How do you implement a custom ORM/query builder in Node.js?

Question

Accepted Answer

**Query builder** — fluent API for building SQL queries.

```javascript
class QueryBuilder {
    constructor(table) {
        this.table = table;
        this._where = [];
        this._orderBy = null;
        this._limit = null;
        this._select = ["*"];
        this.params = [];
    }

select(...columns) {
        this._select = columns;
        return this;
    }

where(column, value) {
        this._where.push(`${column} = $${this.params.length + 1}`);
        this.params.push(value);
        return this;
    }

orderBy(column, dir = "ASC") {
        this._orderBy = `${column} ${dir}`;
        return this;
    }

limit(n) {
        this._limit = n;
        return this;
    }

toSQL() {
        let sql = `SELECT ${this._select.join(", ")} FROM ${this.table}`;
        if (this._where.length) sql += ` WHERE ${this._where.join(" AND ")}`;
        if (this._orderBy) sql += ` ORDER BY ${this._orderBy}`;
        if (this._limit) sql += ` LIMIT ${this._limit}`;
        return { sql, params: this.params };
    }

async execute(db) {
        const { sql, params } = this.toSQL();
        return db.query(sql, params);
    }
}

// Usage
const users = await new QueryBuilder("users")
    .select("id", "name", "email")
    .where("active", true)
    .orderBy("name")
    .limit(10)
    .execute(db);
```

Node.js: How do you implement a custom ORM/query builder in Node.js?