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Definition of Rails Select

In Ruby rails, we use some helpers to make the user ease. Here is one another helper which is known as Select. This helper is used to filter out the required data from the whole dataset. Or user can filter any data from an array of objects. To use select the user should use block. But we can also combine select with other helpers like enumeration or enum. Similar to “GET”, a helper which helps to search and fetch your requirement on a web browser, the helper “Rails select” can be used in Ruby rails.

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What is Rails Select?

As we discussed above, Rails uses some tags or helpers to filter out the required data from any given array. Rails select works almost similar to Rails where. But there is a small difference between these two. They differ in speed. Let me tell you how the Rails select tag works in brief. So, when the helper tag Rails select is given, from a set of objects (array), some iterations will happen to find out and select the given key word.

How to Use rails select?

As we know that we use Ruby select to filter out our desired object, the select needs a block. Inside the block, it tries to evaluate your block with the array of objects like weather it is true or false or if it can select the object from the array and so on. Let’s seen an example on how to use the Ruby rails.

So, if we have an array of numbers and need to select only odd numbers, the code will be as shown in the figure. There are two possible ways where select can be used.

The above two are the codes that can be used in Ruby rails console to select odd number from the given array. The latter code is more simplified form. So, this method works better when we need to call the object directly from the array. We can also use the select tag with hash tag also.

Rails select Method:

In the above section, we saw about the basic method to create Rails select. There are other methods where we combine the select with other helper tags. The other methods are combining with_index and filtering array in-place itself.

Rails select Example:

Creating select boxes in HTML require a substantial amount of markup (one Choice element for each option to choose from), dynamic generation makes the most sense.

The user will be given with array of countries whose names are shown in the above example. Internally, the application just wants to deal with their IDs, therefore they’re used as the value attribute of the options. Let’s explore what Rails can do for us.

Select tag is the most general helper; it just constructs the SELECT tag, which wraps an options string:

This is a start, but the option tags aren’t created dynamically. The options for select helper can be used to create option tags:

With this knowledge, we can use select tag and options for select together to get the complete markup which is needed:

You can pre-select an option by supplying its value to options for select.

Rails will add the selected attribute to an option if the internal value of the option being produced matches this value.

Conclusion Recommended Articles

This is a guide to Rails Select. Here we discuss the Definition, What is Rails Select, How to use rails select, methods and Examples with code implementation. You may also have a look at the following articles to learn more –

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Ruby On Rails 2.1

Ruby on Rails 2.1 – Migrations

Rails Migration uses Ruby to define changes to your database schema, making it possible to use a version control system to keep things synchronized with the actual code.

It has many uses, such as −

Teams of developers − if one person makes a schema change, the other developers just need to update, and run “rake migrate”.

Production servers − run “rake migrate” when you roll out a new release to bring the database up to date as well.

Multiple machines − if you develop on both a desktop and a laptop, or in more than one location, migrations can help you keep them all synchronized.

What can Rails Migration Do?

create_table(name, options)

drop_table(name)

rename_table(old_name, new_name)

add_column(table_name, column_name, type, options)

rename_column(table_name, column_name, new_column_name)

change_column(table_name, column_name, type, options)

remove_column(table_name, column_name)

add_index(table_name, column_name, index_type)

remove_index(table_name, column_name)

Migrations support all the basic data types − string, text, integer, float, date-time, timestamp, time, date, binary and Boolean −

string − is for small data types such as a title.

text − is for longer pieces of textual data, such as the description.

text − is for longer pieces of textual data, such as the description.

integer − is for whole numbers.

float − is for decimals.

date-time and timestamp − stores the date and time into a column.

date and time − stores either the date only or time only.

binary − is for storing data such as images, audio, or movies.

boolean − is for storing true or false values.

Valid column options are −

NOTE − The activities done by Rails Migration can be done using any front-end GUI or direct on SQL prompt, but Rails Migration makes all those activities very easy

See the Rails API for details on these.

