Foreign keys in Rails 3

Question

I understand that according to Rails philosophy, data integrity checks should be done at the application level as opposed to the database level. Like many other developers, I en

Answer 1

http://guides.rubyonrails.org/migrations.html#active-record-and-referential-integrity

"Although Active Record does not provide any tools for working directly with such features, the execute method can be used to execute arbitrary SQL. There are also a number of plugins such as foreign_key_migrations which add foreign key support to Active Record."

Answer 2

I found myself asking the same question the other day, so I did some research and collated my findings in an answer to an older but similar Stack Overflow question. I hope that's of use.

BTW, when you say that you "enthusiastically disagree" that data integrity checks should be done at the application level as opposed to the database level, I assume you mean that they should be done at both levels, rather than just at the database. I hope I'm right in thinking that virtually everyone agrees that having integrity checks at the application level is a Good Thing, and that the only topic being debated is whether they should additionally be done in the database.

Answer 3

It is for this reason that I (and the people who wrote Enterprise Rails - http://oreilly.com/catalog/9780596515201) recommend that you write your entire up and down migrations in SQL.

The advantages are:

• The ability to add foreign keys on table creation - without a separate alter table
• It allows you to use database specific field types - like tsvectors
• It allows you to add different types of indexes - like Gin or Gist
• It allows you to write functions and/or triggers
• You wont have to remember what DSL type relates to what SQL field type - e.g. :number

There are disadvantages:

• It's not database agnostic (who cares and how often will you change your database?)
• It's not Ruby (but every good Rails developer should know SQL, right?)

But, overall I reckon the advantages outweigh the disadvantages.

Quick example:

  def self.up
    execute <<EOS

create table .... (
  ....
);

EOS
   end