Error Handling

The Sales Management System API uses consistent error response patterns to help you handle failures gracefully.

Error Response Format

All error responses follow this structure:

{
  "error": true,
  "msg": "Error description"
}

Some errors include additional context:

{
  "error": true,
  "msg": "Detailed error message",
  "productList": [...],  // For foreign key violations
  "saleList": [...]      // For related records
}

HTTP Status Codes

The API uses standard HTTP status codes:

Status Code	Meaning	When Used
`200`	Success	Operation completed successfully
`400`	Bad Request	Invalid input, validation failed
`404`	Not Found	Resource doesn’t exist
`409`	Conflict	Duplicate entry, foreign key constraint
`500`	Server Error	Database query failed, internal error

Common Errors

Validation Errors

Occur when input doesn’t meet validation requirements.

Empty Request Body

Request:

curl -X POST http://localhost:3000/categories \
  -H "Content-Type: application/json" \
  -d '{}'

Response:

{
  "error": true,
  "msg": "request body is empty"
}

Status Code: 400 Bad Request Solution: Provide required fields in the request body.

Invalid Field Values

Example: Category name too short Request:

curl -X POST http://localhost:3000/categories \
  -H "Content-Type: application/json" \
  -d '{"name":"ab"}'

Response:

{
  "error": true,
  "msg": "categorie name is invalid"
}

Status Code: 400 Bad Request Validation Rules:

Category name: minimum 3 characters
Product name: minimum 3 characters
Product description: minimum 10 characters
Client name: minimum 3 characters
Email: valid email format
Stock: non-negative integer
Price: positive decimal
Quantity: positive integer

Validation is performed using Zod schemas in src/controller/validation/.

Duplicate Entry Errors

Occur when trying to create a record with a value that must be unique.

Duplicate Category Name

Request:

curl -X POST http://localhost:3000/categories \
  -H "Content-Type: application/json" \
  -d '{"name":"bebidas"}'

Response (if “bebidas” already exists):

{
  "error": true,
  "msg": "categorie name exist"
}

Status Code: 409 Conflict Solution: Use a different category name.

Duplicate Client Email

Request:

curl -X POST http://localhost:3000/clients \
  -H "Content-Type: application/json" \
  -d '{"name":"John Doe","email":"[email protected]"}'

Response (if email exists):

{
  "error": true,
  "msg": "Email already registered"
}

Status Code: 409 Conflict Unique Constraints:

categories.name
clients.email
users.email
roles.name

Foreign Key Constraint Violations

Occur when trying to delete a record that other records depend on.

Cannot Delete Category with Products

From the README.md example: Request:

curl -X DELETE http://localhost:3000/categories/1

Response (if products exist with category_id = 1):

{
  "error": true,
  "msg": "there are products with this category",
  "productList": [
    {
      "id": "1373fe00-14e4-11f1-9fcd-2418c6c96a00"
    }
  ]
}

Status Code: 409 Conflict Solution:

Update products to a different category
Delete the products first
Or keep the category

Implementation (from src/model/categorie.model.js:30-48):

export function deleteCategorie(id) {
    return pool.query(
        `SELECT BIN_TO_UUID(id) as id FROM products WHERE category_id = ?`,
        [id]
    ).then((value) => {
        if (value[0].length != 0) {
            throw new Error(JSON.stringify({ 
                error: true, 
                msg: "there are products with this category", 
                productList: value[0] 
            }))
        } else {
            return pool.query(
                "DELETE FROM categories WHERE id = ?",
                [id]
            )
        }
    }).then((row) => {
        return { error: false, msg: "Categorie deleted successfully" };
    }).catch((err) => {
        return JSON.parse(err.message)
    })
}

Cannot Delete Product with Sales

From the README.md example: Request:

curl -X DELETE http://localhost:3000/products/1373fe00-14e4-11f1-9fcd-2418c6c96a00

Response (if product has sales):

{
  "error": true,
  "msg": "there are sales with this product",
  "salesList": [
    {
      "idSaleDetails": "4033e9a1-5858-44c9-b1d7-39c718933372",
      "idSale": "878d89a7-a1a1-4411-a359-1ad08965fb30"
    }
  ]
}

Status Code: 409 Conflict Solution:

Products with sales cannot be deleted (data integrity)
Use the is_deleted flag for soft deletion instead

Cannot Delete Client with Sales

From the README.md example: Request:

curl -X DELETE http://localhost:3000/clients/036c71c5-14e0-11f1-9fcd-2418c6c96a00

Response (if client has sales):

{
  "error": true,
  "msg": "there are sales with this client",
  "saleList": [
    {
      "idSale": "878d89a7-a1a1-4411-a359-1ad08965fb30"
    }
  ]
}

Status Code: 409 Conflict Solution:

Clients with sales history cannot be deleted
This preserves historical sales data

Stock Validation Errors

Occur when trying to sell more items than available in stock. Request:

curl -X POST http://localhost:3000/sales \
  -H "Content-Type: application/json" \
  -d '{
    "clientId": "036c71c5-14e0-11f1-9fcd-2418c6c96a00",
    "ordenDetails": [{
      "productId": "1373fe00-14e4-11f1-9fcd-2418c6c96a00",
      "quantity": 100
    }]
  }'

Response (if product stock < 100):

{
  "error": true,
  "msg": "Insufficient stock for product",
  "available": 40,
  "requested": 100
}

Status Code: 400 Bad Request Solution: Reduce quantity to available stock or restock the product.

