Tutorial by Examples: reat

Many-to-One Relationship from django.db import models class Author(models.Model): name = models.CharField(max_length=50) #Book has a foreignkey (many to one) relationship with author class Book(models.Model): author = models.ForeignKey(Author, on_delete=models.CASCADE) publish_...

Many C interfaces such as SDL2 have their own deletion functions. This means that you cannot use smart pointers directly: std::unique_ptr<SDL_Surface> a; // won't work, UNSAFE! Instead, you need to define your own deleter. The examples here use the SDL_Surface structure which should be fre...

You can create an ordered dictionary which will follow a determined order when iterating over the keys in the dictionary. Use OrderedDict from the collections module. This will always return the dictionary elements in the original insertion order when iterated over. from collections import Ordere...

After following the instructions above and installing Leiningen, start a new project by running: lein new <project-name> This will setup a Clojure project with the default Leiningen template within the <project-name> folder. There are several templates for Leiningen, which affect the...

// This example creates a macro `set!` that functions similarly to the built-in // macro vec! use std::collections::HashSet; macro_rules! set { ( $( $x:expr ),* ) => { // Match zero or more comma delimited items { let mut temp_set = HashSet::new(); // Create a ...

Generally speaking, empty commits (or commits with state that is identical to the parent) is an error. However, when testing build hooks, CI systems, and other systems that trigger off a commit, it's handy to be able to easily create commits without having to edit/touch a dummy file. The --allow-e...

The following will create dist/output.jar from the source code in src and the libraries in lib, and will use src/Main.java as the main class. <project name="Project" default="main" basedir="."> <property name="src.dir" value="src&quot...

// View to hold the CAGradientLayer. let view: UIView = UIView(frame: CGRect(x: 0, y: 0, width: 320, height: 320)) // Initialize gradient layer. let gradientLayer: CAGradientLayer = CAGradientLayer() // Set frame of gradient layer. gradientLayer.frame = view.bounds // Color a...

// View to hold the CAGradientLayer. let view: UIView = UIView(frame: CGRect(x: 0, y: 0, width: 320, height: 320)) // Initialize gradient layer. let gradientLayer: CAGradientLayer = CAGradientLayer() // Set frame of gradient layer. gradientLayer.frame = view.bounds // Color at the top of...

// View to hold the CAGradientLayer. let view: UIView = UIView(frame: CGRect(x: 0, y: 0, width: 320, height: 320)) // Initialize gradient layer. let gradientLayer: CAGradientLayer = CAGradientLayer() // Set frame of gradient layer. gradientLayer.frame = view.bounds // Color at the top of...

Empty array np.empty((2,3)) Note that in this case, the values in this array are not set. This way of creating an array is therefore only useful if the array is filled later in the code. From a list np.array([0,1,2,3]) # Out: array([0, 1, 2, 3]) Create a range np.arange(4) # Out: array(...

In the Web App blade of the Azure Portal, click All settings > WebJobs to show the WebJobs blade: Click Add. The Add WebJob dialog appears. Under Name, provide a name for the WebJob. The name must start with a letter or a number and cannot contain any special characters other than...

This example comes from the official document. Suppose you have a python application using redis as backend. After writing Dockerfile, create a docker-compose.yml file like this: version: '2' services: web: build: . ports: - "5000:5000" volumes: - .:/code ...

This example shows how to create a simple notification that starts an application when the user clicks it. Specify the notification's content: NotificationCompat.Builder mBuilder = new NotificationCompat.Builder(this) .setSmallIcon(R.drawable.ic_launcher) // notification icon .se...

The following (trivial) example function simply returns the constant INT value 12. DELIMITER || CREATE FUNCTION functionname() RETURNS INT BEGIN RETURN 12; END; || DELIMITER ; The first line defines what the delimiter character(DELIMITER ||) is to be changed to, this is needed to be s...

You can restrict the valid types used in a generic class by bounding that type in the class definition. Given the following simple type hierarchy: public abstract class Animal { public abstract String getSound(); } public class Cat extends Animal { public String getSound() { ...

On the server, you can create a publication like this. this.userId is the id of the user who is currently logged in. If no user is logged in, you might want to throw an error and respond to it. import Secrets from '/imports/collections/Secrets'; Meteor.publish('protected_data', function () { ...

Swift 3 let stackView = UIStackView() stackView.axis = .horizontal stackView.alignment = .fill // .leading .firstBaseline .center .trailing .lastBaseline stackView.distribution = .fill // .fillEqually .fillProportionally .equalSpacing .equalCentering let label = UILabel() label.text = "...

Swift let stackView = UIStackView() stackView.axis = .Vertical stackView.alignment = .Fill // .Leading .FirstBaseline .Center .Trailing .LastBaseline stackView.distribution = .Fill // .FillEqually .FillProportionally .EqualSpacing .EqualCentering let label = UILabel(frame: CGRectZero) label....

A tbl_df (pronounced tibble diff) is a variation of a data frame that is often used in tidyverse packages. It is implemented in the tibble package. Use the as_data_frame function to turn a data frame into a tbl_df: library(tibble) mtcars_tbl <- as_data_frame(mtcars) One of the most notable ...