create unique constraints per user - ruby

Question

I am building a small app and at this point I am creating the database schema. I use PostgreSQL with Sequel and I have the two migrations:
Sequel.migration do
change do
Sequel::Model.db.run 'CREATE EXTENSION IF NOT EXISTS "uuid-ossp"'
create_table :user do
String :id, :type => :uuid, :primary_key => true, :default => Sequel.function(:uuid_generate_v4)
DateTime :created_at
DateTime :updated_at
index :id, :unique => true
end
end
end
Sequel.migration do
change do
Sequel::Model.db.run 'CREATE EXTENSION IF NOT EXISTS "uuid-ossp"'
create_table :location do
String :id, :type => :uuid, :primary_key => true, :default => Sequel.function(:uuid_generate_v4)
foreign_key :user_id, :user, :type => :uuid
String :name, :unique => true, :null => false # TODO: unique, per user
Float :latitude, :null => false
Float :longitude, :null => false
DateTime :created_at
DateTime :updated_at
index :id, :unique => true
full_text_index :name, :index_type => :gist
end
end
end
As you can see the name column on the location table is unique, but I am in doubt about it. Because I want to establish a unique constraint on the name, but per user, so a user can have only one location with the same name but in the entire table many users can have locations with the same name (the relation between user and location is a one to many).
I suppose my unique constraint added on the column will make column generally unique, so amongst all users the location name must be unique. If so, how do I create a constraint that makes the name unique on a per user basis?

Answer 1

Just create the unique constraint over both columns:
UNIQUE (user_id, name)
Per documentation:
This specifies that the combination of values in the indicated columns
is unique across the whole table, though any one of the columns need
not be (and ordinarily isn't) unique.
But from the looks of it, you really want another table user_location than implements an n:m relation between locations and users - with a primary key on (user_id, location_id).
And don't call the first table "user", that's a reserved word in standard SQL and in Postgres and shouldn't be used as identifier.