Rails references

Let's say that you have a foreign key called COMPANY_ID in the table PERSON. In the model PERSON, can you write?

validates_presence_of :company_id

or

validates_presence_of :company

or

both?

Which is the prefer开发者_运维问答red and why?

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Prefere validates the foreign_key. It's better because there are no association made so 1 SQL request less.