Good notes posted by cratchit

Gotcha when defining :finder_sql or :counter_sql

When setting custom SQL statements in the :finder_sql or :counter_sql queries, if you need to inject attributes from the current object, such as the ID, make sure to disable string interpolation of the statement by using single quotes or %q().

Example:

has_many :relationships, :class_name => 'Relationship', :finder_sql => %q(
  SELECT DISTINCT relationships.*
  FROM relationships
  WHERE contact_id = #{id}
)

Surrounding this SQL with double-quotes or %Q() will expand #{id} too early, resulting in a warning about Object#id being deprecated and general brokenness.