Tutorial by Examples: u

Simple Pivot - Static Columns

Using Item Sales Table from Example Database, let us calculate and show the total Quantity we sold of each Product. This can be easily done with a group by, but lets assume we to 'rotate' our result table in a way that for each Product Id we have a column. SELECT [100], [145] FROM (SELECT ItemI...

Microsoft SQL Server • PIVOT / UNPIVOT

Prevent Receiving Your Own Messages Using Objective-C

Setting a filter applies to all channels that you will subscribe to from that particular client. This client filter excludes messages that have this subscriber's UUID set at the sender's UUID: NSString *expression = [NSString stringWithFormat:@"(uuid != '%@'", se...

PubNub • Message Filtering

Handling the error when getting metadata for a non-existing path using the Dropbox .NET library

This example uses the Dropbox .NET library to try to get the metadata for an item at a particular path, and checks for a NotFound error: try { var metadata = await this.client.Files.GetMetadataAsync("/non-existant path"); Console.WriteLine(metadata.Name); } catch (Dropbox.Api.A...

Dropbox API • Getting file metadata

Constructor Injection

Constructor injection is the safest way of injecting dependencies that a whole class depends upon. Such dependencies are often referred to as invariants, since an instance of the class cannot be created without supplying them. By requiring the dependency to be injected at construction, it is guara...

unit-testing • Dependency Injection

Squash Recent Commits Without Rebasing

If you want to squash the previous x commits into a single one, you can use the following commands: git reset --soft HEAD~x git commit Replacing x with the number of previous commits you want to be included in the squashed commit. Mind that this will create a new commit, essentially forgetting...

Git • Squashing

Squashing Commits During a Rebase

Commits can be squashed during a git rebase. It is recommended that you understand rebasing before attempting to squash commits in this fashion. Determine which commit you would like to rebase from, and note its commit hash. Run git rebase -i [commit hash]. Alternatively, you can type HE...

Git • Squashing

Getting the active theme URL

<?php echo esc_url( get_bloginfo( 'stylesheet_directory' ) ); ?> Output http://example.com/wp-content/themes/twentysixteen Alternatives Internally, get_bloginfo( 'stylesheet_directory' ) calls get_stylesheet_directory_uri(), so you may want to use that instead: <?php echo esc_url( ...

WordPress • get_bloginfo()

Generalized capture

C++14 Lambdas can capture expressions, rather than just variables. This permits lambdas to store move-only types: auto p = std::make_unique<T>(...); auto lamb = [p = std::move(p)]() //Overrides capture-by-value of `p`. { p->SomeFunc(); }; This moves the outer p variable into th...

C++ • Lambdas

Capture by reference

If you precede a local variable's name with an &, then the variable will be captured by reference. Conceptually, this means that the lambda's closure type will have a reference variable, initialized as a reference to the corresponding variable from outside of the lambda's scope. Any use of the v...

C++ • Lambdas

Default capture

By default, local variables that are not explicitly specified in the capture list, cannot be accessed from within the lambda body. However, it is possible to implicitly capture variables named by the lambda body: int a = 1; int b = 2; // Default capture by value [=]() { return a + b; }; // OK;...

C++ • Lambdas

Your First Controller

A controller is a basic structure used in Angular to preserve scope and handle certain actions within a page. Each controller is coupled with an HTML view. Below is a basic boilerplate for an Angular app: <!DOCTYPE html> <html lang="en" ng-app='MyFirstApp'> <head...

AngularJS • Controllers

Recursive setTimeout

To repeat a function indefinitely, setTimeout can be called recursively: function repeatingFunc() { console.log("It's been 5 seconds. Execute the function again."); setTimeout(repeatingFunc, 5000); } setTimeout(repeatingFunc, 5000); Unlike setInterval, this ensures that t...

JavaScript • Intervals and Timeouts

Creating a backup of a database or table

Create a snapshot of a whole database: mysqldump [options] db_name > filename.sql Create a snapshot of multiple databases: mysqldump [options] --databases db_name1 db_name2 ... > filename.sql mysqldump [options] --all-databases > filename.sql Create a snapshot of one or more tables...

MySQL • Backup using mysqldump

Specifying username and password

> mysqldump -u username -p [other options] Enter password: If you need to specify the password on the command line (e.g. in a script), you can add it after the -p option without a space: > mysqldump -u username -ppassword [other options] If you password contains spaces or special chara...

MySQL • Backup using mysqldump

Restoring a backup of a database or table

mysql [options] db_name < filename.sql Note that: db_name needs to be an existing database; your authenticated user has sufficient privileges to execute all the commands inside your filename.sql; The file extension .sql is fully a matter of style. Any extension would work. You cannot spe...

MySQL • Backup using mysqldump

Conversion to function pointer

If a lambda's capture list is empty, then the lambda has an implicit conversion to a function pointer that takes the same arguments and returns the same return type: auto sorter = [](int lhs, int rhs) -> bool {return lhs < rhs;}; using func_ptr = bool(*)(int, int); func_ptr sorter_func = ...

C++ • Lambdas

High-resolution timestamps

performance.now() returns a precise timestamp: The number of milliseconds, including microseconds, since the current web page started to load. More generally, it returns the time elapsed since the performanceTiming.navigationStart event. t = performance.now(); For example, in a web browser's ma...

JavaScript • Timestamps

Low-resolution timestamps

Date.now() returns the number of whole milliseconds that have elapsed since 1 January 1970 00:00:00 UTC. t = Date.now(); For example, Date.now() returns 1461069314 if it was called on 19 April 2016 at 12:35:14 GMT.

JavaScript • Timestamps

Support for legacy browsers

In older browsers where Date.now() is unavailable, use (new Date()).getTime() instead: t = (new Date()).getTime(); Or, to provide a Date.now() function for use in older browsers, use this polyfill: if (!Date.now) { Date.now = function now() { return new Date().getTime(); }; }

JavaScript • Timestamps

Reading from a file synchronously

For any file operations, you will need the filesystem module: const fs = require('fs'); Reading a String fs.readFileSync behaves similarly to fs.readFile, but does not take a callback as it completes synchronously and therefore blocks the main thread. Most node.js developers prefer the asynch...

Node.js • Filesystem I/O