In an optimistic update the UI behaves as though a change was successfully completed before receiving confirmation from the server that it actually was - it is being optimistic that it will eventually get the confirmation rather than an error. This allows for a more responsive user experience. 

As mentioned in [many][1] [other locations][2] on the web, adding a new column to an existing DataFrame is not straightforward. Unfortunately it is important to have this functionality (even though it is inefficient in a distributed environment) especially when trying to concatenate two `DataFrame`s using `unionAll`.

What is the most elegant workaround for adding a `null` column to a `DataFrame` to facilitate a `unionAll`?

My version goes like this:

    from pyspark.sql.types import StringType
    from pyspark.sql.functions import UserDefinedFunction
    to_none = UserDefinedFunction(lambda x: None, StringType())
    new_df = old_df.withColumn(&#39;new_column&#39;, to_none(df_old[&#39;any_col_from_old&#39;]))



  [1]: https://stackoverflow.com/questions/29483498/append-a-column-to-data-frame-in-apache-spark-1-3
  [2]: http://apache-spark-user-list.1001560.n3.nabble.com/Append-column-to-Data-Frame-or-RDD-td22385.html

Add an empty column to Spark DataFrame

Following is my file *2015_09_14_051851_create_orders_table.php*.
And I want to change `$table-&gt;integer(&#39;category_id&#39;);` as a string with new migration.


    &lt;?php
    
    use Illuminate\Database\Schema\Blueprint;
    use Illuminate\Database\Migrations\Migration;
    
    class CreateOrdersTable extends Migration {
    
    	/**
    	 * Run the migrations.
    	 *
    	 * @return void
    	 */
    	public function up()
    	{
    		Schema::create(&#39;orders&#39;, function(Blueprint $table)
    		{
    			$table-&gt;increments(&#39;id&#39;);
    			$table-&gt;string(&#39;num&#39;);
    			$table-&gt;integer(&#39;user_id&#39;);
    
    			$table-&gt;text(&#39;store_name&#39;);
    			$table-&gt;integer(&#39;store_name_publication&#39;);
    
    			$table-&gt;string(&#39;postal_code&#39;, 255);
    			$table-&gt;string(&#39;phone_number&#39;, 255);
    
    			$table-&gt;text(&#39;title&#39;);
    			$table-&gt;text(&#39;description&#39;);
    
    			$table-&gt;string(&#39;list_image_filename1&#39;, 255);
    			$table-&gt;string(&#39;list_image_filename2&#39;, 255)-&gt;nullable();
    			$table-&gt;string(&#39;list_image_filename3&#39;, 255)-&gt;nullable();
    			$table-&gt;string(&#39;list_image_filename4&#39;, 255)-&gt;nullable();
    			$table-&gt;string(&#39;list_image_filename5&#39;, 255)-&gt;nullable();
    
    			$table-&gt;integer(&#39;term&#39;);
    
    			$table-&gt;datetime(&#39;state0_at&#39;)-&gt;nullable();
    			$table-&gt;datetime(&#39;state1_at&#39;)-&gt;nullable();
    			$table-&gt;datetime(&#39;state2_at&#39;)-&gt;nullable();
    			$table-&gt;datetime(&#39;state3_at&#39;)-&gt;nullable();
    			$table-&gt;datetime(&#39;state4_at&#39;)-&gt;nullable();
    			$table-&gt;datetime(&#39;state5_at&#39;)-&gt;nullable();
    			$table-&gt;datetime(&#39;state6_at&#39;)-&gt;nullable();
    			$table-&gt;datetime(&#39;state7_at&#39;)-&gt;nullable();
    			$table-&gt;datetime(&#39;state8_at&#39;)-&gt;nullable();
    			$table-&gt;datetime(&#39;state9_at&#39;)-&gt;nullable();
    			$table-&gt;datetime(&#39;state10_at&#39;)-&gt;nullable();
    
    			$table-&gt;integer(&#39;category_id&#39;);
    			$table-&gt;integer(&#39;target_customer_sex&#39;);
    			$table-&gt;integer(&#39;target_customer_age&#39;);
    
    			$table-&gt;integer(&#39;payment_order&#39;);
    			$table-&gt;integer(&#39;num_comment&#39;);
    			$table-&gt;integer(&#39;num_view&#39;);
    			$table-&gt;string(&#39;num_pop&#39;);
    
