Exercise Solutions: OMG the ORM!

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!

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@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);
   }
}

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The EventCategoryController Class

displayAllEvents

displayAllEvents 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.

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@GetMapping
public String displayAllCategories(Model model) {
   model.addAttribute("title", "All Categories");
   model.addAttribute("categories", eventCategoryRepository.findAll());
   return "eventCategories/index";
}

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processCreateEventCategoryForm

processCreateEventCategoryForm needs to do the following:

  1. Use @PostMapping.

  2. 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.

  3. Add an attribute for the title and assign it "Create Category".

  4. Add an attribute for a new instance of EventCategory.

  5. Either return "eventCategories/create" or "redirect:".

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@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:";
}

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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.

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    <!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>

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