Tutorial by Examples: ha

After creating a new model or modifying existing models, you will need to generate migrations for your changes and then apply the migrations to the specified database. This can be done by using the Django's built-in migrations system. Using the manage.py utility when in the project root directory: ...

Hash has a default value for keys that are requested but don't exist (nil): a = {} p a[ :b ] # => nil When creating a new Hash, one can specify the default: b = Hash.new 'puppy' p b[ :b ] # => 'puppy' Hash.new also takes a block, which allows you to automatically create n...

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 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...

You can create a new class that inherits from HashSet: Set<String> h = new HashSet<String>() {{ add("a"); add("b"); }}; One line solution: Set<String> h = new HashSet<String>(Arrays.asList("a", "b")); Using guava: Se...

Generally, the syntax is: SELECT <column names> FROM <table name> WHERE <condition> For example: SELECT FirstName, Age FROM Users WHERE LastName = 'Smith' Conditions can be complex: SELECT FirstName, Age FROM Users WHERE LastName = 'Smith' AND (City = 'New York' OR C...

In a nutshell, conditional pre-processing logic is about making code-logic available or unavailable for compilation using macro definitions. Three prominent use-cases are: different app profiles (e.g. debug, release, testing, optimised) that can be candidates of the same app (e.g. with extra log...

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...

In many cases, the Razor parser is smart enough to figure out when the @ sign is meant to be used as part of code, as opposed to being part of something like an email address. In the example below, escaping the @ sign is not necessary: <p>Reach out to us at [email protected]</p> Howev...

Slices have both length and capacity. The length of a slice is the number of elements currently in the slice, while the capacity is the number of elements the slice can hold before needing to be reallocated. When creating a slice using the built-in make() function, you can specify its length, and ...

The background property can be used to set one or more background related properties: ValueDescriptionCSS Ver.background-imageBackground image to use1+background-colorBackground color to apply1+background-positionBackground image's position1+background-sizeBackground image's size3+background-repeat...

CSS div { height: 100px; width: 100px; border: 1px solid; transition-property: height, width; transition-duration: 1s, 500ms; transition-timing-function: linear; transition-delay: 0s, 1s; } div:hover { height: 200px; width: 200px; } HTML <div></div> ...

You may wish to use Model Factories within your seeds. This will create 3 new users. use App\Models\User; class UserTableSeeder extends Illuminate\Database\Seeder{ public function run(){ factory(User::class)->times(3)->create(); } } You may also want to define ...

This a basic example aimed at new users. It does not focus on explaining the difference between char and cellstring. It might happen that you want to get rid of the ' in your strings, although you never added them. In fact, those are artifacts that the command window uses to distinguish between ...

function Invoke-MyCmdlet { [CmdletBinding(SupportsShouldProcess = $true)] param() # ... }

Reading a file line by line public class Main { public static void main(String[] args) { try { Scanner scanner = new Scanner(new File("example.txt")); while(scanner.hasNextLine()) { String line = scanner.nextLine(); ...

Java SE 8 An array of strings can be joined using the static method String.join(): String[] elements = { "foo", "bar", "foobar" }; String singleString = String.join(" + ", elements); System.out.println(singleString); // Prints "foo + bar + foobar&qu...

Swift label1.layer.shadowOffset = CGSize(width: 3, height: 3) label1.layer.shadowOpacity = 0.7 label1.layer.shadowRadius = 2 Swift 3 label1.layer.shadowOffset = CGSize(width: 3, height: 3) label1.layer.shadowOpacity = 0.7 label1.layer.shadowRadius = 2 Objective-C label1.layer.shadowOffs...

Pipes may be chained. <p>Today is {{ today | date:'fullDate' | uppercase}}.</p>

String data types of either fixed length or variable length. Syntax: CHAR [ ( n_chars ) ] VARCHAR [ ( n_chars ) ] Examples: SELECT CAST('ABC' AS CHAR(10)) -- 'ABC ' (padded with spaces on the right) SELECT CAST('ABC' AS VARCHAR(10)) -- 'ABC' (no padding due to variable character) SELE...