Tutorial by Examples: dc

ALTER TABLE Employees ADD CONSTRAINT DefaultSalary DEFAULT ((100)) FOR [Salary] This adds a constraint called DefaultSalary which specifies a default of 100 for the Salary column. A constraint can be added at the table level. Types of constraints Primary Key - prevents a duplicate record in...

To find out the IP address of your container, use: docker inspect <container id> | grep IPAddress or use docker inspect docker inspect --format '{{ .NetworkSettings.IPAddress }}' ${CID}

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...

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 module cmath includes additional functions to use complex numbers. import cmath This module can calculate the phase of a complex number, in radians: z = 2+3j # A complex number cmath.phase(z) # 0.982793723247329 It allows the conversion between the cartesian (rectangular) and polar repr...

Vector size is simply the number of elements in the vector: Current vector size is queried by size() member function. Convenience empty() function returns true if size is 0: vector<int> v = { 1, 2, 3 }; // size is 3 const vector<int>::size_type size = v.size(); cout << size...

In Python 3, many of the dictionary methods are quite different in behaviour from Python 2, and many were removed as well: has_key, iter* and view* are gone. Instead of d.has_key(key), which had been long deprecated, one must now use key in d. In Python 2, dictionary methods keys, values and items ...

A React component can be defined as an ES6 class that extends the base React.Component class. In its minimal form, a component must define a render method that specifies how the component renders to the DOM. The render method returns React nodes, which can be defined using JSX syntax as HTML-like ta...

The -Wildcard parameter allows switch statements to perform wildcard matching against conditions. Example: switch -Wildcard ('Condition') { 'Condition' {'Normal match'} 'Condit*' {'Zero or more wildcard chars.'} 'C[aoc]ndit[f-l]on' {'Range and set of chars...

docker rm can be used to remove a specific containers like this: docker rm <container name or id> To remove all containers you can use this expression: docker rm $(docker ps -qa) By default docker will not delete a container that is running. Any container that is running will produce a...

The basics After making changes to your source code, you should stage those changes with Git before you can commit them. For example, if you change README.md and program.py: git add README.md program.py This tells git that you want to add the files to the next commit you do. Then, commit your...

Channels can be used to send data from one thread to another. Below is an example of a simple producer-consumer system, where the main thread produces the values 0, 1, ..., 9, and the spawned thread prints them: use std::thread; use std::sync::mpsc::channel; fn main() { // Create a channel...

Suppose you have a Dockerfile ending with ENTRYPOINT [ "nethogs"] CMD ["wlan0"] if you build this image with a docker built -t inspector . launch the image built with such a Dockerfile with a command such as docker run -it --net=host --rm inspector ,nethogs will monitor the...

For if you have to fine-tune what is published. import { Mongo } from 'meteor/mongo'; import { Meteor } from 'meteor/meteor'; import { Random } from 'meteor/random'; if (Meteor.isClient) { // established this collection on the client only. // a name is required (first parameter) and this...

Support for type hinting array parameters (and return values after PHP 7.1) was added in PHP 5.1 with the keyword array. Any arrays of any dimensions and types, as well as empty arrays, are valid values. Support for type hinting callables was added in PHP 5.4. Any value that is_callable() is valid ...

It is important for someone traversing through the git log to easily understand what each commit was all about. Good commit messages usually include a number of a task or an issue in a tracker and a concise description of what has been done and why, and sometimes also how it has been done. Better m...

A Broadcast receiver is an Android component which allows you to register for system or application events. A receiver can be registered via the AndroidManifest.xml file or dynamically via the Context.registerReceiver() method. public class MyReceiver extends BroadcastReceiver { @Override ...

Intents can be used to broadcast messages to other components of your application (such as a running background service) or to the entire Android system. To send a broadcast within your application, use the LocalBroadcastManager class: Intent intent = new Intent("com.example.YOUR_ACTION"...

Bear in mind that declaring a destructor inhibits the compiler from generating implicit move constructors and move assignment operators. If you declare a destructor, remember to also add appropriate definitions for the move operations. Furthermore, declaring move operations will suppress the genera...

Define your class that will represent your custom error. public class ErrorDto { public int Code { get; set; } public string Message { get; set; } // other fields public override string ToString() { return JsonConvert.SerializeObject(this); } } Then put nex...