Rails: validate uniqueness of two columns (together)

Question

I have a Release model with medium and country columns (among others). There should not be releases that share identical

Answer 1

All the above answers are missing how to validate the uniqueness of multiple attributes in a model. The code below intends to tell how to use multiple attributes in a scope.

validates :country, uniqueness: { scope: [:medium, :another_medium] }

It validates uniqueness of country in all rows with values of medium and another_medium.

Note: Don't forget to add an index on the above column, this insures fast retrieval and adds a DB level validation for unique records.

Update: For adding an index while creating table

t.index [:medium, :another_medium], unique: true