Using pg_query fingerprinting to prevent SQL injections

output.txt

#my_orm_method("1")
1
#my_orm_method("'abc'")
abc
#my_orm_method("1 UNION SELECT * FROM passwords")
test.rb:8:in `exec_with_fingerprint': Invalid fingerprint, rejecting (RuntimeError)
	from test.rb:16:in `my_orm_method'
	from test.rb:23:in `<main>'

test.rb

require 'pg'
require 'pg_query'

conn = PG::Connection.new(hostaddr: '192.168.99.100', user: 'postgres')

def exec_with_fingerprint(conn, query, fingerprint, &block)
  if PgQuery.fingerprint(query) != fingerprint
    fail 'Invalid fingerprint, rejecting'
  else
    conn.exec(query, &block)
  end
end

def my_orm_method(conn, input_value)
  puts "#my_orm_method(#{input_value.inspect})"
  # 018e1acac181c6d28f4a923392cf1c4eda49ee4cd2 is the fingerprint for "SELECT 1"
  exec_with_fingerprint(conn, "SELECT " + input_value, "018e1acac181c6d28f4a923392cf1c4eda49ee4cd2") do |res|
    res.getvalue(0, 0)
  end
end

puts my_orm_method(conn, '1')
puts my_orm_method(conn, "'abc'")
puts my_orm_method(conn, '1 UNION SELECT * FROM passwords')