Tutorial by Examples: re

CommandDescriptionaAppend text following current cursor positionAAppend text at the end of current lineiInsert text before the current cursor positionIInsert text before first non-blank character of current linegIInsert text in first column of cursor linegiInsert text at same position where it was l...

To create a join table between students and courses, run the command: $ rails g migration CreateJoinTableStudentCourse student course This will generate the following migration: class CreateJoinTableStudentCourse < ActiveRecord::Migration[5.0] def change create_join_table :students, ...

To run migrations in the test environment, run this shell command: rake db:migrate RAILS_ENV=test 5.0 Starting in Rails 5.0, you can use rails instead of rake: rails db:migrate RAILS_ENV=test

To remove existing column name from users table, run the command: rails generate migration RemoveNameFromUsers name:string This will generate the following migration: class RemoveNameFromUsers < ActiveRecord::Migration[5.0] def change remove_column :users, :name, :string end end ...

To add a reference to a team to the users table, run this command: $ rails generate migration AddTeamRefToUsers team:references This generates the following migration: class AddTeamRefToUsers < ActiveRecord::Migration[5.0] def change add_reference :users, :team, foreign_key: true ...

To create a new users table with the columns name and salary, run the command: rails generate migration CreateUsers name:string salary:decimal This will generate the following migration: class CreateUsers < ActiveRecord::Migration[5.0] def change create_table :users do |t| t.s...

Say you want to perform in action (in this case, logging "Foo"), while doing something else (logging "Bar"). Normally, if you don't use concurrency, one of these actions is going to be fully executed, and the other run will run only after it's completely finished. But with concur...

Factors are one way to represent categorical variables in R. A factor is stored internally as a vector of integers. The unique elements of the supplied character vector are known as the levels of the factor. By default, if the levels are not supplied by the user, then R will generate the set of uniq...

When a column name matches a reserved keyword, standard SQL requires that you enclose it in double quotation marks: SELECT "ORDER", ID FROM ORDERS Note that it makes the column name case-sensitive. Some DBMSes have proprietary ways of quoting names. For example, SQL Serve...

This will delete all rows that match the WHERE criteria. DELETE FROM Employees WHERE FName = 'John'

It's a bad idea to hard code paths in your application. One should always use relative urls so that your code can work seamlessly across different machines. The best way to set this up is to define a variable like this import os BASE_DIR = os.path.dirname(os.path.dirname(__file__)) Then use th...

This snippet will grab a JSON formatted resource, decode it and print it in PHP array format. // Fetch $response = wp_remote_get( 'http://www.example.com/resource.json' ); if ( ! is_wp_error( $response ) ) { $headers = wp_remote_retrieve_headers( $response ); if ( isset( $headers[ 'con...

Database seeds are stored in the /database/seeds directory. You can create a seed using an Artisan command. php artisan make:seed UserTableSeeder Alternatively you can create a new class which extends Illuminate\Database\Seeder. The class must a public function named run().

Structure data types are useful way to package related data and have them behave like a single variable. Declaring a simple struct that holds two int members: struct point { int x; int y; }; x and y are called the members (or fields) of point struct. Defining and using structs: ...

While the Java Date class has several constructors, you'll notice that most are deprecated. The only acceptable way of creating a Date instance directly is either by using the empty constructor or passing in a long (number of milliseconds since standard base time). Neither are handy unless you're lo...

// The Option type can either contain Some value or None. fn find(value: i32, slice: &[i32]) -> Option<usize> { for (index, &element) in slice.iter().enumerate() { if element == value { // Return a value (wrapped in Some). return Some(index);...

Inject and reduce are different names for the same thing. In other languages these functions are often called folds (like foldl or foldr). These methods are available on every Enumerable object. Inject takes a two argument function and applies that to all of the pairs of elements in the Array. For...

Here is an example of a service that greets people by the given name, and keeps track of how many users it encountered. See usage below. %% greeter.erl %% Greets people and counts number of times it did so. -module(greeter). -behaviour(gen_server). %% Export API Functions -export([start_link/0...

It is possible to release dynamically allocated memory by calling free(). int *p = malloc(10 * sizeof *p); /* allocation of memory */ if (p == NULL) { perror("malloc failed"); return -1; } free(p); /* release of memory */ /* note that after free(p), even using the *value...

We are going to be showing how to make a GET request to an API that responds with a JSON object or a JSON array. The first thing we need to do is add the Retrofit and GSON Converter dependencies to our module's gradle file. Add the dependencies for retrofit library as described in the Remarks secti...