I am trying to add a foreign key to via migration. It works as expected, but it automatically adds _id to the end (the column name I want to reference doesn't include _id). How can I make it reference the column name as I give it?
Here is the migration
class ChangeRefOnMemberPresentations < ActiveRecord::Migration[5.2]
def change
add_reference :member_presentations, 'employee_number', foreign_key: { to_table: :users }
end
end
Which results in both the reference column name and foreign key reference column being called employee_number_id in schema.rb
The following worked by defining everything manually, but seems messy. If there is a better migration answer, I'll be happy to accept.
def change
# column was added in another migration, but including for completness
add_column :member_presentations, :employee_number, :bigint
add_index :member_presentations, :employee_number, name: "index_member_presentations_on_employee_number"
add_foreign_key :member_presentations, :users, column: "employee_number"
end
Related
I've already created a model in Rails to collect some user information
I created the columns as :string initially but I've since changed the way this data is looked up and entered by using separate populated models.
Now instead of entering into these fields as string - i want these columns to be "references" instead.
Is there an easy way to change from the string to reference without having to create a new model entirely?
*do not need to save the existing data
Is there any data in the strings you would like to save?
Or is it just because it has the same name?
You don't have to create a new model.
You could create a simple migration
remove_column :table, :your_column_name, :string
add_column :table, :your_column_name, :integer, references: :your_parent_model
You can add a temporary string column to save the string column first:
rails g migration add_temporary_string_column_to_model temporary_string_column:string
And run rails console:
SomeModel.all.each do |some_model|
some_mode.temporary_string_column = some_mode.string_column
some_mode.save
end
And now you can change your original string column's type to references which is an int(4) column in MySQL, migration like this:
class ChangeFormatInSomeTable < ActiveRecord::Migration
def change
change_column :some_table, :string_column, :references
end
end
Finally, you can run rails console again to convert the string data to integer like this:
SomeModel.all.each do |some_model|
some_mode.string_column = some_mode.temporary_string_column.to_i
some_mode.save
end
And at last, remove the temporary string column:
rails g migration remove_temporary_string_column_from_model temporary_string_column
Here is another solution, without dropping the column itself (not exactly in my case). I'm not sure though if this is the best solution.
In my case, I have a tickets table that holds purchase_uid in itself. I decided to keep purchases in another table after making the necessary improvements in our backend. Purchases table has uuid as the primary key. Given this background, here is my migration to change my column into a reference.
class AddPurchaseRelationToTickets < ActiveRecord::Migration[5.2]
def up
change_column :tickets, :purchase_uid, :uuid, references: :purchase, foreign_key: true, using: 'purchase_uid::uuid'
end
def down
change_column :tickets, :purchase_uid, :string
end
end
In my case, since string doesn't automatically cast into uuid, purchase_uid were dropped and recreated as well. However, if you decide to keep the column type same, I don't think it will be a problem.
You can create migrations to serve the exact purpose.
rails generate migration AddAddressToUsers address:references
This will create a migration file in db/migrate directory.
Then run: rails db:migrate to run migration and make changes in your database.
Don't forget to create associations in your models (belongs_to, has_many, etc.) depending on your system structure.
Wanted to add a simpler alternative to the accepted answer that preserves data:
class ChangeStringToInt < ActiveRecord::Migration[5.1]
def up
change_column :table_name, :field_name, :integer, null: false, references: :table_referenced, using: 'field_name::integer'
add_index :chapter_actions, :field_name
end
def down
change_column :table_name, :field_name, :string, null: false, using: 'field_name::character varying'
remove_index :table_name, :field_name
end
end
(Rails is version 5.0.0, Ruby 2.3.0p0)
I want to create an association between my Users table and Cards table. I've added belongs_to :user to the Cards model, and has_many :cards to the Users model, and created a migration with:
class AddUserIdToCard < ActiveRecord::Migration[5.0]
def change
add_foreign_key :cards, :users, column: :user_id
end
end
When I run rake db:migrate, I receive the error:
ActiveRecord::StatementInvalid: PG::UndefinedColumn: ERROR: column "user_id" referenced in foreign key constraint does not exist
: ALTER TABLE "cards" ADD CONSTRAINT "fk_rails_8ef7749967"
FOREIGN KEY ("user_id")
REFERENCES "users" ("id")
Now I initially worked around this problem simply by adding add_column :cards, :user_id, :integer to the migration, but that doesn't really seem very tidy, and I'm worried about problems coming up later. Is there a better way to accomplish this?
