Convert instance of a non-primitive class into an object suitable for SQL/find

[davetron5000]

I have something like this:

class Channel
  def initialize(value)
    @value = if value == "sms"
      :sms
    elsif value == "email"
      :email
    else
      raise ArgumentError
    end
  end

  def to_s = @value
end

I'd like to be able to do something like:

channel = Channel.new("sms")
Notification.find(channel: channel)

When I do this, I get can't express #<Channel:0x00007e5e91a71b10 @value="sms"> as a SQL literal

Due to questionable artificially-intelligent advice, I attempted to override sql_literal, and it does get called, but I could not figure out how to safely return a value from that that would work. Sequel.lit(@value) did not work (I got a different error).

Is there a way to modify a class with "here's how to turn this into a SQL string"?

[jeremyevans]

Adding an sql_literal method should work. You need it to return a string that is appended to the SQL being generated.

Your example looks weird, because you have to_s returning a symbol and not a string. Not sure if that is related to the error you are getting.

[davetron5000]

The example is simplified and IRL it returns a string - just typing too fast.

Sounds like I need to return "'#{@value}'", i.e. single-quoting the string, though I guess I have to escape the single quotes that might be in the string - is there a Sequel function for that? I think I was hoping Sequel.lit(...) would do that, but I couldn't figure out how to get it to do that and figured I was doing something wrong so stopped digging through the source

[jeremyevans]

You could try:

  def sql_literal_append(ds, sql)
    ds.literal_append(sql, @value.to_s)
  end

[davetron5000]

Welp, not only did that work, that's what the stupid AI told me at the start, but every bit of explanation about why that worked was imagined, and I assumed it would either not work or I should not do it 👴

Thanks for confirming! :)