Tutorial by Examples: t

A transaction acts on a single database connection. If you have multiple class-specific databases, the transaction will not protect interaction among them. One workaround is to begin a transaction on each class whose models you alter: Student.transaction do Course.transaction do course.enro...

Both #save and #destroy come wrapped in a transaction that ensures that whatever you do in validations or callbacks will happen under its protected cover. So you can use validations to check for values that the transaction depends on or you can raise exceptions in the callbacks to rollback, includin...

ActiveRecord::Base.transaction uses the ActiveRecord::Rollback exception to distinguish a deliberate rollback from other exceptional situations. Normally, raising an exception will cause the .transaction method to rollback the database transaction and pass on the exception. But if you raise an Activ...

Shade is a library developed by OpenStack to simplify interactions with OpenStack clouds, like DreamHost. $ pip install shade

Create a file named launch-server.yaml, that will be our playbook. The first part of the playbook is a list of hosts that your playbook will run on, we only have one, localhost. - hosts: localhost Then we need to define a list of tasks to perform in this playbook. We will only have one that lau...

Run the Ansible playbook: $ ansible-playbook launch-server.yaml You should see output like PLAY [localhost] *************************************************************** TASK [setup] ******************************************************************* ok: [localhost] TASK [launch an U...

Using NuGet Install-Package Cirrious.FluentLayout An expanded example based on the starter example at the GitHub Page, a simple first name, last name labels and fields all stacked one on top of the other: public override void ViewDidLoad() { //create our labels and fields var firstNa...

Built-in functionals: lapply(), sapply(), and mapply() R comes with built-in functionals, of which perhaps the most well-known are the apply family of functions. Here is a description of some of the most common apply functions: lapply() = takes a list as an argument and applies the specified ...

User-defined functionals Users can create their own functionals to varying degrees of complexity. The following examples are from Functionals by Hadley Wickham: randomise <- function(f) f(runif(1e3)) lapply2 <- function(x, f, ...) { out <- vector("list", length(x...

Nesting is probably most often used to create more specific selectors, but it can also be used simply for code organization. Using the @at-root directive, you can ‘jump out’ of where you nest it in your Sass, bringing you back at the top level. Doing this allows you to keep styles grouped without cr...

Using SVG stroke makes it easier to create a Vector drawable with unified stroke length, as per Material Design guidelines: Consistent stroke weights are key to unifying the overall system icon family. Maintain a 2dp width for all stroke instances, including curves, angles, and both interior and ...

infixl vs infixr vs infix describe on which sides the parens will be grouped. For example, consider the following fixity declarations (in base) infixl 6 - infixr 5 : infix 4 == The infixl tells us that - has left associativity, which means that 1 - 2 - 3 - 4 gets parsed as ((1 - 2) - 3) - 4 ...

The following will prompt a user for input, and then store that input as a string (text) in a variable. The variable is then used to give a message to the user. #!/usr/bin/env bash echo "Who are you?" read name echo "Hello, $name." The command read here reads one line of ...

In Sinatra, routing is how your app responds to requests, by the path of the request (e.g. /welcome) and by the HTTP verb used (e.g. GET or POST). The way a request is written is as follows: <http-verb> <path> do <code block to execute when this route is requested> end He...

When matching the path of a route, you can do it explicitly, matching only one path, like so: get "/hello" do return "Hello!" end You can also use a regular expression to match complex routes. Any route which matches the regular expression will run that code block. If m...

To print a test field (TestField) from a test feature class (TestFC) in a test file geodatabase (Test.gdb) located in a temporary folder (C:\Temp): with arcpy.da.SearchCursor(r"C:\Temp\Test.gdb\TestFC",["TestField"]) as cursor: for row in cursor: print row[0]

long fib(long n) { return n < 2 ? n : fib(n - 1) + fib(n - 2); } struct FibStruct(int n) { // Remarks: n is a template ubyte[fib(n)] data; } void main() { import std.stdio : writeln; enum f10 = fib(10); // execute the function at compile-time pragma(msg, f10); /...

class Animal { abstract int maxSize(); // must be implemented by sub-class final float maxSizeInMeters() // can't be overridden by base class { return maxSize() / 100.0; } } class Lion: Animal { override int maxSize() { return 350; } } void main() { ...

class Lion { private double weight; // only accessible with-in class this(double weight) { this.weight = weight; } double weightInPounds() const @property // const guarantees no modifications // @property functions are treated as fields { ret...

void main() { import std.stdio : writeln; int[] arr = [1, 3, 4, 5]; foreach (i, el; arr) { if (i == 0) continue; // continue with the next iteration arr[i] *= 2; if (i == 2) break; // stop the loop iteration } writel...