You're setting a foreign key for cards table with the column user_id. But you haven't created a reference yet. Create a reference and then add foreign key to maintain referential integrity. Rollback and modify your migration with
1 class AddUserIdToCard < ActiveRecord::Migration[5.0]
2 def change
3 add_reference :cards, :users, index:true
4 add_foreign_key :cards, :users
5 end
6 end
Line 3 will create, in the cards table, a reference to id in the users table (by creating a user_id column in cards).
Line 4 will add a foreign key constraint to user_id at the database level.
For more, read Add a reference column migration in Rails 4
The answer provided is not accurate for Rails 5. Scroll to the add_reference bit of the docs for more, but in the case of the above question, you would use:
class AddUserIdToCard < ActiveRecord::Migration[5.0]
def change
add_reference :cards, :users, foreign_key: true
end
end
In rails 6, I believe this is now
def change
add_column :cards, :user_id, :integer, index: true
add_foreign_key :cards, :users
end
class AddUserIdToCard < ActiveRecord::Migration[5.2]
def change
add_foreign_key :cards, :users, column: :user_id, primary_key: :"id", on_delete: :cascade
end
end
Try this migration. I was facing the same problem then I fixed it.
I have some issues. I'm new to RoR
I'm trying to create a join table using Rails migration. Documentation of this is here...
http://api.rubyonrails.org/classes/ActiveRecord/ConnectionAdapters/SchemaStatements.html#method-i-create_join_table
When I do...
rails g migration CreateJoinTableUserOffer users offers
...it creates the following migration
class CreateJoinTableUserOffer < ActiveRecord::Migration
def change
create_join_table:users, :offers do |t|
t.index [:user_id, :offer_id]
t.index [:offer_id, :user_id]
end
end
end
and when I do...
rake db:migrate
it creates...
-- Table: offers_users
-- DROP TABLE offers_users;
CREATE TABLE offers_users
(
user_id integer NOT NULL,
offer_id integer NOT NULL
)
WITH (
OIDS=FALSE
);
ALTER TABLE offers_users
OWNER TO sudeepkaushik;
-- Index: index_offers_users_on_offer_id_and_user_id
-- DROP INDEX index_offers_users_on_offer_id_and_user_id;
CREATE INDEX index_offers_users_on_offer_id_and_user_id
ON offers_users
USING btree
(offer_id, user_id);
-- Index: index_offers_users_on_user_id_and_offer_id
-- DROP INDEX index_offers_users_on_user_id_and_offer_id;
CREATE INDEX index_offers_users_on_user_id_and_offer_id
ON offers_users
USING btree
(user_id, offer_id);
What I want to do is that I first of all want the table name to be users_offers instead of offers_users, for this you can specify the :table_name in the create_join_table migration. I'm not able to get the syntax of setting this option correctly. Need help here!
2nd, I noticed that this migration doesn't create the foreign keys that I would expect with the Users and Offers tables. Need your comments here also. Do I need to manually create the foreign keys myself?
You can define your join tables name with the table_name option.
create_join_table :users, :offers, table_name: :users_offers
There is also an option for setting column options called column_options, but I only got it to work for indexes and not for foreign keys.
create_join_table :users, :offers, column_options: { index: true }
This will create the desired indexes, but it ignores foreign_key: true. So you need to create them separately.
add_foreign_key :users_offers, :users
add_foreign_key :users_offers, :offers
In your models you need to add the relation like this:
# user.rb
has_and_belongs_to_many :offers, join_table: :users_offers
And:
# offers.rb
has_and_belongs_to_many :users, join_table: :users_offers
Is there any difference between using t.references and executing SQL command to create foreign key relationship between products and category table as shown below? In other words, are the two different ways of doing the same thing or am I missing anything here?
class ExampleMigration < ActiveRecord::Migration
def up
create_table :products do |t|
t.references :category
end
#add a foreign key
execute <<-SQL
ALTER TABLE products
ADD CONSTRAINT fk_products_categories
FOREIGN KEY (category_id)
REFERENCES categories(id)
SQL
add_column :users, :home_page_url, :string
rename_column :users, :email, :email_address
end
def down
rename_column :users, :email_address, :email
remove_column :users, :home_page_url
execute <<-SQL
ALTER TABLE products
DROP FOREIGN KEY fk_products_categories
SQL
drop_table :products
end
end
They're not the same thing. Rails by default doesn't enforce foreign keys in the database. Instead, references when creating from the command line also creates a regular index, like this:
add_index :products, :category_id
Update:
Rails 5 actually does exactly the same thing now. So, to answer the original question: Nowadays, both are the same.
