如何在Rails 5中自动增加具有起始值的自定义id？

Question

我正在进行迁移，并删除每个表的默认'id'。我创建了一个特殊的字段，而不是'student_id'，我希望使它从1001开始自动递增。

这是我的代码：

class CreateStudents < ActiveRecord::Migration[5.0]
  def up
    create_table :students, :id => false do |t|
      t.integer "student_id"
      t.string "first_name", :limit => 25
      t.string "last_name", :limit => 50
      t.string "email", :default => ' ', :null => false
      t.string "birthday"
      t.string "subjects"
      t.string "teachers"
      t.string "username", :limit => 25
      t.string "password_digest", :limit => 40
      t.timestamps
    end
    execute "CREATE SEQUENCE students_student_id_seq OWNED BY students.student_id INCREMENT BY 1 START WITH 1001"
  end

  def down
  drop_table :students
  execute "DELETE SEQUENCE students_student_id_seq"
  end

end

我收到了ff错误：

MySQL 2：：error : SQL语法出现错误；请检查与MySQL服务器版本相对应的手册，以获得正确的语法，以便在第1行使用接近“students.student_id增量1 STA所拥有的序列students_student_id_seq”。

如何在Rails 5中自动生成带有起始值的自定义id增量？

Answer 1

execute "CREATE SEQUENCE students_student_id_seq OWNED BY students.student_id INCREMENT BY 1 START WITH 1001"

以上是Postgresql语法，您的数据库似乎是MySQL。

无论如何，您可以通过将student_id设置为主键，然后更新增量起始值来实现您想要的结果。

def change
  create_table :students, :id => false do |t|
    t.integer "student_id", primary_key: true
    t.string "first_name", :limit => 25
    t.string "last_name", :limit => 50
    t.string "email", :default => ' ', :null => false
    t.string "birthday"
    t.string "subjects"
    t.string "teachers"
    t.string "username", :limit => 25
    t.string "password_digest", :limit => 40
    t.timestamps
  end

  reversible do |dir|
    dir.up { execute "ALTER TABLE students AUTO_INCREMENT = 1000" }
  end
end