ruby dynamic abstract factory implementation R

i was looking for some way out to implement abstract factory on ruby code. where i have a VersionControl::ServiceFactory which will take different implementation as factory method. ie. VersionControl::ServiceFactory::subversion, VersionControl::ServiceFactory::git and so on.

though all these “subversion, git, perforce” methods are not predefined, these will be added while new implemention is added. my skeleton (abstract) implementation was in VersionControl::Service, so whatever implemention (svn, git, perforce, other) comes ahead it will implement method from VersionControl::Service method. since ruby doesn’t support class abstraction so this was the only way  i got in head.

so my skeleton implemention was consist of the following code in summary -

module VersionControl

# log entry class for data object
class LogEntry; end

# local repository information
class Information; end

# abstract service class.
# define service which will be exposed for a
# normal version controlling service.
class Service

# retrieve recent logs from the current directory
# required parameters - *base project path* and other options.
def logs(p_path, p_options = {}); raise "not implemented method" end

# generate diff from mentioned revision number
# or current revision number
# required parameters - *base project path* and other options.
def diff(p_path, p_options = {}); raise "not implemented method" end

# find repository information
def info(p_path, p_options = {}); raise "not implemented method" end
# check out content from version control server
def checkout(p_source, p_path, p_options = {}); raise "not implemented method" end

end

# factory class for supporting different version control implementation
class ServiceFactory; end
end

and the implementation is written in this way -

class ServiceFactory

class < < self
# add subversion factory method implementation
@@subversion_instance = SubversionService.new
def subversion
return @@subversion_instance
end
end
end

so every implementation also push it’s factory method to “VersionControl::ServiceFactory” class. so this way i have implemented dynamic abstract factory on ruby.

upcoming project mojar_workflow, workflow engine in ruby R

hi,
we just kicking start a new open source ruby based workflow engine project “mojar workflow“.
we named it after our deshi word “mojar” reason is very clear to
spread out this word.

mojar workflow, is integral solution to execute a flow of business
rules. for example -

you have an action where you have the following set of rules -
1. start transaction
2. verify user account
3. verify user balance
4. verify user dues
5. reduce dues from balance
6. complete transaction

after few days you got a new requirement, where you suppose to reduce
user dues by the 10% because of company new discount policy.
so you have to implement the following rules -
1. start transaction
2. verify user account
3. verify user balance
4. verify user dues
5. reduce dues by 10% of discount
5. reduce discounted dues from balance
6. complete transaction

to implement such scenario you have to again code in your stable
release. but using mojar workflow, you can add that new concern from
the abstract flow maintenance layer. where you can define this flow in
yaml file or an xml document.

keep your eyes on -
http://rubyforge.org/projects/mojarworkflow/

best wishes,

simple fragment cache implementation on ruby on rails R

i was getting serious performance problem with one of my projects. so i came up with a simple fragment cache implementation on ruby on rails.

after implementing this stuff, i replaced “render(:partial => …)” with the following method -

render_from_cache_or_render(:cache_key =>”cache key”, :cache_expire_after => ConstantHelper::TAG_CLOUD_EXPIRED_IN, # minutes :partial => “….”)

let’s have a look on my implementation -

def render_from_cache_or_render(p_args)

return render(p_args) if true == p_args[:cache_off]

# check from cache
cache_key = p_args[:cache_key]
cached_content = CacheService.get_cache(cache_key)

if not cached_content.nil? and not cached_content.empty?
return cached_content
else
content = render(p_args)
# cache expire time if defined
cache_expire_time_in_minutes = p_args[:cache_expire_after] || 60
CacheService.add_cache(cache_key, cache_expire_time_in_minutes, content)
return content
end
end

actually, my implemented “CacheService” class is simply storing all cache in a hash map.
when some cache was requested for peek, cache expiry was checked before returning the cached value.

for CacheService implementation look at the bottom of my post.

anyway, after implementing and utilizing this stuff, i gained 70+ requests capability per second. fyi, before applying cache it was around 10 per second.

module Cache
class Item
attr_accessor :key, :expire_time, :content, :created_on

def initialize(p_key, p_expire_time, p_content)
@key = p_key
@expire_time = p_expire_time * 60 # in minutes
@content = p_content
@created_on = Time.now
end
end
end

class CacheService
@@CACHES = {}
@@CACHE_EXPIRE_TIMES = {}

def self.add_cache(p_key, p_expire_time, p_content)
cache_item = Cache::Item.new(p_key, p_expire_time, p_content)
@@CACHES[p_key.to_sym] = cache_item
end

def self.get_cache(p_key)
# load content from cache
cached_content = @@CACHES[p_key.to_sym]
return nil if cached_content.nil?

