To replace vercel/postgres from the official Next.js tutorial with a local PostgreSQL setup, you simply need to add this /lib/db.ts file, and then change the imports in /lib/data.ts and /seed/router.ts from vercel/postgres to ./db or ../lib/db. Also, don’t forget to run npm install pg.

db.ts

// db.ts
import { Pool, PoolClient } from 'pg';
import dotenv from 'dotenv';

dotenv.config();

const pool = new Pool({
  connectionString: process.env.POSTGRES_URL,
});

async function executeQuery<T = any>(client: PoolClient, query: string, values: any[]): Promise<{ rows: T[] }> {
  const isSimpleCommand = /^BEGIN|COMMIT|ROLLBACK/.test(query.trim().toUpperCase());

  if (isSimpleCommand) {
    // 处理简单的 SQL 命令，如 BEGIN、COMMIT、ROLLBACK
    await client.query(query);
    return { rows: [] };
  } else {
    // 处理带参数的 SQL 查询
    const result = await client.query(query, values);
    return { rows: result.rows };
  }
}

class Client {
  private client: PoolClient | null = null;

  async connect(): Promise<Client> {
    this.client = await pool.connect();
    return this;
  }

  async sql<T = any>(strings: TemplateStringsArray, ...values: any[]): Promise<{ rows: T[] }> {
    if (!this.client) {
      throw new Error('Client is not connected. Call connect() first.');
    }

    const query = strings.reduce((prev, curr, i) => prev + curr + (i < values.length ? '$' + (i + 1) : ''), '');

    return executeQuery(this.client, query, values);
  }

  async release(): Promise<void> {
    if (this.client) {
      await this.client.release();
      this.client = null;
    }
  }
}

export async function sql<T = any>(strings: TemplateStringsArray, ...values: any[]): Promise<{ rows: T[] }> {
  const client = await pool.connect();
  try {
    const query = strings.reduce((prev, curr, i) => prev + curr + (i < values.length ? '$' + (i + 1) : ''), '');

    return executeQuery(client, query, values);
  } finally {
    client.release();
  }
}

export const db = {
  connect: async () => new Client().connect(),
};

What's the use of this? In some cases, connecting to Vercel might not be possible, so I prefer to use a local PostgreSQL setup.

这个有什么用？有的地方可能连接不上 vercel ，你懂的，所以更希望使用本地 postgresql 。