Errata for Advanced Rails Recipes

#37451: in registrations/index.html.erb, the following line of code:
for registration in @registrations
should be
for registration in @event.registrations--Reuben Sivan

#41710: On the bottom of page 50, it says, "we can mix in our custom validation methods only when we need them." I don't understand. They're always mixed in. I see "ActiveRecord::Base.extend(CustomValidations)". Isn't this always mixing them in?--Shannon -jj Behrens

#40573: In the first code example, it shows that "existing_task_attributes" references an array of hashes. I think it just references a hash, and the prose seems to support that.

Also, in the prose, whenever params[something] is used, it's hard to tell if those are parenthesis or brackets. It may be a font thing.

Thanks!--Shannon -jj Behrens

#31852: Hi, there's a delete of a task from inside an iterator. I don't think that's safe, you'll not get to the end of the collection there. I had a collection of two objects where the first was deleted inside the iterator. The iterator never iterated over the second object. Better to collect an array of tasks_to_be_deleted and then call tasks.delete(tasks_to_be_deleted) once outside the iterator. Also, tasks are deleted a different step and not wrapped within the same transaction as the rest of the update when the after_update is called.--Tim Harding

#34712: in the save method of the AlbumService, you have:

if @cover.new_record?
@album.cover.destroy if @album.cover
@cover.album = @album
@cover.save
end

I think this should be

if @cover.new_record?
@album.cover.destroy if @album.cover
@album.cover = @cover
@cover.save
end

as Album has_one Cover and Cover belongs_to Album.

Or I'm missing something. But that's how I got it to work.

--Jim Graham

#31675: DynamicMetaTags has this code which fails on IE:

def meta(name, content)
%(<meta name="#{name}" content="#{content} />" )
end

should be this (end quote incorrect)

def meta(name, content)
%(<meta name="#{name}" content="#{content}" />)
end

But why not use tag helper and be more railsy :-)

def meta(name, content)
tag("meta", :name => name, :content => content)
end--Tom Harrison

#41718: It says, "String-based fields (for example, the MySQL VARCHAR type) can often be easily indexed directly in the database where appropriate."

Because of the way you're using LIKE, it turns out MySQL won't use an index. Because MySQL has to examine every row, it turns out that a linear table scan is faster than scanning the entire index. That's why MySQL won't use an index if it has to scan the entire table (unless the index would help with ordering). It's helpful to use "explain" on the query in order to double check whether MySQL is or isn't using an index.

Happy Hacking!--Shannon -jj Behrens

#41719: It says, "you may want to change the name of the pid_file for the three environments so that you can run servers for each environment simultaneously."

To run more than one server, you're also going to need a different port for each.--Shannon -jj Behrens

#36446: Assuming that the sample results from Article.publicly_viewable and Article.premium are sorted by id, wouldn't Article.publicly_viewable.premium NOT include #<Article id: 1> since nested scopes are AND'd and not OR'd?
It should only include those which are true for ALL of the named_scope filters.

>> Article.publicly_viewable
=> [#<Article id: 1,...]
>> Article.premium
=> [#<Article id: 2,...]
To find all publicly viewable and premium articles, we can nest the scopes:
>> Article.publicly_viewable.premium
=> [#<Article id: 1,...>, #<Article id: 2,...> ]
--Jakeb

#31672: Keep Forms Dry, error_handling_form_builder.rb defines array of helpers; two are removed in the line "%w(label fields_for)" -- this should also include "hidden_field"

BTW -- this was a much needed recipe for my app. Now I need to figure out how to make it work for the scaffold generated "show" views, too :-)--Tom Harrison

#32679: If you don't use the "set_no_auto_load true" option described later in the recipe, the args passed to the create method will be nil which causes a nil error to be raised. Checking args.nil? before running the args loop is recommended.--Mike Clark

#41891: The -otherwise excellent- recipe contains an nginx conf. snippet to make sure all requests return the maintenance page:

if ($request_filename ~* \.(css|jpg|gif|png)$) {
break;
}
if (-f $document_root/system/maintenance.html) {
rewrite ^(.*)$ /system/maintenance.html last;
break;
}

However, that does not work since it gets into an inf. loop on the maintenance page (/system/maintenance.html) itself.

The (or rather 'a') correct config is the following:

if ($request_filename ~* \.(css|jpg|gif|png)$) {
break;
}
if ($request_filename = $document_root/system/maintenance.html) {
break;
}
if (-f $document_root/system/maintenance.html) {
rewrite ^(.*)$ /system/maintenance.html last;
break;
}

I hope that helps,
Bálint--Balint Erdi

#31680: In the first set of code examples on the page, a list of caching commands to execute through the console, in the last example of that section:

>> products = Product.related_products("barney")
>> ActionController::Base.cache_store.fetch("barney") { products }
=> [#<Product id: 21, ...]

The description of fetch just below this says: " When it doesn’t find your key in the cache,
it’ll run the block, save its results into the cache, and give them back
to you."

But in this case the Product#related_products method gets executed before the call to fetch which is then only passed the reference to the already loaded collection.

Should the correct way to handle this not look like:

ActionController::Base.cache_store.fetch("barney") do
Product.related_products("barney")
end

?
--Jesse Clark

#31955: This recipe doesn't work. If I type Status::PENDING on the console, I always get a NameError: uninitialized constant Status::PENDING

Maybe it's because I'm using Postgres?--Lars Fischer

#31659: I still get the "can't Fixnum into String" error when loading a page with '?browser_profile!' appended to the URL.

This was reported for the previous version as #31189 where it is marked as fixed in B1.06.

The line apparently with the problem is:

controller.response.body << printer.print("", 0)

--Chris Stephens

#41724: It says:

message = (String === message ? message : msg.inspect)

Is it really supposed to say "String === message"? Is that really how you check if message is a string?

Where is "msg" coming from?--Shannon -jj Behrens