KeyGenerator is a simple wrapper around OpenSSL's implementation of PBKDF2. It can be used to derive a number of keys for various purposes from a given secret. This lets Rails applications have a single secure secret, but avoid reusing that key in multiple incompatible contexts. Nov 28, 2018 There are many ways to generate a PDF in Ruby on Rails, with the best approach really depending on the types of PDFs you need to generate. This tutorial will provide step-by-step instructions for generating PDFs with very little effort by using wkhtmltopdf.
1 First Contact
When you create an application using the
rails
command, you are in fact using a Rails generator. After that, you can get a list of all available generators by just invoking rails generate
:You will get a list of all generators that comes with Rails. If you need a detailed description of the helper generator, for example, you can simply do:
2 Creating Your First Generator
Since Rails 3.0, generators are built on top of Thor. Thor provides powerful options for parsing and a great API for manipulating files. For instance, let's build a generator that creates an initializer file named
initializer.rb
inside config/initializers
.The first step is to create a file at
lib/generators/initializer_generator.rb
with the following content:create_file
is a method provided by Thor::Actions
. Documentation for create_file
and other Thor methods can be found in Thor's documentationOur new generator is quite simple: it inherits from
Rails::Generators::Base
and has one method definition. When a generator is invoked, each public method in the generator is executed sequentially in the order that it is defined. Finally, we invoke the create_file
method that will create a file at the given destination with the given content. If you are familiar with the Rails Application Templates API, you'll feel right at home with the new generators API.![Generator Generator](https://comidoc.com/wp-content/uploads/2017/09/Ruby-On-Rails-Superhero-Generator-3.jpg)
To invoke our new generator, we just need to do:
Before we go on, let's see our brand new generator description:
Rails is usually able to generate good descriptions if a generator is namespaced, as
ActiveRecord::Generators::ModelGenerator
, but not in this particular case. We can solve this problem in two ways. The first one is calling desc
inside our generator:Now we can see the new description by invoking
--help
on the new generator. The second way to add a description is by creating a file named USAGE
in the same directory as our generator. We are going to do that in the next step.3 Creating Generators with Generators
Generators themselves have a generator:
This is the generator just created:
First, notice that we are inheriting from
Rails::Generators::NamedBase
instead of Rails::Generators::Base
. This means that our generator expects at least one argument, which will be the name of the initializer, and will be available in our code in the variable name
.We can see that by invoking the description of this new generator (don't forget to delete the old generator file):
We can also see that our new generator has a class method called
source_root
. This method points to where our generator templates will be placed, if any, and by default it points to the created directory lib/generators/initializer/templates
.In order to understand what a generator template means, let's create the file
lib/generators/initializer/templates/initializer.rb
with the following content:And now let's change the generator to copy this template when invoked:
And let's execute our generator:
We can see that now an initializer named core_extensions was created at
config/initializers/core_extensions.rb
with the contents of our template. That means that copy_file
copied a file in our source root to the destination path we gave. The method file_name
is automatically created when we inherit from Rails::Generators::NamedBase
.The methods that are available for generators are covered in the final section of this guide.
4 Generators Lookup
When you run
rails generate initializer core_extensions
Rails requires these files in turn until one is found:If none is found you get an error message.
The examples above put files under the application's
lib
because said directory belongs to $LOAD_PATH
.5 Customizing Your Workflow
Rails own generators are flexible enough to let you customize scaffolding. They can be configured in
config/application.rb
, these are some defaults:Before we customize our workflow, let's first see what our scaffold looks like:
Looking at this output, it's easy to understand how generators work in Rails 3.0 and above. The scaffold generator doesn't actually generate anything, it just invokes others to do the work. This allows us to add/replace/remove any of those invocations. For instance, the scaffold generator invokes the scaffold_controller generator, which invokes erb, test_unit and helper generators. Since each generator has a single responsibility, they are easy to reuse, avoiding code duplication.
If we want to avoid generating the default
app/assets/stylesheets/scaffolds.scss
file when scaffolding a new resource we can disable scaffold_stylesheet
:The next customization on the workflow will be to stop generating stylesheet and test fixture files for scaffolds altogether. We can achieve that by changing our configuration to the following:
If we generate another resource with the scaffold generator, we can see that stylesheet, JavaScript, and fixture files are not created anymore. If you want to customize it further, for example to use DataMapper and RSpec instead of Active Record and TestUnit, it's just a matter of adding their gems to your application and configuring your generators.
To demonstrate this, we are going to create a new helper generator that simply adds some instance variable readers. First, we create a generator within the rails namespace, as this is where rails searches for generators used as hooks:
After that, we can delete both the
templates
directory and the source_root
class method call from our new generator, because we are not going to need them.Add the method below, so our generator looks like the following:We can try out our new generator by creating a helper for products:
And it will generate the following helper file in
app/helpers
:Which is what we expected. We can now tell scaffold to use our new helper generator by editing
config/application.rb
once again:and see it in action when invoking the generator:
We can notice on the output that our new helper was invoked instead of the Rails default. However one thing is missing, which is tests for our new generator and to do that, we are going to reuse old helpers test generators.