Create the Migrations

Here is the generic syntax for creating a migration −

This will create the file db/migrate/001_table_name.rb. A migration file contains basic Ruby syntax that describes the data structure of a database table.

NOTE − Before running migration generator, it is recommended to clean the existing migrations generated by model generators.

We will create two migrations corresponding to our three tables – books and subjects..

Notice that you are using lowercase for book and subject and using the plural form while creating migrations. This is a Rails paradigm that you should follow each time you create a Migration. −

Edit the Code to Tell it What to Do

Go to db/migrate subdirectory of your application and edit each file one by one using any simple text editor.

Modify 001_books.rb as follows −

The ID column will be created automatically, so don’t do it here as well.

class Books < ActiveRecord::Migration def self.up t.float :price t.integer :subject_id chúng tôi :description t.timestamp :created_at end end def self.down drop_table :books end end

The method chúng tôi is used when migrating to a new version, self.down is used to roll back any changes if needed. At this moment, the above script will be used to create the books table.

Modify 002_subjects.rb as follows −

class Subjects < ActiveRecord::Migration def self.up t.string :name end end def self.down drop_table :subjects end end

The above script will be used to create subjects table; it will create five records in the subjects table.

Run the Migration

Now that you have created all the required migration files, it is time to execute them against the database. To do this, go to the command prompt and open the library directory in which the application is located, and then type rake migrate as follows −

This will create a “schema_info” table if it doesn’t exist, which tracks the current version of the database. Each new migration will be a new version, and any new migrations will be run, until your database is at the current version.

Running Migrations for Production and Test Databases

If you would like to specify what rails environment to use for the migration, use the RAILS_ENV shell variable.

For example −

NOTE − On Unix, use “export RAILS_ENV=production” instead of set command.

What is Next?

Now we have our database and the required tables available. In the two subsequent chapters, we will explore two important components called Controller (ActionController) and View (ActionView).

Creating Controllers ( Action Controller )

Creating Views ( Action View )

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How To Select And Set Up An Hd Tv Antenna

With cable companies bleeding their customers dry for channels they don’t even watch, many are considering “cutting the cord.” The rise of Internet streaming services gave hope to budget-conscious consumers. It finally seemed as though people could break ties with the cable companies. However, subscriptions to all of the streaming platforms quickly added up, negating any potential savings. There were also some significant drawbacks to eliminating cable, like losing access to your local news and sports.

Before you concede defeat, what if we told you there were high-definition channels that you could watch free of charge? It’s not a fantasy but rather a relic of an older era of television that many people forgot about: over-the-air broadcasting. The antennas of the past have made a comeback, offering sleek, elegant designs that are more sophisticated and powerful than their precursors.

HD TV antennas can pull in channels from many of your local affiliates like ABC, CBS, FOX, NBC, PBS and more. This means you can watch your local news, sports and primetime TV without paying a single cent.

Find out what channels are available in your area

Before you cancel your cable subscription and buy an antenna, you’ll probably want to know what channels you’ll be able to pull in. Fortunately there are a number of websites that can show you which channels are being broadcast in your area. Head to TVFool or AntennaWeb and punch in your address. Both websites will analyze the location of transmission towers relative to your location and present you with a list of channels you are likely to receive.

TVFool has a lot of information but can be somewhat difficult to interpret. AntennaWeb doesn’t have quite as much technical data; however, it does present its findings a little more clearly. Ultimately both websites will tell you what you need to know, so which one you use is up to you.

Directional or omnidirectional?

Now that you have some idea as to which channels you’re likely to receive, you have to select an antenna suitable to your situation. There are two types: directional and omnidirectional. Directional antennas are oriented in one direction and are capable of pulling in transmissions from further away. Omnidirectonal antennas are able to pull in channels from all directions but are generally weaker. To determine which one is best for you, refer back to your results on TVFool or AntennaWeb. You’ll notice that along with a list of channels, there is a geographical map.

