Metaprogram Squeel to search on keypaths - ruby-on-rails

Question

The question
I'm trying to wrap my head around arel and squeel, but I feel like I lack the vocabulary to ask Google what I'm looking for.
TL;DR: Does anyone know how to mimic Squeel's Model.where{related.objects.field.matches string} syntax out of composed Squeel::Node objects?
The problem
This question demonstrates how to build a Squeel KeyPath from a string, like so:
search_relation = 'person.pets'
User.joins{Squeel::Nodes::KeyPath.new(search_relation.split('.'))}
# Mimics User.joins{person.pets}
The plot thickens in this post, where I learned how to metaprogram a search across multiple columns. Cleaned up with a documented Squeel trick (the last line on the page), it looks like this:
search_columns = %w[first_name last_name]
search_term = 'chris'
User.where{
search_columns.map do |column|
column_stub = Squeel::Nodes::Stub.new(column)
Squeel::Nodes::Predicate.new(column_stub, :matches, "%#{search_term}%")
end.compact.inject(&:|)
}
# Mimics User.where{(last_name.matches '%chris%') | (first_name.matches '%chris%')}
What I want is to be able to combine the two, mimicking the syntax of
User.joins{person.pets}.where{person.pets.name.matches '%polly%'}
by building the squeel objects myself.
The first part is easy, demonstrated in the first example. The second part I can do for columns directly on the table being queried, demonstrated in the second example.
However, I can't figure out how to do the second part for columns on joined in tables. I think I need to use the KeyPath object from the first example to scope the Predicate object in the second example. The Predicate object only seems to work with a Stub object that represents a single column on a single table, not a KeyPath.
Previous attempts
Assumming
search_relation = 'key.path'
search_column = 'field'
search_term = '%search%'
keypath = Squeel::Nodes::KeyPath.new(search_relation.split('.') << search_column)
I've tried calling the matches method on the KeyPath:
Model.where{keypath.matches search_term}
#=> NoMethodError: undefined method `matches' for Squeel::Nodes::KeyPath
I've tried using the matches operator, =~:
Model.where{keypath =~ search_term}
#=> TypeError: type mismatch: String given
And I've tried building the Predicate manually, passing in a :matches parameter:
Model.where{Squeel::Nodes::Predicate.new(keypath, :matches, search_term)}
#=> ActiveRecord::StatementInvalid: Mysql2::Error: Unknown column
#=> 'model.key.path.field' in 'where clause':
#=> SELECT `model`.* FROM `model`
#=> INNER JOIN `key` ON `key`.`id` = `model`.`key_id`
#=> INNER JOIN `path` ON `path`.`id` = `key`.`path_id`
#=> WHERE `model`.`key.path.field` LIKE '%search%'
Here, it successfully generates SQL (correctly joining using Model.joins{search_relation} like above, omitted for readability) then assumes the KeyPath is a field instead of traversing it.

Answer 1

Chris,
You're on the right track. Simply calling the matches method on the KeyPath object will create a matches predicate with the keypath on the left side and the argument to matches on the right. Squeel's visitor will traverse the keypath on the left, arrive at the attribute in question, and build the matches ARel predicate against it.

Answer 2

While the KeyPath in the first example is sufficient for joining tables, a KeyPath to be used in WHERE clauses needs to be constructed a little more carefully, by ensuring the last value is indeed a Stub.
search_relation = 'key.path'
search_column = 'field'
search_stub = Squeel::Nodes::Stub(search_column)
search_term = '%search%'
keypath = Squeel::Nodes::KeyPath.new(search_relation.split('.') << search_stub)
Model.where{Squeel::Nodes::Predicate.new(keypath, :matches, search_term)}
#=> SELECT `model`.* FROM `model`
#=> INNER JOIN `key` ON `key`.`id` = `model`.`key_id`
#=> INNER JOIN `path` ON `path`.`id` = `key`.`path_id`
#=> WHERE `path`.`field` LIKE '%search%'