I found some thing intresting in this page.
http://railsforum.com/viewtopic.php?id=17318
From a comment :
Rails doesn't use foreign keys to perform his backend tasks. This
because some db like sqlite doesn't allow foreign keys on its tables.
So Rails doesn't provide an helper to build a foreign key
Also there is a gem foreigner for adding foreign keys to database table.
What creates the FOREIGN KEY constraint in Ruby on Rails 3?
If I create a new rails 3 migration with (for example)
rails g migration tester title:tester user:references
, everything works fine...however if I add a column with something along the lines of:
rails g migration add_user_to_tester user:references
the reference field is not recognised. In short, the question is: how do I add a referencing column to a rails migration from the command line?
If you are using the Rails 4.x you can now generate migrations with references, like this:
rails generate migration AddUserRefToProducts user:references
like you can see on rails guides
EDIT: This is an outdated answer and should not be applied for Rails 4.x+
You don't need to add references when you can use an integer id to your referenced class.
I'd say the advantage of using references instead of a plain integer is that the model will be predefined with belongs_to and since the model is already created and will not be affected when you migrate something existing, the purpose is kind of lost.
So I would do like this instead:
rails g migration add_user_id_to_tester user_id:integer
And then manually add belongs_to :user in the Tester model
Please note that you will most likely need an index on that column too.
class AddUserReferenceToTester < ActiveRecord::Migration
def change
add_column :testers, :user_id, :integer
add_index :testers, :user_id
end
end
With the two previous steps stated above, you're still missing the foreign key constraint. This should work:
class AddUserReferenceToTester < ActiveRecord::Migration
def change
add_column :testers, :user_id, :integer, references: :users
end
end
You can use references in a change migration. This is valid Rails 3.2.13 code:
class AddUserToTester < ActiveRecord::Migration
def change
change_table :testers do |t|
t.references :user, index: true
end
end
def down
change_table :testers do |t|
t.remove :user_id
end
end
end
c.f.: http://apidock.com/rails/ActiveRecord/ConnectionAdapters/SchemaStatements/change_table
Running rails g migration AddUserRefToSponsors user:references will generate the following migration:
def change
add_reference :sponsors, :user, index: true
end
When adding a column you need to make that column an integer and if possible stick with rails conventions. So for your case I am assuming you already have a Tester and User models, and testers and users tables.
To add the foreign key you need to create an integer column with the name user_id (convention):
add_column :tester, :user_id, :integer
Then add a belongs_to to the tester model:
class Tester < ActiveRecord::Base
belongs_to :user
end
And you might also want to add an index for the foreign key (this is something the references already does for you):
add_index :tester, :user_id
That will do the trick:
rails g migration add_user_to_tester user_id:integer:index
You can add references to your model through command line in the following manner:
rails g migration add_column_to_tester user_id:integer
This will generate a migration file like :
class AddColumnToTesters < ActiveRecord::Migration
def change
add_column :testers, :user_id, :integer
end
end
This works fine every time i use it..
For Rails 4
The generator accepts column type as references (also available as belongs_to).
This migration will create a user_id column and appropriate index:
$ rails g migration AddUserRefToProducts user:references
generates:
class AddUserRefToProducts < ActiveRecord::Migration
def change
add_reference :products, :user, index: true
end
end
http://guides.rubyonrails.org/active_record_migrations.html#creating-a-standalone-migration
For Rails 3
Helper is called references (also available as belongs_to).
This migration will create a category_id column of the appropriate type. Note that you pass the model name, not the column name. Active Record adds the _id for you.
change_table :products do |t|
t.references :category
end
If you have polymorphic belongs_to associations then references will add both of the columns required:
change_table :products do |t|
t.references :attachment, :polymorphic => {:default => 'Photo'}
end
Will add an attachment_id column and a string attachment_type column with a default value of Photo.
http://guides.rubyonrails.org/v3.2.21/migrations.html#creating-a-standalone-migration