This map will show a bunch of lines in relation to the location you previously entered. These lines represent the broadcast transmissions for each one of the channels. If all of the transmission lines are coming from a particular direction, grab a directional antenna. If the broadcasts are coming from all directions, pick up an omnidirectional antenna.

Indoor or Outdoor?

Once you’ve decided on a directional or omnidirectional antenna, you now need to consider whether to opt for an indoor or outdoor model. TVFool and AntennaWeb will also tell you how close you are to the broadcast towers in your area. If you live thirty miles or closer to the towers, then an indoor antenna will most likely do the job. If you live further away, then you’ll probably have to look into getting an outdoor antenna. Of course, these predictions won’t apply to everyone, as there are a number of factors that contribute to antenna reception. While distance to the transmission towers is important, there is one other thing you’ll want to consider.

Think about your surroundings. Is your “line of sight” to the broadcast towers obstructed by anything? While it’s not necessary to actually be able to see the towers, obstructions along the way can hamper the signal. Buildings, trees, mountains, etc., can all interfere with your reception. Outdoor antennas tend to be more powerful than the indoor variety. In addition, the outdoor models are not subject to impedances within your own home (e.g. walls).

To amplify or not to amplify

In today’s market you can find antennas with built-in amplifiers or add after-market ones to your existing antenna. In essence, amplifiers are intended to “boost” the broadcast transmissions that your antenna pulls in.

The danger of using an amplifier is that it doesn’t discriminate what it amplifies. That is if you live in an area with spotty reception (e.g. snow), you run the risk of amplifying that distortion. If you live far from your local broadcast towers and are having trouble pulling in channels, an amplifier might help. Just make sure you hang on to the receipt in case it makes matters even worse.

Antenna Placement

Once you’ve settled on an antenna, you’re going to want to think about where you will place it. With outdoor antennas, you really only have to consider which direction it will be facing (unless it is omnidirectional). Indoor antenna placement, however, can make a huge difference in the quality and number of channels you receive.

As with outdoor directional antennas, if your indoor antenna is directional, you’ll want to place it so that it is facing the broadcast signal’s point of origin.

We mentioned before how a clear “line of sight” can drastically improve reception. While you can’t do much about buildings or trees, you can make sure your indoor antenna is near a window or placed against an outward facing wall.

Generally the higher an antenna is placed the better the reception.

Try a variety of different placements to see which one works best.

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How To Select A Network Cable For Good Internet Speed

Network cable classes

At present, the network cables on the market are mainly in five categories.

Category 5

Category 6

Category 7

Category 8

Category 5 and previous cables are gradually leaving the markets. This is due to their low data transmission rates. Their transmission rates can not meet the requirements of household broadband.

Category 5

There is a CAT.5E mark on the outside of the cable. The maximum transmission frequency of these cables is 100MHz. This can meet the transmission rate of 1000Mbps within 100 meters and is suitable for Gigabit networks. The CAT5 super cable is CAT.5E

Category 6

There is also a cable with the CAT.6A mark on the outside of the cable. The maximum transmission frequency is 500MHz, and the maximum transmission rate within 100 meters can reach 10Gbps. It supports up to 10 Gigabit networks. The CAT6 super network cable is CAT.6A. As for some network cables marked as CAT.6E, they do not belong to the standard network cable category. The transmission performance cannot be guaranteed.

Category 7 Category 8

There is a CAT.8 mark on the outside of the network cable, 2000MHz ultra-high bandwidth, and the maximum transmission rate can reach 40Gbps, but it is limited to a transmission distance of 30 meters, so it is generally used for short-distance connections of servers, switches, patch panels and other equipment.

Cable shielding type

The types of network cables mentioned above are all twisted pairs. They are formed by a pair of insulated conductors wound counterclockwise. This way of winding each other can reduce signal interference. The denser the wires are wound, the stronger the anti-interference ability. In order to further strengthen the anti-interference ability, some network cables will also increase the shielding layer. There are two types of cables depending on the shielding layer. There is the shielded twisted pair (STP) and unshielded twisted pair (UTP).

