How to Generate a Migration File

A migration file lets you configure database tables.

Generate a migration file

A migration file is generated using a console command. After it is generated, you write code that configures table fields and then invoke the migration file.

The command to create a migration file is:

mix ecto.gen.migration name_of_migration

For this example, I will add a new field named owner

mix ecto.gen.migration create_owner_field

The migration file after it is created appears in app/priv/repo/migrations

You now need to type code that performs table specific database actions.

In this example below, a field is added to a preexisting table named :testbeds.

  def change do
    alter table(:testbeds) do    # customize to your code
      add :owner, :string
    end
  end

To initiate the migration yoou run this command:

mix ecto.migrate