I would probably make this really explicit:

    // Or private, or maybe even public
    internal static readonly DateTime MagicValueForNullDateTimeInNonNullableColumns
        = DateTime.MinValue;

Okay, so I&#39;d make the name *slightly* less wordy, but you get what I mean. It doesn&#39;t really matter much how you initialize that value - it&#39;s clear what you&#39;re trying to do.

(Of course, use a nullable type any time you can for this. I&#39;m assuming the question was asked because you *couldn&#39;t* do so in certain situations.)

&gt; I need to check a `DateTime` value if it has a value or not.

You&#39;ve pretty-much described the textbook situation requiring a `Nullable&lt;DateTime&gt;`. I&#39;d go with that option.

(You&#39;d obviously need some sort of translation layer if you need to persist the values to a non-null db column, but I&#39;d try to keep any &quot;magic&quot; value as close to the db as possible, and try to keep your C# code clean and idiomatic.)



The &quot;best&quot; practice would be using the nullable `DateTime`. Nullable value types were created *exactly* for that reason of not trusting &quot;magic&quot; numbers.

What&#39;s most important about this approach is its intent - what does it *mean* in your context to have a &quot;default&quot; date/time?

Maybe you can set a default value in your database with getdate() and then update all null values to min value or whatever you like. At least you will have one condition

Method One: Using special g object from http://flask.pocoo.org/docs/tutorial/dbcon/ and http://flask.pocoo.org/docs/patterns/sqlite3/

    import sqlite3
    from flask import g
    
    DATABASE = &#39;/path/to/database.db&#39;
    
    def connect_db():
        return sqlite3.connect(DATABASE)
    
    @app.before_request
    def before_request():
        g.db = connect_db()
    
    @app.teardown_request
    def teardown_request(exception):
        if hasattr(g, &#39;db&#39;):
            g.db.close()

Method Two: Using Mysterious _app_ctx_stack from https://github.com/mitsuhiko/flask/blob/master/examples/flaskr/flaskr.py

    from sqlite3 import dbapi2 as sqlite3
    from flask import Flask, request, session, g, redirect, url_for, abort, \
         render_template, flash, _app_ctx_stack
    def get_db():
        &quot;&quot;&quot;Opens a new database connection if there is none yet for the
        current application context.
        &quot;&quot;&quot;
        top = _app_ctx_stack.top
        if not hasattr(top, &#39;sqlite_db&#39;):
            top.sqlite_db = sqlite3.connect(app.config[&#39;DATABASE&#39;])
        return top.sqlite_db
    
    
    @app.teardown_appcontext
    def close_db_connection(exception):
        &quot;&quot;&quot;Closes the database again at the end of the request.&quot;&quot;&quot;
        top = _app_ctx_stack.top
        if hasattr(top, &#39;sqlite_db&#39;):
            top.sqlite_db.close()

Which method is better? What is the difference?

Connect to a Database in Flask, Which Approach is better?

I have a `&lt;button&gt;` with a hyperlink tag inside, looks like this:

    &lt;button class=&quot;btn&quot;&gt;&lt;a href=&quot;#&quot;&gt;&lt;/a&gt;&lt;/button&gt;

This works well in Chrome and Safari, BUT doesn&#39;t work in Firefox (ver 20 tested).

What&#39;s wrong?

Nesting &lt;a&gt; inside &lt;button&gt; doesn&#39;t work in Firefox

I need to check a `DateTime` value if it has a value or not.

I have several options:

    if (dateTime == default(DateTime))
or

    if (dateTime == DateTime.MinValue)
or using a nullable `DateTime?`

    if (nullableDateTime.HasValue)

Personally I would prefer the third version, since its pretty good readable.
But in our database we have some datetime columns which are defined as not null.
So in some cases I have to go with the first two options.

I read somewhere that the `default` keyword should be used when working with generics, but isn&#39;t it much more readable in this case? When using the second option I have to know that the default value of a new and empty DateTime instance is DateTime.MinValue which has the smell of an implementation detail for me.

So which option should I use to use &quot;best practice&quot;?


How to check for default DateTime value?

I need to check a <code>DateTime</code> value if it has a value or not.
I have several options:
<pre><code class="hljs language-ini">if (dateTime == default(DateTime))
</code></pre>
or
<pre><code class="hljs language-ini">if (dateTime == DateTime.MinValue)
</code></pre>
or using a nullable <code>DateTime?</code>
<pre><code class="hljs language-scss">if (nullableDateTime.HasValue)
</code></pre>
Personally I would prefer the third version, since its pretty good readable.
But in our database we have some datetime columns which are defined as not null.
So in some cases I have to go with the first two options.
I read somewhere that the <code>default</code> keyword should be used when working with generics, but isn't it much more readable in this case? When using the second option I have to know that the default value of a new and empty DateTime instance is DateTime.MinValue which has the smell of an implementation detail for me.
So which option should I use to use "best practice"?