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Shielded Twisted Pair (STP)

Shielded twisted pair adds one or more metal shielding layers in the insulating sheath. The metal shielding layer can reduce radiation and anti-interference. It shields the electromagnetic signal from the outside world. However, it also blocks the electromagnetic leakage of the cable itself. Therefore, the twisted pair signal transmission quality with the shielding layer is higher. Furthermore, it also has a good confidentiality performance. However, the price of shielded cables is higher and the installation process is more complicated.

The double shielding mentioned above means that each pair of cores has an independent shielding layer. The outer layers share one or more shielding layers. As shown in the figure above, each pair of core wires has a layer of aluminium foil shielding. This reduces signal attenuation and crosstalk. The outer layer also has a layer of metal braided shielding. This can reduce the interference of external magnetic fields and signals. It can also increase the pulling force of the cable.

Unshielded Twisted Pair (UTP)

The unshielded twisted pair is only wrapped by a layer of insulating rubber sheath. It has no metal shielding material. It is characterized by a lightweight, small overall wire diameter. This cable is also easy to bend, has flexible networking, and is relatively cheap.

How to choose a home network cable

Choosing a network cable is not as difficult as many people believe. In simple terms, the higher the cable level, the better the cable. Also, the higher the level, the larger the core diameter and other components (shielding layer, cross frame, etc.). This, the higher the cable level, the better the performance and of course, the higher the price.

So when we choose cables, should we buy the more expensive ones?

The Category 7 and Category 8 ultra-high-speed transmission network cables use double shielding. The overall wire diameter is relatively thick and the cable is very rigid. It is not easy to bend the cable and the cost is high. However, there is no complex strong interference in the home environment. Nevertheless, if you need to bend the wire, then you should avoid Category 7 and Category 8 cables. It is important to note that for short-distance transmission, Category 5 cable is sufficient. If you want higher speed and longer stable transmission distance, you can choose Category 6 or Category 6e unshielded cable.

Conclusion

How To Select “Last Child” With A Specific Class Using Css?

CSS or cascading style sheet is an essential part of modern web development, as it allows web developers to style their websites and create visually appealing designs. There are times when we want to select the last child of a specific class using CSS, but how? There are different approaches that can be used to select the last child.

In this article, we will see how to select the last child with a specific class in CSS.

Approach 1: Using :last-child() Selector

The :last-child() selector method is the first method available in CSS. This selector is used in selecting the last child element of its parent element. The process of selecting the last children is very easy. To select the last child with a specific class, we combine the :last-child selector with a class selector.

See the below syntax for more detail on how last-child selector is used to selecting the last element.

Syntax

In this syntax, assume we have a list of items with a class of “item” and we want to style the last item in the list differently, to do that, we can use the following CSS code −

.item:last-child { /* Add your CSS styles here */ }

The above syntax will select the last child element with a class of “item” and apply the specified styles to it.

Example

In this example, we have used the :last-child() selector that select the last div elemen having the class name as “item” and adds the CSS styles to it like background color to green, and padding to 10px.

/* Using the :last-child Selector */ .item:last-child { background-color: green; padding: 10px; }

Approach 2: Using :nth-last-child() Selector

This is the second method for selecting the last child with a specific class in CSS. The :nth-last-child selector is used in selecting the elements based on their position relative to the end of the parent element.

The working of this selector is very easy. To select the last child of a specific class with the help of the :nth-last-child selector, we have to combine it with a class selector and set the value to 1. See the below syntax for more detail on how nth-last-child selector is used to select the last element.

Syntax

In this syntax, assume we have a series of div elements with a class of “div-box” and now to style the last div element in the series we can use the following CSS code −

.div-box:nth-last-child(1) { /* Add your CSS styles here */ }

The above syntax will select the last child element with a class of “div-box” and apply the specified styles to it.

