将具有相同值的Rails模型属性设置更改吗？ 返回真吗？

Question

I'm looking to make my db:seed task a little more dynamic by allowing certain entries in my application to be created or updated (or nothing at all) based on the values of in db/seeds.rb and the current state of the backend database. I'm also looking to simplify the functions that carry this logic out.

I'd like to avoid this:

def create_or_update_config(key, value)

  ...

  if config_entry.value != value
    config_entry.value
  end

  if config_entry.changed?
    config_entry.save
  end

  ...

end

And instead have something simplistic:

def create_or_update_config(key, value)

  ...

  config_entry.value = value

  if config_entry.changed?
    config_entry.save
  end

  ...

end

Is ActiveRecord smart enough to know if attribute values have changed even if they've been set (with the same value)?

Answer 1

Yes. ActiveRecord's changed? method will return true only if there were mutations since the last save. From an example using my own app's console (Rails 5.1.6):

irb(main):013:0> config.value
=> "http://localhost:3100"
irb(main):014:0> config.value = "http://localhost:3100"
=> "http://localhost:3100"
irb(main):015:0> config.changed?
=> false
irb(main):016:0> config.value = "anything else"
=> "anything else"
irb(main):017:0> config.changed?
=> true