Tutorial by Examples: l

This helper validates that the specified attributes are not empty. class Person < ApplicationRecord validates :name, presence: true end Person.create(name: "John").valid? # => true Person.create(name: nil).valid? # => false You can use the absence helper to validate th...

Use following methods if you want to skip the validations. These methods will save the object to the database even if it is invalid. decrement! decrement_counter increment! increment_counter toggle! touch update_all update_attribute update_column update_columns update_counters You ca...

class Person < ApplicationRecord validates :name, length: { minimum: 2 } validates :bio, length: { maximum: 500 } validates :password, length: { in: 6..20 } validates :registration_number, length: { is: 6 } end The possible length constraint options are: :minimum - The attribut...

The special attribute __name__ of a function, class or module is a string containing its name. import os class C: pass def f(x): x += 2 return x print(f) # <function f at 0x029976B0> print(f.__name__) # f print(C) # <class '__main__.C'> print(C.__name__...

Overload resolution occurs after name lookup. This means that a better-matching function will not be selected by overload resolution if it loses name lookup: void f(int x); struct S { void f(double x); void g() { f(42); } // calls S::f because global f is not visible here, ...

While it might seem counterintuitive, you can use logical operators to determine whether or not a statement is run. For instance: File.exist?(filename) or STDERR.puts "#{filename} does not exist!" This will check to see if the file exists and only print the error message if it doesn't....

First: The path structure If you don't have it you need to create the middleware folder within your app following the structure: yourproject/yourapp/middleware The folder middleware should be placed in the same folder as settings.py, urls, templates... Important: Don't forget to create the ini...

Boolean logic expressions, in addition to evaluating to True or False, return the value that was interpreted as True or False. It is Pythonic way to represent logic that might otherwise require an if-else test. And operator The and operator evaluates all expressions and returns the last expressi...

Say we have the following tree: root - A - AA - AB - B - BA - BB - BBA Now, if we wish to list all the names of the elements, we could do this with a simple for-loop. We assume there is a function get_name() to return a string of the name of a node, a function get_children() t...

If you have your data stored in a list and you want to convert this list to a data frame the do.call function is an easy way to achieve this. However, it is important that all list elements have the same length in order to prevent unintended recycling of values. dataList <- list(1:3,4:6,7:9) ...

class PostsController < ApplicationController before_action :set_post, only: [:show, :edit, :update, :destroy] def index @posts = Post.all end def show end def new @post = Post.new end def edit end def create @post = Post.new(post_par...

Number of unique elements in a series: In [1]: id_numbers = pd.Series([111, 112, 112, 114, 115, 118, 114, 118, 112]) In [2]: id_numbers.nunique() Out[2]: 5 Get unique elements in a series: In [3]: id_numbers.unique() Out[3]: array([111, 112, 114, 115, 118], dtype=int64) In [4]: df = pd.Da...

Detailed instructions on getting tomcat set up or installed.

SAS can be run in client-server model, using either the Enterprise Guide thick client or the SAS Studio thin (web-enabled) client, or in "local server" mode where a fully functional SAS system is present on a local machine (Windows or Unix/Linux desktop or server running in interactive mod...

Ever wanted to call a multicast delegate but you want the entire invokation list to be called even if an exception occurs in any in the chain. Then you are in luck, I have created an extension method that does just that, throwing an AggregateException only after execution of the entire list complete...

To increase the maximum amount of heap memory used Eclipse, edit the eclipse.ini file located in the Eclipse installation directory. This file specifies options for the startup of Eclipse, such as which JVM to use, and the options for the JVM. Specifically, you need to edit the value of the -Xmx JV...

OnClick Listener: @OnClick(R.id.login) public void login(View view) { // Additional logic } All arguments to the listener method are optional: @OnClick(R.id.login) public void login() { // Additional logic } Specific type will be automatically casted: @OnClick(R.id.submit) publi...

You need to set who you are *before* creating any commit. That will allow commits to have the right author name and email associated to them. It has nothing to do with authentication when pushing to a remote repository (e.g. when pushing to a remote repository using your GitHub, BitBucket, or Gi...

Using parse_line() of Text::ParseWords: use 5.010; use Text::ParseWords; my $line = q{"a quoted, comma", word1, word2}; my @parsed = parse_line(',', 1, $line); say for @parsed; Output: "a quoted, comma" word1 word2

Similar to the built-in function zip(), itertools.zip_longest will continue iterating beyond the end of the shorter of two iterables. from itertools import zip_longest a = [i for i in range(5)] # Length is 5 b = ['a', 'b', 'c', 'd', 'e', 'f', 'g'] # Length is 7 for i in zip_longest(a, b): x...