Rails uniqueness constraint and matching db unique index for null column
- by Dave
I have the following in my migration file
def self.up
create_table :payment_agreements do |t|
t.boolean :automatic, :default => true, :null => false
t.string :payment_trigger_on_order
t.references :supplier
t.references :seller
t.references :product
t.timestamps
end
end
I want to ensure that if a product_id is specified it is unique but I also want to allow null so I have the following in my model:
validates :product_id,
:uniqueness => true,
:allow_nil => true
Works great but I should then add an index to the migration file
add_index :payment_agreements, :product_id, :unique => true
Obviously this will throw an exception when two null values are inserted for product_id. I could just simply omit the index in the migration but then there's the chance that I'll get two PaymentAgreements with the same product_id as shown here: Concurrency and integrity
My question is what is the best/most common way to deal with this problem