# verify cache validity
return cached_content.content if not expired?(cached_content)
return nil
end

private
def self.expired?(p_cache)
# find time difference
time_difference = Time.now - p_cache.created_on
return true if time_difference > p_cache.expire_time
end
end

best wishes,

thats why i like ruby!!! thanks dynamic scripting… R

if you have rails deployment on windows environment with mongrel service, i think you might face the following problem -

Errno::EINVAL (Invalid argument):
/app/models/index_service.rb:63:in `write’
/app/models/index_service.rb:63:in `puts’

this problem was because of “puts” what i forgot to remove before deploying on test server.
if your deployment on windows service environment and if your code has few “puts” usages, you must face this problem with mongrel

on mongrel group, i found they are working with this, hopefully they will replace puts with logger and other things.
anyway, the quickest solution i had in mind was just use the dynamic behavior of ruby. here is what i did -

def puts(p_args)
logger.debug(p_args)
end

thats all fixed my problem

thank ruby, thanks for dynamic scripting…

simple AOP implementation in ruby R

i was suppose to work on some of my other projects, but i passed my time by writing a simple aop implementation in ruby.
it is neither powerful like AspectJ nor comparable with AspectR. however, i was having fun with my day off.

here is how my simple example is running-

def test_aop
# apply pointcuts
apply_advices(:before, /^do_.+/, SimpleService, SimpleServiceAdvice, :before_do)
apply_advices(:around, /^do_.+/, SimpleService, SimpleServiceAdvice, :around_do)
apply_advices(:after, /^do_.+/, SimpleService, SimpleServiceAdvice, :after_do)

simple_service = SimpleService.new
simple_service.do_1(”A”)
end

here is the parameter name.

apply_advices(type_of_advice, pointcuts_in_regex, service_class, advice_class, advice_method)

instead of making aspectJ type pointcuts syntax, i have used regex, which is fine for the time being.

if you run this code you will find the following output -

Before execution.
Around {
1 performed - A
}
After execution.

now let’s have a look on my SimpleService class.

class SimpleService

def do_1(p_param)
puts “1 performed - #{p_param}”
end

def do_2
puts “2 performed.”
end

def no_do
puts “No do”
end
end

and here is my aspect class,

class SimpleServiceAdvice

def around_do(p_invoke)
puts “Around { ”
output = p_invoke.proceede()
puts “}”
return output
end

def before_do(p_invoke)
puts “Before execution.”
end

def after_do(p_params, p_output)
puts “After execution.”
end
end

my implementation is very straight forward, actually during implementing this stuff, i really felt the strength of meta programming. it is so flexible and so easy that sky is the limit.

here is the attached source code.

much better and complete aop implementation in ruby

Fat Refactoring: use include module to reduce number of lines R

if i didn’t mention that before, i should tell it now, here at somewhere in… rnd team we are playing a lot with ruby on rails. these days our rails team is completely focusing on a product(which is secret for the time being ) where we
found a lot of interesting stuffs, for instance.

few days back, we found our application_helper and few controllers are growing too fast and getting extra fat (lines of code). so we had few refactoring to reduce the extra fat.

now have a look on the code we had with in application_helper.rb taken from tag/v-0.3

this code is not completely visible over the screen snap, this is 340 number of lines. which was the output of our 3 iterations.

though these number of lines are not that much problematic, but we had a scenario which was difficult to make it more concern aware and single concerned.

now have a look on our code which is taken from the current trunk,

Wow, now it is 50 lines only including the header copyright information.
the trick was very simple, we followed the following conventions -

1. find out all related and same concerned functions
2. stick team together in a module
3. include the module to statically import all functions
no integration error, nothing has occurred.
we are happy with this

i think, our ruby learning process is going smooth

split out test case into “preparation” and “verification” state. R

i was wondering how i could make my test method more organized and DR(Y)ied.
so i had a nice time while i was writing test to ensure my current modification works ok with existing setup.

i don’t know whether any design pattern or best practice is already exist on this topic.
i came up with something that is really good for me. here is a bit about my task and also the explanation about what i did.

i have a model “category” where i have the following relations -

has_many :category_mappings, :dependent => :destroy
has_many :items, :through => :category_mappings

has_many :categories, :foreign_key => “parent_id”, :dependent => :destroy

has_many :attribute_category_mappings, :dependent => :destroy
has_many :properties, :through => :attribute_category_mappings

belongs_to :category

i was applying :dependent = > :destroy with the mapping model and child categories, which are needs to be removed as a part of the category destroy process.

so i had a messy unit test method to ensure this is working fine. sorry for not keeping my old code snaps otherwise i could show the messy one. anyway here what i wrote later to make it bit cleaner than the previous messy version -

def test_destroy_category_with_dependent
category = Category.find(3)

# prepare for verification
prepare_for_verifying_related_property_mappings(category)
prepare_for_verifying_category_mappings(category)
prepare_for_verifying_child_category(category)

# perform action
category.destroy

# ensure the action
assert_raise(ActiveRecord::RecordNotFound) {
Category.find(category.id)
}

# perform verification
verify_related_property_mappings(category)
verify_related_category_mappings(category)
verify_related_child_category(category)
end

here i just sliced my test method in 2 different roles,

1. preparation stage
2. verification stage

1. preparation stage -
in this stage, i just keep log for current state or other steps which are important for later testing.

