Tutorial by Examples: di

Some teams find that they want to leave console log statements in their code, but not have them display in production. They will override the logging functions if a variable isn't set (possibly an environment variable). Additionally, this may qualify as a security feature in some situations. if (...

SELECT DISTINCT ContinentCode FROM Countries; This query will return all DISTINCT (unique, different) values from ContinentCode column from Countries table ContinentCodeOCEUASNAAF SQLFiddle Demo

In the assets initalizer (config/initializers/assets.rb) are a few files explicitly defined to be precompiled. # Precompile additional assets. # application.coffee, application.scss, and all non-JS/CSS in app/assets folder are already added. # Rails.application.config.assets.precompile += %w( sea...

If you want to remove duplicates from a result, you can use .distinct(): Customers.select(:country).distinct This queries the database as follows: SELECT DISTINCT "customers"."country" FROM "customers" .uniq() has the same effect. With Rails 5.0 it got deprecate...

When reading tabular datasets with the read.* functions, R automatically looks for missing values that look like "NA". However, missing values are not always represented by NA. Sometimes a dot (.), a hyphen(-) or a character-value (e.g.: empty) indicates that a value is NA. The na.strings ...

The symbol NA is for a logical missing value: class(NA) #[1] "logical" This is convenient, since it can easily be coerced to other atomic vector types, and is therefore usually the only NA you will need: x <- c(1, NA, 1) class(x[2]) #[1] "numeric" If you do need a s...

DatePickerDialog is the simplest way to use DatePicker, because you can show dialog anywhere in your app. You don't have to implement your own layout with DatePicker widget. How to show dialog: DatePickerDialog datePickerDialog = new DatePickerDialog(context, listener, year, month, day); datePick...

To use multiple databases in Django, just specify each one in settings.py: DATABASES = { 'default': { 'NAME': 'app_data', 'ENGINE': 'django.db.backends.postgresql', 'USER': 'django_db_user', 'PASSWORD': os.environ['LOCAL_DB_PASSWORD'] }, 'users': {...

The normal obj.save() method will use the default database, or if a database router is used, it will use the database as specified in db_for_write. You can override it by using: obj.save(using='other_db') obj.delete(using='other_db') Similarly, for reading: MyModel.objects.using('other_db').al...

The special LOOP NAMED foo syntax allows you to create a loop that you can exit early from. The exit is performed using return-from, and can be used from within nested loops. The following uses a nested loop to look for a complex number in a 2D array: (loop named top for x from 0 below (arr...

Encoding and decoding functions for a variety of Unicode encodings can be found in the Data.Text.Encoding module. ghci> import Data.Text.Encoding ghci> decodeUtf8 (encodeUtf8 "my text") "my text" Note that decodeUtf8 will throw an exception on invalid input. If you wa...

The :l or :load command type-checks and loads a file. $ echo "f = putStrLn \"example\"" > example.hs $ ghci GHCi, version 8.0.1: http://www.haskell.org/ghc/ :? for help ghci> :l example.hs [1 of 1] Compiling Main ( example.hs, interpreted ) Ok, modules ...

You can apply the same change shown in the Index Settings example to all existing indices with one request, or even a subset of them: PUT /*/_settings { "index": { "indexing.slowlog.threshold.index.warn": "1s", "search.slowlog.threshold": { ...

Input must must read from the Update function. Reference for all the available Keycode enum. 1. Reading key press with Input.GetKey: Input.GetKey will repeatedly return true while the user holds down the specified key. This can be used to repeatedly fire a weapon while holding the specified key ...

Often you design coroutines to naturally end when certain goals are met. IEnumerator TickFiveSeconds() { var wait = new WaitForSeconds(1f); int counter = 1; while(counter < 5) { Debug.Log("Tick"); counter++; yield return wait; } ...

Use appearanceWhenContainedInInstancesOfClasses: to customize the appearance for instance of a class when contained within an instance of container class. For example customization of UILabel's textColor and backgroundColor within ViewController class will look like this: Set UILabel text color Sw...

Editing or updating a resource is a common purpose for APIs. Edits can be achieved by sending either POST, PUT or PATCH requests to the respective resource. Although POST is allowed to append data to a resource's existing representation it is recommended to use either PUT or PATCH as they convey a m...

A cross-origin request must be sent including the Origin header. This indicates from where the request originated. For example, a cross-origin request from http://example.com to http://example.org would look like this: GET /cors HTTP/1.1 Host: example.org Origin: example.com The server will us...

The response to a CORS request must include an Access-Control-Allow-Origin header, which dictates what origins are allowed to use the CORS resource. This header can take one of three values: An origin. Doing this permits requests from that origin only. The character *. This permits requests from...

When a server receives a preflight request, it must check if it supports the requested method and headers, and send back a response that indicates its ability to support the request, as well as any other permitted data (such as credentials). These are indicated in access-control Allow headers. The ...