Tutorial by Examples: an

First off, let's assume this is your initial model, inside an application called discography: from django.db import models class Album(models.Model): name = models.CharField(max_length=255) artist = models.CharField(max_length=255) Now, you realize that you want to use a ForeignKey ...

The BigInteger class has a constructor dedicated to generate random BigIntegers, given an instance of java.util.Random and an int that specifies how many bits will the BigInteger have. Its usage is quite simple - when you call the constructor BigInteger(int, Random) like this: BigInteger randomBigI...

By utilizing the pre_save we can determine if a save action on our database was about updating an existing object or creating a new one. In order to achieve this you can check the state of the model object: @receiver(pre_save, sender=User) def pre_save_user(sender, instance, **kwargs): ...

Objective-C Add the delegate and a text-formatter to the ViewController.h file @interface ViewController : UIViewController <UIPrintInteractionControllerDelegate> { UISimpleTextPrintFormatter *_textFormatter; } In the ViewController.m file define the following constants #define Def...

Consider this example: private void button1_Click(object sender, EventArgs e) { label1.Text = RunTooLong(); } This method will freeze UI application until the RunTooLong will be completed. The application will be unresponsive. You can try run inner code asynchronously: private void butt...

The members of a union share the same space in memory. This means that writing to one member overwrites the data in all other members and that reading from one member results in the same data as reading from all other members. However, because union members can have differing types and sizes, the da...

Catalan numbers algorithm is Dynamic Programming algorithm. In combinatorial mathematics, the Catalan numbers form a sequence of natural numbers that occur in various counting problems, often involving recursively-defined objects. The Catalan numbers on nonnegative integers n are a set of numbers t...

Suppose, that we have three users : The Administrator of the database > admin The application with a full access for her data > read_write The read only access > read_only With below queries, you can set access privileges on objects created in the future in specified schema. ALTER ...

If you're Using VueJS2 and like to use JSX along with it. In this case,to use the slot, the solution with example is below.We have to use this.$slots.default It's almost like this.props.children in React JS. Component.js : export default { render(h) { //eslint-disable-line return ( ...

Installation $ npm install gulp-jslint --save-dev Usage In gulpfile.js add: var gulp = require('gulp'); var jslint = require('gulp-jslint'); gulp.task('lint', function(){ return gulp.src(['source.js']) .pipe(jslint({ /* this object represents the JSLint directives being passe...

Aggregation is used to perform complex data search operations in the mongo query which can't be done in normal "find" query. Create some dummy data: db.employees.insert({"name":"Adma","dept":"Admin","languages":["german","f...

This is an example code to create and execute the aggregate query in MongoDB using Spring Data. try { MongoClient mongo = new MongoClient(); DB db = mongo.getDB("so"); DBCollection coll = db.getCollection("employees"); //Equivalent to $m...

In this Example we are going to take a sqaure shaped line plotted using line and perform transformations on it. Then we are going to use the same tranformations but in different order and see how it influences the results. First we open a figure and set some initial parameters (square point coordin...

By default, PHP Curl supports GET and POST requests. It is possible to also send custom requests, such as DELETE, PUT or PATCH (or even non-standard methods) using the CURLOPT_CUSTOMREQUEST parameter. $method = 'DELETE'; // Create a DELETE request $ch = curl_init($url); curl_setopt($ch, CURLOPT...

Assuming a default server running on localhost with the default port, the command to connect to that Redis server would be: $redis = new Redis(); $redis->connect('127.0.0.1', 6379);

The Redis PHP module gives access to the same commands as the Redis CLI client so it is quite straightforward to use. The syntax is as follow: // Creates two new keys: $redis->set('mykey-1', 123); $redis->set('mykey-2', 'abcd'); // Gets one key (prints '123') var_dump($redis->get('m...

For small functions that get called often, the overhead associated with the function call can be a significant fraction of the total execution time of that function. One way of improving performance, then, is to eliminate the overhead. In this example we use four functions (plus main()) in three so...

Go to the [https://developers.facebook.com/](https://developers.facebook.com/) and create your app. Click Add product and choose Facebook Login

Add button Login as facebook account to your login view: Edit site/login.php in views folder, add theses line to content of page login: <?= yii\authclient\widgets\AuthChoice::widget([ 'baseAuthUrl' => ['site/auth'], 'popupMode' => false, ]) ?> Above, we set that aut...

We need to create a container to mount the volume. Then archive it and download the archive to our host. Let's create first a data volume with some data: docker volume create --name=data echo "Hello World" | docker run -i --rm=true -v data:/data ubuntu:trusty tee /data/hello.txt Let...