Programming language: Go
License: Apache License 2.0
Latest version: v3.0.0

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Mongo Go Models

The Mongo ODM for Go


  • Define your models and perform CRUD operations with hooks before/after each operation.
  • mgm makes Mongo search and aggregation super easy to do in Golang.
  • Just set up your configs once and get collections anywhere you need them.
  • mgm predefines all Mongo operators and keys, so you don't have to hardcode them yourself.
  • mgm wraps the official Mongo Go Driver.


  • Go 1.10 or higher.
  • MongoDB 2.6 and higher.


go get github.com/kamva/mgm/v3


To get started, import the mgm package and setup the default config:

import (

func init() {
   // Setup the mgm default config
   err := mgm.SetDefaultConfig(nil, "mgm_lab", options.Client().ApplyURI("mongodb://root:12345@localhost:27017"))

Define your model:

type Book struct {
   // DefaultModel adds _id, created_at and updated_at fields to the Model
   mgm.DefaultModel `bson:",inline"`
   Name             string `json:"name" bson:"name"`
   Pages            int    `json:"pages" bson:"pages"`

func NewBook(name string, pages int) *Book {
   return &Book{
      Name:  name,
      Pages: pages,

Insert new document:

book := NewBook("Pride and Prejudice", 345)

// Make sure to pass the model by reference (to update the model's "updated_at", "created_at" and "id" fields by mgm).
err := mgm.Coll(book).Create(book)

Find one document

// Get the document's collection
book := &Book{}
coll := mgm.Coll(book)

// Find and decode the doc to a book model.
_ = coll.FindByID("5e0518aa8f1a52b0b9410ee3", book)

// Get the first doc of the collection 
_ = coll.First(bson.M{}, book)

// Get the first doc of a collection using a filter
_ = coll.First(bson.M{"pages":400}, book)

Update a document

// Find your book
book := findMyFavoriteBook()

// and update it
book.Name = "Moulin Rouge!"
err := mgm.Coll(book).Update(book)

Delete a document

// Just find and delete your document
err := mgm.Coll(book).Delete(book)

Find and decode a result:

result := []Book{}

err := mgm.Coll(&Book{}).SimpleFind(&result, bson.M{"pages": bson.M{operator.Gt: 24}})

A Model's Default Fields

Each model by default (by using DefaultModel struct) has the following fields:

  • _id : The document ID.

  • created_at: The creation date of a doc. When saving a new doc, this is automatically populated by the Creating hook.

  • updated_at: The last updated date of a doc. When saving a doc, this is automatically populated by the Saving hook.

A Model's Hooks

Each model has the following hooks:

  • Creating: Called when creating a new model. Signature : Creating(context.Context) error

  • Created: Called after a new model is created. Signature : Created(context.Context) error

  • Updating: Called when updating model. Signature : Updating(context.Context) error

  • Updated : Called after a model is updated. Signature : Updated(ctx context.Context, result *mongo.UpdateResult) error

  • Saving: Called when creating or updating a model. Signature : Saving(context.Context) error

  • Saved: Called after a model is created or updated. Signature: Saved(context.Context) error

  • Deleting: Called when deleting a model. Signature: Deleting(context.Context) error

  • Deleted: Called after a model is deleted. Signature: Deleted(ctx context.Context, result *mongo.DeleteResult) error

Notes about hooks:

  • Each model by default uses the Creating and Saving hooks, so if you want to define those hooks yourself, remember to invoke the DefaultModel hooks from your own hooks.
  • Collection methods that call these hooks:
    • Create & CreateWithCtx
    • Update & UpdateWithCtx
    • Delete & DeleteWithCtx


func (model *Book) Creating(ctx context.Context) error {
   // Call the DefaultModel Creating hook
   if err := model.DefaultModel.Creating(ctx); err!=nil {
      return err

   // We can validate the fields of a model and return an error to prevent a document's insertion.
   if model.Pages < 1 {
      return errors.New("book must have at least one page")

   return nil


The mgm default configuration has a context timeout:

func init() {
   _ = mgm.SetDefaultConfig(&mgm.Config{CtxTimeout:12 * time.Second}, "mgm_lab", options.Client().ApplyURI("mongodb://root:12345@localhost:27017"))

// To get the context, just call the Ctx() method, assign it to a variable
ctx := mgm.Ctx()

// and use it
coll := mgm.Coll(&Book{})
coll.FindOne(ctx, bson.M{})

// Or invoke Ctx() and use it directly
coll.FindOne(mgm.Ctx(), bson.M{})


Get a model's collection:

coll := mgm.Coll(&Book{})

// Do something with the collection

mgm automatically detects the name of a model's collection:

book := Book{}

// Print your model's collection name.
collName := mgm.CollName(&book)
fmt.Println(collName) // output: books

