A decorator is more of a &quot;let&#39;s add some functionality to this entity&quot;. A presenter is more of a &quot;let&#39;s build a bridge between the model/backend and view&quot;. The presenter pattern has several interpretations.

Decorators are generic/general purpose. Presenters have a narrower range of responsibilities/uses. Decorators are used across domains, presenters are almost always related to view-like functionality.

* [Draper](https://github.com/drapergem/draper) site
* [RailsCasts Draper Episode](http://railscasts.com/episodes/286-draper)

I suggest you to check this - [Exhibit vs Presenter][1].

Decorator is a design pattern that is used to extend the functionality of a specific object by wrapping it, without effecting other instances of that object. In general, the decorator pattern is an example of the  [open/close principle][2] (the class is closed for modifications, but available for extensions).

Both the exhibit and presenter patterns are a kind of the decorator pattern.

  [1]: http://mikepackdev.com/blog_posts/31-exhibit-vs-presenter
  [2]: https://en.wikipedia.org/wiki/Open/closed_principle


How can I get the [HTML][1] source in a variable using the Selenium module with Python?

I wanted to do something like this:

    from selenium import webdriver

    browser = webdriver.Firefox()
    browser.get(&quot;http://example.com&quot;)
    if &quot;whatever&quot; in html_source:
	    # Do something
    else:
	    # Do something else

How can I do this? I don&#39;t know how to access the HTML source.

  [1]: http://en.wikipedia.org/wiki/HTML


Python Selenium accessing HTML source

I&#39;m trying to run `git clone` without ssh checking the repository host&#39;s key. I can do it from ssh like that:

    ssh -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no user@host

Is there any way to pass the same ssh options to the git clone command?

Edit: There is a restriction that I can&#39;t modify `~/.ssh/config` or any other files on that machine.

Passing ssh options to git clone

There is all sorts of talk lately in the Ruby on Rails community about [decorators][1] and presenters.

What is the essential difference between the two? If there is, what are the clues that tell me which one to use over the other? Or perhaps to use the two in conjunction?

  [1]: https://en.wikipedia.org/wiki/Decorator_pattern


Ruby on Rails patterns - decorator vs presenter

<p>There is all sorts of talk lately in the Ruby on Rails community about <a href="https://en.wikipedia.org/wiki/Decorator_pattern" target="_blank" rel="noopener noreferrer">decorators</a> and presenters.</p>
<p>What is the essential difference between the two? If there is, what are the clues that tell me which one to use over the other? Or perhaps to use the two in conjunction?</p>


I&#39;m confused on how to generate a model that belongs_to another model. My book uses this syntax to associate Micropost with User:

    rails generate model Micropost user_id:integer

but https://guides.rubyonrails.org/active_record_migrations.html#creating-a-standalone-migration says to do it like this:

    rails generate model Micropost user:references

The migrations generated by these 2 are different. Also, for the former, how does rails know that `user_id` is a foreign key referencing `user`? Thanks!

Generate model in Rails using user_id:integer vs user:references

I have installed PostgreSQL on my Mac OS Lion, and am working on a rails app. I use RVM to keep everything separate from my other Rails apps.

For some reason when I try to migrate the db for the first time rake cannot find the postgres user. I get the error

     FATAL:  role &quot;postgres&quot; does not exist

I have pgAdmin so I can clearly see there is a postgres user in the DB - the admin account in fact - so I&#39;m not sure what else to do.

I read somewhere about people having issues with PostgreSQL because of which path it was installed in, but then I don&#39;t think I would have gotten that far if it couldn&#39;t find the db.

Rails and PostgreSQL: Role postgres does not exist

I need validate some attributes ONLY if they are not empty. 

For example the user may have a logo. If we try to load it - validation should work. If we simply update the user&#39;s data without the logo, validation must be skipped.

