Editing rails migration table doesn't affect tables generated

Question

I realized that I managed to generate a model improperly and am having trouble "rollingback" the mistake. I was generating a model to contain questions for a parent form, writing it as follows:

class CreateQuestions < ActiveRecord::Migration
  def change
create_table :questions do |t|
  t.integer  :legalform_id
  t.integer :question_number
  t.string :type
  t.text :the_question

  t.timestamps
end
  end
end

and then running rake db:migrate to generate the relevant tables.

The attribute legalform_id was to contain the id of the parent form to which the question was associated. ...I then learned about rails and associations, realizing that what I was attempting to do was baked into the framework. So I changed the legalform_id line, so that the migration table read like this:

class CreateQuestions < ActiveRecord::Migration
  def change
create_table :questions do |t|
  t.references :legalform
  t.integer :question_number
  t.string :type
  t.text :the_question

  t.timestamps
end
  end
end

I entered the command rake db:rollback which dropped the questions table and then ran rake db:migrate , assuming that the change I'd made to the migration table would generate the mysql table accordingly. Much to my surprise, the new table contained the same attributes as specified by the original migration table reading as follows:

mysql> show columns in questions;
+-----------------+--------------+------+-----+---------+----------------+
| Field           | Type         | Null | Key | Default | Extra          |
+-----------------+--------------+------+-----+---------+----------------+
| id              | int(11)      | NO   | PRI | NULL    | auto_increment |
| legalform_id    | int(11)      | YES  |     | NULL    |                |
| question_number | int(11)      | YES  |     | NULL    |                |
| type            | varchar(255) | YES  |     | NULL    |                |
| the_question    | text         | YES  |     | NULL    |                |
| created_at      | datetime     | YES  |     | NULL    |                |
| updated_at      | datetime     | YES  |     | NULL    |                |
+-----------------+--------------+------+-----+---------+----------------+

What might be the cause of this? Am I missing something? Many thanks for any guidance.

Answer 1

This is exactly what you want. It creates the same column, while adding an index as well. add_reference creates the column with the name you specified, which in your case is the same as the original migration. If you run SHOW INDEXES on the table, you should see the newly created index as well.

Answer 2

references也创建相同的外键约束，你的情况legalform_id ，两者的区别references VS legalform_id是，当使用references它会自动在模型中加入适当关系的定义，也为现场增添指数