在 Rails 中撤消先前播种的数据

Question

I have seeded a row of data to my table by editing db/seed.rb file and executing rake db:seed command. Unknowingly, I put some wrong information in to that row. So I want to remove the previously added row of data. Is there any rake command for the same like rake db:rollback for rake db:migrate .

Answer 1

There are a couple of aspects to this:

1: You want to change the seed data when no other data is present in the database:

You should simply redo the rake db:seed after updating the seed.rb file. Make sure you have MyModel.delete_all before you try to add anything to that model.

2: You want to change the seed data, but there are other data added to the database

This is a bit harder. Often the simplest thing to do here is to manually change the data with either raw sql-statements, or with the use of tools like PhpPpAdmin , PhpMyAdmin etc.

---

Now, there is possiby one way to hack this together, and that would be to do some voodoo in the seed.rb file. So you could run rake db:seed deseed=true , then in your seed.rb:

if ENV['deseed'] 
   #Do your deseeding action here
else
   #Do your seeding here.
end

You could even get real crazy and do something like this:

deseed = ENV['desee']

#DANGER: Dirty hacks upcoming:
deseed? myModelCall = MyModel.method(:destroy_all): myModelCall = MyModel.method(:create)

myModelCall.call :user_id_or_whatevs => 23 #this creates or deletes a MyModel entity with the given parameters
#NOTE this might not work in all cases and I would not necessarily recommend doing this. 

#<3uby

Answer 2

I had similar issues when I seeded my data. In fact, I ran the seed command twice and I couldn't find a way to revoke the second seed. However, I had to run rails db:reset command and then run the rails db:seed command again and that fixed the problem for me.