Hongbo Zhen bobzhen

Participants should have a recent version of Node.js installed on their system (preferably the latest LTS version, which is 6.9.1 as of this writing—but anything from 0.10 on should work). Participants should clone the following repositories and run npm install in each of them prior to the start of the workshop.

Optional: It might be helpful to install Electron globally so that you can use it from the command line in case there are any issues with any of the dependencies in the project above. You can install this through npm install -g electron.

Finally, debugging the main process is easiest using Visual Studio Code, which is available for all platforms (Windows, Linux, and macOS). This is not a hard requirement, but helpful if you'd like to follow along for that small segment of the workshop.

Optimistic Locking assumes that a database transaction conflict is very rare to happen. It uses a version number of the record to track the changes. It raise an error when other user tries to update the record while it is lock.

usage

Just add a lock_version column to the table you want to place the lock and Rails will automatically check this column before updating the record.

Pessimistic locking assumes that database transaction conflict is very likely to happen. It locks the record until the transaction is done. If the record is currently lock and the other user make a transaction, that second transaction will wait until the lock in first transaction is release.

usage

Realtime Notifications with ActionCable

In this episode we're going to be adding realtime notifications into your app using ActionCable. We've talked about notifications a few times in the past and we used AJAX polling for that. 95% of the time, polling is the solution that would be recommended for it.

But if you're looking for a good introduction into ActionCable then this is a decent one because we're only really using it for one way from the server side to the client side.

Getting started

So to get started we're starting with an app that has Bootstrap installed and then we created a Main controller with an index view which is where we will list our Notifications as for this example.

Before we generate our channels let's install a few things

Install wkhtmltopdf on Ubuntu

This was tested on:

Ubuntu 14.04 x64
Ubuntu 16.04 x64

Installation

How to Install Wkhtmltopdf and Wkhtmltoimage in Ubuntu

wget http://download.gna.org/wkhtmltopdf/0.12/0.12.3/wkhtmltox-0.12.3_linux-generic-amd64.tar.xz
tar -xvf wkhtmltox-0.12.3_linux-generic-amd64.tar.xz
cd wkhtmltox/bin/
sudo mv wkhtmltopdf  /usr/bin/wkhtmltopdf
sudo mv wkhtmltoimage  /usr/bin/wkhtmltoimage

	# The trick is to link the DeviceSupport folder from the beta to the stable version.
	# sudo needed if you run the Mac App Store version. Always download the dmg instead... you'll thank me later :)

	# Support iOS 15 devices (Xcode 13.0) with Xcode 12.5:
	sudo ln -s /Applications/Xcode-beta.app/Contents/Developer/Platforms/iPhoneOS.platform/DeviceSupport/15.0 /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/DeviceSupport

	# Then restart Xcode and reconnect your devices. You will need to do that for every beta of future iOS versions

	# (A similar approach works for older versions too, just change the version number after DeviceSupport)

	Run this
	"sudo -u postgres psql"
	in your terminal to get into postgres

	postgres=#

	Run "CREATE USER new_username;"

	Note: Replace new_username with the user you want to create,

	// connect() is a function that injects Redux-related props into your component.
	// You can inject data and callbacks that change that data by dispatching actions.
	function connect(mapStateToProps, mapDispatchToProps) {
	// It lets us inject component as the last step so people can use it as a decorator.
	// Generally you don't need to worry about it.
	return function (WrappedComponent) {
	// It returns a component
	return class extends React.Component {
	render() {
	return (