Now i have:

The form has a choice of two files. One - logo, second - avatar.
Both of this attributes is part of User model. In User model a have validation:

    validates_preference_of :logo_file_name, :message=&gt;I18n.t(&quot;...&quot;)
    validates_format_of :logo_file_name, :with=&gt;/\.(jpeg|jpg|png|gif)$/i, :message=&gt; I18n.t(&quot;...&quot;)
    validates_preference_of :avatar_file_name, :message=&gt;I18n.t(&quot;...&quot;)
    validates_format_of :avatar_file_name, :with=&gt;/\.(jpeg|jpg|png|gif)$/i, :message=&gt; I18n.t(&quot;...&quot;)

In this case, if we try to create a new User without selected logo and avatar, we will have errors (our validation). I tryed change validation and add &quot;:on =&gt; :update&quot; like this:

    validates_preference_of :logo_file_name, :message=&gt;I18n.t(&quot;...&quot;), :on =&gt; :update
    validates_format_of :logo_file_name, :with=&gt;/\.(jpeg|jpg|png|gif)$/i, :message=&gt; I18n.t(&quot;...&quot;), :on =&gt; :update
    validates_preference_of :avatar_file_name, :message=&gt;I18n.t(&quot;...&quot;), :on =&gt; :update
    validates_format_of :avatar_file_name, :with=&gt;/\.(jpeg|jpg|png|gif)$/i, :message=&gt; I18n.t(&quot;...&quot;), :on =&gt; :update

Now i can create user without selected logo and avatar, but if i try edit user and try upload only logo - i have validation errors of avatar. If i choose file for avatar and logo leave blank - i have validation errors for logo.

How i can run validation ony for attribute that I want to change?

Validate attribute only if it present (only if user fill in it)

I keep getting conflicting opinions on the practice of storing information in the `Thread.current` hash (e.g., the current_user, the current subdomain, etc.). The technique has been proposed as a way to simplify later processing within the model layer (query scoping, auditing, etc.). 

 - https://stackoverflow.com/questions/4217911/why-are-my-thread-variables-intermittent-in-rails
 - https://stackoverflow.com/questions/7509883/alternative-to-using-thread-current-in-api-wrapper-for-rails
 - https://stackoverflow.com/questions/6659221/are-thread-current-values-and-class-level-attributes-safe-to-use-in-rails

Many consider the practice unacceptable because it breaks the MVC pattern.
Others express concerns about reliability/safety of the approach, and my 2-part question focuses on the latter aspect.

1. Is the `Thread.current` hash guaranteed to be available and private to one and only one response, throughout its entire cycle?

2. I understand that a thread, at the end of a response, may well be handed over to other incoming requests, thereby leaking any information stored in `Thread.current`. Would clearing such information before the end of the response (e.g. by executing `Thread.current[:user] = nil` from a controller&#39;s `after_filter`) suffice in preventing such security breach?

Thanks!
Giuseppe

Safety of Thread.current[] usage in rails

I&#39;m using Paperclip to manage user-uploaded images on a site that is served entirely under HTTPS.  In order to avoid the silly security warnings on IE7/IE8, I need to also serve these images over SSL.  I typically render my images using something like the following:

    &lt;%= image_tag @product.image.url(:large) %&gt;


where

    class Product &lt; ActiveRecord::Base

      has_attached_file :image,
                      :styles =&gt; {
                          :large =&gt; {:geometry =&gt; &quot;616x450#&quot;}
                      },
                      :storage =&gt; :s3,
                      :s3_credentials =&gt; {:access_key_id =&gt; &quot;xxx&quot;, :secret_access_key =&gt; &quot;xxx&quot;},
                      :path =&gt; &quot;:attachment/:id/:style/:basename.:extension&quot;,
                      :bucket =&gt; CONFIG[&#39;s3_media_bucket&#39;],
                      :default_url =&gt; &quot;/assets/image_missing.png&quot;

and the image URL produced is something like:

    http://s3.amazonaws.com/media.example.com/images/6/large/image123.JPG

Is there a magic Paperclip option to change this to:

    https://s3.amazonaws.com/media.example.com/images/6/large/image123.JPG

Is it possible to configure Paperclip to produce HTTPS urls for S3?

