Add add Link usecase

3-Domain/src/main/java/category/CategoryRepository.java

@@ -1,9 +1,10 @@
 package category;
 
 import abstraction.CustomSet;
-import abstraction.PersistenceAdapter;
 import abstraction.CustomSetPersistenceDecorator;
+import abstraction.PersistenceAdapter;
 import exeptions.CategoryAlreadyExists;
+import exeptions.CategroyDoesNotExist;
 import exeptions.NonUniqueId;
 
 import java.util.Optional;
@@ -11,7 +12,6 @@ import java.util.Set;
 
 public class CategoryRepository {
 
-
 	final private CustomSet<Category> categories;
 
 	public CategoryRepository(PersistenceAdapter<Category> categoryPersistenceAdapter) {
@@ -22,11 +22,19 @@ public class CategoryRepository {
 		return categories.stream().filter(category -> category.getName().equals(name)).findFirst();
 	}
 
+	public CategoryId getIdByName(CategoryName name) {
+
+		return getByName(name)
+				.orElseThrow(() -> new CategroyDoesNotExist("A Category with name " + name + " does not exits. You must create it first."))
+				.getId();
+
+	}
+
 	public Optional<Category> getById(CategoryId id) {
 		return categories.stream().filter(category -> category.getId().equals(id)).findFirst();
 	}
 
-	public Set<Category> getAll(){
+	public Set<Category> getAll() {
 		return categories.getSet();
 	}
 
@@ -37,6 +45,7 @@ public class CategoryRepository {
 
 	/**
 	 * Check for duplicates with the domain rules
+	 *
 	 * @param category
 	 */
 	private void checkDuplicates(Category category) {

3-Domain/src/main/java/exeptions/CategroyDoesNotExist.java

@@ -0,0 +1,8 @@
+package exeptions;
+
+public class CategroyDoesNotExist extends RuntimeException {
+
+	public CategroyDoesNotExist(String message) {
+		super(message);
+	}
+}