package main

import (
   "go.mongodb.org/mongo-driver/bson"
   "go.mongodb.org/mongo-driver/mongo"
   "go.mongodb.org/mongo-driver/mongo/options"
   "log"
)

// fatalErr is a helper method for errors
func fatalErr(err error) {
   if err != nil {
      log.Fatal(err)
   }
}

// Connects to the database and returns a client or calls log.Fatal on error
func connectDb() *mongo.Client {
   opt := options.Client().ApplyURI("mongodb://localhost:27017")
   client, err := mongo.NewClient(opt)
   fatalErr(err)

   fatalErr(client.Connect(nil))
   return client
}

func main() {
   db := connectDb()
   coll := db.Database("test").Collection("user")

   // When I use coll.FindOne(nil, bson.D{}) instead, it finds a document.

   // test.user contains multiple records. Find still returns nothing.
   cur, err := coll.Find(nil, bson.D{})
   fatalErr(err)
   defer fatalErr(cur.Close(nil))

   for cur.Next(nil) {
      // Never called
      log.Println("->", cur.ID())
   }

   fatalErr(cur.Err())
   log.Println("Done.")
}