For writing text files; especially line by line, it’s perfectly acceptable to use puts. But, be warned that this will append a line break after the data being written. This behaviour is not desirable when working with binary files, when IO::write is a better choice to avoid unwanted line break characters.
For example:
file = File.new('temp.file', 'w+')
file.sync = true
while data = get_data
file.write data
end
file.rewind
I switched to Mac around 10 years ago and have picked up a variety of shortcuts over the years to streamline my workflow. But, something I only found out about this weekend was the “long-hold”.
What’s a long-hold?
Hit your Dashboard key. Your dashboard appears. Hit the key again and it disappears in an equally pleasing manner. Now try it this way: press your Dashboard key (and keep it held), your Dashboard will appear. To make it disappear simply let go of the key!
Where else does this awesome trick work?
Well, since I’ve only just found this out, I’ve not had a huge chance to uncover many goodies, but here’s what I’ve found so far. Leave a comment if you know of any others.
What other shortcut modifiers don’t I know about?
Clicking menu items, or shortcut keys whilst holding shift or option can do slightly different things, here’s a list of things I’ve discovered, some of which are useful, some not so much:
Those were cool, are there any other shortcuts that need a place in my life?
Yep. Some of these are amazingly handy, some not so much!
Please leave a comment if there are any other hidden gems you want to share with the world.
The [recently in webkit] supported onbeforeunload window event can be very useful to inform the user if they are about to loose some data which they haven’t saved yet etc. So, in your method that the event calls you will probably have some logic to decide if the method should return or not (returning a string from the method causes the message to be displayed to the user).
This is all very well and good, but we came across an instance where outside of this method we wanted to set a variable to stop the message, request a new window.location (to download an file) and then turn the variable on again. The code looked a little like this:
window.shouldWarnTheUser = false; window.location = '/download/my.file'; window.shouldWarnTheUser = true;
And the onbeforeunload callback looked a bit like this:
window.onbeforeunload = function() {
if (window.shouldWarnTheUser) {
return "Some warning!";
}
}
This gave us different results between different browsers and took some time for us to figure out why.
Consider the following example:
window.onbeforeunload = function() {
console.log("3");
}
console.log("1");
window.location = '/download/my.file';
console.log("2");
What order do the numbers get logged out?
Both understandable depending on how you think the events are fired
There are a few blog posts on writing model validators – this is another one which follows the DRY (don’t repeat yourself) philosophy.
Suppose you want to check that an attribute value is present in a table of tags in our database. Now, this isn’t a particularly good use case as you could use validates_inclusion_of, but lets assume that we want to DRY that up a bit.
Let’s write the validation to make the following work:
validates_inclusion_in_tags :primary_tag, :secondary_tag
The validation method would look a little bit like this:
def validates_inclusion_in_tags(*attr_names)
validates_each attr_names do |record, attr_name, value|
acceptable_values = Tag.find.all.map{ |obj| obj.name }
record.errors.add(attr_name, "does not match any available values") unless acceptable_values.include?(value)
end
end
What’s going on here? Firstly we attach our custom validation to the model using validates_each. This runs the block for each of the attribute names (symbols) in the attr_names array (note that we have used the splat operator in our argument list to flatten the arguments into an array so we can pass a list of attribute to validate). The validation block is passed three arguments: the record being validated, the attribute name (as a symbol) and the current value of the attribute that is being validated. We then execute a find on our Tag model to get an array of AR records which we then map to extract the name of each object into an array. Finally we associate an error to the attribute that we are validating if its value is not in the list of acceptable values we have created.
To make the validation method a little more configurable and a little more generic we can allow the validation method to be called with a hash of options. Maybe we want to define a different error message, supply a different model to validate against, or supply a different attribute to be selected from our model. This can be easily achieved like so:
def validates_inclusion_in_model(*attr_names)
# Set up any default configuration options and merge on any passed to the validation
configuration = {
:message => "does not match any available values",
:model => Tag,
:model_attribute => :name,
}.merge(attr_names.extract_options!)
validates_each attr_names do |record, attr_name, value|
acceptable_values = configuration[:model].find.all.map{ |obj| obj.send configuration[:model_attribute] }
record.errors.add(attr_name, configuration[:message]) unless acceptable_values.include?(value)
end
end
You’ll note that the default configuration options are merged with the configuration options that were passed into the validation method. This (very common) technique makes use of the extract_options! method which returns either the last item of an array if it is a Hash or an empty Hash.
