How to change column to nullable with modify in Ecto migration

Although I came across many different examples where a raw SQL has been used to perform this type of operation in Ecto, it's actually super easy to do it with modify/3 function.

Let's assume that your migration looks like this:

create table(:blog_posts) do
  add :title, :string, null: false
  add :intro, :text, null: false
  add :body, :text, null: false
  add :category_id, references(:blog_categories, on_delete: :delete_all)
end

... and at some point, you realize that you don't want to force passing the intro column value.

You can change it easily this way:

alter table(:blog_posts) do
  modify :intro, :text, null: true, from: :text
end

It's also worth mentioning that it's possible to modify foreign keys with modify:

alter table(:blog_posts) do
  modify :category_id,
    references(:blog_categories, on_delete: :delete_all),
    null: false,
    from: references(:blog_categories, on_delete: :delete_all)
end