foriegn keys missing in ruby on rails schema.rb file after running rake db:schema:dump

Question

I had a data model generation script which works fine by invoking mysql command line utility. I want RoR to use this data model that includes several foreign key dependencies within the tables. I found that $ rake db:schema:dump creates the db/schema.rb file and it did, but it is missing all the foreign key constraints/clauses. This is obviously a problem.

I've watched the RoR tutorial on lynda.com and the foriegn key functionality is pretty basic and assumes a lot of conventions like there can only be one foreign key and it needs to have a naming convention of table1_table2_id or something.

I was chatting on IRC yesterday in the #rubyonrails channel and one person said that RoR ignores foriegn keys and the rake db:schema:dump seems to be doing so.

For example this is the mysql statement:

CREATE TABLE IF NOT EXISTS students ( studentid INT NOT NULL AUTO_INCREMENT, teacherid INT NOT NULL, parentid INT NULL, firstname VARCHAR(45) NOT NULL, lastname VARCHAR(45) NOT NULL, dob DATETIME NOT NULL, isadult TINYINT(1) NOT NULL, email VARCHAR(45) NOT NULL, cellphone INT NULL, username VARCHAR(45) NOT NULL, password VARCHAR(45) NOT NULL, addr_streetno VARCHAR(45) NULL, addr_aptno INT NULL, addr_city VARCHAR(45) NULL, addr_state VARCHAR(45) NULL, addr_zip INT NULL, photo MEDIUMBLOB NULL, PRIMARY KEY ( studentid ), INDEX parentid_idx ( parentid ASC), INDEX teacherid_idx ( teacherid ASC), CONSTRAINT parentid FOREIGN KEY ( parentid ) REFERENCES parents ( parentid ) ON DELETE NO ACTION ON UPDATE NO ACTION, CONSTRAINT teacherid FOREIGN KEY ( teacherid ) REFERENCES teachers ( teacherid ) ON DELETE NO ACTION ON UPDATE NO ACTION) ENGINE = InnoDB;

In the schema.rb, it shows up as this and doesn't have any directives for foreign keys. what gives:

create_table "students", primary_key: "studentid", force: true do |t|
   t.integer  "teacherid",                      null: false
   t.integer  "parentid"
   t.string   "firstname",     limit: 45,       null: false
   t.string   "lastname",      limit: 45,       null: false
   t.datetime "dob",                            null: false
   t.boolean  "isadult",                        null: false
   t.string   "email",         limit: 45,       null: false
   t.integer  "cellphone"
   t.string   "username",      limit: 45,       null: false
   t.string   "password",      limit: 45,       null: false
   t.string   "addr_streetno", limit: 45
   t.integer  "addr_aptno"
   t.string   "addr_city",     limit: 45
   t.string   "addr_state",    limit: 45
   t.integer  "addr_zip"
   t.binary   "photo",         limit: 16777215
end

add_index "students", ["parentid"], name: "parentid_idx", using: :btree
add_index "students", ["teacherid"], name: "teacherid_idx", using: :btree

Answer 1

in Rails, where to place the foreign key is determined by the association of your models.

Let's say you have the following two models:

class Parent < ActiveRecord::Base
  has_many :children
end

class Child < ActiveRecord::Base
  belongs_to :parent
end

the foreign key will be placed in the table declaring the belongs_to association. in this case, the children table.

the foreign key is the name of the parent model with the suffix _id . in this case, it would be parent_id .

In Rails, this is how you add parent_id to the children_table :

rails g migration AddParentIdToChild parent_id:integer

then run rake db:migrate . afterwards, the foreign key should show up in your schema

I hope I didn't misunderstood your question.
For more info about foreign keys and tables, see the documentation