Example usage of MongoDB's official Go Driver with nested struct types

main.go

package main

import (
  "context"
  "fmt"
  "log"

  "github.com/mongodb/mongo-go-driver/bson"
  "github.com/mongodb/mongo-go-driver/mongo"
  "github.com/mongodb/mongo-go-driver/mongo/options"
)

type Exercise struct {
  Type string `bson:"type"`
  Weight float32 `bson:"weight"`
  Set []int `bson:"set"`
}

type Workout struct {
  Exercises []Exercise `bson:"exercises"`
}

func main() {
  // 1. Establish connection with Mongo DB
  client, err := mongo.Connect(context.TODO(), "mongodb://localhost:27017")

  if err != nil {
      log.Fatal(err)
  }

  // Check the connection
  err = client.Ping(context.TODO(), nil)

  if err != nil {
      log.Fatal(err)
  }

  fmt.Println("Connected to MongoDB!")
  
  collection := client.Database("test").Collection("trainers")
  
  // 2. Implement CRUD operations on DB
  squatExercise := models.Exercise{"squat", 200, []int{5, 5, 5}}
  benchExercise := models.Exercise{"bench", 185, []int{5, 5, 5}}
  workout1 := models.Workout{Exercises: []models.Exercise{squatExercise, benchExercise}}

  squatEx2 := models.Exercise{"squat", 205, []int{5, 5, 5}}
  benchEx2 := models.Exercise{"bench", 190, []int{5, 5, 5}}
  workout2 := models.Workout{Exercises: []models.Exercise{squatEx2, benchEx2}}

  squatEx3 := models.Exercise{"squat", 210, []int{5, 5, 5}}
  benchEx3 := models.Exercise{"bench", 195, []int{5, 5, 5}}
  workout3 := models.Workout{Exercises: []models.Exercise{squatEx3, benchEx3}}

  ////////////////////////////////////////////////////////////
  //                                                        //
  //  Insert single document using collection.InsertOne()   //
  //                                                        //
  ////////////////////////////////////////////////////////////

  insertResult, err := collection.InsertOne(context.TODO(), workout1)
  if err != nil {
    log.Fatal(err)
  }

  fmt.Println("Inserted a single document: ", insertResult.InsertedID)

  // Insert multiple documents using collection.InsertMany()
  workouts := []interface{}{workout2, workout3}

  insertManyResults, err := collection.InsertMany(context.TODO(), workouts)
  if err != nil {
    log.Fatal(err)
  }

  fmt.Println("Inserted multiple documents: ", insertManyResults.InsertedIDs)
  
  ///////////////////////////////////////////////////////////////////////////////
  //                                                                           // 
  //  Find single document using collection.FindOne                            //
  //  Reference: https://stackoverflow.com/questions/53816611/                 //
  //            golang-mongo-go-driver-beta-1-using-greater-than-operator      //
  //                                                                           //
  ///////////////////////////////////////////////////////////////////////////////
  
  objectID, _ := primitive.ObjectIDFromHex("5c1f555640722cc207956c86")        
  filter := bson.M{"_id": objectID}
  var result models.Workout
  err = collection.FindOne(context.TODO(), filter).Decode(&result)
  if err != nil {
    log.Fatal(err)
  }

  fmt.Printf("Found a single document: %+v\n", result)
  //////////////////////////////////////////////////////////
  //                                                      //
  //    Find multiple documents using collection.Find     //
  //                                                      //
  //////////////////////////////////////////////////////////

  options := options.Find()

  cur, err := collection.Find(context.TODO(), nil, options)
   if err != nil {
     log.Fatal(err)
   }
  defer cur.Close(context.TODO())

  count := 0
  var results []*models.Workout
  for cur.Next(context.TODO()) {
    // create a value into which the single document can be decoded
    var elem models.Workout
    count++
    err := cur.Decode(&elem)
    if err != nil {
      log.Fatal(err)
    }

    results = append(results, &elem)
  }

  for _, exercise := range results {
    stringJson, _ := json.Marshal(*exercise)
    fmt.Printf("JSON string: %s", stringJson)
  }
}