Validation failed on rake db:seed

Question

I'm doing chapter 12 of hartle's tutorial. When I ran bundle exec rake db:seed I got this error:

ActiveRecord::RecordInvalid: Validation failed: Email has already been taken

I try running

rake db:reset
rake db:migrate
rake db:test:prepare

And at last

rake db:populate 

but they didn't solve the problem. When I run rake db:populate it gives:

Don't know how to build task 'db:populate'

This is my seeds.rb file:

    # Users
User.create!(name:  "Example User",
             email: "[email protected]",
             password:              "foobar",
             password_confirmation: "foobar",
             admin:     true,
             activated: true,
             activated_at: Time.zone.now)

99.times do |n|
  name  = Faker::Name.name
  email = "example-#{n+1}@railstutorial.org"
  password = "password"
  User.create!(name: name,
              email: email,
              password:              password,
              password_confirmation: password,
              activated: true,
              activated_at: Time.zone.now)
end

# Microposts
users = User.order(:created_at).take(6)
50.times do
  content = Faker::Lorem.sentence(5)
  users.each { |user| user.microposts.create!(content: content) }
end

# Following relationships
users = User.all
user  = users.first
following = users[2..50]
followers = users[3..40]
following.each { |followed| user.follow(followed) }
followers.each { |follower| follower.follow(user) }

I guess maybe the problem is with this line email = "example-#{n+1}@railstutorial.org"

Answer 1

Your problem is that rake db:reset not only drops and recreates the database, but it also migrates and seeds it as well. So essentially what's happening is this:

rake db:drop
rake db:create
rake db:schema:load # (think of this as running all the migrations you've run before)
rake db:seed # (creates your 100 database users)

and then you run:

rake db:migrate # (likely unnecessary, but it causes no harm)
rake db:test:prepare # (prepares the test database)
rake db:prepare # (runs the seeds AGAIN and causes your errors)

Obviously, from this if you just stop running the rake db:prepare command your problem will go away. However, to avoid these things in the future, I strongly recommend putting a little bit of logic in your seed file. It's just Ruby, so you could wrap the User creates in an unless statement, such as:

unless User.find_by( email: "[email protected]" )
  # create all 100 users
end

This will prove to be especially valuable if you have a site on production that still uses seed data (such as a SiteSetting table); you need to make sure the data makes its way into your production database, but you'll create duplicate records (or errors) running the seed again without dropping.

As an additional reference for the answer to your question, see the selected answer to this one.

I hope this provides all the information you need!