In my web app I&#39;m using Newtonsoft.Json and I have following object

    [Newtonsoft.Json.JsonObject(Title = &quot;MyCar&quot;)]
    public class Car
    {
        [Newtonsoft.Json.JsonProperty(PropertyName = &quot;name&quot;)]
        public string Name{get;set;}

        [Newtonsoft.Json.JsonProperty(PropertyName = &quot;owner&quot;)]
        public string Owner{get;set;}
    }

and I want serialize them with root name (class name). This is desired format using 

    {&#39;MyCar&#39;:
     {
       &#39;name&#39;: &#39;Ford&#39;,
       &#39;owner&#39;: &#39;John Smith&#39;
     }
    }


I know that I can do that with anonymous object, but is any property or another way in Newtonsoft.Json library?

Json.NET serialize object with root name

The following code results in _use of unassigned local variable &quot;numberOfGroups&quot;_:

    int numberOfGroups;
    if(options.NumberOfGroups == null || !int.TryParse(options.NumberOfGroups, out numberOfGroups))
    {
        numberOfGroups = 10;
    }

However, this code works fine (though, [ReSharper][1] says the `= 10` is redundant):

    int numberOfGroups = 10;
    if(options.NumberOfGroups == null || !int.TryParse(options.NumberOfGroups, out numberOfGroups))
    {
        numberOfGroups = 10;
    }

Am I missing something, or is the compiler not liking my `||`?

I&#39;ve narrowed this down to `dynamic` causing the issues (`options` was a dynamic variable in my above code). The question still remains, **why can&#39;t I do this**?

This code *doesn&#39;t* compile:

	internal class Program
	{
		#region Static Methods

		private static void Main(string[] args)
		{
			dynamic myString = args[0];

			int myInt;
			if(myString == null || !int.TryParse(myString, out myInt))
			{
				myInt = 10;
			}

			Console.WriteLine(myInt);
		}

		#endregion
	}

However, this code *does*:

	internal class Program
	{
		#region Static Methods

		private static void Main(string[] args)
		{
			var myString = args[0]; // var would be string

			int myInt;
			if(myString == null || !int.TryParse(myString, out myInt))
			{
				myInt = 10;
			}

			Console.WriteLine(myInt);
		}

		#endregion
	}

I didn&#39;t realize `dynamic` would be a factor in this.

  [1]: http://en.wikipedia.org/wiki/ReSharper


Why does this (null || !TryParse) conditional result in &quot;use of unassigned local variable&quot;?

I&#39;m curious about the differences between calling a `Func&lt;T&gt;` directly vs. using `Invoke()` on it.  Is there a difference? Is the first syntactical sugar and calls `Invoke()` underneath anyway?

```c#
public T DoWork&lt;T&gt;(Func&lt;T&gt; method)
{
    return (T)method.Invoke();
}
```

vs.

```c#
public T DoWork&lt;T&gt;(Func&lt;T&gt; method)
{
    return (T)method();
}
```

Or am I on the wrong track entirely?

Func&lt;T&gt;() vs Func&lt;T&gt;.Invoke()

We had an issue where one developer creates the below code and it works on his DEV environment. But when it&#39;s checked into QA, the code breaks with the below error message:

    myRecord.UTCStartTime = TimeZoneInfo.ConvertTimeToUtc(myRecord.StartTime, myTimeZone);

&gt; The conversion could not be completed because the supplied DateTime
&gt; did not have the Kind property set correctly.  For example, when the
&gt; Kind property is DateTimeKind.Local, the source time zone must be
&gt; TimeZoneInfo.Local.


On my DEV environment, the above code generates the same error as the QA server. I applied the below change to fix the problem:

    DateTime utcStart = DateTime.SpecifyKind(myRecord.StartTime, DateTimeKind.Unspecified);
    myRecord.UTCStartTime = TimeZoneInfo.ConvertTimeToUtc(utcStart, myTimeZone);


Why does the first code example work on DEV1&#39;s environment but break on my DEV environment and on our QA server?


TimeZoneInfo.ConvertTimeToUtc issue

I understand why log4net uses `app.config` files for setting up logging - so you can easily change how information is logged without needing to recompile your code. But in my case I do not want to pack a `app.config` file with my executable. And I have no desire to modify my logging setup.

Is there a way for me to set up logging in code rather than using the `app.config`?

