validation - Rails & Primary Keys / Uniqueness. How do you use multiple columns for a primary key? -

my question quite identical 1 (multicolumn primary keys in rails) i'm still not understanding 100%.

let's have model visit

visits     id     room_id     date     created_at     updated_at

in case, want (room_id, date) 'primary key'. now, post saying don't need change primary key, jus add uniqueness validations , stuff?

so need

add_index :visits, [:room_id, :date]

add_index :visits, [:id, :room_id] add_index :visits, [:id, :date]

? tie each column want in 'primary key' :id latter code, or put desired columns []'s former code.

also, how do validations? don't want either of :room_id or :date unique, combination. how do in rails?

according previous question, right 1 is:

add_index :visits, [:room_id, :date], :unique => true

this piece of code prevents database inserting room_id same date. in terms of model validation, need add:

validates_uniqueness_of :date,    :scope => :room_id

this way, activerecord can , validate record before trying insert.

p.s.: change date column name more specific start_date, creation_date, etc. believe cause potential problems in future.

WIKI