mix mongo (mongodb-driver v1.4.0) View Source

Migrations are used to modify your database collection over time.

This module provides some helpers for migrating the database, allowing developers to use Elixir to alter their storage in a way that is database independent.

Migrations typically provide two operations: up and down, allowing us to migrate the database forward or roll it back in case of errors.

In order to manage migrations, the driver creates a collection called migrations in the database, which stores all migrations that have already been executed. You can configure the name of this collection with the :collection configuration option.

Creating your first migration

Migrations are defined inside the "priv/mongo/migrations". You can change the path using the configuration key :path.

Each file in the migrations directory has the following structure:

NUMBER_NAME.exs The NUMBER is a unique number that identifies the migration. It is usually the timestamp of when the migration was created. The NAME must also be unique and it quickly identifies what the migration does. For example, if you need to track the "weather" in your system, you can start a new file at "priv/mongo/migrations/20190417140000_add_weather_index.exs" that will have the following contents:

defmodule Mongo.Migrations.AddWeatherIndex do
  def up() do
    indexes = [[key: [files_id: 1, n: 1], name: "files_n_index", unique: true]]
    Mongo.create_indexes(:mongo, "weather", indexes)
  end

  def down() do
        Mongo.drop_index(:mongo, "weather", "files_n_index")
  end
end

The up/0 function is responsible to migrate your database forward. The down/0 function is executed whenever you want to rollback. The down/0 function must always do the opposite of up/0. Inside those functions, we invoke the API defined in this module, you will find conveniences for managing collections, indexes, as well as running custom MongoDB commands.

To run a migration, we generally use Mix tasks. For example, you can run the migration above by going to the root of your project and typing:

  $ mix mongo.migrate

You can also roll it back by calling:

  $ mix mongo.drop

In practice, we don't create migration files by hand either, we typically use mix mongo.gen.migration to generate the file with the proper timestamp and then we just fill in its contents:

  $ mix mongo.gen.migration add_weather_index

Configuration

  config :mongodb_driver,
    migration: [
      path: "migrations",
      otp_app: :mongodb_driver,
      topology: :mongo,
      collection: "migrations"
    ]

The following migration configuration options are available:

• :collection - Version numbers of migrations will be saved in a collection named migrations by default. You can configure the name of the collection via:

  config :mongodb_driver, :migration, collection: "my_migrations"

• :path - the priv sub-directory for migrations. :path defaults to "migrations" and migrations should be placed at "priv/mongo/migrations"

• :otp_app - the name of the otp_app to resolve the priv folder, defaults to :mongodb_driver. In most cases you use your application name.

• :topology - the topology for running the migrations, :topology defaults to :mongo