Tutorial by Examples: u

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 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...

Use the : operator to create sequences of numbers, such as for use in vectorizing larger chunks of your code: x <- 1:5 x ## [1] 1 2 3 4 5 This works both ways 10:4 # [1] 10 9 8 7 6 5 4 and even with floating point numbers 1.25:5 # [1] 1.25 2.25 3.25 4.25 or negatives -4:4 ...

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...

From the official documentation: With Gradle: repositories { mavenCentral() // jcenter() works as well because it pulls from Maven Central } dependencies { compile 'com.github.bumptech.glide:glide:4.0.0' compile 'com.android.support:support-v4:25.3.1' annotationProcessor 'com.githu...

In short: XPages is part of IBM Domino Designer. Extra setup or installation isn't required for XPages. First XPage / Hello-World-Example To create your first XPage you have to create a new NSF first. Open the IBM Domino Designer, and open the menu "File" -> "New" -> &...

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...

Variables inside single quotes ' don't get expanded by POSIX compatible shells, so using a shell variable in a sed substitution requires the use of double quotes " instead of single quotes ': $ var="he" $ echo "hello" | sed "s/$var/XX/" XXllo $ var="he&q...

A method of a struct that change the value of the struct itself must be prefixed with the mutating keyword struct Counter { private var value = 0 mutating func next() { value += 1 } } When you can use mutating methods The mutating methods are only available on str...

c := exec.Command(name, arg...) b := &bytes.Buffer{} c.Stdout = b c.Stdin = stdin if err := c.Start(); err != nil { return nil, err } timedOut := false intTimer := time.AfterFunc(timeout, func() { log.Printf("Process taking too long. Interrupting: %s %s", name, strings...

// Execute a command a capture standard out. exec.Command creates the command // and then the chained Output method gets standard out. Use CombinedOutput() // if you want both standard out and standerr output out, err := exec.Command("echo", "foo").Output() if err != nil { ...

cmd := exec.Command("sleep", "5") // Does not wait for command to complete before returning err := cmd.Start() if err != nil { log.Fatal(err) } // Wait for cmd to Return err = cmd.Wait() log.Printf("Command finished with error: %v", err)

A header file may be included by other header files. A source file (compilation unit) that includes multiple headers may therefore, indirectly, include some headers more than once. If such a header file that is included more than once contains definitions, the compiler (after preprocessing) dete...

In PowerShell, there are many ways to achieve the same result. This can be illustrated nicely with the simple & familiar Hello World example: Using Write-Host: Write-Host "Hello World" Using Write-Output: Write-Output 'Hello world' It's worth noting that although Write-Outp...

./mongo localhost:27017/mydb myjsfile.js Explanation: This operation executes the myjsfile.js script in a mongo shell that connects to the mydb database on the mongod instance accessible via the localhost interface on port 27017. localhost:27017 is not mandatory as this is the default port mongo...

To make all the characters in a String uppercase or lowercase: 2.2 let text = "AaBbCc" let uppercase = text.uppercaseString // "AABBCC" let lowercase = text.lowercaseString // "aabbcc" 3.0 let text = "AaBbCc" let uppercase = text.uppercased() // &qu...

It can also be installed by downloading the source code and placing it in a directory of your project. However there are many benefits to using composer. require '/path/to/lib/Twig/Autoloader.php'; Twig_Autoloader::register(); $loader = new Twig_Loader_Filesystem('/path/to/templates'); $opti...