Feat: Complete Expense Management CRUD Functionality

README.md

@@ -4,8 +4,8 @@ A REST-ful API designed to manage personal financial expenses and categories. Th
 
 ## Features
 
-- [ ] Category Management (CRUD): Add, view, update, and delete spending categories
-- [ ] Record transactions with details like description, amount and date, linking each to a specific category
+- [x] Category Management (CRUD): Add, view, update, and delete spending categories
+- [ ] Record expenses with details like description, amount and date, linking each to a specific category
 - [ ] Uses `Decimal(10, 2)` for amount to ensure accurate financial calculations.
 - [ ] Auditing: Automatic timestamping for creation and last update (`createdAt`, `updateAt`).
 - [ ] Documentation: Fully documented endpoints using Swagger (OpenAPI).

Requests.http

@@ -63,4 +63,66 @@ Content-Type: application/json
 }
 
 ### Delete a category
-DELETE http://localhost:8080/api/categories/3
+DELETE http://localhost:8080/api/categories/3
+
+### Create a new expense
+POST http://localhost:8080/api/expenses
+Content-Type: application/json
+
+{
+  "amount": 1200,
+  "description": "January Rent",
+  "categoryId": 1
+}
+
+### Create another expense
+POST http://localhost:8080/api/expenses
+Content-Type: application/json
+
+{
+  "amount": 1500,
+  "description": "February Rent",
+  "categoryId": 1
+}
+
+### Get all expenses
+GET http://localhost:8080/api/expenses
+
+### Get a single expense
+GET http://localhost:8080/api/expenses/1
+
+### Update an expense
+PUT http://localhost:8080/api/expenses/2
+Content-Type: application/json
+
+{
+    "amount": 1600,
+    "description": "February Rent Updated",
+    "categoryId": 1
+}
+
+### Create an expense with missing fields
+POST http://localhost:8080/api/expenses
+Content-Type: application/json
+
+{
+  "amount": 300,
+  "expense_description": "Groceries",
+  "categoryId": 4
+}
+
+### Create an expense with a non-existent category
+POST http://localhost:8080/api/expenses
+Content-Type: application/json
+
+{
+  "amount": 300,
+  "description": "Groceries",
+  "categoryId": 99
+}
+
+### Delete an expense
+DELETE http://localhost:8080/api/expenses/1
+
+### Delete a non-existent expense
+DELETE http://localhost:8080/api/expenses/99

src/main/java/com/muchemi/expense_tracker/controllers/CategoryController.java

@@ -1,7 +1,7 @@
 package com.muchemi.expense_tracker.controllers;
 
-import com.muchemi.expense_tracker.dto.CategoryRequestDTO;
-import com.muchemi.expense_tracker.dto.CategoryResponseDTO;
+import com.muchemi.expense_tracker.dto.category.CategoryRequestDTO;
+import com.muchemi.expense_tracker.dto.category.CategoryResponseDTO;
 import com.muchemi.expense_tracker.services.CategoryService;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.http.ResponseEntity;

