Tutorial by Examples: at

Detect errors when reading data on Android

A frequent reason why your read operation may not work is because your security rules reject the operation, for example because you're not authenticated (by default a database can only be accessed by an authenticated user). You can see these security rule violations in the logcat output. But it's e...

firebase • How do I listen for errors when accessing the database?

Using different Properties/Configuration for different environments like dev, qa, staging etc.

Large scale applications often need different properties when running on different environments. we can achieve this by passing arguments to NodeJs application and using same argument in node process to load specific environment property file. Suppose we have two property files for different enviro...

Node.js • Environment

Builder Pattern

Separate the construction of a complex object from its representation so that the same construction process can create different representations and and provides a high level of control over the assembly of the objects. In this example demonstrates the Builder pattern in which different vehicles ar...

C# Language • Creational Design Patterns

Prototype Pattern

Specify the kind of objects to create using a prototypical instance, and create new objects by copying this prototype. In this example demonstrates the Prototype pattern in which new Color objects are created by copying pre-existing, user-defined Colors of the same type. using System; using Syste...

C# Language • Creational Design Patterns

Abstract Factory Pattern

Provide an interface for creating families of related or dependent objects without specifying their concrete classes. In this example demonstrates the creation of different animal worlds for a computer game using different factories. Although the animals created by the Continent factories are diffe...

C# Language • Creational Design Patterns

Code that will always/never be executed

if true; then echo Always executed fi if false; then echo Never executed fi

Bash • true, false and : commands

Common HTML Operations

If the input HTML DOM is <html> <body> <a>link</a> <div class='container' id='divone'> <p class='common' id='enclosedone'>Element One</p> <p class='common' id='enclosedtwo'>Element Two</p> ...

xpath • Getting started with xpath

Bilateral Filtering

In image processing applications, the bilateral filters are a special type of non-linear filters. There is a trade off between loosing structure and noise removal, because the most popular method to remove noise is Gaussian blurring which is not aware of structure of image; therefore, it also remov...

opencv • Image Processing

Creating custom interceptors

Interceptors require the IInterceptor interface. Any public method within the intercepted class will be intercepted (including getters and setters) public class MyInterceptor : IInterceptor { public void Intercept(IInvocation invocation) { //Calls the next method in the chain - T...

castle-windsor • Interceptors

Accessing a filtered list from outside an ng-repeat

Occasionally you will want to access the result of your filters from outside the ng-repeat, perhaps to indicate the number of items that have been filtered out. You can do this using as [variablename] syntax on the ng-repeat. <ul> <li ng-repeat="item in vm.listItems | filter:vm.myF...

AngularJS • Filters

Database First in Entity Framework Core with a Class Library and SQL Server

Okay it took me about a day to figure it out so here I am posting the steps I followed to get my Database First working in a Class Project (.NET Core), with a .NET Core Web App. Step 1 - Install .NET Core Make Sure you are using .NET Core not DNX (Hint: You should be able to see the .NET Core opti...

Entity Framework Core • Getting started with Entity Framework Core

simple daemon application

A daemon process executes a program in the background, usually without user interaction. The example below shows how to create a daemon and register a listener, which monitors all open applications. The main part is the function call NSRunLoop.mainRunLoop().run(), which starts the daemon. class MyO...

osx • NSRunLoop

Serialization using Json.NET with JsonSerializerSettings

This serializer has some nice features that the default .net json serializer doesn't have, like Null value handling, you just need to create the JsonSerializerSettings : public static string Serialize(T obj) { string result = JsonConvert.SerializeObject(obj, new JsonSerializerSettings { NullVa...

.NET Framework • JSON Serialization

Ratio_To_Report

Provides the ratio of the current rows value to all the values within the window. --Data CREATE TABLE Employees (Name Varchar2(30), Salary Number(10)); INSERT INTO Employees Values ('Bob',2500); INSERT INTO Employees Values ('Alice',3500); INSERT INTO Employees Values ('Tom',2700); INSERT INTO...

Oracle Database • Window Functions

Aggregation in a Server Method

Another way of doing aggregations is by using the Mongo.Collection#rawCollection() This can only be run on the Server. Here is an example you can use in Meteor 1.3 and higher: Meteor.methods({ 'aggregateUsers'(someId) { const collection = MyCollection.rawCollection() const aggre...

meteor • MongoDB Aggregation

Create a simple self-hosted Nancy application

Use Nuget to install the Nancy and Nancy.Hosting.Self packages into the project. Instantiate a new NancyHost object and pass in the relevant URL using( var host = new NancyHost( hostConfiguration, new Uri( "http://localhost:1234" ) ) ) { host.Start(); Console.WriteLine( "Running o...

nancy • Getting started with nancy

Operations with arrays.

When you want to work with the data entries in arrays you first need to unwind the array. The unwind operation creates a document for each entry in the array. When you have lot's of documents with large arrays you will see an explosion in number of documents. { "_id" : 1, "item"...

MongoDB • Aggregation

Append a DataFrame to another DataFrame

Let us assume we have the following two DataFrames: In [7]: df1 Out[7]: A B 0 a1 b1 1 a2 b2 In [8]: df2 Out[8]: B C 0 b1 c1 The two DataFrames are not required to have the same set of columns. The append method does not change either of the original DataFrames. Inst...

pandas • Appending to DataFrame

Single match

You can quickly determine if a text includes a specific pattern using Regex. There are multiple ways to work with Regex in PowerShell. #Sample text $text = @" This is (a) sample text, this is a (sample text) "@ #Sample pattern: Content wrapped in () $pattern = '$.*?$' Using ...

PowerShell • Regular Expressions

Replace text with dynamic value using a MatchEvalutor

Sometimes you need to replace a value matching a pattern with a new value that's based on that specific match, making it impossible to predict the new value. For these types of scenarios, a MatchEvaluator can be very useful. In PowerShell, a MatchEvaluator is as simple as a scriptblock with a singl...

PowerShell • Regular Expressions