old_contents: import mongoose from 'mongoose'
  
  const MONGODB_URI = process.env.MONGODB_URI
  
  if (!MONGODB_URI) {
    throw new Error(
      'Please define the MONGODB_URI environment variable inside .env.local'
    )
  }
  
  /**
   * Global is used here to maintain a cached connection across hot reloads
   * in development. This prevents connections growing exponentially
   * during API Route usage.
   */
  let cached = global.mongoose
  
  if (!cached) {
    cached = global.mongoose = { conn: null, promise: null }
  }
  
  async function dbConnect() {
    if (cached.conn) {
      return cached.conn
    }
  
    if (!cached.promise) {
      const opts = {
        bufferCommands: false,
      }
  
      cached.promise = mongoose.connect(MONGODB_URI, opts).then((mongoose) => {
        return mongoose
      })
    }
    cached.conn = await cached.promise
    return cached.conn
  }
  
  export default dbConnect
  
new_contents: import mongoose from 'mongoose'
  
  const MONGODB_URI = process.env.MONGODB_URI
  
  if (!MONGODB_URI) {
    throw new Error(
      'Please define the MONGODB_URI environment variable inside .env.local'
    )
  }
  
  /**
   * Global is used here to maintain a cached connection across hot reloads
   * in development. This prevents connections growing exponentially
   * during API Route usage.
   */
  let cached = global.mongoose
  
  if (!cached) {
    cached = global.mongoose = { conn: null, promise: null }
  }
  
  async function dbConnect() {
    if (cached.conn) {
      return cached.conn
    }
  
    if (!cached.promise) {
      const opts = {
        bufferCommands: false,
      }
  
      cached.promise = mongoose.connect(MONGODB_URI, opts).then((mongoose) => {
        return mongoose
      })
    }
  
    try {
      cached.conn = await cached.promise
    } catch (e) {
      cached.promise = null
      throw e
    }
  
    return cached.conn
  }
  
  export default dbConnect
  
subject: fix error connection handling (#40633)