How do you change the db schema?

Questions / Help
1

Hi,

I am still very new to Elixir/Phoenix/Ecto. I have a question regarding migrations. You can use a command

$ mix phoenix.gen.html User users name:string email:string bio:string number_of_pets:integer
$ mix ecto.migrate

to generate the Ecto model. This command generates the initial migration file for you. Now if I want to say add a new field to this model (for e.g. “address:string”), how do I go about doing it? Please tell me if I am doing something wrong here

  1. Create a new migration file named YYYYMMDDSSSSSS_alter_users.exs in repo/migrations directory with contents as follows

    defmodule HelloPhoenix.Repo.Migrations.AlterUser do
    use Ecto.Migration

    def change do
    alter table(:users) do
    add :address, string
    add :usertype_id, references(:usertypes, on_delete: :nothing)
    end
    end

  2. run $mix ecto.migrate

How will Ecto know to not run other migration files already in the repo/migrations directory? I don’t want to run something and find out that I messed up big time.

Thanks
Sudheer

2

If you check your database you will see that Ecto created a table of its own called schema_migrations, and it is this table that holds meta information about what state the database schema is in (consequently, never touch this table manually).

2 Likes
3

Your migration looks good.

You can use mix ecto.gen.migration to create the file for you. See mix help ecto.gen.migration for more information.

2 Likes
4

@OvermindDL1 and @dsissitka: Thanks for the quick reply. That gave me a relief.

Sudheer