Rails 3 migrations Adding reference column

Question

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

User · Answer

EDIT  This is an outdated answer and should not be applied for Rails 4 x   You don t need to add references when you can use an integer id to your referenced class   I d say the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

User · Answer

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  lt  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   gt    default   gt   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

User · Answer

Please note that you will most likely need an index on that column too   class AddUserReferenceToTester  lt  ActiveRecord  Migration   def change     add column  testers   user id   integer     add index   testers   user id   end end

User · Answer

With the two previous steps stated above  you re still missing the foreign key constraint  This should work     class AddUserReferenceToTester  lt  ActiveRecord  Migration       def change           add column  testers   user id   integer  references   users       end   end

User · Answer

Running rails g migration AddUserRefToSponsors user references will generate the following migration   def change   add reference  sponsors   user  index  true end

User · Answer

That will do the trick        rails g migration add user to tester user id integer index

User · Answer

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  lt  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

User · Answer

You can use references in a change migration  This is valid Rails 3 2 13 code   class AddUserToTester  lt  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

User · Answer

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  lt  ActiveRecord  Migration   def change     add column  testers   user id   integer   end end   This works fine every time i use it

User · Answer

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

[ruby-on-rails] Rails 3 migrations: Adding reference column?

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