Example

The above syntax will select the last child element with a class of “div-box” and apply the specified styles to it.

/* Using the :last-child Selector */ .item:nth-last-child(1) { background-color: lightblue; padding: 10px; }

Approach 3: Using JavaScript

In this approach, we are using JavaScript to select the last child with a specific class. CSS is the preferred approach for styling the web pages, on the other hand JavaScript can also be used to perform the Document Object Model operations and select the HTML elements dynamically.

In JavaScript, the querySelector() method is used with a combination of the class and :last-child selectors to select the last children with a specific class.

The process to select last child using javascript is also easy. To select the last child of a specific class with the help of the javascript, we have to combine it with a class and :last-child-selector of CSS. See the below syntax for more detail on how javascript is used to select the last element.

Syntax

In this syntax, we have a series of div elements with a class of “div” and we want to add a class of “add-color” to the last div in the list, we can use the following JavaScript code −

ar lastDiv = document.querySelector('.div:last-child'); lastDiv.classList.add(add-color);

The above syntax will select the last child element with a class of “div” and add the “add-color” class to it.

Example

In this example, we have defined a list of div elements having its class name as “item” and after which we have also added some CSS styles. Now to select the last child, we have defined a class called “highlight” twitch will style the last div element.

Here we have used the querySelector() method from JavaScript that selects the last child element with a class of “item”. After which we have also added the “highlight” class to the selected element with the help of the classList.add() method.

/* Styling for divs */ .item { background-color: #f1f1f1; padding: 10px; margin-bottom: 10px; } /* Styling for last div */ .highlight { background-color: yellow;}

var lastDiv = document.querySelector(‘.item:last-child’);

lastDiv.classList.add(‘highlight’);

Conclusion

Selecting the last child with a specific class in CSS is a task that can be achieved using different approaches. The: last-child() selector and :nth-last-child() selector are two methods that can be used to achieve this task.

The :last-child() selector is used to select the last child element of its parent element. To select the last child with a specific class, we combine the :last-child selector with a class selector. On the other hand, the :nth-last-child() selector is used in selecting the elements based on their position relative to the end of the parent element. To select the last child of a specific class with the help of the :nth-last-child selector, we have to combine it with a class selector and set the value to 1.

In conclusion, both approaches are effective in selecting the last child element with a specific class, and the approach to use depends on the specific needs of the web developer. By using these selectors, web developers can enhance the appearance and functionality of their websites, making them more appealing to users.

How To Install Ruby On Rails On Ubuntu 20.04 With Mysql, Nginx, Passenger, Ssl

How to Install Ruby On Rails on Ubuntu 20.04 with MySQL, Nginx, Passenger, SSL. Ruby is a dynamic, open-source programming language that prioritizes simplicity and productivity. It features an easy syntax that is natural to read and write. Ruby on Rails is a widely used web framework for Ruby that was created to help software developers be more productive.

Nginx is a web server which can provide HTTP transactions and serve static files but cannot run Ruby applications directly. So we use Phusion Passenger which is a free, open-source web application server. It is designed to handle HTTP requests, monitor and manage processes and resources, as well as allow administration, monitoring, and problem diagnosis.

In this guide, you will set up Passenger to assist Nginx with serving your Ruby on Rails web application and install Let’sEncrypt SSL to secure your application.

Prerequisites

A server with Ubuntu 20.04

Root access to your server or user with sudo privileges.

Intermediate knowledge in using Linux terminal commands.

Domain name which is pointed to the external IP of your server.

Initial Server Setup

Update your server packages to its latest.

sudo apt update sudo apt dist-upgrade -y Install Ruby on Rails with Rbenv

To make sure the setup goes fine we shall start by adding the chúng tôi and Yarn repositories.

