# README

Versioned migrations for MongoDB

This package allows to perform versioned migrations on your MongoDB using mongo-go-driver. Inspired by go-pg migrations.

package migrations

import (
	"go.mongodb.org/mongo-driver/bson"
	"go.mongodb.org/mongo-driver/mongo"
	"go.mongodb.org/mongo-driver/mongo/options"
	migrate "github.com/xakep666/mongo-migrate"
)

func init() {
	migrate.Register(func(db *mongo.Database) error {
		opt := options.Index().SetName("my-index")
		keys := bson.D{{"my-key", 1}}
		model := mongo.IndexModel{Keys: keys, Options: opt}
		_, err := db.Collection("my-coll").Indexes().CreateOne(context.TODO(), model)
		if err != nil {
			return err
		}

		return nil
	}, func(db *mongo.Database) error {
		_, err := db.Collection("my-coll").Indexes().DropOne(context.TODO(), "my-index")
		if err != nil {
			return err
		}
		return nil
	})
}

Import it in your application.

import (
    ...
    migrate "github.com/xakep666/mongo-migrate"
    _ "path/to/migrations_package" // database migrations
    ...
)

Run migrations.

func MongoConnect(host, user, password, database string) (*mongo.Database, error) {
	uri := fmt.Sprintf("mongodb://%s:%s@%s:27017", user, password, host)
	opt := options.Client().ApplyURI(uri)
	client, err := mongo.NewClient(opt)
	if err != nil {
		return nil, err
	}
	ctx, cancel := context.WithTimeout(context.Background(), 20*time.Second)
	defer cancel()
	err = client.Connect(ctx)
	if err != nil {
		return nil, err
	}
	db = client.Database(database)
	migrate.SetDatabase(db)
	if err := migrate.Up(migrate.AllAvailable); err != nil {
		return nil, err
	}
	return db, nil
}

Use case #2. Migrations in application code.

Just define it anywhere you want and run it.

func MongoConnect(host, user, password, database string) (*mongo.Database, error) {
	uri := fmt.Sprintf("mongodb://%s:%s@%s:27017", user, password, host)
	opt := options.Client().ApplyURI(uri)
	client, err := mongo.NewClient(opt)
	if err != nil {
		return nil, err
	}
	ctx, cancel := context.WithTimeout(context.Background(), 20*time.Second)
	defer cancel()
	err = client.Connect(ctx)
	if err != nil {
		return nil, err
	}
	db = client.Database(database)
	m := migrate.NewMigrate(db, migrate.Migration{
		Version: 1,
		Description: "add my-index",
		Up: func(db *mongo.Database) error {
			opt := options.Index().SetName("my-index")
			keys := bson.D{{"my-key", 1}}
			model := mongo.IndexModel{Keys: keys, Options: opt}
			_, err := db.Collection("my-coll").Indexes().CreateOne(context.TODO(), model)
			if err != nil {
				return err
			}

			return nil
		},
		Down: func(db *mongo.Database) error {
			_, err := db.Collection("my-coll").Indexes().DropOne(context.TODO(), "my-index")
			if err != nil {
				return err
			}
			return nil
		},
	})
	if err := m.Up(migrate.AllAvailable); err != nil {
		return nil, err
	}
	return db, nil
}

How it works?

This package creates a special collection (by default it`s name is "migrations") for versioning. In this collection stored documents like

{
    "_id": "<mongodb-generated id>",
    "version": 1,
    "description": "add my-index",
    "timestamp": "<when applied>"
}

Current database version determined as version from latest inserted document.

You can change collection name using SetMigrationsCollection methods. Remember that if you want to use custom collection name you need to set it before running migrations.