Resource Not Found Errors

Occur when requesting a non-existent resource. Request:

curl http://localhost:3000/categories/999

Response:

{
  "error": true,
  "msg": "Categorie no exits"
}

Status Code: 404 Not Found (or 400 depending on implementation) Common scenarios:

Invalid category ID
Invalid product UUID
Invalid client UUID
Invalid sale UUID

Database Query Errors

Occur when database operations fail. Response:

{
  "error": true,
  "msg": "Query of createCategories fail"
}

Status Code: 500 Internal Server Error Common causes:

Database connection lost
MySQL server down
Table doesn’t exist
Insufficient permissions

Troubleshooting:

Check database connection in src/config.js
Verify MySQL is running: sudo systemctl status mysql
Check database exists: SHOW DATABASES;
Verify user permissions: SHOW GRANTS FOR 'user'@'localhost';

Error Handling in Code

Controller Layer

Controllers validate input and handle model errors:

const createCategorieController = async (req, res) => {
    // Check empty body
    if (isEmpty(req.body)) 
        return res.status(400).json({ 
            error: true, 
            msg: "request body is empty" 
        });

    const { name } = req.body;

    // Validate input
    const validCategorie = await validateCategorie(name)
    if (!validCategorie) 
        return res.status(400).json({ 
            error: true, 
            msg: "categorie name is invalid" 
        });

    // Call model
    const data = await createCategorie(name)
    if (data.error) 
        return res.status(409).json({ 
            error: true, 
            msg: "categorie name exist" 
        });
    
    return res.status(200).json({ 
        error: false, 
        msg: "categorie was created sucessfully" 
    });
}

Model Layer

Models catch database errors and return standardized responses:

export function createCategorie(name) {
    return pool.query(
        "INSERT INTO categories (name) VALUES (?)",
        [name]
    ).then(() => {
        return { error: false, msg: "categorie created sucessfully" }
    }).catch((err) => {
        return { error: true, msg: "Query of createCategories fail" }
    })
}

Validation Layer

Zod schemas validate data types and constraints:

import z from "zod";

const schemmaName = z.string().min(3)

export const validateCategorie = async (categorie) => {
    let result = await schemmaName.safeParseAsync(categorie)
    return result.success;
}

safeParseAsync doesn’t throw exceptions, making error handling cleaner.

Client-Side Error Handling

JavaScript/Node.js Example

try {
    const response = await fetch('http://localhost:3000/categories', {
        method: 'POST',
        headers: { 'Content-Type': 'application/json' },
        body: JSON.stringify({ name: 'bebidas' })
    });
    
    const data = await response.json();
    
    if (data.error) {
        // Handle API error
        console.error('API Error:', data.msg);
        
        if (data.productList) {
            console.log('Affected products:', data.productList);
        }
    } else {
        // Success
        console.log('Success:', data.msg);
    }
} catch (err) {
    // Handle network/parse errors
    console.error('Request failed:', err);
}

Python Example

import requests

try:
    response = requests.post(
        'http://localhost:3000/categories',
        json={'name': 'bebidas'}
    )
    data = response.json()
    
    if data.get('error'):
        print(f"API Error: {data['msg']}")
        if 'productList' in data:
            print(f"Affected products: {data['productList']}")
    else:
        print(f"Success: {data['msg']}")
        
except requests.exceptions.RequestException as e:
    print(f"Request failed: {e}")

cURL with Error Checking

response=$(curl -s -X POST http://localhost:3000/categories \
  -H "Content-Type: application/json" \
  -d '{"name":"bebidas"}')

error=$(echo $response | jq -r '.error')

if [ "$error" = "true" ]; then
    msg=$(echo $response | jq -r '.msg')
    echo "Error: $msg"
    exit 1
else
    echo "Success"
fi

Error Recovery Strategies

Validation Errors (400)

Strategy: Fix the input and retry

Check validation rules in the documentation
Ensure all required fields are present
Verify data types and formats
Retry with corrected data

Duplicate Entries (409)

Strategy: Use a different value or update existing record

Check if the record already exists (GET request)
If it exists and is correct, use it
If it exists but needs changes, use UPDATE (PATCH)
If it must be unique, choose a different value

Foreign Key Violations (409)

Strategy: Handle dependencies before deletion

Check for dependent records (the error includes IDs)
Update or delete dependent records first
Or keep the parent record if dependencies exist
Consider soft deletion instead of hard deletion

Resource Not Found (404)

Strategy: Verify the ID and handle gracefully

Check if the ID/UUID is correct
Verify the resource exists (GET request)
Handle missing resources in your UI/logic
Don’t assume resources exist

