What determines if rails includes id: :serial in a table definition?

Question

I'm working with an existing rails app, using postgresql. Its schema.rb file has id: :serial for many, but not all, tables:

create_table "foos", id: :serial, force: :cascade do |t|

When I run rails db:migrate:reset, id: :serial is removed. We are all on the same version of postgres, but different OSes. I haven't exhaustively tested the behavior between machines, but I think there is a difference between machines.

The rails version is the same as it was when the project started.

The project did start with sqlite3. When I switch to that and regenerate the file, same behavior.

What could cause this option to be removed in my environment?

here's some code that is probably relevant:

• https://github.com/rails/rails/blob/b2eb1d1c55a59fee1e6c4cba7030d8ceb524267c/activerecord/lib/active_record/connection_adapters/postgresql/column.rb#L15-L21
• https://github.com/rails/rails/blob/b2eb1d1c55a59fee1e6c4cba7030d8ceb524267c/activerecord/lib/active_record/connection_adapters/postgresql/schema_dumper.rb#L26-L42

update

• I just tried rails db:migrate:reset on colleague's machines, and I was wrong! their environments also remove id: :serial.
• I looked closer at recent migrations from a colleague, and the most recent one did not create id: :serial in schema.rb either.

Answer 1

The answer is simply rails 5.0 vs 5.1 migrations. I had previously thought that the project started in 5.1, so I didin't test this. But then I dug deeper and discovered it started in 5.0, and experimentation shows that's the answer.

5.0, no id specified

class SerialIdTest < ActiveRecord::Migration[5.0]
  def change
    create_table "test" do |t|
      t.integer "foo_id"
      t.string "foo_role"
    end
  end
end

create_table "test", id: :serial, force: :cascade do |t|
  t.integer "foo_id"
  t.string "foo_role"
end

# \d test
                                   Table "public.test"
      Column      |       Type        |                       Modifiers                       
------------------+-------------------+-------------------------------------------------------
 id               | integer           | not null default nextval('test_id_seq'::regclass)
 foo_id   | integer           | 
 foo_role | character varying | 
Indexes:
    "test_pkey" PRIMARY KEY, btree (id)

5.1, no id specified

class SerialIdTest < ActiveRecord::Migration[5.1]
  def change
    create_table "test" do |t|
      t.integer "foo_id"
      t.string "foo_role"
    end
  end
end

create_table "test", force: :cascade do |t|
  t.integer "foo_id"
  t.string "foo_role"
end

# \d test
                                   Table "public.test"
      Column      |       Type        |                       Modifiers                       
------------------+-------------------+-------------------------------------------------------
 id               | bigint            | not null default nextval('test_id_seq'::regclass)
 foo_id   | integer           | 
 foo_role | character varying | 
Indexes:
    "test_pkey" PRIMARY KEY, btree (id)

5.1, id serial specified

class SerialIdTest < ActiveRecord::Migration[5.1]
  def change
    create_table "test", id: :serial do |t|
      t.integer "foo_id"
      t.string "foo_role"
    end
  end
end

create_table "test", id: :serial, force: :cascade do |t|
  t.integer "foo_id"
  t.string "foo_role"
end

# \d test
                                   Table "public.test"
      Column      |       Type        |                       Modifiers                       
------------------+-------------------+-------------------------------------------------------
 id               | integer           | not null default nextval('test_id_seq'::regclass)
 foo_id   | integer           | 
 foo_role | character varying | 
Indexes:
    "test_pkey" PRIMARY KEY, btree (id)