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I'm new to Ruby/ROR and I'm kind of confused with something. A simple explanation would help.
Say I was linking to another page in Ruby on Rails. Would the keyword link_to be considered a method? Also, if so, where would I be able to learn more about these?
Symbols. What is the difference between a symbol with a colon on the :left or a symbol with a colon on the right:? Where would I be able to learn more about these?
You could use Google, e.g. https://www.google.de/search?q=rails+link_to. The link_to method is, well, a method which is defined by Rails and is not a Ruby keyword.
Symbols are different from Strings. In Ruby code, they are always written with a colon on the left. An "exception" of this rule is when it is used in a Hash using the new json-like Hash syntax from Ruby 1.9, where {foo: "bar"} is equivalent to {:foo => "bar"} Which variant you use is up to you, they are 100% equivalent.
Generally, it is probably a good idea to first read an introductional book about both Ruby and Rails or take an online-course, e.g. http://ruby.railstutorial.org/ for learning Rails or http://rubykoans.com/ for learning Ruby.
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In Ruby there is a nifty method of creating an array of symbols.
Percent i method.
%i[a b c]
I am working in a team based environment, and although I can see this being useful with a large list of array, I have this is being implemented for everything
a = %i[] # Empty array
cancan abilities
can :manage, :all
cannot %i[create show update], AModel
cannot %i[create], BModel
cannot %i[show], CModel
Is it good to initialize all arrays using this methods or just
cannot [:create, :show, :update], AModel
I know there is no 'right' way but I would like the pros and cons to help me decide
In terms of the language itself, there are no important differences between the two, so it really comes down to a matter of preference. Personally, I think that the array of symbol literals ([:create, :show, :update]) looks more Ruby-like and that is what I'd use, but you should discuss it with your team. The most important part is being consistent, and you don't want to make the decision alone.
In the general case of when to use %i instead of writing out a literal array of symbols, I'd consider using the former if it was a list of symbols that had certain meaning, like a class constant or something, and there were more than just a couple. I've been using Ruby for a while now and until this question didn't really register the existence of %i, so it's relatively uncommonly used. It's maybe not in the average Rubyist's vocabulary, so that might be another reason to stay away from it.
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We always read people saying "keeps things dry" with rails. But to what level?
For example, we have 3 models Project, Offer, Revision. This 3 models can have many Attachment.
On the "models" side it is quite straight forward we end up with
/app/models/project.rb
/app/models/offer.rb
/app/models/revision.rb
But for the controllers side I have problems keeping it DRY. I end up with at least:
GET /projects/:id/attachments -> Projects/Attachments#index
POST /projects/:id/attachments -> Projects/Attachments#create
GET /offers/:id/attachments -> Offers/Attachments#index
POST /offers/:id/attachments -> Offers/Attachments#create
GET /revisions/:id/attachments -> Revisions/Attachments#index
POST /revisions/:id/attachments -> Revisions/Attachments#create
So basically, I've almost the same code in this 3 locations:
controllers/projects/attachments_controller.rb
controllers/offers/attachments_controller.rb
controllers/revisions/attachments_controller.rb
My question, should I DRY it up and how?
DRY or "don't repeat yourself" is a general rule of thumb.
in case you find a pattern in your code that repeats itself in several places it might be worth looking into it.
if it's possible to extract a common functionality into, say a module, then you should probably do that.
if you think it's not worth your time, to complex or whatever reason there is not to do it, that is totally fine.
KISS (keeping things simple and stupid) > DRY
make sure your code is simple to follow and refactor and DRY out afterwards.
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I have a string which is something like:
ABC:Something|Hello World
I want the data after '|' character so I am using regex for it.
sample_str = "ABC:Something|Hello World"
puts sample_str.match(/[^|]*$/)
This works on rubular and returns me "Hello World" as the output, but doesn't work in my ruby code. What am I missing here? I get #<MatchData ""> in Ruby.
UPDATE: Nevermind. If I use the regex and do match on the string it works now. I was doing it other way round i.e. I did (regex).match(string) instead of (string).match(regex).
Thanks for looking!
Using regex seems excessive:
string.split('|').last
Below regex should help you.
^[\S\s]+?\|([\w\s]+)$
Dont forget to select global and multiline options.
Look at the regex demo here.
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I am building a rails app that i need to update totals of managers each time someone is added. The method that updates the totals to me is looking really bad there is a lot of repetition going on that could be solved with a bit of metaprogramming. so i have a private method being called on before_save called update_totals
So we categorize them like this there is four races, african, coloured, indian and white there are three kinds of managements senior, middle and junior and then obviously two kinds of genders male and female. I need to be able to assign each possible variation of the three so i end up with something like this.
self.number_of_african_female_senior_managers = managers.native.african.female.senior.count
self.number_of_african_male_senior_managers = managers.native.african.male.senior.count
self.number_of_african_female_middle_managers = managers.native.african.female.middle.count
self.number_of_african_male_middle_managers = managers.native.african.male.middle.count
self.number_of_african_female_junior_managers = managers.native.african.female.junior.count
self.number_of_african_male_junior_managers = managers.native.african.male.junior.count
I would need to do this for each race. So i thought of building them dynamically and then having them assigned.
So something like this:
["african", "indian", "coloured", "white"].each do |race|
["senior","middle","junior"].each do |management_type|
["male","Female"].each do |gender|
"number_of_#{race}_#{gender}_#{management_type}_managers" = managers.native.race.gender.management_type.count
end
end
end
But this will return strings and not variables that be assigned. I saw there is a define_method method that can dynamically build methods but that looks like you have to call it outside of the constructor in this example, and i saw that you can use Object#send like this example, but i cant see that working in this situation either.
Is this a good ruby practice? Its adding a bit of complexity but removing a lot of DRY code.
Is this a good ruby practice?
DRY is a good ruby practice, so the answer to your question is: YES
Regarding your code you will probably use send in such a situation.
something like self.send("number_of_#{race}_#{gender}_#{management_type}_managers=", managers.send(native).send(race).send(gender).send(management_type).count)
This still looks pretty ugly to me. I am kind of asking myself why that datastructure is so insane. Why are you not using a simple hash structure here?
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I am trying to design an edifact parser, I was planning on having one class to read the file, one class to map the data and then one other class to deal with data storage. The part where I am having a major problem is in how instances of those classes should communicate with each other. Any advice would be appreciated.
I don't see a need for the classes to communicate (pass messages) but would suggest some Strategy pattern be used.
You'll have a class to read the file and make sense of it's Syntax. For example, something which can handle whitespace and return formatted information like 'token', 'word' etc.
The class which reads and parses syntax is passed into the Semantic parser. The Semantic parser makes sense of the meaning. For example you might expect "Id, command, token, string" in that order. The Semantic parser might use a Command pattern.
The Semantic class outputs structured data, so is passed into your structure builder (builder pattern).
So your code might look like;
MyDataStructure = DataBuilder(SemanticParser(SyntaxParse(FileReader(filename))));
HTH