Tutorial by Examples: d

When Oracle implicitly converts from a DATE to a string or vice-versa (or when TO_CHAR() or TO_DATE() are explicitly called without a format model) the NLS_DATE_FORMAT session parameter will be used as the format model in the conversion. If the literal does not match the format model then an excepti...

When SQL/Plus or SQL Developer display dates they will perform an implicit conversion to a string using the default date format model (see the Setting the Default Date Format Model example). You can change how a date is displayed by changing the NLS_DATE_FORMAT parameter.

set(my_global_string "a string value" CACHE STRING "a description about the string variable") set(my_global_bool TRUE CACHE BOOL "a description on the boolean cache entry") In case a cached variable is already defined in the cache when CMake processes the ...

When it comes to geographic data, R shows to be a powerful tool for data handling, analysis and visualisation. Often, spatial data is avaliable as an XY coordinate data set in tabular form. This example will show how to create a spatial data set from an XY data set. The packages rgdal and sp provi...

package { import flash.text.TextField; import flash.display.Sprite; public class TextHello extends Sprite { public function TextHello() { var tf:TextField = new TextField(); tf.text = "Hello World!" tf.x = 50; tf...

macro(set_my_variable _INPUT) if("${_INPUT}" STREQUAL "Foo") set(my_output_variable "foo") else() set(my_output_variable "bar") endif() endmacro(set_my_variable) Use the macro: set_my_variable("Foo") message(STATUS ${my_outpu...

function listener(e:Event):void { var m:MovieClip=e.target as MovieClip; m.x++; } If such a listener is attached to an object that's not a MovieClip descendant (for example, a Sprite), the typecast will fail, and any subsequent operations with its result will throw the 1009 error.

var a:Object; trace(a); // null trace(a.b); // Error 1009 Here, an object reference is declared, but is never assigned a value, be it with new or assignment of a non-null value. Requesting its properties or method results in a 1009 error.

x=anObject.aProperty.anotherProperty.getSomething().data; Here, any object before the dot can end up being null, and using methods that return complex objects only increases the complication to debug the null error. Worst case if the method is prone to extraneous failures, say retrieving data ove...

s=this.getChildByName("garbage"); if (s.parent==this) {...} getChildByName() is one of the many functions that can return null if an error occurred when processing its input. Therefore, if you are receiving an object from any function that can possibly return null, check for null first...

interface ITable { // an indexer can be declared in an interface object this[int x, int y] { get; set; } } class DataTable : ITable { private object[,] cells = new object[10, 10]; /// <summary> /// implementation of the indexer declared in the interface //...

To destroy, delete, or unset an array: unset array To destroy, delete, or unset a single array element: unset array[10]

Get the list of inialized indexes in an array $ arr[2]='second' $ arr[10]='tenth' $ arr[25]='twenty five' $ echo ${!arr[@]} 2 10 25

Rescue from record not found error instead of showing an exception or white page: class ApplicationController < ActionController::Base # ... your other stuff here rescue_from ActiveRecord::RecordNotFound do |exception| redirect_to root_path, 404, alert: 'Record not found' en...

The JsonPipe can be used for debugging the state of any given internal. Code @Component({ selector: 'json-example', template: `<div> <p>Without JSON pipe:</p> <pre>{{object}}</pre> <p>With JSON pipe:</p> <pre>{{object | json...

This validation restricts the insertion of only numeric values. class Player < ApplicationRecord validates :points, numericality: true validates :games_played, numericality: { only_integer: true } end Besides :only_integer, this helper also accepts the following options to add constrai...

This helper validates that the attribute's value is unique right before the object gets saved. class Account < ApplicationRecord validates :email, uniqueness: true end There is a :scope option that you can use to specify one or more attributes that are used to limit the uniqueness check: ...

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...