schemalens-engine

SchemaLens core diff engine — semantic SQL schema diff, breaking change detection, and migration generation. Zero dependencies. MIT licensed.

Install

npm install schemalens-engine

Quick Start

const { diffSchemas, generateMigration, detectBreakingChanges, calculateRiskScore } = require('schemalens-engine');

const oldSQL = `CREATE TABLE users (id INT PRIMARY KEY, name VARCHAR(100));`;
const newSQL = `CREATE TABLE users (id INT PRIMARY KEY, name VARCHAR(255), email VARCHAR(255));`;

const result = diffSchemas(oldSQL, newSQL, { dialect: 'postgres' });

console.log('Added tables:', result.addedTables.length);
console.log('Removed tables:', result.removedTables.length);
console.log('Modified tables:', result.modifiedTables.length);

const migration = generateMigration(result, { dialect: 'postgres' });
console.log(migration);

const breaking = detectBreakingChanges(result);
console.log('Breaking changes:', breaking.length);

const risk = calculateRiskScore(result);
console.log('Risk score:', risk.score, risk.label);

API

diffSchemas(oldSQL, newSQL, options)

Compare two SQL schema dumps and return a structured diff.

Options:

• dialect — 'postgres' | 'mysql' | 'sqlite' | 'mssql' | 'oracle' | 'generic'
• renameThreshold — Number 0–1 for rename detection sensitivity (default: 0.6)

Returns:

{
  addedTables: [...],
  removedTables: [...],
  modifiedTables: [...],
  addedIndexes: [...],
  removedIndexes: [...],
  addedViews: [...],
  removedViews: [...],
  modifiedViews: [...],
  addedFunctions: [...],
  removedFunctions: [...],
  // ...
}

generateMigration(diffResult, options)

Generate a dialect-specific migration script from a diff result.

Options:

• dialect — same as above
• safeMode — if true, wraps dangerous changes in transactions/conditionals where supported

detectBreakingChanges(diffResult)

Returns an array of breaking change objects with type, table, column, and message.

calculateRiskScore(diffResult)

Returns { score: number, label: 'Low' | 'Medium' | 'High' }.

Supported Dialects

| Dialect | Tables | Columns | Indexes | Constraints | Views | Functions | Triggers | |---------|--------|---------|---------|-------------|-------|-----------|----------| | PostgreSQL | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | | MySQL / MariaDB | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | | SQLite | ✅ | ✅ | ✅ | ✅ | ✅ | ❌ | ❌ | | SQL Server / Azure SQL | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | | Oracle | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |

Testing

Run the full test suite:

npm test

License

MIT — see LICENSE for details.