Validation code is a snippet of code that checks whether a data value or input meets certain criteria or specifications. It is used to ensure that data submitted is accurate, complete, and within acceptable limits.

Purpose of Validation Code:

• Data Integrity: Prevent invalid data from being stored or processed.
• Data Consistency: Ensure that data values are consistent with each other and the system.
• Error Handling: Identify and flag invalid data for correction or further processing.

Types of Validation Code:

• Client-Side Validation: Performed on the user’s device before data is submitted to the server.
• Server-Side Validation: Performed on the server side after data is received from the client.
• Database Validation: Enforced in the database to prevent invalid data from being stored.

Examples of Validation Code:

“`python

Client-Side Validation (JavaScript):

if (document.getElementById(“name”).value == “”) { alert(“Please enter your name.”); return false;}

Server-Side Validation (Python):

def validate_user(user_data): if not user_data[“name”]: return {“error”: “Name is required.”}

Check if the user’s name is too long: if len(user_data[“name”]) > 255: return {“error”: “Name is too long.”}

Validate email address format: if not validate_email(user_data[“email”]): return {“error”: “Invalid email address.”}

Database Validation (using SQL): user_data_check = cursor.execute(“””SELECT * FROM users WHERE name = %s”””, (user_data[“name”])) if user_data_check.fetchone(): return {“error”: “User name already exists.”}

return {“status”: “Success”}“`

Best Practices for Validation Code:

• Keep validation code separate from other code.
• Use clear and concise validation rules.
• Document validation rules clearly.
• Test validation code thoroughly.
• Consider using validation frameworks or libraries.