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Querying guide: add mention of scoped, unscoped and default_scope to querying guide

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Ryan Bigg 2011-06-26 15:39:12 +10:00
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railties/guides/source/active_record_querying.textile
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@ -965,6 +965,47 @@ Using a class method is the preferred way to accept arguments for scopes. These
category.posts.1_week_before(time)
</ruby>
h4. Working with scopes
Where a relational object is required, the +scoped+ method may come in handy. This will return an +ActiveRecord::Relation+ object which can have further scoping applied to it afterwards. A place where this may come in handy is on associations
<ruby>
client = Client.find_by_first_name("Ryan")
orders = client.orders.scoped
</ruby>
With this new +orders+ object, we are able to ascertain that this object can have more scopes applied to it. For instance, if we wanted to return orders only in the last 30 days at a later point.
<ruby>
orders.where("created_at > ?", 30.days.ago)
</ruby>
h4. Applying a default scope
If we wish for a scope to be applied across all queries to the model we can use the +default_scope+ method within the model itself.
<ruby>
class Client < ActiveRecord::Base
default_scope where("removed_at IS NULL")
end
</ruby>
When queries are executed on this model, the SQL query will now look something like this:
<ruby>
SELECT * FROM clients WHERE removed_at IS NULL
</ruby>
h4. Removing all scoping
If we wish to remove scoping for any reason we can use the +unscoped+ method. This is especially useful if a +default_scope+ is specified in the model and should not be applied for this particular query.
<ruby>
Client.unscoped.all
</ruby>
This method removes all scoping and will do a normal query on the table.
h3. Dynamic Finders
For every field (also known as an attribute) you define in your table, Active Record provides a finder method. If you have a field called +first_name+ on your +Client+ model for example, you get +find_by_first_name+ and +find_all_by_first_name+ for free from Active Record. If you have a +locked+ field on the +Client+ model, you also get +find_by_locked+ and +find_all_by_locked+ methods.