Fragments seem to be very nice for separation of UI logic into some modules. But along with `ViewPager` its lifecycle is still misty to me. So Guru thoughts are badly needed! 
###Edit###
See dumb solution below ;-)
##Scope##
Main activity has a `ViewPager` with fragments. Those fragments could implement a little bit different logic for other (submain) activities, so the fragments&#39; data is filled via a callback interface inside the activity. And everything works fine on first launch, but!...
##Problem##
When the activity gets recreated (e.g. on orientation change) so do the `ViewPager`&#39;s fragments. The code (you&#39;ll find below) says that every time the activity is created I try to create a new `ViewPager` fragments adapter the same as fragments (maybe this is the problem) but FragmentManager already has all these fragments stored somewhere (where?) and starts the recreation mechanism for those. So the recreation mechanism calls the &quot;old&quot; fragment&#39;s onAttach, onCreateView, etc. with my callback interface call for initiating data via the Activity&#39;s implemented method. But this method points to the newly created fragment which is created via the Activity&#39;s onCreate method.
##Issue##
Maybe I&#39;m using wrong patterns but even Android 3 Pro book doesn&#39;t have much about it. So, **please**, give me one-two punch and point out how to do it the right way. Many thanks!
##Code##
*Main Activity*

    public class DashboardActivity extends BasePagerActivity implements OnMessageListActionListener {

	private MessagesFragment mMessagesFragment;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		Logger.d(&quot;Dash onCreate&quot;);
		super.onCreate(savedInstanceState);

		setContentView(R.layout.viewpager_container);
		new DefaultToolbar(this);

		// create fragments to use
		mMessagesFragment = new MessagesFragment();
		mStreamsFragment = new StreamsFragment();

		// set titles and fragments for view pager
		Map&lt;String, Fragment&gt; screens = new LinkedHashMap&lt;String, Fragment&gt;();
		screens.put(getApplicationContext().getString(R.string.dashboard_title_dumb), new DumbFragment());
		screens.put(getApplicationContext().getString(R.string.dashboard_title_messages), mMessagesFragment);

		// instantiate view pager via adapter
		mPager = (ViewPager) findViewById(R.id.viewpager_pager);
		mPagerAdapter = new BasePagerAdapter(screens, getSupportFragmentManager());
		mPager.setAdapter(mPagerAdapter);

		// set title indicator
		TitlePageIndicator indicator = (TitlePageIndicator) findViewById(R.id.viewpager_titles);
		indicator.setViewPager(mPager, 1);

	}

	/* set of fragments callback interface implementations */

	@Override
	public void onMessageInitialisation() {

		Logger.d(&quot;Dash onMessageInitialisation&quot;);
		if (mMessagesFragment != null)
			mMessagesFragment.loadLastMessages();
	}

	@Override
	public void onMessageSelected(Message selectedMessage) {

		Intent intent = new Intent(this, StreamActivity.class);
		intent.putExtra(Message.class.getName(), selectedMessage);
		startActivity(intent);
	}

*BasePagerActivity aka helper*

    public class BasePagerActivity extends FragmentActivity {

	BasePagerAdapter mPagerAdapter;
	ViewPager mPager;
    }
*Adapter*

    public class BasePagerAdapter extends FragmentPagerAdapter implements TitleProvider {

	private Map&lt;String, Fragment&gt; mScreens;

	public BasePagerAdapter(Map&lt;String, Fragment&gt; screenMap, FragmentManager fm) {

		super(fm);
		this.mScreens = screenMap;
	}

	@Override
	public Fragment getItem(int position) {

		return mScreens.values().toArray(new Fragment[mScreens.size()])[position];
	}

	@Override
	public int getCount() {

		return mScreens.size();
	}

	@Override
	public String getTitle(int position) {

		return mScreens.keySet().toArray(new String[mScreens.size()])[position];
	}

	// hack. we don&#39;t want to destroy our fragments and re-initiate them after
	@Override
	public void destroyItem(View container, int position, Object object) {

		// TODO Auto-generated method stub
	}

    }


*Fragment*

    public class MessagesFragment extends ListFragment {

	private boolean mIsLastMessages;

	private List&lt;Message&gt; mMessagesList;
	private MessageArrayAdapter mAdapter;

	private LoadMessagesTask mLoadMessagesTask;
	private OnMessageListActionListener mListener;

	// define callback interface
	public interface OnMessageListActionListener {
		public void onMessageInitialisation();
		public void onMessageSelected(Message selectedMessage);
	}