Since Rails 3.0, this is easy to do due to the hooks concept. Our new helper does not need to be focused in one specific test framework, it can simply provide a hook and a test framework just needs to implement this hook in order to be compatible.
To do that, we can change the generator this way:
Now, when the helper generator is invoked and TestUnit is configured as the test framework, it will try to invoke both
Rails::TestUnitGenerator
and TestUnit::MyHelperGenerator
. Since none of those are defined, we can tell our generator to invoke TestUnit::Generators::HelperGenerator
instead, which is defined since it's a Rails generator. To do that, we just need to add:And now you can re-run scaffold for another resource and see it generating tests as well!
6 Customizing Your Workflow by Changing Generators Templates
In the step above we simply wanted to add a line to the generated helper, without adding any extra functionality. There is a simpler way to do that, and it's by replacing the templates of already existing generators, in that case
Rails::Generators::HelperGenerator
.In Rails 3.0 and above, generators don't just look in the source root for templates, they also search for templates in other paths. And one of them is
lib/templates
. Since we want to customize Rails::Generators::HelperGenerator
, we can do that by simply making a template copy inside lib/templates/rails/helper
with the name helper.rb
. So let's create that file with the following content:and revert the last change in
config/application.rb
:If you generate another resource, you can see that we get exactly the same result! This is useful if you want to customize your scaffold templates and/or layout by just creating
edit.html.erb
, index.html.erb
and so on inside lib/templates/erb/scaffold
.Scaffold templates in Rails frequently use ERB tags; these tags need to beescaped so that the generated output is valid ERB code.
For example, the following escaped ERB tag would be needed in the template(note the extra
%
)......to generate the following output:
7 Adding Generators Fallbacks
One last feature about generators which is quite useful for plugin generators is fallbacks. For example, imagine that you want to add a feature on top of TestUnit like shoulda does. Since TestUnit already implements all generators required by Rails and shoulda just wants to overwrite part of it, there is no need for shoulda to reimplement some generators again, it can simply tell Rails to use a
TestUnit
generator if none was found under the Shoulda
namespace.We can easily simulate this behavior by changing our
config/application.rb
once again:Now, if you create a Comment scaffold, you will see that the shoulda generators are being invoked, and at the end, they are just falling back to TestUnit generators:
Fallbacks allow your generators to have a single responsibility, increasing code reuse and reducing the amount of duplication.
8 Application Templates
Now that you've seen how generators can be used inside an application, did you know they can also be used to generate applications too? This kind of generator is referred to as a 'template'. This is a brief overview of the Templates API. For detailed documentation see the Rails Application Templates guide.
In the above template we specify that the application relies on the
rspec-rails
and cucumber-rails
gem so these two will be added to the test
group in the Gemfile
. Then we pose a question to the user about whether or not they would like to install Devise. If the user replies 'y' or 'yes' to this question, then the template will add Devise to the Gemfile
outside of any group and then runs the devise:install
generator. This template then takes the users input and runs the devise
generator, with the user's answer from the last question being passed to this generator.Imagine that this template was in a file called
template.rb
. We can use it to modify the outcome of the rails new
command by using the -m
option and passing in the filename:This command will generate the
Thud
application, and then apply the template to the generated output.Templates don't have to be stored on the local system, the
-m
option also supports online templates:Whilst the final section of this guide doesn't cover how to generate the most awesome template known to man, it will take you through the methods available at your disposal so that you can develop it yourself. These same methods are also available for generators.
9 Adding Command Line Arguments
Rails generators can be easily modified to accept custom command line arguments. This functionality comes from Thor:
Now our generator can be invoked as follows:
The command line arguments are accessed through the
options
method inside the generator class. e.g:10 Generator methods
The following are methods available for both generators and templates for Rails.
Methods provided by Thor are not covered this guide and can be found in Thor's documentation
10.1 gem
Specifies a gem dependency of the application.
Available options are:
:group
- The group in theGemfile
where this gem should go.:version
- The version string of the gem you want to use. Can also be specified as the second argument to the method.:git
- The URL to the git repository for this gem.
Any additional options passed to this method are put on the end of the line:
The above code will put the following line into
Gemfile
:10.2 gem_group
Wraps gem entries inside a group:
10.3 add_source
Adds a specified source to
Gemfile
:This method also takes a block:
10.4 inject_into_file
Injects a block of code into a defined position in your file.
10.5 gsub_file
Replaces text inside a file.
