Exercises: OMG the ORM!

For the exercises, we are going to continue building on our codingevents application. The exercise instructions assume that your code resembles the persistent-controller branch of CodingEventsJava. Create a new branch off of your own persistent-controller code to get started on the exercises.

Note

You will be making one entity class, one repository, and one controller. If you are not sure what these classes and interface should look like, refer back to the sections on persistent models and controllers and repositories .

The EventCategory Class

First, create a new class called EventCategory in the models directory.

EventCategory needs to have the following:

  1. An id field of type int.
  2. A name field of type String.
  3. A constructor.
  4. The appropriate getters and setters.

EventCategory represents data that will be stored in our database, so you need to use the @Entity annotation!

@Entity
public class EventCategory {

   @Id
   @GeneratedValue
   private int id;

   @Size(min=3, message="Name must be at least 3 characters long")
   private String name;

   public EventCategory(@Size(min = 3, message = "Name must be at least 3 characters long") String name) {
      this.name = name;
   }

   public EventCategory() {}

   public String getName() {
      return name;
   }

   public void setName(String name) {
      this.name = name;
   }

   public int getId() {
      return id;
   }

   @Override
   public String toString() {
      return name;
   }

   @Override
   public boolean equals(Object o) {
      if (this == o) return true;
      if (o == null || getClass() != o.getClass()) return false;
      EventCategory that = (EventCategory) o;
      return id == that.id;
   }

   @Override
   public int hashCode() {
      return Objects.hash(id);
   }
}

The EventCategoryRepository Interface

Once you have created EventCategory, you need to create the EventCategoryRepository in the data folder. EventCategoryRepository will extend the CrudRepository interface.

The EventCategoryController Class

Create EventCategoryController in the controllers directory. You can use the @RequestMapping annotation to map to "eventCategories". To get our handlers working, we also need a variable of type EventCategoryRepository.

We will be creating 3 handlers in our controller:

  1. displayAllCategories
  2. renderCreateEventCategoryForm
  3. processCreateEventCategoryForm

displayAllCategories

displayAllCategories needs to do the following:

  1. Use @GetMapping and return "eventCategories/index".
  2. Add an attribute for the title that uses "All Categories".
  3. Add an attribute for the categories that uses all of the values in your EventCategoryRepository variable.
@GetMapping
public String displayAllCategories(Model model) {
   model.addAttribute("title", "All Categories");
   model.addAttribute("categories", eventCategoryRepository.findAll());
   return "eventCategories/index";
}

renderCreateEventCategoryForm

renderCreateEventCategoryForm needs to do the following:

  1. Use @GetMapping and return "eventCategories/create".
  2. Add an attribute for the title and assign it "Create Category".
  3. Add an attribute for a new instance of EventCategory.

processCreateEventCategoryForm

processCreateEventCategoryForm needs to do the following:

  1. Use @PostMapping.
  1. Use error validation and the Errors object appropriately. If you want to review how to use the Errors object, check out the section on error validation .
  2. Add an attribute for the title and assign it "Create Category".
  3. Add an attribute for a new instance of EventCategory.
  4. Either return "eventCategories/create" or "redirect:".
@PostMapping("create")
public String processCreateEventCategoryForm(@Valid @ModelAttribute EventCategory eventCategory, Errors errors, Model model) {

   if (errors.hasErrors()) {
      model.addAttribute("title", "Create Category");
      model.addAttribute(new EventCategory());
      return "eventCategories/create";
   }

   eventCategoryRepository.save(eventCategory);
   return "redirect:";
}

Thymeleaf Templates

To finish the exercises, we need to make two new templates.

  1. eventCategories/index, which will contain a table of the event categories.

    <!DOCTYPE html>
   <html lang="en" xmlns:th="http://www.thymeleaf.org/">
      <head th:replace="fragments :: head"></head>
      <body class="container">

         <header th:replace="fragments :: header"></header>

         <table class="table table-striped">
            <thead>
            <tr>
               <th>Category Name</th>
            </tr>
            </thead>
            <tr th:each="category : ${categories}">
               <td th:text="${category.name}"></td>
            </tr>

         </table>

      </body>
   </html>

  2. eventCategories/create, which will contain a form for adding new event categories.

The Final Application

Once you are done, launch your app and head to localhost:8080/eventCategories! If you added categories already, you will see any categories already stored in the database. In this case, we added “Meetup” as a category the first time we ran our app to test it.

Screenshot showing the categories table with only “Meetup” in it. Screenshot showing the categories table with only “Meetup” in it.

If you click on “Create Category”, you should be directed to localhost:8080/eventCategories/create. We decided to add “Networking” as a category and filled out the form.

Screenshot showing the category form filled out with the word “Networking”. Screenshot showing the category form filled out with the word “Networking”.

Once you hit submit, you are redirected back to localhost:8080/eventCategories, and your table now contains the newest event category!

Screenshot showing the categories table with “Meetup” and “Networking” in it. Screenshot showing the categories table with “Meetup” and “Networking” in it.