search for: specifying_company_id

All, If I have a table that has several discrete fields that all point to the same associated field, how do I model it. Specifically, If I have a project table that has 2 fields: specifying_company, and responsible_company. And one table of associated companies, how do I do the :belongs_to / :has_many stuff ie. For a given project company A may be writing the spec, but company B may be paying