Here is my simple config file:

&lt;!-- language: xml --&gt;

    &lt;?xml version=&quot;1.0&quot; encoding=&quot;utf-8&quot; ?&gt;
    &lt;configuration&gt;
      &lt;configSections&gt;
        &lt;section name=&quot;log4net&quot; type=&quot;log4net.Config.Log4NetConfigurationSectionHandler, log4net&quot; /&gt;
      &lt;/configSections&gt;
      &lt;log4net&gt;
        &lt;appender name=&quot;RollingLogFileAppender&quot; type=&quot;log4net.Appender.RollingFileAppender&quot;&gt;
          &lt;file value=&quot;Logs\EventLog.txt&quot; /&gt;
          &lt;appendToFile value=&quot;false&quot; /&gt;
          &lt;rollingStyle value=&quot;Size&quot; /&gt;
          &lt;maxSizeRollBackups value=&quot;5&quot; /&gt;
          &lt;maximumFileSize value=&quot;1GB&quot; /&gt;
          &lt;layout type=&quot;log4net.Layout.PatternLayout&quot;&gt;
            &lt;conversionPattern value=&quot;%date [%thread] %-5level %logger - %message%newline&quot; /&gt;
          &lt;/layout&gt;
        &lt;/appender&gt;
        &lt;appender name=&quot;MemoryAppender&quot; type=&quot;log4net.Appender.MemoryAppender&quot;&gt;
        &lt;/appender&gt;
        &lt;root&gt;
          &lt;level value=&quot;Info&quot; /&gt;
          &lt;appender-ref ref=&quot;RollingLogFileAppender&quot; /&gt;
          &lt;appender-ref ref=&quot;MemoryAppender&quot; /&gt;
        &lt;/root&gt;
      &lt;/log4net&gt;
    &lt;/configuration&gt;

**EDIT:**

To be completely clear: It is my goal to have no XML file. Not even as an embedded resource that I turn into a stream. My goal was to define the logger completely programmatically. Just curious if it&#39;s possible and if so where I might find an example of the syntax.



Can you configure log4net in code instead of using a config file?

The VB.NET method `String.Join(separator, stringArray)` is similar to PHP&#39;s implode, but any null elements in the array are replaced with an empty string, so thatc:

    Dim myArray() as String = { &quot;a&quot;, null, &quot;c&quot; }
    Console.WriteLine(String.Join(&quot;, &quot;, myArray));
    // Prints &quot;a, , c&quot;

Is there a simple way to concatenate a set of strings with a separator that ignores empty strings? 

I don&#39;t necessarily need to use arrays or String.Join or anything else. I just need the following transformations:

    (&quot;a&quot;, &quot;b&quot;, &quot;c&quot;) --&gt; &quot;a, b, c&quot;
    (&quot;a&quot;, null, &quot;c&quot;) --&gt; &quot;a, c&quot;

String.Join method that ignores empty strings?

I want to know how much time a procedure/function/order takes to finish, for testing purposes.

This is what I did but my method is wrong &#39;cause if the difference of seconds is 0 can&#39;t return the elapsed milliseconds:

Notice the sleep value is 500 ms so elapsed seconds is 0 then it can&#39;t return milliseconds.

        Dim Execution_Start As System.DateTime = System.DateTime.Now
        Threading.Thread.Sleep(500)

        Dim Execution_End As System.DateTime = System.DateTime.Now
        MsgBox(String.Format(&quot;H:{0} M:{1} S:{2} MS:{3}&quot;, _
        DateDiff(DateInterval.Hour, Execution_Start, Execution_End), _
        DateDiff(DateInterval.Minute, Execution_Start, Execution_End), _
        DateDiff(DateInterval.Second, Execution_Start, Execution_End), _
        DateDiff(DateInterval.Second, Execution_Start, Execution_End) * 60))

Can someone show me a better way to do this? Maybe with a `TimeSpan`?

The solution:

    Dim Execution_Start As New Stopwatch
    Execution_Start.Start()

    Threading.Thread.Sleep(500)

    MessageBox.Show(&quot;H:&quot; &amp; Execution_Start.Elapsed.Hours &amp; vbNewLine &amp; _
           &quot;M:&quot; &amp; Execution_Start.Elapsed.Minutes &amp; vbNewLine &amp; _
           &quot;S:&quot; &amp; Execution_Start.Elapsed.Seconds &amp; vbNewLine &amp; _
           &quot;MS:&quot; &amp; Execution_Start.Elapsed.Milliseconds &amp; vbNewLine, _
           &quot;Code execution time&quot;, MessageBoxButtons.OK, MessageBoxIcon.Information)

Measuring code execution time

After doing a few Projects using the MVVM Pattern, Im still struggling with the Role of the ViewModel:

What I did in the past:
Using the Model only as a Data Container.
Putting the Logic to manipulate the Data in the ViewModel. (Thats the Business Logic right?)
Con: Logic is not reusable.

