Ruby on Rails: 如何使用 rake db: shift 恢复迁移？

在安装设计模型用户我得到了这个。

class DeviseCreateUsers < ActiveRecord::Migration
def self.up
create_table(:users) do |t|
t.database_authenticatable :null => false
t.recoverable
t.rememberable
t.trackable


# t.encryptable
# t.confirmable
# t.lockable :lock_strategy => :failed_attempts, :unlock_strategy => :both
# t.token_authenticatable




t.timestamps
end


add_index :users, :email,                :unique => true
add_index :users, :reset_password_token, :unique => true
# add_index :users, :confirmation_token,   :unique => true
# add_index :users, :unlock_token,         :unique => true
# add_index :users, :authentication_token, :unique => true
end


def self.down
drop_table :users
end
end

现在，如果我这样做 rake 数据库: 迁移用户表将被创建。

我怎样才能恢复这个迁移，也就是说，我怎样才能再次使用 rake 删除用户表？

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Just run this command:

rake db:rollback
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I believe there are three options available for reverting migrations (they also overlap):

  1. Roll down the most recent migration:

    rake db:migrate:down # Rails 2 only.

  2. Roll down a number(n) of recent migrations:

    rake db:rollback STEP=n

  3. Roll down to a previous, specific version:

    $ rake db:migrate:down VERSION=nnn # Rails 3 (provide version number also).

Version Number means the SHA(Secure Hash Algorithm) for the commit which is a long hexadecimal number which looks something like 886af3194768917c78e... You can see it by doing git log

You can see these commands (and others) with their descriptions by using rake -T db: which for rails 3.2 includes:

rake db:migrate         # Migrate the database (options: VERSION=x, VERBOSE=false)
rake db:migrate:status  # Display status of migrations
rake db:rollback        # Rolls the schema back to the previous version (specify steps w/ STEP=n)
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最佳答案

Run the following command

rake db:migrate:down VERSION=<version>

where <version> is the version number of your migration file you want to revert.

eg. if you want to revert a migration with file name 3846656238_create_users.rb

rake db:migrate:down VERSION=3846656238

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You can do rollback and specify how many last migrations will be rollbacked, e.g.

rake db:rollback STEP=3

for 3 last migrations.

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rake db:migrate:redo

It will undo and reapply the last migration.

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As an new programmer (or to other new programmers)

rake db:rollback works about half the time. I start there.

If not, rake db:migrate:down VERSION=3846656238

plug in VERSION for the version number of your migration file you want to revert.

小开

Run this command in your terminal:

rake db:migrate:status

or 

bundle exec rake db:migrate:status

It shows the status, migration ID's, migration name for all migration we ran previously. select your migration id (i.e your version number) and put that id in the following command after version= ,,, and press enter

bundle exec rake db:migrate:down VERSION=
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For rails 5 we can use rails command instead of rake

rails db:migrate:down VERSION=<version>

example

rails db:migrate:down VERSION=20170330090327

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How to Roll back a migration

Another way. I prefer this because you need to be explicit, rather than rolling back - just in case you might make a mistake.

(1) First Identify The Migration ID

rake db:migrate:status

  • Copy the ID number.

Identify the migration to roll back.

(2) Then Roll back the migration

rake db:migrate:down VERSION=20190802023239

  • Paste the relevant ID number above. Of course, in your case, the migration ID will be different!

.......and now you're off to the races!


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