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0 # creates the Fixnum 0 123 # creates the Fixnum 123 1_000 # creates the Fixnum 1000. You can use _ as separator for readability By default the notation is base 10. However, there are some other built-in notations for different bases: 0xFF # Hexadecimal representation of 255, s...

You can use the Integer method to convert a String to an Integer: Integer("123") # => 123 Integer("0xFF") # => 255 Integer("0b100") # => 4 Integer("0555") # => 365 You can also pass a base parameter to the Integer method to c...

Library cargo new my-library This creates a new directory called my-library containing the cargo config file and a source directory containing a single Rust source file: my-library/Cargo.toml my-library/src/lib.rs These two files will already contain the basic skeleton of a library, such th...

Debug cargo build Release Building with the --release flag enables certain compiler optimizations that aren't done when building a debug build. This makes the code run faster, but makes the compile time a bit longer too. For optimal performance, this command should be used once a release build ...

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...

Android supports several configuration qualifiers that allow you to control how the system selects your alternative resources based on the characteristics of the current device screen. A configuration qualifier is a string that you can append to a resource directory in your Android project and speci...

To run a specific migration up or down, use db:migrate:up or db:migrate:down. Up a specific migration: 5.0 rake db:migrate:up VERSION=20090408054555 5.0 rails db:migrate:up VERSION=20090408054555 Down a specific migration: 5.0 rake db:migrate:down VERSION=20090408054555 5.0 ra...

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 add a new column name to the users table, run the command: rails generate migration AddNameToUsers name This generates the following migration: class AddNameToUsers < ActiveRecord::Migration[5.0] def change add_column :users, :name, :string end end When the migration name i...

To add a new indexed column email to the users table, run the command: rails generate migration AddEmailToUsers email:string:index This will generate the following migration: class AddEmailToUsers < ActiveRecord::Migration[5.0] def change add_column :users, :email, :string add_i...

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...

To add multiple columns to a table, separate field:type pairs with spaces when using rails generate migration command. The general syntax is: rails generate migration NAME [field[:type][:index] field[:type][:index]] [options] For example, the following will add name, salary and email fields to ...

Run command: 5.0 rake db:migrate 5.0 rails db:migrate Specifying target version will run the required migrations (up, down, change) until it has reached the specified version. Here, version number is the numerical prefix on the migration's filename. 5.0 rake db:migrate VERSION=2008090...

To rollback the latest migration, either by reverting the change method or by running the down method. Run command: 5.0 rake db:rollback 5.0 rails db:rollback Rollback the last 3 migrations 5.0 rake db:rollback STEP=3 5.0 rails db:rollback STEP=3 STEP provide the number of ...

To broaden the selections of a structured query language (SQL-SELECT) statement, wildcard characters, the percent sign (%) and the underscore (_), can be used. The _ (underscore) character can be used as a wildcard for any single character in a pattern match. Find all employees whose Fname start w...

Match any single character within the specified range (e.g.: [a-f]) or set (e.g.: [abcdef]). This range pattern would match "gary" but not "mary": SELECT * FROM Employees WHERE FName LIKE '[a-g]ary' This set pattern would match "mary" but not "gary": SEL...

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...