src/main/java/com/muchemi/expense_tracker/controllers/ExpenseController.java

@@ -0,0 +1,58 @@
+package com.muchemi.expense_tracker.controllers;
+
+
+import com.muchemi.expense_tracker.dto.expense.ExpenseRequestDTO;
+import com.muchemi.expense_tracker.dto.expense.ExpenseResponseDTO;
+import com.muchemi.expense_tracker.repositories.CategoryRepository;
+import com.muchemi.expense_tracker.services.CategoryService;
+import com.muchemi.expense_tracker.services.ExpenseService;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.*;
+
+import java.util.List;
+
+@RestController
+@RequestMapping("api/expenses")
+public class ExpenseController {
+    private final ExpenseService expenseService;
+    private final CategoryService categoryService;
+
+    @Autowired
+    public ExpenseController(ExpenseService expenseService, CategoryService categoryService) {
+        this.categoryService = categoryService;
+        this.expenseService = expenseService;
+    }
+
+    @PostMapping
+    public ResponseEntity<ExpenseResponseDTO> createExpense(@RequestBody ExpenseRequestDTO dto) {
+        ExpenseResponseDTO response = expenseService.createNewExpense(dto);
+
+        return ResponseEntity.ok(response);
+    }
+
+    @GetMapping
+    public ResponseEntity<List<ExpenseResponseDTO>> getAllExpenses() {
+        List<ExpenseResponseDTO> expenses = expenseService.getAllExpenses();
+
+        return ResponseEntity.ok(expenses);
+    }
+
+    @GetMapping("{id}")
+    public ResponseEntity<ExpenseResponseDTO> getExpenseById(@PathVariable Long id) {
+        ExpenseResponseDTO response = expenseService.getExpenseById(id);
+        return ResponseEntity.ok(response);
+    }
+
+    @PutMapping("{id}")
+    public ResponseEntity<ExpenseResponseDTO> updateExpense(@PathVariable Long id, @RequestBody ExpenseRequestDTO dto) {
+        ExpenseResponseDTO updatedExpense = expenseService.updateExpense(id, dto);
+        return ResponseEntity.ok(updatedExpense);
+    }
+
+    @DeleteMapping("{id}")
+    public ResponseEntity<Long> deleteExpenseById(@PathVariable Long id) {
+        Long deletedId = expenseService.removeExpenseById(id);
+        return ResponseEntity.ok(deletedId);
+    }
+}

src/main/java/com/muchemi/expense_tracker/dto/CategoryRequestDTO.java → src/main/java/com/muchemi/expense_tracker/dto/category/CategoryRequestDTO.java

@@ -1,4 +1,4 @@
-package com.muchemi.expense_tracker.dto;
+package com.muchemi.expense_tracker.dto.category;
 
 public record CategoryRequestDTO(String name) {
 }

src/main/java/com/muchemi/expense_tracker/dto/CategoryResponseDTO.java → src/main/java/com/muchemi/expense_tracker/dto/category/CategoryResponseDTO.java

@@ -1,4 +1,4 @@
-package com.muchemi.expense_tracker.dto;
+package com.muchemi.expense_tracker.dto.category;
 
 public record CategoryResponseDTO(Long id, String name) {
 }

src/main/java/com/muchemi/expense_tracker/dto/expense/ExpenseRequestDTO.java

@@ -0,0 +1,11 @@
+package com.muchemi.expense_tracker.dto.expense;
+
+import java.math.BigDecimal;
+import java.time.LocalDate;
+
+public record ExpenseRequestDTO(
+        String description,
+        BigDecimal amount,
+        Long categoryId,
+        LocalDate date
+) {}

src/main/java/com/muchemi/expense_tracker/dto/expense/ExpenseResponseDTO.java

@@ -0,0 +1,7 @@
+package com.muchemi.expense_tracker.dto.expense;
+
+import java.math.BigDecimal;
+import java.time.LocalDate;
+
+public record ExpenseResponseDTO(Long id, String description, BigDecimal amount, LocalDate date, Long categoryId) {
+}

src/main/java/com/muchemi/expense_tracker/dto/mappers/ExpenseResponseDTOMapper.java

@@ -0,0 +1,16 @@
+package com.muchemi.expense_tracker.dto.mappers;
+
+import com.muchemi.expense_tracker.dto.expense.ExpenseResponseDTO;
+import com.muchemi.expense_tracker.entities.Expense;
+
+public class ExpenseResponseDTOMapper {
+    public static ExpenseResponseDTO toDTO(Expense expense) {
+        return new ExpenseResponseDTO(
+            expense.getId(),
+            expense.getDescription(),
+            expense.getAmount(),
+            expense.getDate(),
+            expense.getCategory().getId()
+        );
+    }
+}

src/main/java/com/muchemi/expense_tracker/entities/Expense.java

@@ -5,16 +5,18 @@
 import lombok.Data;
 import lombok.NoArgsConstructor;
 import org.hibernate.annotations.Check;
+import org.hibernate.annotations.CreationTimestamp;
+import org.hibernate.annotations.UpdateTimestamp;
 import org.springframework.data.annotation.CreatedDate;
 import org.springframework.data.annotation.LastModifiedDate;
 import org.springframework.data.jpa.domain.support.AuditingEntityListener;
 
 import java.math.BigDecimal;
 import java.time.Instant;
+import java.time.LocalDate;
 
