I am new to Ruby, so let me describe the context of my problem first:
I have a json as input which has the following key / value pair:
{
"service": "update"
}
The value has many different values for example: insert,delete etc.
Next there is a method x which handles the different requests:
def x(input)
case input[:service]
services = GenericService.new
when "update"
result = services.service(UpdateService.new,input)
when "insert"
result = services.service(InsertService.new,input)
when "delete"
result = services.service(DeleteService.new,input)
....
....
else
raise "Unknown service"
end
puts JSON.pretty_generate(result)
end
What is bothering me is that I still need to use a switch statement to check the String values (reminds me of 'instance of' ugh..). Is there a cleaner way (not need to use a switch)?
Finally I tried to search for an answer to my question and did not succeed, if however I missed it feel free to comment the related question.
Update: I was thinking to maybe cast the string to the related class name as follows: How do I create a class instance from a string name in ruby? and then call result = services.services(x.constantize.new,input) , then the class names ofcourse needs to match the input of the json.
You can try something like:
def x(input)
service_class_name = "#{input[:service].capitalize}Service"
service_class = Kernel.const_get(service_class_name)
service_class.new(input).process
end
In addition you might want to check if this is a valid Service class name at all.
I don't understand why you want to pass the service to GenericService this seems strange. let the service do it's job.
If you're trying to instatiate a class by it's name you're actually speaking about Reflection rather than Polymorphism.
In Ruby you can achieve this in this way:
byName = Object.const_get('YourClassName')
or if you are in a Rails app
byName= 'YourClassName'.constantize
Hope this helps
Just first thoughts, but you can do:
eval(services.service("#{input[:service].capitalize}Service.new, #{input})") if valid_service? input[:service]
def valid_service?
w%(delete update insert).include? input[:service]
end
As folks will no doubt shout, eval needs to be used with alot of care
Related
I want to mock this function:
def self.set_segment_info(segment_info, history_record)
history_record.segment_info = segment_info
end
In my test, I want a mock that only confirms that I called set_segment_info with an expected value. I don't care about what I pass in for history_record.
How would I do this? I tried
SegmentHistoryRecord.expects(:set_segment_info).with(:segment_info => expected_segment_info, :history_record => anything)
But that doesn't work.
I ran into this today and ended up doing something like:
SegmentHistoryRecord.expects(:set_segment_info).with(
expected_segment_info,
anything
)
I find it more readable that the do version and it helped me avoid a rubocop issue with too many parameters.
Here's an implementation where, if your function takes a lot of parameters, it's more convenient to specify a value for just the one you care about, instead of for all of them:
expected_segment_info = # ...
SegmentHistoryRecord.expects(:set_segment_info).with() { |actual_parameters| actual_parameters[:segment_info] == expected_segment_info }
(Where, as in the original question, set_segment_info is the function being mocked, and segment_info is the parameter whose value you want to match. Note that the history_record parameter -- and any others that might be present -- don't need to be included.)
SegmentHistoryRecord.expects(:set_segment_info).with() do |param1, param2|
# change below to your verification for :segment_info
# and leave param2 doing nothing, the expectation will ignore param2
param1 == expected_segment_info
end
Method find_something may return nil. In the following code,
something = find_something(id) ? find_something(id) : create_something(foo)
find_something(id) is called twice. This is a smell that I want to avoid. Is there a way to avoid redundancy in this expression?
Anything like this?
something = find_something(id) || create_something(foo)
There's not quite enough detail given to say this with confidence, though it might be this is a case for find_or_create_by.
If this does suit, you would just do:
something = YourModel.find_or_create_by(id: id)
You can also provide a block to this, which is passed to the create method if no record is found. For example:
something = YourModel.find_or_create_by(id: id) do |instance|
# this block only gets executed on create
instance.some_new_attribute = 'goes here'
end
Hope that's useful - let me know if it suits your use case.
My question model holds the prompt and the answer choices for questions that students can answer. It includes columns named :choice_0, :choice_1, :choice_2, :choice_3, :choice_4, and :choice_5.
In one section of my controller, I've used the following code:
correct_array.push(these_params[:choice_0]) if !these_params[:choice_0].blank?
correct_array.push(these_params[:choice_1]) if !these_params[:choice_1].blank?
correct_array.push(these_params[:choice_2]) if !these_params[:choice_2].blank?
correct_array.push(these_params[:choice_3]) if !these_params[:choice_3].blank?
correct_array.push(these_params[:choice_4]) if !these_params[:choice_4].blank?
correct_array.push(these_params[:choice_5]) if !these_params[:choice_5].blank?