	@Override
	public void onAttach(Activity activity) {
		super.onAttach(activity);
		// setting callback
		mListener = (OnMessageListActionListener) activity;
		mIsLastMessages = activity instanceof DashboardActivity;

	}

	@Override
	public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
		inflater.inflate(R.layout.fragment_listview, container);
		mProgressView = inflater.inflate(R.layout.listrow_progress, null);
		mEmptyView = inflater.inflate(R.layout.fragment_nodata, null);
		return super.onCreateView(inflater, container, savedInstanceState);
	}

	@Override
	public void onActivityCreated(Bundle savedInstanceState) {
		super.onActivityCreated(savedInstanceState);

		// instantiate loading task
		mLoadMessagesTask = new LoadMessagesTask();

		// instantiate list of messages
		mMessagesList = new ArrayList&lt;Message&gt;();
		mAdapter = new MessageArrayAdapter(getActivity(), mMessagesList);
		setListAdapter(mAdapter);
	}

	@Override
	public void onResume() {
		mListener.onMessageInitialisation();
		super.onResume();
	}

	public void onListItemClick(ListView l, View v, int position, long id) {
		Message selectedMessage = (Message) getListAdapter().getItem(position);
		mListener.onMessageSelected(selectedMessage);
		super.onListItemClick(l, v, position, id);
	}

	/* public methods to load messages from host acitivity, etc... */
    }

##Solution##
The dumb solution is to save the fragments inside onSaveInstanceState (of host Activity) with putFragment and get them inside onCreate via getFragment. But I still have a strange feeling that things shouldn&#39;t work like that... See code below:

    	@Override
	protected void onSaveInstanceState(Bundle outState) {

		super.onSaveInstanceState(outState);
		getSupportFragmentManager()
				.putFragment(outState, MessagesFragment.class.getName(), mMessagesFragment);
	}

    protected void onCreate(Bundle savedInstanceState) {
		Logger.d(&quot;Dash onCreate&quot;);
		super.onCreate(savedInstanceState);

        ...
		// create fragments to use
		if (savedInstanceState != null) {
			mMessagesFragment = (MessagesFragment) getSupportFragmentManager().getFragment(
					savedInstanceState, MessagesFragment.class.getName());
					StreamsFragment.class.getName());
		}
		if (mMessagesFragment == null)
			mMessagesFragment = new MessagesFragment();
        ...
    }

ViewPager and fragments — what&#39;s the right way to store fragment&#39;s state?

I&#39;m a software developer. I love to code, but I hate databases... Currently, I&#39;m creating a website on which a user will be allowed to mark an entity as *liked* (like in FB), *tag* it and *comment*.

I get stuck on database tables design for handling this functionality. Solution is trivial, if we can do this only for one type of thing (eg. photos). But I need to enable this for 5 different things (for now, but I also assume that this number can grow, as the whole service grows).

I found some similar questions here, but none of them have a satisfying answer, so I&#39;m asking this question again.

The question is, how to properly, *efficiently* and *elastically* design the database, so that it can store comments for different *tables*, *likes* for different *tables* and *tags* for them. Some design pattern as answer will be best ;)

**Detailed description**:
I have a *table* `User` with some user data, and 3 more *tables*: `Photo` with *photographs*, `Articles` with *articles*, `Places` with *places*. I want to enable any logged user to:

- comment on any of those 3 tables

- mark any of them as liked

- tag any of them with some tag

- I also want to count the number of likes for every element and the number of times that particular tag was used.
&lt;br/&gt;&lt;br/&gt;

**1&lt;sup&gt;st&lt;/sup&gt; approach**:

 a) For *tags*, I will create a *table* `Tag [TagId, tagName, tagCounter]`, then I will create *many-to-many* relationships *tables* for: `Photo_has_tags`, `Place_has_tag`, `Article_has_tag`.

 b) The same counts for comments.

 c) I will create a *table* `LikedPhotos [idUser, idPhoto]`, `LikedArticles[idUser, idArticle]`, `LikedPlace [idUser, idPlace]`. Number of *likes* will be calculated by *queries* (which, I assume is bad). And... 