2. verification stage -
in this stage, i just verified my new state comparing with the old state (which was kept during preparation stage).
so let’s have a look on the typical code which i wrote in  my preparation and verification stage -

def verify_related_child_category(p_category)
puts “verify related child categories - #{p_category}”
now_category_count = Category.count
assert_equal(true, ((@old_category_count - now_category_count) > 1),
“No category has been removed.”)
end

this seem pretty good for me, as long as i can make my code bunch simple and easy to change.

best wishes,

on your active record model define has_many with dependent models. R

i was refactoring our Item model, where we have 3 has_many with 3 mapping models.
as we are not using InnoDB based foreign key constraint, we were searching some sort of reliable solution,
which will take pressure in application layer instead of leaving it to the database.

so later we introduced “:dependent” with has_may relation. here is our top of Item model.
has_many :category_mappings, :dependent => :destroy
has_many :categories, :through => :category_mappings

has_many :property_values, :dependent => :destroy
has_many :properties, :through => :property_value

has_many :item_location_mappings, :dependent => :destroy
has_many :locations, :through => :item_location_mappings

our “dependent” flagship is destroying all related items in the item destroy process which has introduced
our flexibility and reduced a lot of code to manage such stuff in a DRY(ied) manner.

so the following unit test worked fine for us.

some bad side,
dependent delete each and every item one by one, which is big issue when you have a big chunk of dependent data.
but that is not suppose to be common in every context. we have no problem with this issue.

best of luck!

“work for fun”

attributes: rails reserved variable :( R

yesterday, i had a pretty rough working day, i was stucked (along with my team) with some simple joining. we had the following models -

Attribute
———–
class Attribute < AR:B
belongs_to :category
end

class AttributeValue < AR:B
belongs_to :item
belongs_to :attribute
end

class Item < AR:B
has_many :attribute_values
has_many :attributes, :through => :attribute_values
end

rails wasn’t giving much better error message, instead it was saying, “invalid type, String to Integer..”, so far i understood ActiveRecord stuff was trying to cast a string to integer.

we even didn’t know which field was doing this stupidity and so on…
so later we dug down to the rails scripts, we added few debug messages. we found “[]” was invoked to set “id” string value.

anyway, after digging more into to this issue, today i gave another try after 7 hours of nice sleep. it was about rails reserve words.

though i heard something from the rails community, but i was expecting some message or  errors which explain this issue.

anyway, i always like fail first approach. if something is not possible it should fail first. at least it should return a meaningful exception.

i believe Active Record should be patched with more clear warning or exception, if any reserved word is used for model or controller or others it should let us inform .

EiD recipe special : few conventions and best practice for software developer R

i just gathered a few of my known conventions and best practices. i belief this will help many of us.

few of my previously written posts -
usages of “final” keyword in java -
http://www.somewhereinblog.net/blog/hasan/28708715

usages of comment and coding
http://www.somewhereinblog.net/blog/hasan/28704020

let’s check out my recipes -

1. code from your peer developer perspective view.
while you writing your code, always think your code will be reviewed by some other developers, who is not like you,
who is very serious in simple fault and ignorance in writing code. your code will reflect who you are, so better be careful while you exposing yourselves (through writing code).

2. variable convention -
never write short variable name, always write variable which reflects it usages.
for example -

$user = new User() instead of $u = new User(). follow same convention when you have nested “loop”

3. source file naming convention (except java)
set your file name in such a way that will reflect the usages of the file.
for example -

verify_user_authentication.php (or in a packaging manner - user_util_verify_authentication.php). in java you better know how to write package.

4. keep your url domain centric
all urls should be inherited by some specific problem domain for example -

http://abc.com/user/login
http://abc.com/user/register
http://abc.com/user/update

here “user” is problem domain and “login|register|update” are actions or you could say problem.

5. method naming convention -
write method name in such a format that will reflect it usages. or simply make it self describing.
for example -

function verify_user_credentials() {}
def verify_whether_user_profile_is_complete() {}
private void checkUserFlyLimit() {}

6. don’t write query from controller:
build or execute query from DAO or helper or utility or domain itself. don’t put it over controller which limits the reuability and later extendability and interception

7. single concern
while coding, keep your method slim and less concerned about other implementation. for example -

private void isAuthorizedUser(pUser, pAction) {
if (userAlreadyLoggedOn(pUser) && userIsNotBlocked(pUser) && userHasPermission(pUser, pAction)) {
// boooooooooooooooomm…
}
}

8. think from testability
while writing your code always think from testable perspective view. this means, how you could testify your work or module
or bunch of code which your company is paying for.

9. follow coding norms -
i. think before coding

whatever you want to put on your code try to think or imagine before start coding.

ii. dump your think in comment

whatever you thought just write it down over comment or paper or in a common place where you or future developers could have look on. (better place in comment)

iii. write your algorithm in comment.

whatever you planned write in comment before kick start your coding.

iv. set up your unit test case.

find all probable assertion points from use case, put them over your unit test case.

v. write your code
vi. coding routine -

(1) test -> (2) code - go to > (1) [recursively]

10. always put your tag over the source file,
whatever you wrote, that reflects your confident and work efficiency, so better you tag your name over every source code you have written or modified. good for tech lead or project manager, because tagging each file with author name, it creates a hidden responsibility for the author good for both parties.
for example -

/**
* @author someone
*/