 @Entity
 @Table(name = "expense")
-@EntityListeners(AuditingEntityListener.class)
 @NoArgsConstructor
 @AllArgsConstructor
 @Data
@@ -30,15 +32,18 @@ public class Expense {
     @Check(constraints = "amount > 0", name = "amount_must_be_positive")
     private BigDecimal amount;
 
+    @Column(nullable = false)
+    private LocalDate date;
+
     @ManyToOne(fetch = FetchType.LAZY)
     @JoinColumn(name = "category_id", nullable = false)
     private Category category;
 
-    @CreatedDate
+    @CreationTimestamp
     @Column(nullable = false, updatable = false)
     private Instant createdAt;
 
-    @LastModifiedDate
+    @UpdateTimestamp
     @Column(nullable = false)
     private Instant updatedAt;
 }

src/main/java/com/muchemi/expense_tracker/exceptions/GlobalExceptionHandler.java

@@ -38,6 +38,18 @@ public ResponseEntity<Object> handleResourceConflictException(ResourceConflictEx
         return new ResponseEntity<>(body, HttpStatus.CONFLICT);
     }
 
+    @ExceptionHandler(IllegalArgumentException.class)
+    public ResponseEntity<Object> handleIllegalArgumentException(IllegalArgumentException ex, WebRequest request) {
+        Map<String, Object> body = new LinkedHashMap<>();
+        body.put("timestamp", Instant.now());
+        body.put("status", HttpStatus.BAD_REQUEST.value());
+        body.put("error", "Bad Request");
+        body.put("message", ex.getMessage());
+        body.put("path", request.getDescription(false).replace("uri=", ""));
+
+        return new ResponseEntity<>(body, HttpStatus.BAD_REQUEST);
+    }
+
     @ExceptionHandler(Exception.class)
     public ResponseEntity<Object> handleGenericException(Exception ex, WebRequest request) {
         Map<String, Object> body = new LinkedHashMap<>();

src/main/java/com/muchemi/expense_tracker/repositories/ExpenseRepository.java

@@ -4,4 +4,5 @@
 import org.springframework.data.jpa.repository.JpaRepository;
 
 public interface ExpenseRepository extends JpaRepository<Expense, Long> {
+    boolean existsByDescriptionIgnoreCase(String normalizedDescription);
 }

src/main/java/com/muchemi/expense_tracker/services/CategoryService.java

@@ -1,7 +1,7 @@
 package com.muchemi.expense_tracker.services;
 
-import com.muchemi.expense_tracker.dto.CategoryRequestDTO;
-import com.muchemi.expense_tracker.dto.CategoryResponseDTO;
+import com.muchemi.expense_tracker.dto.category.CategoryRequestDTO;
+import com.muchemi.expense_tracker.dto.category.CategoryResponseDTO;
 import com.muchemi.expense_tracker.entities.Category;
 import com.muchemi.expense_tracker.exceptions.ResourceConflictException;
 import com.muchemi.expense_tracker.exceptions.ResourceNotFoundException;
@@ -11,6 +11,7 @@
 
 import java.util.List;
 
+// TODO: Refactor to reduce code duplication
 @Service
 public class CategoryService {
     private static CategoryRepository categoryRepository = null;
@@ -20,7 +21,7 @@ public CategoryService(CategoryRepository categoryRepository) {
     }
 
     public CategoryResponseDTO createNewCategory(CategoryRequestDTO dto) {
-        if (dto.name() == null || dto.name().trim().isEmpty()) {
+            if (dto.name() == null || dto.name().trim().isEmpty()) {
             throw new ResourceConflictException("Category name cannot be empty or null.");
         }
 