    			$table-&gt;integer(&#39;money&#39;);
    			$table-&gt;integer(&#39;point&#39;);
    
    			$table-&gt;datetime(&#39;closed_at&#39;);
    			$table-&gt;timestamps();
    			$table-&gt;softDeletes();
    		});
    	}
    
    	/**
    	 * Reverse the migrations.
    	 *
    	 * @return void
    	 */
    	public function down()
    	{
    		Schema::drop(&#39;orders&#39;);
    	}
    
    }

Laravel migration table field&#39;s type change

I&#39;m reading the [intro to `redux` pattern](https://redux.js.org/introduction/motivation), and there is the following paragraph there:

&gt; ... consider the new requirements becoming common in front-end product
&gt; development, such as handling optimistic updates, rendering on the
&gt; server, fetching data before performing route transitions, and so on.

My question is what is *optimistic updates* here?

what is `optimistic updates` in front-end development

I'm reading the <a href="https://redux.js.org/introduction/motivation" target="_blank" rel="noopener noreferrer">intro to <code>redux</code> pattern</a>, and there is the following paragraph there:
> ... consider the new requirements becoming common in front-end product
> development, such as handling optimistic updates, rendering on the
> server, fetching data before performing route transitions, and so on.
My question is what is optimistic updates here?

I am writing RESTful services using spring and hibernate. I read many resource in internet, but they did not clarify my doubts. Please explain me in details what are *DAO*, *DTO* and *Service* layers in spring framework? And why usage of these layers is required in spring to develop RESTfull API services.

What are the DAO, DTO and Service layers in Spring Framework?

What is an Interactor? How does it fit within the MVP Design? What are the advantages/disadvantages of using an interactor vs putting the interactor code in the presenter?

Android MVP: What is an Interactor?

Hi I am a newbie in the Kotlin world. I like what I see so far and started to think to convert some of our libraries we use in our application from Java to Kotlin.

These libraries are full of Pojos with setters, getters and Builder classes. Now I have googled to find what is the best way to implement Builders in Kotlin but no success.

2nd Update: The question is how to write a Builder design-pattern for a simple pojo with some parameters in Kotlin? The code below is my attempt by writing java code and then using the eclipse-kotlin-plugin to convert to Kotlin.

    class Car private constructor(builder:Car.Builder) {
	    var model:String? = null
	    var year:Int = 0
	    init {
		    this.model = builder.model
		    this.year = builder.year
	    }
	    companion object Builder {
		    var model:String? = null
		    private set
		
		    var year:Int = 0
		    private set
		
		    fun model(model:String):Builder {
			    this.model = model
			    return this
		    }
		    fun year(year:Int):Builder {
			    this.year = year
			    return this
		    }
		    fun build():Car {
			    val car = Car(this)
			    return car
		    }
	    }
    }


How to implement Builder pattern in Kotlin?

Angular 1.x (AngularJS) was following more or less the MV* design principle because of its two-way data binding functionality.

Angular2 is adopting a component-based UI, a concept that might be familiar to React developers. In a sense, the Angular 1.x controllers and directives blur into the new Angular 2 Component.

This means that in Angular 2 there are no controllers and no directives. Instead, a component has a selector which corresponds to the html tag that the component will represent and a @View to specify an HTML template for the component to populate.

Angular2 still implements two-way data-binding but does not consist of models for example if I have a `@Component` that displays a list of articles and a `class` that defines the article object:

    class Article {
    title: string;
    link: string;
    votes: number;

    constructor(title: string, link: string, votes?: number){
        this.title = title;
        this.link = link;
        this.votes = votes || 0;
    }

This, in the MVC pattern would be considered the model.

So considering this what design pattern does `Angular` follow the closest?

  

Angular design pattern: MVC, MVVM or MV*?

I am starting to look into Laravel but I don&#39;t understand the concept of Service Container.

How does it work and what do developers need to know to fully utilize this concept in Laravel?

Content Type	Original Author	Original Content on Stackoverflow
Question	Max Koretskyi	View Question on Stackoverflow
Solution 1 - Design Patterns	doublesharp	View Answer on Stackoverflow

what is `optimistic updates` in front-end development

Design Patterns Problem Overview

Design Patterns Solutions

Solution 1 - Design Patterns

Laravel migration table field's type change

Add an empty column to Spark DataFrame

Attributions