[rails 4] add a reference to a table with another name

They default way in rails 4 to add foreign keys is simply

add_reference :people, :user

And this will add a column user_id to the people table, if the table exists. I have been looking in the rails code where this is handled, and it is really straightforward.

Note that standard rails does not really do anything for referential integrity, it creates the correct columns and an index if so specified.

But we use the schema_plus gem, for two reasons:

• it does handle referential constraints correctly (on the database level)
• it allows to specify the creation of views in a migration more cleanly

So, with schema_plus, if you write something like:

add_reference :people, :owner

and there is no owners table, this will give an error.

So instead you need to write :

add_reference :people, :owner, references: :users

This will correctly generate an owner_id which is a foreign key to users(id).

If you want to create a self-referential link, that is really easy. Just write

add_reference :people, :parent

This will create a self-referential link. Awesome :)

For completeness, the add_reference will add a reference columns to an already existing table. The same can be done when creating (or changing) a table with the following syntax:

create_table :people do |t| 
  t.references :owner, references: :users
  t.references :parent
end

So, in short, if you were not using the schema_plus gem already, start doing so now :)

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