Install Dependencies

Now you can install all the dependencies.

sudo apt-get update sudo apt-get install git-core zlib1g-dev build-essential libssl-dev libreadline-dev libyaml-dev libsqlite3-dev sqlite3 libxml2-dev libxslt1-dev libcurl4-openssl-dev software-properties-common libffi-dev nodejs yarn Install Rbenv and Rbenv Build

Rbenv is a Ruby version manager which is used to install Ruby.

Here we will install Rbenv and Rbenv-build.

Install Rbenv cd exec $SHELL Install Rbenv Build

exec $SHELL

Configure Ruby Version

Now you can setup default and global Ruby version.

rbenv install 3.1.1 rbenv global 3.1.1

Confirm Ruby version using the following command.

ruby -v

Now you need to install bundler.

gem install bundler Install Rails gem install rails -v 7.0.2.3

Make rails command to be executable.

rbenv rehash

Confirm Rails version.

rails -v Install MySQL

In this tutorial we shall use MySQL for database.

sudo apt-get install mysql-server mysql-client libmysqlclient-dev sudo mysql_secure_installation

You can configure new user and password in MySQL if you need.

Configure Rails for MySQL

Now install MySQL adapter for Rails

gem install mysql2 Install Passenger and Nginx

Now we will install Nginx and configure Passenger.

Install Nginx.

sudo apt -y install nginx

Install Passenger.

Add Passenger APY repository.

Update and install Passenger.

sudo apt update

Now a new passenger configuration will be added inside conf.d directory of Nginx installation.

Restart Nginx for the Passenger module installation to take effect.

sudo service nginx start Configure Passenger with Rbenv

Edit the Passenger configuration file.

Comment out lines starting with passenger_root and passenger_ruby.

Append the following lines into the file.

Replace username in the passenger_ruby option path with the username through which you have installed Rbenv.

passenger_ruby /home/example_user/.rbenv/shims/ruby; passenger_root /usr/lib/ruby/vendor_ruby/phusion_passenger/locations.ini;

Save and exit the file.

Restart Nginx.

sudo service nginx restart Create New Rails Project

Create a new directory for your Rails project or just navigate to any directory. Here we are navigating to the default Nginx web directory.

cd /var/www

Create Rails project.

rails new

project-name

-d mysql cd

project-name

Edit the database configuration to connect to your database.

sudo nano config/database.yml

Replace the username with your username, password with your password

Make sure your database.yml looks like this

default: &default adapter: mysql2 encoding: utf8 username:

username

password:

password

host:

locahost

database:

database_name

development: <<: *default test: <<: *default production: <<: *default

Initialize Rails database.

rake db:create

Restart Rails.

rails restart Configure Nginx with Ruby on Rails

Remove default Nginx configurations.

sudo rm -rf /etc/nginx/sites-available/default sudo rm -rf /etc/nginx/sites-enabled/default

Create a new configuration for your Ruby application

sudo nano /etc/nginx/sites-available/

domainname.co

nf

Paste this new configuration setting and hit Ctrl+X followed by Y to save the file

server { listen 80 default_server; passenger_enabled on; passenger_app_env production; root /

var/www/html/project

-name/public; }

Enable your new configuration

sudo ln -s chúng tôi /etc/nginx/sites-enabled/domainname.conf

Validate Nginx configuration and restart nginx

sudo nginx -t sudo service nginx restart Install Let’sEncrypt SSL

We can use Certbot to install free Let’s Encrypt SSL certificate for your domain.

sudo apt install python3-certbot-nginx

Execute the following command to install certificate and configure redirect to HTTPS automatically.

Now you should receive SSL certificate and it will be configured automatically.

Setup auto renewal.

sudo certbot renew --dry-run

Now Ruby on Rails is installed and configured with Passenger and Nginx and connected with MySQL database.

Visit your domain name on your browser, you can view the Ruby on Rails welcome page.

Conclusion

Now you have learned how to Install Ruby On Rails on Ubuntu 20.04 with MySQL and configure Nginx with Passenger and configure Let’sEncrypt SSL.

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