I really don&#39;t like this design for the last part, it smells badly for me ;)

&lt;br/&gt;
**2&lt;sup&gt;nd&lt;/sup&gt; approach**:

 I will create a table `ElementType [idType, TypeName == some table name]` which will be populated by the administrator (me) with the names of *tables* that can be *liked*, *commented* or *tagged*. Then I will create *tables*:

 a) `LikedElement [idLike, idUser, idElementType, idLikedElement]` and the same for Comments and Tags with the proper columns for each. Now, when I want to make a photo liked I will insert:

    typeId = SELECT id FROM ElementType WHERE TypeName == &#39;Photo&#39;
    INSERT (user id, typeId, photoId)

and for places:

    typeId = SELECT id FROM ElementType WHERE TypeName == &#39;Place&#39;
    INSERT (user id, typeId, placeId)

and so on... I think that the second approach is better, but I also feel like something is missing in this design as well...

At last, I also wonder which the best place to store counter for how many times the element was liked is. I can think of only two ways:

1. in element (`Photo/Article/Place`) table
2. by select count().

I hope that my explanation of the issue is more thorough now.

Implementing Comments and Likes in database

When I read docs about repositories, it is often to work with entities &amp; collection but in a &quot;read-only&quot; manner.

There are never examples where repositories have methods like `insertUser(User $user)` or `updateUser(User $user)`.

However, when using SOA, Service should not be working with Entity Manager (that&#39;s right, isn&#39;t it?) so: 

1. Should my service be aware of the global EntityManager?
2. Should my service know only about the used Repositories (let&#39;s say, UserRepository &amp; ArticleRepository)

From that both questions, another one, should my service ever explicitly `persist()` &amp; `flush()` my entities ?



Are Doctrine2 repositories a good place to save my entities?

My team and I have been discussing using the CQRS (Command Query Responsibility Segregation) design pattern and we are still trying to asses the pros and cons of using it. According to: [http://martinfowler.com/bliki/CQRS.html][1] 

&gt; we haven&#39;t seen enough uses of CQRS in the field yet to be confident
&gt; that we understand its pros and cons

So what do you guys think, when does a problem call for using CQRS? 


  [1]: http://martinfowler.com/bliki/CQRS.html

When to use the CQRS design pattern?

There is a lot of talk on decoupling the algorithms from the classes. But, one thing stays aside not explained. 

They use visitor like this

    abstract class Expr {
      public &lt;T&gt; T accept(Visitor&lt;T&gt; visitor) { return visitor.visit(this); }
    }
    
    class ExprVisitor extends Visitor{
      public Integer visit(Num num) {
        return num.value;
      }

      public Integer visit(Sum sum) {
        return sum.getLeft().accept(this) + sum.getRight().accept(this);
      }
    
      public Integer visit(Prod prod) {
        return prod.getLeft().accept(this) * prod.getRight().accept(this);
      }
    

Instead of calling visit(element) directly, Visitor asks the element to call its visit method. It contradicts the declared idea of class unawareness about visitors. 

PS1 Please explain with your own words or point to exact explanation. Because two responses I got refer to something general and uncertain. 

PS2 My guess: Since `getLeft()` returns the basic `Expression`, calling `visit(getLeft())` would result in `visit(Expression)`, whereas `getLeft()` calling `visit(this)` will result in another, more appropriate, visit invocation. So, `accept()` performs the type conversion (aka casting).

PS3 [Scala&#39;s Pattern Matching = Visitor Pattern on Steroid][2] shows how much simpler the Visitor pattern is without the accept method. [Wikipedia adds to this statement][1]: by linking a paper showing &quot;that `accept()` methods are unnecessary when reflection is available; introduces term &#39;Walkabout&#39; for the technique.&quot; 


  [1]: http://en.wikipedia.org/wiki/Visitor_pattern#External_links
  [2]: http://andymaleh.blogspot.com/2008/04/scalas-pattern-matching-visitor-pattern.html

What is the point of accept() method in Visitor pattern?

This might be pushing things a little too far, but mostly out of curiosity..

Would it be possible to have a callable object (function/class) that acts as *both* a Context Manager and a decorator at the same time:

    def xxx(*args, **kw):
        # or as a class

    @xxx(foo, bar)
    def im_decorated(a, b):
        print(&#39;do the stuff&#39;)

    with xxx(foo, bar):
        print(&#39;do the stuff&#39;)


Function acting as both decorator and context manager in Python?

