Validating within a Transaction

gistfile1.rb

# == Schema Information
#  bar        :integer
class Foo < ActiveRecord::Base
  validates_uniqueness_of :bar
end

a=Foo.new(bar: 1)
a.valid? # => true

b=Foo.new(bar: 1)
b.valid? # => true

a.save # => #<Foo id: 1, bar: 1>
b.valid? # => false
b.errors # => {:bar=>["has already been taken"]}

# Now with a transaction
a=Foo.new(bar: 2)
b=Foo.new(bar: 2)

ActiveRecord::Base.transaction do
  a.save # validates here and INSERTS into local transaction
  sleep 10
# commits here
end # => #<Foo id: 3, bar: 2>

# In a separate process within 10 seconds of issuing previous command
b.save # => #<Foo id: 4, bar: 2>

a.valid? # => false
a.errors # => {:bar=>["has already been taken"]}
b.valid? # => false
b.errors # => {:bar=>["has already been taken"]}

ActiveRecord::Base.transaction do
Account.create!(name: "foo", plan: SubscriptionPlan.find(1))
sleep 30
end

Run in two consoles at the same time. reproduces