Don't use this:
scope :red, where(color: 'red')
default_scope where(color: 'red')
Use this:
scope :red, -> { where(color: 'red') }
default_scope { where(color: 'red') }
The former has numerous issues. It is a common newbie gotcha to do
the following:
scope :recent, where(published_at: Time.now - 2.weeks)
Or a more subtle variant:
scope :recent, -> { where(published_at: Time.now - 2.weeks) }
scope :recent_red, recent.where(color: 'red')
Eager scopes are also very complex to implement within Active
Record, and there are still bugs. For example, the following does
not do what you expect:
scope :remove_conditions, except(:where)
where(...).remove_conditions # => still has conditions
The `add_index` method now supports a `where` option that receives a
string with the partial index criteria.
add_index(:accounts, :code, :where => "active")
Generates
CREATE INDEX index_accounts_on_code ON accounts(code) WHERE active
Add a `with_lock` method to ActiveRecord objects, which starts
a transaction, locks the object (pessimistically) and yields to the block.
The method takes one (optional) parameter and passes it to `lock!`.
Before:
class Order < ActiveRecord::Base
def cancel!
transaction do
lock!
# ... cancelling logic
end
end
end
After:
class Order < ActiveRecord::Base
def cancel!
with_lock do
# ... cancelling logic
end
end
end
Scope in migrations can be defined by adding suffix in filename,
like: 01_a_migration.blog.rb. Such migration have blog scope.
Scope is automatically added while copying migrations from engine,
so if you want to revert all of the migrations from given engine,
you can just run db:migrate with SCOPE, like:
rake db:migrate SCOPE=blog
Rationale: As discussed with José and Jon, this convenience
shortcut is not clearly justified and it could let the user
thing the disabled EXPLAINs are related to the model instance
rather than being globally disabled.
the following code is deprecated:
Thread.new { Post.find(1) }.join
It should be changed to close the database connection at the end of
the thread:
Thread.new {
Post.find(1)
Post.connection.close
}.join
Only people who spawn threads in their application code need to worry
about this change.
