inanzzz | Using MongoDB one-to-many relationships with embedded documents in Golang

In this example we are going to keep multiple documents in another document. This is called "embedded document model" in MongoDB. Our example uses "tokens" collection. Each token document will contain zero or many "permission" documents in it.

Database content

Preparation

db.createCollection("tokens")
db.tokens.createIndex({"uuid":1},{unique:true,name:"UQ_uuid"})

Tokens data

[
  {
    "_id": {
      "$oid": "6050986944799a96c0f7b1f4"
    },
    "uuid": "7d5e2a9f-b6b9-4356-af3c-be772b3cf821",
    "type": "access token",
    "permissions": [
      {
        "uuid": "f2222ef5-7f9b-46fa-a7e6-c88b4126e9fe",
        "type": "accounts",
        "actions": [
          "read",
          "write"
        ]
      },
      {
        "uuid": "2cffcc36-0efc-4d09-bb0a-a36f2b6433be",
        "type": "balances",
        "actions": [
          "read"
        ]
      }
    ]
  },
  {
    "_id": {
      "$oid": "605098e921410aa61d2be92b"
    },
    "uuid": "38a934d7-73cf-4874-8af1-874d4c03335f",
    "type": "refresh token",
    "permissions": null
  }
]

Storage

Models

package storage

import "context"

type TokenStorer interface {
	Insert(ctx context.Context, token Token) error
	Find(ctx context.Context, uuid string) (Token, error)
}

type Token struct {
	ID          string       `bson:"_id,omitempty"`
	UUID        string       `bson:"uuid"`
	Type        string       `bson:"type"`
	Permissions []Permission `bson:"permissions"`
}

type Permission struct {
	UUID    string   `bson:"uuid"`
	Type    string   `bson:"type"`
	Actions []string `bson:"actions"`
}

Storer

package mongodb

import (
	"context"
	"log"
	"time"

	"github.com/you/mongo/internal/pkg/domain"
	"github.com/you/mongo/internal/pkg/storage"
	"go.mongodb.org/mongo-driver/bson"
	"go.mongodb.org/mongo-driver/mongo"
)

var _ storage.TokenStorer = TokenStorage{}

type TokenStorage struct {
	Database *mongo.Database
	Timeout  time.Duration
}

func (t TokenStorage) Insert(ctx context.Context, token storage.Token) error {
	ctx, cancel := context.WithTimeout(ctx, t.Timeout)
	defer cancel()

	if _, err := t.Database.Collection("tokens").InsertOne(ctx, token); err != nil {
		log.Println(err)

		if er, ok := err.(mongo.WriteException); ok && er.WriteErrors[0].Code == 11000 {
			return domain.ErrConflict
		}

		return domain.ErrInternal
	}

	return nil
}

func (t TokenStorage) Find(ctx context.Context, uuid string) (storage.Token, error) {
	ctx, cancel := context.WithTimeout(ctx, t.Timeout)
	defer cancel()

	var tok storage.Token

	qry := bson.M{"uuid": uuid}

	err := t.Database.Collection("tokens").FindOne(ctx, qry).Decode(&tok)
	if err != nil {
		log.Println(err)

		if err == mongo.ErrNoDocuments {
			return storage.Token{}, domain.ErrNotFound
		}

		return storage.Token{}, domain.ErrInternal
	}

	return tok, nil
}

Test

Insert

storer := TokenStorage{Database: database, Timeout: time.Second * 5}

if err := storer.Insert(context.Background(), Token{
    UUID: uuid.New().String(),
    Type: "access token",
    Permissions: []Permission{
        {
            UUID:    uuid.New().String(),
            Type:    "accounts",
            Actions: []string{"read", "write"},
        },
        {
            UUID:    uuid.New().String(),
            Type:    "balances",
            Actions: []string{"read"},
        },
    },
}); err != nil {
    log.Fatalln(err)
}

Find

storer := TokenStorage{Database: database, Timeout: time.Second * 5}

token, err := storer.Find(context.Background(), "7d5e2a9f-b6b9-4356-af3c-be772b3cf821")
if err != nil {
    log.Fatalln(err)
}

data, _ := json.MarshalIndent(token, "", "  ")
log.Println(string(data))

{
  "ID": "6050986944799a96c0f7b1f4",
  "UUID": "7d5e2a9f-b6b9-4356-af3c-be772b3cf821",
  "Type": "access token",
  "Permissions": [
    {
      "UUID": "f2222ef5-7f9b-46fa-a7e6-c88b4126e9fe",
      "Type": "accounts",
      "Actions": [
        "read",
        "write"
      ]
    },
    {
      "UUID": "2cffcc36-0efc-4d09-bb0a-a36f2b6433be",
      "Type": "balances",
      "Actions": [
        "read"
      ]
    }
  ]
}