has_and_belongs_to_many associations

rubyonrails-talk
1

Hi!

I have a User model that has_and_belongs_to_many Awards. The awards table is pre-populated, and there's an awards_users join table.

In a rails console, If I do: u = User.find(1) u.awards.build(award_id: 1)

the award model that is built is an actual Award model, not an AwardsUser model, like I would expect. so, If i try to save the user model it violates the primary key index because it is also trying to save a new Award, with the id 1. I was expecting this to create a new row in the awards_users table instead, with the user_id and award_id of 1.

Any ideas where I've gone wrong?

2

Hi!

I have a User model that has_and_belongs_to_many Awards. The awards table is pre-populated, and there's an awards_users join table.

In a rails console, If I do: u = User.find(1) u.awards.build(award_id: 1)

the award model that is built is an actual Award model, not an AwardsUser model, like I would expect. so, If i try to save the user model it violates the primary key index because it is also trying to save a new Award, with the id 1. I was expecting this to create a new row in the awards_users table instead, with the user_id and award_id of 1.

Any ideas where I've gone wrong?

You should not try and set the id manually, let Rails take care of that. award = u.awards.build should build an award object, then award.save should save it.

Having said that I much prefer to use has_many through and manage the join table myself. I find it easier to follow what is happening.

Colin

3

Hmm, perhaps I dont understand the meaning of rails' has_and_belongs_to_many.

I require only the join table to be populated, NOT additional Award objects to be created in the DB. A User should have many rows in awards_users (user_id, award_id).

So in terms of a user admin interface, I want to be able to select several (even duplicate) Awards that belong to a particular user (lets say awards with the ID's 1,2,3,3,4 and 6).

The result of saving this user would be rows in awards_users like:

award_id | user_id     1 | 1     2 | 1     3 | 1     3 | 1     4 | 1     6 | 1

Thanks.

Colin Law wrote in post #1106758:

4

Please don't top post, it makes it difficult to follow the thread. Insert your reply inline at appropriate point(s) in previous message. Thanks.

Hmm, perhaps I dont understand the meaning of rails' has_and_belongs_to_many.

I require only the join table to be populated, NOT additional Award objects to be created in the DB. A User should have many rows in awards_users (user_id, award_id).

So in terms of a user admin interface, I want to be able to select several (even duplicate) Awards that belong to a particular user (lets say awards with the ID's 1,2,3,3,4 and 6).

The result of saving this user would be rows in awards_users like:

award_id | user_id     1 | 1     2 | 1     3 | 1     3 | 1     4 | 1     6 | 1

In that case I am sure it would definitely be easier to use has_many through (see the Rails Guide on ActiveRecord associations) then you will have full control of the join table.

Colin