可能是由于使用 Dotenv 存储的 MongoDB URI 早于 Dotenv 的初始化，将 Dotenv 初始化放在引入 AppModule 之前即可解决。例如：
typescript
// ./src/initDotEnv.ts
import { config as dotenvConfig } from "dotenv";
dotenvConfig();
typescript
// ./src/main.ts
// init dotenv before AppModule, otherwise process.env.MONGODB_URI will be undefined in AppModule
import "./initDotEnv";
import { NestFactory } from "@nestjs/core";
import { AppModule } from "./app.module";
async function bootstrap() {
const app = await NestFactory.create(AppModule);
await app.listen(3000);
}
bootstrap();
错误信息示例：
ERROR [ExceptionHandler] The `uri` parameter to `openUri()` must be a string, got "undefined". Make sure the first parameter to `mongoose.connect()` or `mongoose.createConnection()` is a string.
MongooseError: The `uri` parameter to `openUri()` must be a string, got "undefined". Make sure the first parameter to `mongoose.connect()` or `mongoose.createConnection()` is a string.