how to change data in db from string to id - Rails, Mysql - mysql

Question

Hello I have maybe easy problem maybe not...
History: I wanted to replace yaml file with statuses to db(mysql) and i had in user table column: status. When i replacing logic to db i have created model Status, created table and configured relationship with user...
Describe problem: When i created status_id in user table i have 2 columns: "status" and "status_id". The column "status" is string and have a lot of string value for example "confirmed". How to (using seed migration with statuses) and fill the "status_id" column. I mean if "status" column have value "confirmed" i'd like to have in "status_id" column value: 1.
statuses table:
id name
1 confirmed
2 not confirmed
3 something else
Users table
id status status_id
1 confirmed empty
2 confirmed empty
3 confirmed empty
4 not confirmed empty
5 not confirmed empty
6 something else empty
7 something else empty
User belongs_to :status
Status has_many :users
question: Why i didnt just change name and type in "status" column on
"status_id" with data type: "id"?
answer: Because i need to deploy it using capistrano to production
server and i cant losing data and remove data from status column.

Answer 1

Given the following (your) sample data:
create table statuses (id int, name char(20));
insert into statuses (id, name) values
(1, 'confirmed'),
(2, 'not confirmed'),
(3, 'something else');
create table users (id int, status char(20), status_id int);
insert into users (id, status) values
(1,'confirmed'),
(2,'confirmed'),
(3,'confirmed'),
(4,'not confirmed'),
(5,'not confirmed'),
(6,'something else'),
(7,'something else');
select * from users;
+------+----------------+-----------+
| id | status | status_id |
+------+----------------+-----------+
| 1 | confirmed | NULL |
| 2 | confirmed | NULL |
| 3 | confirmed | NULL |
| 4 | not confirmed | NULL |
| 5 | not confirmed | NULL |
| 6 | something else | NULL |
| 7 | something else | NULL |
+------+----------------+-----------+
7 rows in set (0.00 sec)
This update statement updates the status_id column in users with the appropriate values from statuses:
update users u
set u.status_id=(select s.id from statuses s where u.status=s.name);
Query OK, 7 rows affected (0.01 sec)
Rows matched: 7 Changed: 7 Warnings: 0
select * from users;
+------+----------------+-----------+
| id | status | status_id |
+------+----------------+-----------+
| 1 | confirmed | 1 |
| 2 | confirmed | 1 |
| 3 | confirmed | 1 |
| 4 | not confirmed | 2 |
| 5 | not confirmed | 2 |
| 6 | something else | 3 |
| 7 | something else | 3 |
+------+----------------+-----------+
7 rows in set (0.00 sec)
Hope this is what you asked for, because my answer does neither involve ruby, yaml, nor rails.

Answer 2

This sounds like a one-off data migration which can be handled in several different ways. One way is to write a one-off script or rake task which will update all the users.
some_task.rake
desc 'Add status id to existing users'
namespace :users do
task assign_status: :environment do
statuses = {}
Status.all.each {|status| statuses[status.name] = status.id}
User.all.each do |user|
user.update_attribute(status_id: statuses[user.status])
end
end
end
If you have a lot of users, you may want to use find_each which is more performant as it uses batching. You may also want to add some kind of progress reporting in the rake task.
This approach allows you to test the task against a copy of your existing database.