Please tell me how to obtain the id of the data saved in activecord.

As long as I tried using the rails console at hand, I was able to get an id in the form of data.id.

irb(main): 001:0>c=Company.create:name=>'hoge'
=>#<Company id:4, name: "hoge", created_at: "2015-02-0203:53:58", updated_at: "2015-02-0203:53:58" >
irb(main): 002:0>c.id
=>4

Perhaps there is a validation error somewhere?

#name is required
irb(main): 004:0>c=Company.create:name=>'
=>#<Company id:nil,name:",created_at:nil,updated_at:nil>
irb(main): 005:0>c.id
=>nil
irb(main): 006:0>c.valid?
=>false
irb(main): 007:0>c.errors
=>#<ActiveModel::Errors:0x007ffc5b8646d8@base=#<Company id:nil,name:",created_at:nil,updated_at:nil,@messages={:name=>["US>" }>

If the id cannot be retrieved, check the return value of data.valid?.
false has a validation error and cannot be saved.
Check data.errors for the contents of the error.

I was able to retrieve it with data.attributes ['id'].
Is there any problem with this way?

In my case, data.attributes['id'] is not the same way to retrieve it, most of the time it is retrieved from data.id.
data.attributes['id'] is probably not the only thing you can get, so you should investigate the root cause.

Just in case.

class User<ActiveRecord::Base
  defined
  end
end
user=User.cerate(nane:'nazka')
=>#<User:1,name:"nazka">
user.id
=>nil
user.attributes ['id']
=>1

Are there any id methods defined?
Maybe if you do User.first.id ('hogehoge'...) or something like that,
ArgumentError: wrong number of arguments (1 for 0)
It would be an error like from...activerecord-4.1.9/lib/active_record/... which would be an error in the gem...What do you think?
※ If possible, please let me know what adapter you are using.