[EDIT] 変更したテーブルに合わせてメソッドを修正しました。

src/main/java/com/example/demo/app/domain/service/GoalService.java

@@ -1,16 +1,18 @@
 package com.example.demo.app.domain.service;
 
+import java.util.List;
+
 import com.example.demo.app.domain.model.GoalModel;
 
 public interface GoalService {
 
 	GoalModel getGoalById(Long goalId);
 	
-	GoalModel getGoalByUserId(Long userId); 
+	public List<GoalModel> getGoalByUserId(Long userId); 
 
-	GoalModel createGoal(GoalModel goalModel);
+	public GoalModel createGoal(GoalModel goalModel, Long userId);
 
-	GoalModel updateGoal(GoalModel goalModel);
+	GoalModel updateGoal(GoalModel goalModel, Long userId);
 
 //	void deleteGoal(Long goalId);
 

src/main/java/com/example/demo/app/domain/service/impl/GoalServiceImpl.java

@@ -1,5 +1,8 @@
 package com.example.demo.app.domain.service.impl;
 
+import java.util.ArrayList;
+import java.util.List;
+
 import org.springframework.stereotype.Service;
 
 import com.example.demo.app.domain.model.GoalModel;
@@ -21,14 +24,14 @@ public class GoalServiceImpl implements GoalService {
 	@Override
 	public GoalModel getGoalById(Long goalId) {
 		GoalEntity goalEntity = goalRepository.findById(goalId).orElse(null);
-		return GoalModel.convertFrom(goalEntity);
+		return GoalModel.convertFrom(goalEntity, 0, 0);
 	}
 
 	@Override
-	public GoalModel getGoalByUserId(Long userId) {
+	public List<GoalModel> getGoalByUserId(Long userId) {
 
 		UserEntity userEntity = userRepository.findById(userId).orElseThrow();
-		GoalEntity goalEntity = userEntity.getGoalEntity();
+		List<GoalEntity> goalEntityList = goalRepository.findAllByUserId(userId);
 
 		// 収支の合計を計算(収入はプラス、支出はマイナス)
 		int transactionTotal = userEntity.getTransactionEntityList().stream()
@@ -42,42 +45,38 @@ public class GoalServiceImpl implements GoalService {
 		int currentAmount = userEntity.getSaving() + transactionTotal;
 
 		// 達成率(%) = 現在の資産 ÷ 目標金額 × 100
-		int achievementRate = 
-				(goalEntity.getTargetAmount() == null)
-				? 0	: 
-				(int) ((currentAmount * 100.0) / goalEntity.getTargetAmount());
 
-		GoalModel goalModel = GoalModel.convertFrom(goalEntity);
+		List<GoalModel> goalModelList = new ArrayList<GoalModel>();
 
-		return new GoalModel(
-				goalModel.getGoalId(),
-				goalModel.getGoalTitle(),
-				goalModel.getGoalSubtitle(),
-				goalModel.getTargetAmount(),
-				goalModel.getDeadline(),
-				goalModel.getGoalComplete(),
-				achievementRate,
-				currentAmount);   
+		goalEntityList.stream()
+				.forEach(goalEntity -> goalModelList.add(GoalModel.convertFrom(goalEntity,
+						(goalEntity.getTargetAmount() == null)
+								? 0
+								: (int) ((currentAmount * 100.0) / goalEntity.getTargetAmount()),
+						currentAmount)));
+
+
+		return goalModelList;
 	}
-	
-	@Override
-	public GoalModel createGoal(GoalModel goalModel) {
 
-		GoalEntity goalEntity = GoalModel.convertTo(goalModel);
+	@Override
+	public GoalModel createGoal(GoalModel goalModel, Long userId) {
+
+		GoalEntity goalEntity = GoalModel.convertTo(goalModel, userRepository.findById(userId).get());
 
 		GoalEntity savedGoalEntity = goalRepository.save(goalEntity);
 
-		return GoalModel.convertFrom(savedGoalEntity);
+		return GoalModel.convertFrom(savedGoalEntity, 0, 0);
 	}
 
 	@Override
-	public GoalModel updateGoal(GoalModel goalModel) {
+	public GoalModel updateGoal(GoalModel goalModel, Long userId) {
 
-		GoalEntity goalEntity = GoalModel.convertTo(goalModel);
+		GoalEntity goalEntity = GoalModel.convertTo(goalModel, userRepository.findById(userId).get());
 
 		GoalEntity updatedGoalEntity = goalRepository.save(goalEntity);
 
-		return GoalModel.convertFrom(updatedGoalEntity);
+		return GoalModel.convertFrom(updatedGoalEntity, 0, 0);
 	}
 
 }

src/main/java/com/example/demo/app/infra/repository/GoalRepository.java

@@ -1,6 +1,9 @@
 package com.example.demo.app.infra.repository;
 
+import java.util.List;
+
 import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.data.jpa.repository.Query;
 import org.springframework.stereotype.Repository;
 
 import com.example.demo.app.infra.entity.GoalEntity;
@@ -8,4 +11,7 @@ import com.example.demo.app.infra.entity.GoalEntity;
 @Repository
 public interface GoalRepository extends JpaRepository<GoalEntity, Long> {
 	
+	@Query("select g from GoalEntity g where g.userEntity.userId = :userId")
+	public List<GoalEntity> findAllByUserId(Long userId);
+	
 }

src/main/java/com/example/demo/app/presentation/controller/GoalController.java

@@ -69,7 +69,7 @@ public class GoalController {
 		}
 
 		GoalModel goalModel = GoalModel.convertFrom(goalForm);
-		goalService.updateGoal(goalModel);
+		goalService.updateGoal(goalModel, userId);
 
 		return "redirect:/goal";
 	}