What I&#39;m trying now:
Keeping the ViewModel as thin as possible.
Moving all Logic into the Model Layer.
Only keeping presentation Logic in the ViewModel.
Con: Makes UI Notification realy painful If Data is Changed inside the Model Layer.


So I will  give you an Example to make it more clearer:

Scenario:
Tool to Rename Files. 
Classes:
File : Representing each File;
Rule: Contains Logic how to Rename a File;

If Im following approach 1:
Creating a ViewModel for File, Rule and the View -&gt; RenamerViewModel.
Putting all Logic in the RenamerViewModel: 
Containing a List of FileViewModel and RuleViewModel and the proceeding Logic.
Easy and fast, but not reusable.

If Im following approach 2:
Creating a new Model Class -&gt; Renamer, which contains a List of File, Rule und the proceeding Logic to interate over each File and apply each Rule.
Creating a Viewmodel for File, Rule and Renamer.
Now the RenamerViewModel only contains an instance of Renamer Model, plus two ObservableCollections to wrap the File und Rule List of the Renamer.
But the whole Logic is in the Renamer Model. So if the Renamer Model is triggered to manipulate some Data by Method Calls, the ViewModel has no Clue which Data is manipulated.
Because the Model doesnt Contain any PropertyChange Notification and I will avoid that.
So the Business and Presentation Logic is seperated, but this makes it hard to notify the UI.





MVVM: ViewModel and Business Logic Connection

## The Problem

This answer has been answered before but are old and not up to date. I have over 2000 lines of code in a single file, and as we all know this is bad practice, especially when i&#39;m looking through code or adding new features. I want to better organize my code, for now and for the future. 

I should mention that I&#39;m building a tool (not a simple website) with lots of buttons, UI elements, drag, drops, action listeners/handlers and function in the global scope where several listeners may use the same function.

### Example code

    $(&#39;#button1&#39;).on(&#39;click&#39;, function(e){
        // Determined action.
        update_html();
    });

    ... // Around 75 more of this

    function update_html(){ .... }

    ...

[More example code](http://pastebin.com/PrbwanNZ) 

### Conclusion

I really need to organize this code for best use and not to repeat myself and be able to add new features and update old ones. I will be working on this by myself. Some selectors can be 100 lines of code others are 1. I have looked a bit at `require.js` and found it kinda repetitive, and actually writing more code than needed . I&#39;m open to any possible solution that fit this criteria and link to resource / examples are always a plus.

Thanks.

Best way to organize jQuery/JavaScript code (2013)

I have a class called `Writer` that has a function `writeVector` like so:

    void Drawer::writeVector(vector&lt;T&gt; vec, bool index=true)
    {
        for (unsigned int i = 0; i &lt; vec.size(); i++) {
            if (index) {
                cout &lt;&lt; i &lt;&lt; &quot;\t&quot;;
            }
            cout &lt;&lt; vec[i] &lt;&lt; &quot;\n&quot;;
        }
    }

I&#39;m trying not to have a duplicate code, while still worrying about the performance.
In the function, I&#39;m doing the `if (index)` check on every round of my `for`-loop, even though the result is always the same.
This is against &quot;worrying about the performance&quot;.

I could easily avoid this by placing the check outside of my `for`-loop.
However, I&#39;ll get loads of duplicate code:

    void Drawer::writeVector(...)
    {
        if (index) {
            for (...) {
                cout &lt;&lt; i &lt;&lt; &quot;\t&quot; &lt;&lt; vec[i] &lt;&lt; &quot;\n&quot;;
            }
        }
        else {
            for (...) {
                cout &lt;&lt; vec[i] &lt;&lt; &quot;\n&quot;;
            }
        }
    }

So these are both &quot;bad&quot; solutions for me.
What I&#39;ve been thinking, is two private functions, one of them outs the index and then calls the other.
The other one only outs the value.
However, I can&#39;t figure out how to use it with my program, I&#39;d still need the `if` check to see which one to call...

According to the problem, polymorphism seems like a correct solution.
But I can&#39;t see how should I use it here.
What would be the preferred way to solve this kind of problem?

This is not a real program, **I&#39;m just interested in learning how this kind of problem should be solved.**

Avoiding if statement inside a for loop?

