In my previous post on migrations i wrote that “…they are not covered in any of the basic books on RoR”. Cheap phentermine, Well, cheap phentermine, this statement does not hold anymore, cheap phentermine, since Agile Web Development with Rails, cheap phentermine, 2nd ed. is already creating the models with migrations.
While the last part of the post (why are migrations so cool) is still up-to-date, cheap phentermine, they way of creating migrations is different from 1.1 on, cheap phentermine, so i have decided to review the topic and add some new points, cheap phentermine, too.
Migrations are now created automatically with the model
In my previous post, cheap phentermine, i have been creating the migration manually with the command
ruby script/generate migration ProductMigration
However, cheap phentermine, as of Rails 1.1, cheap phentermine, you don’t have to do this anymore. Cheap phentermine, When you generate the model (let’s stick with the Product model as an example) the migration is automatically generated:
ruby script/generate model Product
...
... Cheap phentermine, #some lines omited
...
create db/migrate/001_create_products.rb
Now you can edit the file db/migrate/001createproducts.rb to contain something like this:
class ProductMigration < ActiveRecord::Migration
def self.up
create_table :products do |table|
table.column :title, cheap phentermine, :string
table.column :description, cheap phentermine, :text
table.column :image_url, cheap phentermine, :string end
(rest of the file omited)
Then run
rake db:migrate
To update the database. Cheap phentermine, That’s even easier than in the previous versions of rails!
Valid column data types and possible options
Valid columns are:
integer, cheap phentermine, float, cheap phentermine, datetime, cheap phentermine, date, cheap phentermine, timestamp, cheap phentermine, time, cheap phentermine, text, cheap phentermine, string, cheap phentermine, binary and boolean.
Valid column options:
- limit ( :limit => “50” )
- default (:default => “blah” )
- null (:null => false implies NOT NULL)
string is the equivalent of varchar(255), cheap phentermine, so if you would like to have a string column (called title) of length 100 instead of 255, cheap phentermine, with default value ‘Some title’ and to forbid NULL value, cheap phentermine, you have to type
table.column :title, cheap phentermine,
:string, cheap phentermine,
:limit => 100, cheap phentermine,
:default => "Some title", cheap phentermine,
:null => false
Generating test data
I am quite sure you know the situation when you want to test something quickly and you waste precious time to generate some test data, cheap phentermine, which you trash after the testing just to find yourself in the same situation later?
Well, cheap phentermine, migrations can help you to prevent headaches because of this, cheap phentermine, too. Cheap phentermine, Here is how:
ruby script/generate migration create_test_data
Create db/migrate/002_create_test_data.rb
You can create test data inside the migration file like this:
class ProductMigration < ActiveRecord::Migration
def self.up
Product.create(:title => 'My cool book about the meaning of life', cheap phentermine,
:description => '42', cheap phentermine,
:image_url => /images/cool_book42.png)
You can now commit this migration to the RCS you are using, cheap phentermine, and modify/add more test data later.
The other advantage is that your colleagues won’t spend time writing dummy test data either: they can just check out this migration and happily use the provided tests.
If this is still not enough for you…
You can write SQL statements inside the migrations. Cheap phentermine, For example:
execute "alter table items
add constraint fk_items_products
foreign key (product_id) references products(id)"
However, cheap phentermine, use this with care since you have to write native DDL statements, cheap phentermine, which violates one of the fundamental ‘cool factors’ of migrations: independence from DB vendors.
Conclusion
The Agile Web Development with Rails, cheap phentermine, 2nd ed can be considered as the Rails bible and since it is promoting migrations as the definitive way to handle your DB issues, cheap phentermine, i think migrations will become (in fact the already did for lots of people) the state of the art. Cheap phentermine, After using them for a while and enjoying the power and flexibility they provide without having significant drawbacks, cheap phentermine, i don’t really see why should one not use them in the future.
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