Implemented MySQLAdapter with tests and added SchemaField interface

[AryanMishra1789]

Description

• Implemented MySQLAdapter extending BaseAdapter with methods: connect, disconnect, getCollections, insertDocuments, ensureCollection.
• Added unit tests in MySQLAdapter.test.ts using vitest with mocked mysql2/promise.
• Introduced SchemaField interface in types.ts for table schema support.

Testing

• All unit tests passed successfully, verifying the functionality of the MySQLAdapter.

#3

[Sauvikn98]

Critical SQL Injection Vulnerability

[Sauvikn98]

Thanks @AryanMishra1789 for this contribution! The adapter structure is solid and your testing approach with vitest mocking is great. Before we can merge, please address these important issues:

Critical: SQL Injection Vulnerabilities

Multiple methods directly interpolate table/field names without escaping:

• insertDocuments (line 30): INSERT INTO ${collection}
• ensureCollection (line 41): CREATE TABLE IF NOT EXISTS ${collectionName}
• clearCollection (line 47): DELETE FROM ${collection}
• collectionExists (line 53): Table name and WHERE clause
• getCollectionDetails (line 61): DESCRIBE ${collection}
• getDocumentCount (line 67): SELECT FROM ${collection}
• validateReference (line 74): ${collectionName} and ${fieldName}

Fix: Add an identifier escaping helper:

private escapeIdentifier(id: string): string {
  return '`' + id.replace(/`/g, '``') + '`';
}

High: insertDocuments Logic

The current implementation may not handle column ordering correctly:

const placeholders = documents.map(() => '(?)').join(', ');
const values = documents.map((doc) => Object.values(doc));

This doesn't explicitly list columns. Compare with other adapters to align on the correct pattern.

Medium Issues

1. Schema creation is incomplete - Handle PRIMARY KEY, NOT NULL, DEFAULT, and other constraints
2. addForeignKeyConstraints() throws NotImplementedError - Should be implemented or properly inherited
3. Type safety - getCollectionDetails() returns any instead of proper CollectionDetails type
4. Missing implementation - getCollectionSchema() method

Test Coverage

Consider adding tests for:

• Connection failures
• Invalid table/field names
• Edge cases in data insertion

[AryanMishra1789]

The PR feedback has been addressed. I have also added SQLiteAdapter.ts and SQLiteAdapter.test.ts to fully implement and test secure SQLite generation.

[Sauvikn98]

@AryanMishra1789 looks good to me. Merging it. Thank you for the contribution.