Why I get an error "client disconnected" when trying to get documents from mongo collection in go? - mongodb

Question

I have mongo capped collection and a simple API, written on Go. I built and run it. When I try to sent Get request or simply go localhost:8000/logger in browser - my process closes. Debug shows this happens, while executing "find" in collection. It produces error "client is disconnected". Collection has 1 document, and debug shows it is connected with my helper.
Go version 1.13
My code:
func main() {
r := mux.NewRouter()
r.HandleFunc("/logger", getDocs).Methods("GET")
r.HandleFunc("/logger", createDoc).Methods("POST")
log.Fatal(http.ListenAndServe("localhost:8000", r))
}
func getDocs(w http.ResponseWriter, r *http.Request) {
w.Header().Set("Content-Type", "application/json")
var docs []models.Logger
//Connection mongoDB with helper class
collection := helper.ConnectDB()
cur, err := collection.Find(context.TODO(), bson.M{})
if err != nil {
helper.GetError(err, w)
return
}
defer cur.Close(context.TODO())
for cur.Next(context.TODO()) {
var doc models.Logger
err := cur.Decode(&doc)
if err != nil {
log.Fatal(err)
}
docs = append(docs, doc)
}
if err := cur.Err(); err != nil {
log.Fatal(err)
}
json.NewEncoder(w).Encode(docs)
}
func ConnectDB() *mongo.Collection {
client, err := mongo.NewClient(options.Client().ApplyURI("mongodb://127.0.0.1:27017"))
if err != nil {
log.Fatal(err)
}
fmt.Println("Connected to MongoDB!")
logCollection := client.Database("local").Collection("loggerCollection")
return logCollection
}

Answer 1

According to the documentation, the call to mongo.NewClient doesn't ensure that you can connect the Mongo server. You should first call mongo.Client.Ping() to verify if you can connect to the database or not.
client, err := mongo.NewClient(options.Client().ApplyURI("mongodb://127.0.0.1:27017"))
if err != nil {
log.Fatal(err)
}
if err := client.Ping(context.TODO(), readpref.Primary()); err != nil {
// Can't connect to Mongo server
log.Fatal(err)
}
There could be several reasons behind failing to connect, the most obvious one is incorrect setup of ports. Is your mongodb server up and listening on port 27017? Is there any change you're running mongodb with Docker and it's not forwarding to the correct port?

Answer 2

I faced similar issue , read #Jay answer it definitely helped , as I checked my MongoDB was running using "MongoDB Compass" , then I changed the location of my insert statement , previously I was calling before the call of "context.WithTimeout". Below is working code.
package main
import (
"context"
"log"
"time"
"go.mongodb.org/mongo-driver/mongo"
"go.mongodb.org/mongo-driver/mongo/options"
)
type Book struct {
Name string `json:"name,omitempty"`
PublisherID string `json:"publisherid,omitempty"`
Cost string `json:"cost,omitempty"`
StartTime string `json:"starttime,omitempty"`
EndTime string `json:"endtime,omitempty"`
}
func main() {
client, err := mongo.NewClient(options.Client().ApplyURI("mongodb://localhost:27017"))
if err != nil {
log.Fatal(err)
}
ctx, _ := context.WithTimeout(context.Background(), 10*time.Second)
err = client.Connect(ctx)
if err != nil {
log.Fatal(err)
}
defer client.Disconnect(ctx)
testCollection := client.Database("BooksCollection").Collection("BooksRead")
inserRes, err := testCollection.InsertOne(context.TODO(), Book{Name: "Harry Potter", PublisherID: "IBN123", Cost: "1232", StartTime: "2013-10-01T01:11:18.965Z", EndTime: "2013-10-01T01:11:18.965Z"})
log.Println("InsertResponse : ", inserRes)
log.Println("Error : ", err)
}
I can see document inserted in console as well as in "MongoDB Comapass."

Answer 3

In heiper function "ConnectDB" after "NewClient" I must use "client.Connect(context.TODO())"
before any other use of client