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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 enthusiastically disagree.
I've found a lot of discussions addressing this problem but they all seem to be old and, dismayingly, they seem to point to divergent solutions.
I have to imagine there's a de-facto standard way of doing foreign key constraints in Rails 3. However, whatever it is (if it does exist) seems to be smothered by all the past discussions because I can't find it.
Are Rails developers by this point mostly on the same page with foreign keys? If so, I would love to know how they're generally handled.
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In Rails 5, adding foreign key constraints was added to have the database protect the integrity of associated data. Once a foreign key constraint is defined, your database will not allow you to remove records that are required by other tables.
A foreign key is a field in one database that uniquely identifies a row in another table. For this example, our foreign key in the expenses table will identify which category each expense should fall under.
If you want you can always use add_index on the fields that you want as foreign keys. Or you can write your migrations in SQL or perhaps even force rails to do the foreign keys somehow. But the thing is you won't even look for a way to do it if you don't know rails is not doing itin the first place.
They essentially do the same thing, the only difference is what side of the relationship you are on. If a User has a Profile , then in the User class you'd have has_one :profile and in the Profile class you'd have belongs_to :user . To determine who "has" the other object, look at where the foreign key is.
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:
There are disadvantages:
But, overall I reckon the advantages outweigh the disadvantages.
Quick example:
def self.up
execute <<EOS
create table .... (
....
);
EOS
end
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."
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