Add a reference column migration in Rails 4

Question

A user has many uploads  I want to add a column to the uploads table that references the user  What should the migration look like    Here is what I have  I m not sure if I should use  1   user id   int or  2   user   references  I m not even sure if  2  works  Just trying to do this the  rails  way   class AddUserToUploads  lt  ActiveRecord  Migration   def change     add column  uploads   user id   integer   end end   Relevant question except for Rails 3  Rails 3 migrations  Adding reference column

User · Answer

Just to document if someone has the same problem...

In my situation I've been using :uuid fields, and the above answers does not work to my case, because rails 5 are creating a column using :bigint instead :uuid:

add_reference :uploads, :user, index: true, type: :uuid

Reference: Active Record Postgresql UUID

User · Answer

Rails 5 You can still use this command to create the migration  rails g migration AddUserToUploads user references  The migration looks a bit different to before  but still works  class AddUserToUploads  lt  ActiveRecord  Migration 5 0    def change     add reference  uploads   user  foreign key  true   end end  Note that it s  user  not  user id

User · Answer

Using Rails 5   Generate migration   rails generate migration add user reference to uploads user references   This will create the migration file   class AddUserReferenceToUploads  lt  ActiveRecord  Migration 5 1    def change     add reference  uploads   user  foreign key  true   end end   Now if you observe the schema file  you will see that the uploads table contains a new field  Something like  t bigint  user id  or t integer  user id    Migrate database   rails db migrate

User · Answer

Create a migration file  rails generate migration add references to uploads user references   Default foreign key name  This would create a user id column in uploads table as a foreign key  class AddReferencesToUploads  lt  ActiveRecord  Migration 5 2    def change     add reference  uploads   user  foreign key  true   end end   user model   class User  lt  ApplicationRecord   has many  uploads end   upload model   class Upload  lt  ApplicationRecord   belongs to  user end   Customize foreign key name   add reference  uploads   author  references   user  foreign key  true   This would create an author id column in the uploads tables as the foreign key    user model   class User  lt  ApplicationRecord   has many  uploads  foreign key   author id  end   upload model   class Upload  lt  ApplicationRecord   belongs to  user end

User · Answer

Rails 4 x  When you already have users and uploads tables and wish to add a new relationship between them   All you need to do is  just generate a migration using the following command   rails g migration AddUserToUploads user references   Which will create a migration file as   class AddUserToUploads  lt  ActiveRecord  Migration   def change     add reference  uploads   user  index  true   end end   Then  run the migration using rake db migrate  This migration will take care of adding a new column named user id to uploads table  referencing id column in users table   PLUS it will also add an index on the new column   UPDATE  For Rails 4 2   Rails can   t be trusted to maintain referential integrity  relational databases come to our rescue here  What that means is that we can add foreign key constraints at the database level itself and ensure that database would reject any operation that violates this set referential integrity  As  infoget commented  Rails 4 2 ships with native support for foreign keys referential integrity   It s not required but you might want to add foreign key as it s very useful  to the reference that we created above    To add foreign key to an existing reference  create a new migration to add a foreign key   class AddForeignKeyToUploads  lt  ActiveRecord  Migration   def change     add foreign key  uploads   users   end end   To create a completely brand new reference with a foreign key in Rails 4 2   generate a migration using the following command   rails g migration AddUserToUploads user references   which will create a migration file as   class AddUserToUploads  lt  ActiveRecord  Migration   def change     add reference  uploads   user  index  true     add foreign key  uploads   users   end end   This will add a new foreign key to the user id column of the uploads table  The key references the id column in users table   NOTE  This is in addition to adding a reference so you still need to create a reference first then foreign key  you can choose to create a foreign key in the same migration or a separate migration file   Active Record only supports single column foreign keys and currently only mysql  mysql2 and PostgreSQL adapters are supported  Don t try this with other adapters like sqlite3  etc  Refer to Rails Guides  Foreign Keys for your reference

User · Answer

Another syntax of doing the same thing is   rails g migration AddUserToUpload user belongs to

User · Answer

if you like another alternate approach with up and down method try this     def up     change table  uploads do  t        t references  user  index  true     end   end    def down     change table  uploads do  t        t remove references  user  index  true     end   end

[ruby-on-rails] Add a reference column migration in Rails 4

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