrudRepository methods, such as delete(T entity), deleteById(ID id), findAll(), findById(ID id), and save(S entity).

Using Persistence in a Controller - Video

The following video explains how we can add a controller to manage persistence in our codingevents application. The accompanying text is a quick rundown of what happens in the video. To get started, create a branch off of your persistent-model branch.

Using Persistence in a Controller - Text

Inside of EventController, we can add a variable of type EventRepository and give it an @Autowired annotation. For events, we want to be able to display all of the events in our database as well as add and delete events.

When displaying the events in our database, we write a method, displayAllEvents. We want to use displayAllEvents to display a table that contains all of our events. We did something similar to this before, but we used a list or iterable containing all of the objects we wanted to display. Since we have set up ORM between the MySQL database and our MVC application, we need to use the methods from CrudRepository to get all of the instances of the Event class. We can use the findAll() method to return an iterable containing all of the events in our database.

As you write the methods necessary for EventController, you might notice that this controller doesn’t look too different from other controllers we previously created.

Now we need to use the methods in CrudRepository to fetch the necessary information or update the correct table. Update your methods within EventController so that they no longer use the EventData class and instead use our newly created eventRepository.

Since we no longer use the EventData class it can be safely removed.

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