Forum: Ruby on Rails destroy_all and has_and_belongs_to_many

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Dave D. (Guest)
on 2007-06-12 07:21
I have a single class with a many-to-many relationship to itself.

class Connection

  has_and_belongs_to_many :matches,
                          :class_name => "Connection",
                          :join_table => "matched_connections",
                          :foreign_key => "connection_id",
                          :association_foreign_key => "match_id"

  has_and_belongs_to_many :requests,
                          :class_name => "Connection",
                          :join_table => "matched_connections",
                          :foreign_key => "match_id",
                          :association_foreign_key => "connection_id"
end

I want to be able to destroy all the matches without deleting the
dependent connections.  Essentially, I want to remove all the entries in
matched_connections that have the correct connection_id.  However, if I
run:

con.matches.destroy_all

It deletes the con object as well.  I can't add :dependent to the habtm,
so I how do I only destroy the rows in matched_connections and still
keep the objects in sync?
Thorsten (Guest)
on 2007-06-12 12:53
(Received via mailing list)
Use has:_many :through

class MatchedConnection
# This is your Join Table, now as a real Model. The Table also now
should have an primary key "id" column

belongs_to: matching_connection, :class_name =>
"Connection", :foreign_key => "match_id"
belongs_to: requesting_connnection, :class_name =>
"Connection", :foreign_key => "request_id"

end

class Connection

  # a Request connection has these associations to its corresponding
matches:
  has_many :match_connections, :class_name => "MatchedConnection",
foreign_key => "request_id"
  has_many :matches,
                          :through => :match_connections,
                          :class_name => "Connection"
                          :foreign_key => "match_id"

  # a Match connection has these associations to its corresponding
requests:
  has_many :requested_connections, :class_name =>
"MatchedConnection", :foreign_key => "match_id"
  has_many :requests,
                          :through => :request_connections,
                          :class_name => "Connection"
                          :foreign_key => "request_id"
end

Explanation:
>From a connection on the Match side to the request side:
->(match_id ) request_connections (request_id) -> requests
>From a connection on the request side to the Match side:
->(request_id ) request_connections (match_id) -> requests

As the join Table now is a real model, you can access the join items:
@Con = Connection.find(1)
@con.match_connections.destroy_all

don't let the names of the associations i used confuse you, i don't
know exactly what your Models should do, so the naming could be a
little inconvinient.

On 12 Jun., 05:21, Dave D. <removed_email_address@domain.invalid>
Thorsten (Guest)
on 2007-06-12 12:56
(Received via mailing list)
My explanation is a little wrong, no time to correct it atm. Code
should be fine though, just check it out.
Dave D. (Guest)
on 2007-06-12 14:23
Thanks, I was able to make this work elsewhere in my app using the same
technique, but I guess habtm always wants to destroy dependencies.  I
also tried

con.matches.delete(all)
con.matches.reload

That seemed to work as well, but I wasn't sure of the side effects.
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