OK, that’s all good – what’s the best way to get this method available to our models. The best ways are as follows: Either create a validators.rb file in config/initializers and open up the ActiveRecord::Base class like so:
ActiveRecord::Base.class_eval do # define your validation methods here end
Or, the way I prefer is to to create a validations.rb file in your lib directory and use the following code:
module Validations
# Extend the caller with the ClassMethods module
def self.included(base) # :nodoc:
base.extend ClassMethods
end
module ClassMethods
# define your validation methods here
end
end
Now you can pick and chose which validations are available to your models rather than extend every model that inherits from AR Base by using:
class Person < ActiveRecord::Base include Validations end
Of course, if all of your AR models inherit from a shared base class which in turn inherits from AR Base, then you could also include the validations model at your shared base model level to give all your models access to your new validations.
The validation method here would load all the Tag records into AR objects in memory just to throw them away again. Also, this problem is exacerbated if you were to compare two attributes against the list as the objects are loaded for each call into validates_each.
It’s a question that often comes up and there are many places on the internet that give an inaccurate answer, so here’s the real-deal.
Javascript has three primitive datatypes:
There are another two special datatypes:
The others are variations of object:
See here for further reading.
When parsing a date in Javascript, it is important to ensure that the resultant object has been parsed correctly. This is made slightly tricky as the resultant object will always be a Date object if created with new Date().
The problem is compounded by differences between IE and other browsers. IE will return a NaN whereas other browsers will report "Invalid Date".
Use the following code to be sure:
var d = new Date("Malformed date")
if (d != "NaN" && d != "Invalid Date") {
// date is good
} else {
// date is bad
}
Does anyone else have any good ways of doing this detection?
An open community event for techy-types is getting underway in Reading. These events are for people to get together in an informal setting, share knowledge and have a couple of beers!
The first of these monthly events is happening next Tuesday on the 10th November. Add http://readinggeeknight.com/ to your bookmarks and check it out regularly for updates. You can also follow @rdggeek on twitter or the #rdggeek hashtag.
Talks lined up for the first event are:
Who do you think you are? Ben Nunney – The internet is everywhere, and all of us in the tech community are connected in some way, shape or form. But how powerful is your digital identity, and what does it actu- ally matter to you? The talk will be a brief look at what your digital identity is, was, and can be – who are you, in the eyes of the internet? Does your boss really care what you had for lunch?
A practical introduction to Ruby on Rails Chris Tingley – This live code demonstration will take you from your first line of Ruby code, through some fundamental features of Rails with pit stops in MVC, CRUD, REST, automated testing and meta-programming, crossing the finish line with a functional web app! Hold on to your hats, all this WILL happen in 15 minutes.
What Is Windows Azure? Dom Green – What is Windows Azure? How will cloud computing change how we develop applications, manage our IT infrastructure, or even set up an online business? This whirl-wind talk will introduce Windows Azure, Microsoftʼs cloud computing platform.
Coding for kids Jim Anning – Coding is not routinely taught in UK schools until 6th form level. How can we encourage a new generation of kids to code? A quick introduction to MIT’s Scratch programming environment.
It’s not an uncommon scenario for Apache to not play nicely with Rails when dealing with multipart forms and large uploaded files. There are a few solutions out there, but the best we have seen is modporter from the guys at ActionRails.
So, you’ll need a few things to beef up Apache; if you haven’t got them already:
sudo apt-get install libapache2-mod-apreq2 sudo apt-get install libapreq2-dev sudo apt-get install apache2-threaded-dev
Now fetch the latest ModPorter from github from here. Once you have downloaded and unpacked this, edit the Rakefile and change the apxs variable to apxs2, then type:
cd modporter-directory rake
And, you’ll probably want the modporter plugin for Rails to give you a nice consistent interface for uploaded files rather than differentiate String IOs and UploadedFile objects.
If you have git:
script/plugin install git://github.com/actionrails/modporter-plugin.git
Otherwise, download the tar from here, unpack and stick in your vendor/plugins directory.
Now configure Apache to use load some additional modules, edit your apache.conf file to include (your path to modules may be different):
LoadModule apreq_module modules/mod_apreq2.so LoadModule porter_module modules/mod_porter.so
This is a bit off-topic, but worthwhile sharing.
I recently, rather unfortunately had my laptop stolen and now I have a replacement; I remember hearing about software that could use the built in iSight to take photos of the thieves and mail them back to me.
After looking on the net and finding some rather good, but pay-ware applications, I came across the Prey Project offering an open source free alternative. I went about installing the software and after checking that it worked went about tweaking it to work with how I have my laptop set up.
I use file vault (thank God it was switched on the laptop that was stolen) and have a password on wake so my personal files are secure. However, even with crontab running Prey once a minute, I figured that if the thief couldn’t log into my laptop, it was a bit pointless. So I have used two tactics that will hopefully result in my getting some pictures if the unfortunate were to happen again:
in /private/etc/crontab (this may not exist):
*/1 * * * * cd /usr/share/prey; ./prey.sh
Of course, there are no guarantees, but it’s better than nothing.
Just a quick note to say we have just reached 10,000 hits to the Workbooks Technical Blog. Thanks for reading!
