Tutorial by Examples: d

Problem statement: Find the minimum (over x, y) of the function f(x,y), subject to g(x,y)=0, where f(x,y) = 2 * x**2 + 3 * y**2 and g(x,y) = x**2 + y**2 - 4. Solution: We will solve this problem by performing the following steps: Specify the Lagrangian function for the problem Determine the K...

Xamarin is becoming more and more popular - it is hard to decide when to use Xamarin.Forms and when Xamarin.Platform (so Xamarin.iOS and Xamarin.Android). First of all you should know for what kind of applications you can use Xamarin.Forms: Prototypes - to visualize how your application will l...

public static IWebDriver dismissAlert(this IWebDriver driver) { try { IAlert alert = driver.SwitchTo().Alert(); alert.Dismiss(); } catch {} return driver; } public static IWebDriver acceptAlert(this IWebDriver driver) { try { IAlert a...

The function show is automatically exported when use Data::Show; is executed. This function takes a variable as its sole argument and it outputs: the name of the variable the contents of that variable (in a readable format) the line of the file that show is run from the file show is run from ...

Sympy is a Python library for doing symbolic — rather than numeric — calculations. For instance, consider the quadratic equation in x, x**2 + HELLO * x + WORLD = 0 where HELLO and WORLD are constants. What's the solution of this equation? In Python, using Sympy we can code, from sympy import s...

jQuery accepts a wide variety of parameters, and one of them is an actual DOM element. Passing a DOM element to jQuery will cause the underlying array-like structure of the jQuery object to hold that element. jQuery will detect that the argument is a DOM element by inspecting its nodeType. The mos...

In some cases, you would need to execute SQL query placed in string. EXEC, EXECUTE, or system procedure sp_executesql can execute any SQL query provided as string: sp_executesql N'SELECT * FROM sys.objects' -- or sp_executesql @stmt = N'SELECT * FROM sys.objects' -- or EXEC sp_executesql N'SEL...

You can execute SQL query as different user using AS USER = 'name of database user' EXEC(N'SELECT * FROM product') AS USER = 'dbo' SQL query will be executed under dbo database user. All permission checks applicable to dbo user will be checked on SQL query.

Dynamic queries are SET @sql = N'SELECT COUNT(*) FROM AppUsers WHERE Username = ''' + @user + ''' AND Password = ''' + @pass + '''' EXEC(@sql) If value of user variable is myusername'' OR 1=1 -- the following query will be executed: SELECT COUNT(*) FROM AppUsers WHERE Username = 'myusername...

In order to avoid injection and escaping problems, dynamic SQL queries should be executed with parameters, e.g.: SET @sql = N'SELECT COUNT(*) FROM AppUsers WHERE Username = @user AND Password = @pass EXEC sp_executesql @sql, '@user nvarchar(50), @pass nvarchar(50)', @username, @password Second ...

Django's built-in User model is not always appropiate for some kinds of projects. On some sites it might make more sense to use an email address instead of a username for instance. You can override the default User model adding your customized User model to the AUTH_USER_MODEL setting, in your proj...

Your code will not work in projects where you reference the User model (and where the AUTH_USER_MODEL setting has been changed) directly. For example: if you want to create Post model for a blog with a customized User model, you should specify the custom User model like this: from django.conf impo...

There are many reasons a write operation may fail. A frequent one 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 output of your...

Writing a gzipped file To write a gzipped file, use the module IO::Compress::Gzip and create a filehandle by creating a new instance of IO::Compress::Gzip for the desired output file: use strict; use warnings; use open qw( :encoding(UTF-8) :std ); # Make UTF-8 default encoding use IO::Compres...

HTML DOM is Expensive Each web page is represented internally as a tree of objects. This representation is called Document Object Model. Moreover, it is a language-neutral interface that allows programming languages (such as JavaScript) to access the HTML elements. In other words The HTML DOM...

Generating the minimum number of operations to transform one tree into another have a complexity in the order of O(n^3) where n is the number of nodes in the tree. React relies on two assumptions to solve this problem in a linear time - O(n) Two components of the same class will generate sim...

Sometimes, it's better to have only three options style="@android:style/TextAppearance.Small" style="@android:style/TextAppearance.Medium" style="@android:style/TextAppearance.Large" Use small and large to differentiate from normal screen size. <TextView ...

To handle a command, you must have a class that implements the CommandExecutor interface. The JavaPlugin class (your plugin's main class) already implements this. When implementing the CommandExecutor interface, the following method must be implemented: public boolean onCommand(CommandSender sende...

url: /api/data/v8.0/quotedetails json: { "[email protected]": "/products(11c0dbad-91df-e311-b8e5-6c3be5a8b200)", "[email protected]" : "/quotes(69b5e1ae-037f-e611-80ed-fc15b428dcdc)", "[email protected]" : "/uoms(73a5daea-6dd...

Specifies the max degree of parallelism for the query specifying this option. SELECT OrderID, AVG(Quantity) FROM Sales.OrderLines GROUP BY OrderID OPTION (MAXDOP 2); This option overrides the MAXDOP configuration option of sp_configure and Resource Governor. If MAXDOP is set to zero then...