ActiveRecord Unique key association

Hi, I am in the process of incorporating a legacy database into my first ruby/rails project. All is going well so far (he says crossing all toes/fingers!).

I have a User tbl which has a unique key association on two columns, username and userpassword. So far I have:

class Usertbl < ActiveRecord::Base set_primary_key “user_id” end

and I want to add a line after the primary_key declaration, something like:

set_unique_key “username, userpassword”

How would I do this?

Hi Andrew

You need something along the lines of

validates_uniqueness_of :username, :password

I think

I am still fairly new at this myself!

Hi Rod,

validates_uniqueness_of :username, :password

I think you have it. What I have done is:

validates_uniqueness_of :username,:userpassword, :scope => :user_id

which I believe means, there can only be one username/userpassword combination for any given user_id? If one of you more knowledgeable chaps would like to chime in at this juncture, that would be appreciated :wink:

i don't see why you would want a unique combination of username AND password. just a unique key on username should suffice. if you've got one on both, that would allow two users could have the same username with different passwords and which would satisfy the unique restriction, and that is something you don't want.


username unique => good (username, password) unique => bad


create table testusers (

    -> id int auto_increment,     -> username varchar(20),     -> password varchar(20),     -> primary key(id),     -> unique username_password (username, password));

so i have a unique index on the username AND password combination.

insert into testusers values ('', 'bob', 'bobpw1');

Query OK, 1 row affected, 1 warning (0.10 sec)

insert into testusers values ('', 'bob', 'bobpw2');

Query OK, 1 row affected, 1 warning (0.00 sec)

Hi Chris,

username unique => good (username, password) unique => bad

Yes, you are correct! So noted and amended. Thanks.