Database Errors (500)

Strategy: Check connection and retry

Verify database is running
Check network connectivity
Implement exponential backoff retry logic
Log errors for investigation
Consider circuit breaker pattern for production

Best Practices

Always Check the error Field

Every response includes "error": true/false. Always check this before processing data:

if (data.error) {
    // Handle error
} else {
    // Process success data
}

Display User-Friendly Messages

Convert API error messages to user-friendly text:

const errorMessages = {
    'categorie name is invalid': 'Category name must be at least 3 characters',
    'request body is empty': 'Please provide the required information',
    'categorie name exist': 'A category with this name already exists'
};

const userMessage = errorMessages[data.msg] || 'An error occurred';

Log Errors for Debugging

Keep detailed logs of errors:

console.error('API Error:', {
    endpoint: '/categories',
    method: 'POST',
    status: response.status,
    error: data.msg,
    timestamp: new Date().toISOString()
});

Implement Retry Logic

For transient errors (500), implement retry with exponential backoff:

async function apiCallWithRetry(url, options, maxRetries = 3) {
    for (let i = 0; i < maxRetries; i++) {
        try {
            const response = await fetch(url, options);
            const data = await response.json();
            
            if (!data.error || response.status < 500) {
                return data;
            }
            
            // Wait before retry (exponential backoff)
            await new Promise(r => setTimeout(r, Math.pow(2, i) * 1000));
        } catch (err) {
            if (i === maxRetries - 1) throw err;
        }
    }
}

Handle Network Errors

Network failures are different from API errors:

try {
    const response = await fetch(url, options);
    const data = await response.json();
    
    if (data.error) {
        // API returned an error
    }
} catch (err) {
    // Network error, parse error, etc.
    console.error('Network error:', err);
}

Testing Error Scenarios

Test your error handling with these scenarios:

# Validation error
curl -X POST http://localhost:3000/categories \
  -H "Content-Type: application/json" \
  -d '{"name":"ab"}'

# Duplicate entry
curl -X POST http://localhost:3000/categories \
  -H "Content-Type: application/json" \
  -d '{"name":"bebidas"}' # Run twice

# Foreign key violation
# First create a product with category 1, then:
curl -X DELETE http://localhost:3000/categories/1

# Not found
curl http://localhost:3000/categories/99999

# Empty body
curl -X POST http://localhost:3000/categories \
  -H "Content-Type: application/json" \
  -d '{}'

Next Steps

API Reference

See all endpoints and their error responses

Database Schema

Understand foreign key relationships

Architecture

Learn how errors flow through the system

Configuration

Fix database connection errors

Get Started

Core Concepts

Guides

Error Handling

Error Handling

Error Response Format

HTTP Status Codes

Common Errors

Validation Errors

Empty Request Body

Invalid Field Values

Duplicate Entry Errors

Duplicate Category Name

Duplicate Client Email

Foreign Key Constraint Violations

Cannot Delete Category with Products

Cannot Delete Product with Sales

Cannot Delete Client with Sales

Stock Validation Errors

Resource Not Found Errors

Database Query Errors

Error Handling in Code

Controller Layer

Model Layer

Validation Layer

Client-Side Error Handling

JavaScript/Node.js Example

Python Example

cURL with Error Checking

Error Recovery Strategies

Best Practices

Testing Error Scenarios

Next Steps

API Reference

Database Schema

Architecture

Configuration

Build docs developers (and LLMs) love

Get Started

Core Concepts

Guides

​Error Handling

​Error Response Format

​HTTP Status Codes

​Common Errors

​Validation Errors

​Empty Request Body

​Invalid Field Values

​Duplicate Entry Errors

​Duplicate Category Name

​Duplicate Client Email

​Foreign Key Constraint Violations

​Cannot Delete Category with Products

​Cannot Delete Product with Sales

​Cannot Delete Client with Sales

​Stock Validation Errors

​Resource Not Found Errors

​Database Query Errors

​Error Handling in Code

​Controller Layer

​Model Layer

​Validation Layer

​Client-Side Error Handling

​JavaScript/Node.js Example

​Python Example

​cURL with Error Checking

​Error Recovery Strategies

​Best Practices

​Testing Error Scenarios

​Next Steps

API Reference

Database Schema

Architecture

Configuration

Build docs developers (and LLMs) love

Error Handling

Error Response Format

HTTP Status Codes

Common Errors

Validation Errors

Empty Request Body

Invalid Field Values

Duplicate Entry Errors

Duplicate Category Name

Duplicate Client Email

Foreign Key Constraint Violations

Cannot Delete Category with Products

Cannot Delete Product with Sales

Cannot Delete Client with Sales

Stock Validation Errors

Resource Not Found Errors

Database Query Errors

Error Handling in Code

Controller Layer

Model Layer

Validation Layer

Client-Side Error Handling

JavaScript/Node.js Example

Python Example

cURL with Error Checking

Error Recovery Strategies

Best Practices

Testing Error Scenarios

Next Steps