Mongo Go Models

Important Note: We changed the package name from github.com/Kamva/mgm/v3 (uppercase Kamva) to github.com/kamva/mgm/v3 (lowercase kamva) starting with version 3.1.0.

The Mongo ODM for Go

Features
Requirements
Installation
Usage
Bugs / Feature Requests
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Contributing
License

Features

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.

Requirements

Go 1.10 or higher.
MongoDB 2.6 and higher.

Installation

Important Note: We changed the package name from github.com/Kamva/mgm/v3 (uppercase Kamva) to github.com/kamva/mgm/v3 (lowercase kamva) starting with version 3.1.0.

go get github.com/kamva/mgm/v3

Usage

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

import (
   "github.com/kamva/mgm/v3"
   "go.mongodb.org/mongo-driver/mongo/options"
)

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.
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{"page":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{"age": 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() error
Created: Called after a new model is created. Signature : Created() error
Updating: Called when updating model. Signature : Updating() error
Updated : Called after a model is updated. Signature : Updated(result *mongo.UpdateResult) error
Saving: Called when creating or updating a model. Signature : Saving() error
Saved: Called after a model is created or updated. Signature: Saved() error
Deleting: Called when deleting a model. Signature: Deleting() error
Deleted: Called after a model is deleted. Signature: Deleted(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

Example:

func (model *Book) Creating() error {
   // Call the DefaultModel Creating hook
   if err := model.DefaultModel.Creating(); 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
}

Configuration

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{})

Collections

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 {
      panic(err)
   }

   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 {
      panic(err)
   }

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

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

Aggregation

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 (
   "github.com/kamva/mgm/v3"
   "github.com/kamva/mgm/v3/builder"
   "github.com/kamva/mgm/v3/field"
   . "go.mongodb.org/mongo-driver/bson"
   "go.mongodb.org/mongo-driver/bson/primitive"
)

// 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 (
   "github.com/kamva/mgm/v3"
   "github.com/kamva/mgm/v3/builder"
   "github.com/kamva/mgm/v3/field"
   "github.com/kamva/mgm/v3/operator"
   . "go.mongodb.org/mongo-driver/bson"
   "go.mongodb.org/mongo-driver/bson/primitive"
)

// 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 {
    panic(err)
}

Transactions

To run a transaction on the default connection use the mgm.Transaction() function, e.g:

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")