Find by id - This can either be a specific id (1), a list of ids (1, 5, 6), or an array of ids ([5, 6, 10]). If one or more records cannot be found for the requested ids, then ActiveRecord::RecordNotFound will be raised. If the primary key is an integer, find by id coerces its arguments by using to_i .

Person.find(1) # returns the object for ID = 1 Person.find("1") # returns the object for ID = 1 Person.find("31-sarah") # returns the object for ID = 31 Person.find(1, 2, 6) # returns an array for objects with IDs in (1, 2, 6) Person.find([7, 17]) # returns an array for objects with IDs in (7, 17) Person.find([1]) # returns an array for the object with ID = 1 Person.where("administrator = 1").order("created_on DESC").find(1)

NOTE: The returned records are in the same order as the ids you provide. If you want the results to be sorted by database, you can use ActiveRecord::QueryMethods#where method and provide an explicit ActiveRecord::QueryMethods#order option. But ActiveRecord::QueryMethods#where method doesn't raise ActiveRecord::RecordNotFound .

Find with lock

Example for find with a lock: Imagine two concurrent transactions: each will read person.visits == 2 , add 1 to it, and save, resulting in two saves of person.visits = 3 . By locking the row, the second transaction has to wait until the first is finished; we get the expected person.visits == 4 .

Person.transaction do person = Person.lock(true).find(1) person.visits += 1 person.save! end

Variations of find

Person.where(name: 'Spartacus', rating: 4) # returns a chainable list (which can be empty). Person.find_by(name: 'Spartacus', rating: 4) # returns the first item or nil. Person.find_or_initialize_by(name: 'Spartacus', rating: 4) # returns the first item or returns a new instance (requires you call .save to persist against the database). Person.find_or_create_by(name: 'Spartacus', rating: 4) # returns the first item or creates it and returns it.

Alternatives for find