src/main/java/com/muchemi/expense_tracker/services/ExpenseService.java

@@ -0,0 +1,98 @@
+package com.muchemi.expense_tracker.services;
+
+import com.muchemi.expense_tracker.dto.expense.ExpenseRequestDTO;
+import com.muchemi.expense_tracker.dto.expense.ExpenseResponseDTO;
+import com.muchemi.expense_tracker.dto.mappers.ExpenseResponseDTOMapper;
+import com.muchemi.expense_tracker.entities.Category;
+import com.muchemi.expense_tracker.entities.Expense;
+import com.muchemi.expense_tracker.exceptions.ResourceNotFoundException;
+import com.muchemi.expense_tracker.repositories.CategoryRepository;
+import com.muchemi.expense_tracker.repositories.ExpenseRepository;
+import org.springframework.stereotype.Service;
+
+import java.time.LocalDate;
+import java.util.List;
+
+@Service
+public class ExpenseService {
+    private final ExpenseRepository expenseRepository;
+    private final CategoryRepository categoryRepository;
+
+    public ExpenseService(ExpenseRepository expenseRepository, CategoryRepository categoryRepository) {
+        this.expenseRepository = expenseRepository;
+        this.categoryRepository = categoryRepository;
+    }
+
+    public boolean isDescriptionTaken(String description) {
+        String normalizedDescription = description.trim().toLowerCase();
+        return expenseRepository.existsByDescriptionIgnoreCase(normalizedDescription);
+    }
+
+    public ExpenseResponseDTO createNewExpense(ExpenseRequestDTO dto) {
+        Expense preparedExpense = prepareExpense(new Expense(), dto);
+
+        try {
+            Expense savedExpense = expenseRepository.save(preparedExpense);
+            return ExpenseResponseDTOMapper.toDTO(savedExpense);
+        } catch (Exception exception) {
+            throw new RuntimeException("An error occurred while saving the expense: " + exception.getMessage());
+        }
+    }
+
+    public List<ExpenseResponseDTO> getAllExpenses() {
+        return expenseRepository.findAll()
+            .stream()
+            .map(ExpenseResponseDTOMapper::toDTO)
+            .toList();
+    }
+
+    public ExpenseResponseDTO getExpenseById(Long id) {
+        Expense expense = expenseRepository.findById(id)
+            .orElseThrow(() -> new ResourceNotFoundException("Expense not found with id: " + id));
+        return ExpenseResponseDTOMapper.toDTO(expense);
+    }
+
+    public Long removeExpenseById(Long id) {
+        if (!expenseRepository.existsById(id)) {
+            throw new ResourceNotFoundException("Expense not found with id: " + id);
+        }
+        expenseRepository.deleteById(id);
+        return id;
+    }
+
+    public ExpenseResponseDTO updateExpense(Long id, ExpenseRequestDTO dto) {
+        Expense expense = expenseRepository.findById(id)
+            .orElseThrow(() -> new ResourceNotFoundException("Expense not found with id: " + id));
+        Expense preparedExpense = prepareExpense(expense, dto);
+
+        try {
+            Expense updatedExpense = expenseRepository.save(preparedExpense);
+            return ExpenseResponseDTOMapper.toDTO(updatedExpense);
+        } catch (Exception exception) {
+            throw new RuntimeException("An error occurred while updating the expense: " + exception.getMessage());
+        }
+    }
+
+    private Expense prepareExpense(Expense expense, ExpenseRequestDTO dto) {
+        if (dto.description() == null || dto.description().trim().isEmpty()) {
+            throw new IllegalArgumentException("Expense description cannot be empty or null.");
+        }
+        if (dto.description().length() > 255) {
+            throw new IllegalArgumentException("Expense description cannot exceed 255 characters.");
+        }
+        if (isDescriptionTaken(dto.description())) {
+            throw new IllegalArgumentException("Expense description '" + dto.description() + "' already exists.");
+        }
+        LocalDate expenseDate = dto.date() != null ? dto.date() : LocalDate.now();
+        expense.setDate(expenseDate);
+
+        Category category = categoryRepository.findById(dto.categoryId())
+          .orElseThrow(() -> new ResourceNotFoundException("Category not found with id: " + dto.categoryId()));
+
+        expense.setDescription(dto.description());
+        expense.setAmount(dto.amount());
+        expense.setCategory(category);
+
+        return expense;
+    }
+}