You can also set a custom collection name for your model by implementing the CollectionNameGetter interface:

func (model *Book) CollectionName() string {
   return "my_books"

// mgm returns the "my_books" collection
coll := mgm.Coll(&Book{})

Get a collection by its name (without needing to define a model for it):

coll := mgm.CollectionByName("my_coll")

// Do Aggregation, etc. with the collection

Customize the model db by implementing the CollectionGetter interface:

func (model *Book) Collection() *mgm.Collection {
    // Get default connection client
   _, client, _, err := mgm.DefaultConfigs()

   if err != nil {

   db := client.Database("another_db")
   return mgm.NewCollection(db, "my_collection")

Or return a model's collection from another connection:

func (model *Book) Collection() *mgm.Collection {
   // Create new client
   client, err := mgm.NewClient(options.Client().ApplyURI("mongodb://root:12345@localhost:27017"))

   if err != nil {

   // Get the model's db
   db := client.Database("my_second_db")

   // return the model's custom collection
   return mgm.NewCollection(db, "my_collection")


While we can use Mongo Go Driver Aggregate features, mgm also provides simpler methods to perform aggregations:

Run an aggregation and decode the result:

authorCollName := mgm.Coll(&Author{}).Name()
result := []Book{}

// Lookup with just a single line of code
_ := mgm.Coll(&Book{}).SimpleAggregate(&result, builder.Lookup(authorCollName, "auth_id", "_id", "author"))

// Multi stage (mix of mgm builders and raw stages)
_ := mgm.Coll(&Book{}).SimpleAggregate(&result,
        builder.Lookup(authorCollName, "auth_id", "_id", "author"),
        M{operator.Project: M{"pages": 0}},

// Do something with result...

Do aggregations using the mongo Aggregation method:

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

// The Author model collection
authorColl := mgm.Coll(&Author{})

cur, err := mgm.Coll(&Book{}).Aggregate(mgm.Ctx(), A{
    // The S function accepts operators as parameters and returns a bson.M type.
    builder.S(builder.Lookup(authorColl.Name(), "author_id", field.Id, "author")),

A more complex example and mixes with mongo raw pipelines:

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

// Author model collection
authorColl := mgm.Coll(&Author{})

_, err := mgm.Coll(&Book{}).Aggregate(mgm.Ctx(), A{
    // S function get operators and return bson.M type.
    builder.S(builder.Lookup(authorColl.Name(), "author_id", field.Id, "author")),
    builder.S(builder.Group("pages", M{"books": M{operator.Push: M{"name": "$name", "author": "$author"}}})),
    M{operator.Unwind: "$books"},

if err != nil {


  • To run a transaction on the default connection use the mgm.Transaction() function, e.g: ```go d := &Doc{Name: "Mehran", Age: 10}

err := mgm.Transaction(func(session mongo.Session, sc mongo.SessionContext) error {

// do not forget to pass the session's context to the collection methods. err := mgm.Coll(d).CreateWithCtx(sc, d)

if err != nil {
    return err

return session.CommitTransaction(sc)


- To run a transaction with your own context, use the `mgm.TransactionWithCtx()` method.
- To run a transaction on another connection, use the `mgm.TransactionWithClient()` method.

## Other Mongo Go Models Packages

**We implemented these packages to simplify queries and aggregations in mongo**

`builder`: simplify mongo queries and aggregations.  

`operator` : contains mongo operators as predefined variables.  
(e.g `Eq  = "$eq"` , `Gt  = "$gt"`)  

`field` : contains mongo fields used in aggregations and ... as predefined variable.
(e.g `LocalField = "localField"`, `ForeignField = "foreignField"`) 

import (
   f "github.com/kamva/mgm/v3/field"
   o "github.com/kamva/mgm/v3/operator"

// Instead of hard-coding mongo operators and fields
_, _ = mgm.Coll(&Book{}).Aggregate(mgm.Ctx(), bson.A{
    bson.M{"$count": ""},
    bson.M{"$project": bson.M{"_id": 0}},

// Use the predefined operators and pipeline fields.
_, _ = mgm.Coll(&Book{}).Aggregate(mgm.Ctx(), bson.A{
    bson.M{o.Count: ""},
    bson.M{o.Project: bson.M{f.Id: 0}},

Bugs / Feature request

New features can be requested and bugs can be reported on Github issue tracker.

Communicate With Us


Open in Gitpod FOSSA Status

  1. Fork the repository
  2. Clone your fork (git clone https://github.com/<your_username>/mgm && cd mgm)
  3. Create your feature branch (git checkout -b my-new-feature)
  4. Make changes and add them (git add .)
  5. Commit your changes (git commit -m 'Add some feature')
  6. Push to the branch (git push origin my-new-feature)
  7. Create new pull request


Mongo Go Models is released under the Apache License

FOSSA Status

*Note that all licence references and agreements mentioned in the mgm README section above are relevant to that project's source code only.