Many try/except/finally-clauses not only &quot;uglify&quot; my code, but i find myself often using identical exception-handling for similar tasks. So i was considering reducing redundancy by &quot;outsourcing&quot; them to a ... decorator.

Because i was sure not to be the 1st one to come to this conclusion, I googled and found this - imho - ingenious [recipe][1] which added the possibility to handle more than one exception.

But i was surprised why this doesn&#39;t seem to be a wide known and used practice per se, so i was wondering if there is maybe an aspect i wasn&#39;t considering? 

1. Is it bogus to use the decorator pattern for exception-handling or did i just miss it the whole time? Please enlighten me! What are the pitfalls? 

2. Is there maybe even a package/module out there which supports the creation of such exception-handling in a reasonable way?

  [1]: http://code.activestate.com/recipes/408937-basic-exception-handling-idiom-using-decorators/

&quot;outsourcing&quot; exception-handling to a decorator

As I&#39;ve understood it there are two ways to do a Python decorator, to either use the `__call__` of a class or to define and call a function as the decorator. What&#39;s the advantages/disadvantages of these methods? Is there one preferred method?

Example 1

    class dec1(object):
        def __init__(self, f):
            self.f = f
        def __call__(self):
            print &quot;Decorating&quot;, self.f.__name__
            self.f()

    @dec1
    def func1():
        print &quot;inside func1()&quot;

    func1()

    # Decorating func1
    # inside func1()


Example 2

    def dec2(f):
        def new_f():
            print &quot;Decorating&quot;, f.__name__
            f()
        return new_f

    @dec2
    def func2():
        print &quot;inside func2()&quot;

    func2()

    # Decorating func2
    # inside func2()

Python decorator best practice, using a class vs a function

Is it possible to decorator a function conditionally.  For example, I want to decorate the function `foo()` with a timer function (`timeit`) only doing_performance_analysis is `True` (see the psuedo-code below).

    if doing_performance_analysis:
      @timeit
      def foo():
        &quot;&quot;&quot;
        do something, timeit function will return the time it takes
        &quot;&quot;&quot;
        time.sleep(2)
    else:
      def foo():
        time.sleep(2)  

how to do a conditional decorator in python

When I attempt to use a static method from within the body of the class, and define the static method using the built-in `staticmethod` function as a decorator, like this:

    class Klass(object):

        @staticmethod  # use as decorator
        def _stat_func():
            return 42

        _ANS = _stat_func()  # call the staticmethod

        def method(self):
            ret = Klass._stat_func() + Klass._ANS
            return ret

I get the following error:

&lt;!-- language: lang-none --&gt;

    Traceback (most recent call last):
      File &quot;call_staticmethod.py&quot;, line 1, in &lt;module&gt;
        class Klass(object): 
      File &quot;call_staticmethod.py&quot;, line 7, in Klass
        _ANS = _stat_func() 
      TypeError: &#39;staticmethod&#39; object is not callable

*I understand why this is happening (descriptor binding)*, and can work around it by manually converting `_stat_func()` into a staticmethod after its last use, like so:

    class Klass(object):

        def _stat_func():
            return 42

        _ANS = _stat_func()  # use the non-staticmethod version

        _stat_func = staticmethod(_stat_func)  # convert function to a static method

        def method(self):
            ret = Klass._stat_func() + Klass._ANS
            return ret

So my question is:

&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;**Are there cleaner or more &quot;Pythonic&quot; ways to accomplish this?**


Content Type	Original Author	Original Content on Stackoverflow
Question	keruilin	View Question on Stackoverflow
Solution 1 - Ruby on-Rails	Dave Newton	View Answer on Stackoverflow
Solution 2 - Ruby on-Rails	dpaluy	View Answer on Stackoverflow

Ruby on Rails patterns - decorator vs presenter

Ruby on-Rails Problem Overview

Ruby on-Rails Solutions

Solution 1 - Ruby on-Rails

Solution 2 - Ruby on-Rails

Passing ssh options to git clone

Python Selenium accessing HTML source

Attributions