Ruby: What does binds mean in ActiveRecord gem?

Question

I saw binds as argument in lots of methods, but without any documentation.

e.g. Rails Source code

def find_by_sql(sql, binds = [], preparable: nil, &block)
  result_set = connection.select_all(sanitize_sql(sql), "#{name} Load", binds, preparable: preparable)
  column_types = result_set.column_types.dup
  columns_hash.each_key { |k| column_types.delete k }
  message_bus = ActiveSupport::Notifications.instrumenter

  payload = {
    record_count: result_set.length,
    class_name: name
  }

  message_bus.instrument("instantiation.active_record", payload) do
    result_set.map { |record| instantiate(record, column_types, &block) }
  end
end

1. what does binds mean?
2. How to use it?

Answer 1

When your SQL contain question marks ? the binds are used to replace these marks. For example if you have a query like this: SELECT * from posts where id = 3 you can write in Ruby:

Post.find_by_sql(["SELECT * from posts where id = ?", 3])

We have binded the ? with the value 3. If we have more ? they will be binded with the binds array in that order. If there are not ? in the SQL string binds are ignored.