Regular Expressions can be used to make this method more precise. You can also use
append_file
and prepend_file
in the same way to place code at the beginning and end of a file respectively.10.6 application
Adds a line to
config/application.rb
directly after the application class definition.This method can also take a block:
Available options are:
:env
- Specify an environment for this configuration option. If you wish to use this option with the block syntax the recommended syntax is as follows:
10.7 git
Ruby On Rails Key Generator For Sale
Runs the specified git command:
The values of the hash here being the arguments or options passed to the specific git command. As per the final example shown here, multiple git commands can be specified at a time, but the order of their running is not guaranteed to be the same as the order that they were specified in.
10.8 vendor
Places a file into
vendor
which contains the specified code.This method also takes a block:
10.9 lib
Places a file into
lib
which contains the specified code.This method also takes a block:
10.10 rakefile
Creates a Rake file in the
lib/tasks
directory of the application.This method also takes a block:
10.11 initializer
Creates an initializer in the
config/initializers
directory of the application:This method also takes a block, expected to return a string:
10.12 generate
Runs the specified generator where the first argument is the generator name and the remaining arguments are passed directly to the generator.
10.13 rake
Runs the specified Rake task.
Available options are:
:env
- Specifies the environment in which to run this rake task.:sudo
- Whether or not to run this task usingsudo
. Defaults tofalse
.
10.14 route
Adds text to the
config/routes.rb
file:10.15 readme
Output the contents of a file in the template's
source_path
, usually a README.Feedback
You're encouraged to help improve the quality of this guide.
Please contribute if you see any typos or factual errors. To get started, you can read our documentation contributions section.
You may also find incomplete content or stuff that is not up to date. Please do add any missing documentation for master. Make sure to check Edge Guides first to verify if the issues are already fixed or not on the master branch. Check the Ruby on Rails Guides Guidelines for style and conventions.
If for whatever reason you spot something to fix but cannot patch it yourself, please open an issue.
And last but not least, any kind of discussion regarding Ruby on Rails documentation is very welcome on the rubyonrails-docs mailing list.
Methods
- Thor::Actions
Public Class methods
Returns the base root for a common set of generators. This is used todynamically guess the default source root.
[ show source ]
Returns the default source root for a given generator. This is usedinternally by rails to set its generators source root. If you want tocustomize your source root, you should use source_root.
[ show source ]
Tries to get the description from a USAGE file one folder above the sourceroot otherwise uses a default description.
[ show source ]
Invoke a generator based on the value supplied by the user to the givenoption named “name”. A class option is created when this methodis invoked and you can set a hash to customize it.
Examples
The example above will create a test framework option and will invoke agenerator based on the user supplied value.
For example, if the user invoke the controller generator as:
The controller generator will then try to invoke the following generators:
Notice that “rails:generators:test_unit“ could be loaded aswell, what Rails looks for is the first andlast parts of the namespace. This is what allows any test framework to hookinto Rails as long as it provides any of thehooks above.
Options
The first and last part used to find the generator to be invoked areguessed based on class invokes hook_for, as noticed in the exampleabove. This can be customized with two options: :base and :as.
Let’s suppose you are creating a generator that needs to invoke thecontroller generator from test unit. Your first attempt is:
Ruby Generator
The lookup in this case for test_unit as input is:
Which is not the desired the lookup. You can change it by providing the :asoption:
And now it will lookup at:
Similarly, if you want it to also lookup in the rails namespace, you justneed to provide the :base value:
And the lookup is exactly the same as previously:
Switches
All hooks come with switches for user interface. If the user don’twant to use any test framework, he can do:
Or similarly:
Boolean hooks
In some cases, you want to provide a boolean hook. For example, webratdevelopers might want to have webrat available on controller generator.This can be achieved as:
Then, if you want, webrat to be invoked, just supply:
The hooks lookup is similar as above:
Ruby Programming Language
Custom invocations
You can also supply a block to hook_for to customize how the hookis going to be invoked. The block receives two arguments, an instance ofthe current class and the klass to be invoked.
For example, in the resource generator, the controller should be invokedwith a pluralized class name. But by default it is invoked with the samename as the resource generator, which is singular. To change this, we cangive a block to customize how the controller can be invoked.
[ show source ]
Convenience method to get the namespace from the class name. It’s thesame as Thor default except that the Generator at the end of the class isremoved.
[ show source ]
Remove a previously added hook.
Examples
[ show source ]
Returns the source root for this generator using default_source_root asdefault.
[ show source ]
Protected Class methods
Small macro to add ruby as an option to the generator with proper defaultvalue plus an instance helper method called shebang.
[ show source ]
Use Rails default banner.
[ show source ]
Sets the base_name taking intoaccount the current class namespace.
[ show source ]
Return default aliases for the option name given doing a lookup inRails::Generators.aliases.
[ show source ]
default_for_option(config, name, options, default)
Return default for the option name given doing a lookup in config.
[ show source ]
Return the default value for the option name given doing a lookup inRails::Generators.options.
[ show source ]
Removes the namespaces and get the generator name. For example, Rails::Generators::ModelGenerator willreturn “model” as generator name.
[ show source ]