HABTM - primary key problem

rubyonrails-talk
1

Hi everyone,

I ran into a serious problem when I was trying to do something similar to twitter follow mechanism. The thing is like this:

First, I have a self-referential table, named "users"   create_table :users do |t|       t.column :name, :string       t.column :user_name, :string       t.column :password, :string       t.column :email, :string   end

I also have a HABTM join table, named "follow_relations"   create_table :follow_realtions do |t|       t.column :a_id, :integer # a_id follows b_id       t.column :b_id, :integer   end

My HABTM join is defined as follows    has_and_belongs_to_many :followers,                                                  :class_name => "User",                                                  :join_table => "follow_relations",                                                  :foreign_key => "b_id",                                                  :association_foreign_key => "a_id"

  has_and_belongs_to_many :followings,                                                 :class_name => "User",                                                 :join_table => "follow_relations",                                                 :foreign_key => "a_id",                                                 :association_foreign_key => "b_id"

When I executed:     gaoxh = User.create(:name => "gaoxh")     micai = User.create(:name => "micai")     xiexin = User.create(:name => "xiexin")     gaoxh.followers << micai     xiexin.followers << micai

The first << operation executes the following SQL : INSERT INTO `follow_relations (`id`, `b_id`, `a_id`) VALUES (3, 1, 3) The second << operation executes the following SQL: INSERT INTO `follow_relations (`id`, `b_id`, `a_id`) VALUES (3, 2, 3) Thus, key id is duplicated. It looks like that every time, the value of column id is copied from column a_id. What's going on here? How to fix this problem?

Thanks in advance, xiahong

2

Xiahong Gao wrote:

Hi everyone,

I ran into a serious problem when I was trying to do something similar to twitter follow mechanism. The thing is like this:

First, I have a self-referential table, named "users"   create_table :users do |t|       t.column :name, :string       t.column :user_name, :string       t.column :password, :string       t.column :email, :string   end

I also have a HABTM join table, named "follow_relations"   create_table :follow_realtions do |t|       t.column :a_id, :integer # a_id follows b_id       t.column :b_id, :integer   end

My HABTM join is defined as follows    has_and_belongs_to_many :followers,                                                  :class_name => "User",                                                  :join_table => "follow_relations",                                                  :foreign_key => "b_id",                                                  :association_foreign_key => "a_id"

  has_and_belongs_to_many :followings,                                                 :class_name => "User",                                                 :join_table => "follow_relations",                                                 :foreign_key => "a_id",                                                 :association_foreign_key => "b_id"

[...]

The first << operation executes the following SQL : INSERT INTO `follow_relations (`id`, `b_id`, `a_id`) VALUES (3, 1, 3) The second << operation executes the following SQL: INSERT INTO `follow_relations (`id`, `b_id`, `a_id`) VALUES (3, 2, 3) Thus, key id is duplicated. It looks like that every time, the value of column id is copied from column a_id. What's going on here? How to fix this problem?

If you're using HABTM, the join table (follow_relations) should not have an id column. Remove it and see if that does the trick.

Thanks in advance, xiahong

Best,

3

If I remove id column, what is the primary key?

4

If I remove id column, what is the primary key?

Have a look at the rails guides, particularly the one on ActiveRecord associations at Ruby on Rails Guides

Colin

5

thanks all… problem solved.