将自动增量添加回Rails中的主键列

Question

我错误地从表格的id字段中删除了自动增量选项.谁能告诉我如何通过迁移重新插入自动增量选项？

Answer 1

尝试:

change_column :my_table, :id, :primary_key

要么

my_table.change_column :id, :primary_key

某些Rails数据库适配器可能不允许您调用change_column主键.如果是这种情况,那么您可以随时调用execute直接使用SQL执行更改:

MySQL的:

execute('ALTER TABLE "my_table" CHANGE "id" "id"
  bigint DEFAULT NULL auto_increment PRIMARY KEY')

PostgreSQL(方法1):

max_id = execute(%%Q{SELECT id FROM "my_table" ORDER BY "id" DESC
  LIMIT 1}).to_a.first
execute(%%Q{CREATE SEQUENCE "my_table_id_seq" START #{max_id+1}})
execute(%%Q{ALTER TABLE "my_table" ALTER COLUMN "id"
  TYPE bigint})
execute(%%Q{ALTER TABLE "my_table" ALTER COLUMN "id"
  SET DEFAULT nextval('my_table_id_seq'::regclass)})
execute(%%Q{ALTER TABLE "my_table" ADD PRIMARY KEY("id")}) 

PostgreSQL(方法2):

max_id = execute(%%Q{SELECT "id" FROM "my_table" ORDER BY "id" DESC
  LIMIT 1}).to_a.first
execute(%%Q{ALTER TABLE "my_table" RENAME COLUMN "id" TO "id_orig"})
execute(%%Q{ALTER TABLE "my_table" ADD COLUMN "id" bigserial NOT NULL})
execute(%%Q{UPDATE "my_table" SET "id"="id_orig"})
execute(%%Q{ALTER SEQUENCE "my_table_id_seq" RESTART #{max_id+1}})
execute(%%Q{ALTER TABLE "my_table" DROP COLUMN "id_orig"})

如果你不希望使用bigint/ bigserial(64位),使用int(11)/ integer/ serial来代替.

Answer 2

我没有检查其他版本，但是在Rails 5上，您可以设置以下auto_increment选项：

change_column :table_name, :id, :int, null: false, unique: true, auto_increment: true

或者，如果您想要bigint：

change_column :table_name, :id, :bigint, null: false, unique: true, auto_increment: true