Question

I have a table in my db which saves a config as a yaml-file.
The respective column is called config.

I would like to read, let’s say, the first 5 config entries, and convert them back to yaml.

I tried in the rails console, as follows:

Person.pluck(:config).first(5).each do {|c| c.to_yaml}

This seems to be quite wrong, I know. The first thing that got me tripping:

• Why will Person.first(5).pluck(:config) yield a NoMethodError?
• Doing it the way I do it above will first pluck ALL configs and then retrieve the first 5 rows, correct? How can I speed up the query?

Second question:

• What would be the correct way, to iterate over the returned table rows (e.g. the first 5), and convert the content of each config-column back to yaml via the to_yaml-method?

Answer 1

Why will Person.first(5).pluck(:config) yield a NoMethodError?

It yields a NoMethodError because you are trying to send the message pluck to an Array, which has no such method.

Doing it the way I do it above will first pluck ALL configs and then retrieve the first 5 rows, correct? How can I speed up the query?

Yes, that is correct. If you want to pluck the config out of just the first five records, use limit:

Person.limit(5).pluck(:config)

For info on how to parse the config values as YAML, see this thread.