Give [this Dr Dobbs article](http://www.drdobbs.com/jvm/creating-and-destroying-java-objects-par/208403883?pgno=2), and the Builder Pattern in particular, how do we handle the case of subclassing a Builder? Taking a cut-down version of the example where we want to subclass to add GMO labelling, a naive implementation would be:

    public class NutritionFacts {                                                                                                    
                                                                                                                                     
        private final int calories;                                                                                                  
                                                                                                                                     
        public static class Builder {                                                                                                
            private int calories = 0;                                                                                                
                                                                                                                                     
            public Builder() {}                                                                                                      
                                                                                                                                     
            public Builder calories(int val) { calories = val; return this; }                                                                                                                        
                                                                                                                                     
            public NutritionFacts build() { return new NutritionFacts(this); }                                                       
        }                                                                                                                            
                                                                                                                                     
        protected NutritionFacts(Builder builder) {                                                                                  
            calories = builder.calories;                                                                                             
        }                                                                                                                            
    }

Subclass:

    public class GMOFacts extends NutritionFacts {                                                                                   
                                                                                                                                     
        private final boolean hasGMO;                                                                                                
                                                                                                                                     
        public static class Builder extends NutritionFacts.Builder {                                                                 
                                                                                                                                     
            private boolean hasGMO = false;                                                                                          
                                                                                                                                     
            public Builder() {}                                                                                                      
                                                                                                                                     
            public Builder GMO(boolean val) { hasGMO = val; return this; }                                                           
                                                                                                                                     
            public GMOFacts build() { return new GMOFacts(this); }                                                                   
        }                                                                                                                            
                                                                                                                                     
        protected GMOFacts(Builder builder) {                                                                                        
            super(builder);                                                                                                          
            hasGMO = builder.hasGMO;                                                                                                 
        }                                                                                                                            
    }


Now, we can write code like this:

    GMOFacts.Builder b = new GMOFacts.Builder();
    b.GMO(true).calories(100);

But, if we get the order wrong, it all fails:

    GMOFacts.Builder b = new GMOFacts.Builder();
    b.calories(100).GMO(true);

The problem is of course that `NutritionFacts.Builder` returns a `NutritionFacts.Builder`, not a `GMOFacts.Builder`, so how do we solve this problem, or is there a better Pattern to use?

Note: [this answer to a similar question](https://stackoverflow.com/a/10092517/1270789) offers up the classes I have above; my question is regarding the problem of ensuring the builder calls are in the correct order.



Subclassing a Java Builder class

I have been reading a lot about Singletons, when they should and shouldn&#39;t be used, and how to implement them safely.  I am writing in C++11, and have come across the Meyer&#39;s lazy initialized implementation of a singleton, as seen in [this question.][1]

This implementation is:

    static Singleton&amp; instance()
    {
         static Singleton s;
         return s;
    }

I understand how this is thread safe from other questions here on SO, but what I don&#39;t understand is how this is actually a singleton pattern.  I have implemented singletons in other languages, and these always end up something like this example from [Wikipedia][2]:

    public class SingletonDemo {
            private static volatile SingletonDemo instance = null;
     
            private SingletonDemo() {       }
     
            public static SingletonDemo getInstance() {
                    if (instance == null) {
                            synchronized (SingletonDemo .class){
                                    if (instance == null) {
                                            instance = new SingletonDemo ();
                                    }
                          }
                    }
                    return instance;
            }
    }

When I look at this second example, it is very intuitive how this is a singleton, since the class holds a reference to one instance of itself, and only ever returns that instance.  However, in the first example, I don&#39;t understand how this prevents there ever existing two instances of the object.  So my questions are:

 1. How does the first implementation enforce a singleton pattern?  I assume it has to do with the static keyword, but I am hoping that someone can explain to me in depth what is happening under the hood.
 2. Between these two implementation styles, is one preferable over the other? What are the pros and cons?

Thanks for any help,

  [1]: https://stackoverflow.com/questions/1661529/is-meyers-implementation-of-singleton-pattern-thread-safe
  [2]: http://en.wikipedia.org/wiki/Singleton_pattern

Content Type	Original Author	Original Content on Stackoverflow
Question	dasheddot	View Question on Stackoverflow
Solution 1 - C#	Jon Skeet	View Answer on Stackoverflow
Solution 2 - C#	LukeH	View Answer on Stackoverflow
Solution 3 - C#	Igal Tabachnik	View Answer on Stackoverflow
Solution 4 - C#	Kuzgun	View Answer on Stackoverflow

How to check for default DateTime value?

C# Problem Overview

C# Solutions

Solution 1 - C#

Solution 2 - C#

Solution 3 - C#

Solution 4 - C#

Nesting <a> inside <button> doesn't work in Firefox

Connect to a Database in Flask, Which Approach is better?

Attributions