In other areas of my app, I've used the #{} syntax, for example:
params[:choice_#{n}]
But that doesn't work within a params hash for some reason. I'm sure that there is a drier way to accomplish these five lines.
Thank you in advance for any insight.
A more Ruby way to do this is:
correct_array = (0..5).map { |i| these_params["choice_#{i}".to_sym] }.select(&:present?)
Or as a method:
def correct_array
(0..5).map { |i| these_params["choice_#{i}".to_sym] }.select(&:present?)
end
In either case, you have the added bonus of not having to initialize correct_array as it is created on the fly.
You may try this
(0..5).each do |i|
param_i = these_params["choice_#{i}".to_sym]
correct_array.push(param_i) if param_i.present?
end
How do I create an object if one is not found? This is the query I was running:
#event_object = #event_entry.event_objects.find_all_by_plantype('dog')
and I was trying this:
#event_object = EventObject.new unless #event_entry.event_objects.find_all_by_plantype('dog')
but that does not seem to work. I know I'm missing something very simple like normal :( Thanks for any help!!! :)
find_all style methods return an array of matching records. That is an empty array if no matching records are found. And an empty is truthy. Which means:
arr = []
if arr
puts 'arr is considered turthy!' # this line will execute
end
Also, the dynamic finder methods (like find_by_whatever) are officially depreacted So you shouldn't be using them.
You probably want something more like:
#event_object = #event_entry.event_objects.where(plantype: 'dog').first || EventObject.new
But you can also configure the event object better, since you obviously want it to belong to #event_entry.
#event_object = #event_entry.event_objects.where(plantype: 'dog').first
#event_object ||= #event_entry.event_objects.build(plantype: dog)
In this last example, we try to find an existing object by getting an array of matching records and asking for the first item. If there are no items, #event_object will be nil.
Then we use the ||= operator that says "assign the value on the right if this is currently set to a falsy value". And nil is falsy. So if it's nil we can build the object form the association it should belong to. And we can preset it's attributes while we are at it.
Why not use built in query methods like find_or_create_by or find_or_initialize_by
#event_object = #event_entry.event_objects.find_or_create_by(plantype:'dog')
This will find an #event_entry.event_object with plantype = 'dog' if one does not exist it will then create one instead.
find_or_initialize_by is probably more what you want as it will leave #event_object in an unsaved state with just the association and plantype set
#event_object = #event_entry.event_objects.find_or_initialize_by(plantype:'dog')
This assumes you are looking for a single event_object as it will return the first one it finds with plantype = 'dog'. If more than 1 event_object can have the plantype ='dog' within the #event_entry scope then this might not be the best solution but it seems to fit with your description.
I'm using xml-mapping in Ruby (on Sinatra) for some XML stuff. Generally I follow this tutorial: http://xml-mapping.rubyforge.org/. I can create objects and write them to XML strings using
login.save_to_xml.to_s
But when I try
login = Login.load_from_xml(xml_string)
I get the following error:
XML::MappingError - no value, and no default value: Attribute username not set (XXPathError: path not found: username):
Here is the XML string I receive:
<login><username>ali</username><password>baba</password></login>
This is what the class looks like:
class Login
include XML::Mapping
text_node :username, "username"
text_node :password, "password"
end
So the class name is the same, the nodes are named the same. I actually get the exact same string when I create an instance of my object and fill it with ali/baba:
test = Login.new
test.username = "ali"
test.password = "baba"
p test.save_to_xml.to_s
<login><username>ali</username><password>baba</password></login>
What am I missing?
Thanks,
MrB
EDIT:
When I do
test = login.save_to_xml
And then
login = Login.load_from_xml(test)
it works. So the problem seems to be that I'm passing a string, while the method is expecting.. well, something else. There is definitely a load_from_xml(string) method in the rubydocs, so not sure what to pass here. I guess I need some kind of reverse to_s?
It looks like you save_to_xml creates a REXML::Element. Since that works, you may want to try:
Login.load_from_xml(REXML::Document.new(xml_string).root)
See the section on "choice_node" for a more detailed example http://xml-mapping.rubyforge.org/