How to delete join table?

Rails
1

Hi -

I have a join table that joins a people table and a roles table. It’s
configured using the has_and_belongs_to_many statement in the model
files.

How do I delete the join table? I have code that migrates from a legacy
db into my rails db, and as part of the migration I want to delete the
people, roles, and people_roles tables to start with a clean db. It’s
easy to delete the people table with Person.delete_all and likewise with
the roles table. But the join table gets left behind. How would I
delete the people_roles table?

Thanks!

2

If you had a model instead of a has_and_belongs_to_many, you could do
that.

app/models/people.rb
has_many :people_roles
has_many :roles, :through => :people_roles

app/models/role.rb
has_many :people_roles
has_many :roles, :through => :people_roles

app/models/people_role.rb
belongs_to :person
belongs_to :role

And then you can call PeopleRole.delete_all.

On Mon, May 19, 2008 at 9:15 AM, Steven L. <
[email protected]> wrote:

db into my rails db, and as part of the migration I want to delete the

–
Ryan B.

Feel free to add me to MSN and/or GTalk as this email.

3

Thanks! I figured out another way, involving some trickery. Your way
is probably more recommended.

I created a model named people_role.rb. Note the first part of the name
is the plural form of Person, and the second part is the singular of the
Role table. I did that because rails will pluralize the word
people_role into people_roles, and people_roles is the name of my table.

Then I can call PeopleRole.delete_all and it appears to work.

4

Hmm, ran into a glitch further down the road so I redid everything your
way and that works better.

For some reason each join table row had it’s own id. In this case the
join table columns were role_id, person_id, and id. My problem was that
when saving each join table row, it was setting the id to the role_id,
and since my role_id’s weren’t unique within the join table, the saves
were failing. I have no idea why it was doing that.

5

Probably due to you creating the table like this:

create_table :people_roles do |t|
t.references :person, :role

OR

t.integer :person_id, :role_id
end

instead of create_table :people_roles, :id => false which would not put
in
that id column automatically.

6

What was the exact error you were getting and what code were you using
to
get it? You should be able to assign many roles to many people and
vice-versa ad infinitum ergo (and any other trippy words)

7

Hmm, I don’t really have the code available, I’ve changed it.

Thanks for your help. It was very good.

8

interesting . . . next question then, why when I save a person with a
role would active record be setting the id of the join row to the
role_id? Since I reuse roles I was getting constraint violation type
errors because it was trying to save a people_roles row the the same id
as another row.