feat: enhance Notice schema validation and data integrity

[jikrana1]

📋 Pull Request — Enhance Notice Schema Validation and Data Integrity

🔗 Related Issue

Closes #130 — Enhance Notice Schema Validation and Data Integrity

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📝 Summary

The existing Notice schema validated only a few fields and lacked proper sanitization and validation for several string fields. This allowed empty or improperly formatted data to be stored in the database. This PR improves the Notice schema by adding minlength, maxlength, trim, custom error messages, database indexes, and model overwrite protection.

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🐛 Root Cause

#	Problem	Fix Applied
1	category, content, message had no trim	Added trim: true to all string fields
2	title, content, message, category had no minlength	Added minlength with custom error messages
3	category, targetClass, teacherName had no maxlength	Added maxlength with custom error messages
4	category, content, postedBy had no custom required error messages	Added descriptive custom messages to all required fields
5	No indexes on frequently queried fields	Added indexes on category, targetClass, date
6	mongoose.model('Notice', noticeSchema) — could throw overwrite error in dev/hot-reload	Changed to mongoose.models.Notice || mongoose.model('Notice', noticeSchema)

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✅ Changes Made

Modified Files

File	What Changed
models/Notice.js	Added trim, minlength, maxlength, custom error messages to all string fields; added 3 indexes; fixed model overwrite issue

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🛡️ Validation Changes Summary

Field	Before	After
title	required, trim, maxlength: 200	+ minlength: 3 with custom message
category	required: true only	+ trim, minlength: 2, maxlength: 100, custom messages
content	required: true only	+ trim, minlength: 10, custom messages
message	required, trim	+ minlength: 5, custom message
targetClass	default: 'All' only	+ trim, maxlength: 50
teacherName	No validation	+ trim, maxlength: 100
postedBy	required: true only	+ custom required error message

📈 Indexes Added

Field	Index	Reason
category	{ category: 1 }	Frequently filtered by category
targetClass	{ targetClass: 1 }	Frequently filtered by class
date	{ date: -1 }	Notices usually sorted by latest date

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🧪 Testing Checklist

• Creating a notice without title returns Title is required
• Creating a notice with title less than 3 chars returns Title must be at least 3 characters
• Creating a notice without category returns Category is required
• Creating a notice with content less than 10 chars returns Content must be at least 10 characters
• Creating a notice with message less than 5 chars returns Message must be at least 5 characters
• String fields are trimmed before saving (no leading/trailing spaces stored)
• Valid notice saves successfully with no errors
• No OverwriteModelError in development/hot-reload environments
• Indexes visible in MongoDB Atlas or via db.notices.getIndexes()

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💻 How to Test Locally

# Start server
npm run dev

# Test validation via API
curl -X POST http://localhost:5000/api/notices \
  -H "Content-Type: application/json" \
  -d '{"title": "Hi", "category": "", "content": "short"}'
# Expected: validation error responses

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📌 Coding Standards Followed

• Mongoose built-in validators only — no external libraries added
• Custom error messages on all validators for better API error responses
• Indexes defined at schema level (not manually in DB)
• Model overwrite protection consistent with Next.js/hot-reload best practices
• No change to controller or route logic