How to select N Random Items from the List in C#

This post is about, how to select N Random Items from any T list in C# 

 e.g. Say we have IList with total count of 1000 and we need to get 100 random items from the List. We should use following function to return N Random Items from any List in C#

public IEnumerable <T> PickRandom<T>(IEnumerable<T> list, int number)
{
    var random = new Random();
    var total = list.Count();
    var required = number;
    foreach (var item in list)
    {
        if (random.Next(total) < required)
        {
            required--;
            yield return item;
            if (required == 0)
            {
                break;
            }
        }
        total--;
    }
}

How to add/embed custom font in xamarin forms

 Embedding fonts in Xamarin Forms is the best way to use fonts, there is no need to add platform specific fonts and code. Its just adding one file and adding one attribute in shared code; that's it; we are ready to use fonts in our code. 

How to add fonts in Xamarin Forms

 In just three steps we shall add custom fonts in Xamarin forms and use it across all the platforms i.e. Android, iOS and UWP.

Before we get into Embedding fonts in Xamarin Forms, lets create a Xamarin Form project using following steps.

After creating project make sure it builds and we are able to see it on Emulator or on Mobile Device

After building the Xamarin Form and running it on simulator, we see simple (default) UI as follows

For Demo purpose we shall use a custom fonts named - Game Of Squids, you can download it using the link - https://www.dafont.com/game-of-squids.font 

Add the font file (ttf or otf) to our project and mark it as embedded resource

Now to Embed or Add above custom font in Xamarin Forms, use following steps

Create folder structure - Resources > Fonts > GameOfSquids.ttf

 Copy font and then click on properties as shown in following image

We have to make sure we select Build Action as Embedded Resource as per following image

If we don't set Build Action as Embedded resource then font added in Xamarin forms will not get applied. We have to make sure Font added in Xamarin forms had build Action set as Embedded Resource.

Add ExportFont attribute in our shared code

We shall add ExportFont attribute to one of the files either App.xml.cs or AssemblyInfo.cs, since the attribute will register it on assembly level, we can put it at any one of the location

Anywhere outside the namespace add following line

[assembly: ExportFont("GameOfSquids.ttf", Alias = "GameOfSquids")]

 AssemblyInfo.cs code changes to following

using Xamarin.Forms;
using Xamarin.Forms.Xaml;

[assembly: XamlCompilation(XamlCompilationOptions.Compile)]
[assembly: ExportFont("GameOfSquids.ttf", Alias = "GameOfSquids")]

Now simply Consume the font in our controls

Check following code, we simply added FontFamily="GamesOfSquids" in the autogenerated MainPage.xaml file

That's it, now if we compile code it and put it on Emulator, we can see the changed font. Default font changes to GamesOfSquids

This is how we add custom fonts in Xamarin form

How to Temporarily disable all foreign key constraints

 While working with MSSQL and Asp.net Core with Entity Framework, many times we have came across a situation where we have to migrate data from one database to newly created database. e.g. Copying all the data from Production DB to Testing DB. 

• Using Entity Framework Code First approach, we create database
• Once database is created, need to copy all the data from MSSQL (Generate script > Dataonly); create Database script for the data
• Now while running the script generated from PROD db to Test DB (there could me some modifications in test db, some columns are added) , we need to disable foreign key constraint and then re-enable foreign key constraints

 

How to disable all the foreign key constraints in MSSQL and then again re-enable all the foreign key constraints in MSSQL 

We can use following scripts

-- Disable all the constraint in database
EXEC sp_msforeachtable 'ALTER TABLE ? NOCHECK CONSTRAINT all'

-- Enable all the constraint in database
EXEC sp_msforeachtable 'ALTER TABLE ? WITH CHECK CHECK CONSTRAINT all'

This is the most easiest way to Disable and Enable all the Foreign key constraints on MSSQL.

Calculate next due date based on start date frequency and current date in c#

During one project development there is one scenario which made me write this post.

Scenario is as follows

Company has clients, each has different invoice start date and invoice frequency. I had to calculate and display next invoice date from current date + next month. i.e. invoice will always be raised in next month of service completion. e.g. Client A has invoice start date 01-Jan-2021 and invoice frequency is 5 months. Date when I am writing this post is 17-April-2021. So now next invoice date for Client A is 01-June-2021. For client B invoice start date is 01-March-2021 and invoice frequency is 3 months, then its next invoice date is 01-June-2021 and so on for all other client. 

To handle this scenarios I have written following function in c# which will always returns next invoice date from Current date. 

public class DateHelper
{
 public static DateTime nextInvoiceDate(DateTime? InvoicingStartDate,
    string invoicingFrequency)
     {
     int occurrence =
     (DateTime.Now.Month - Convert.ToInt32(InvoicingStartDate?.Month)) 
     / Convert.ToInt32(invoicingFrequency);
     
     int restInt = 
     (DateTime.Now.Month - Convert.ToInt32(InvoicingStartDate?.Month)) 
     % Convert.ToInt32(invoicingFrequency);
     DateTime next = InvoicingStartDate.Value;
            int multi;
            if (restInt == 0 && DateTime.Now < InvoicingStartDate)
            {
                if (Convert.ToInt32(invoicingFrequency) == 1 && occurrence < 0)
                {
                    multi = 1;
                }
                else
                {
                    multi = Convert.ToInt32(invoicingFrequency)
                    * Math.Abs(occurrence);
                }
                
            }
            else
            {
                if (Convert.ToInt32(invoicingFrequency) == 1)
                {
                    multi = Convert.ToInt32(invoicingFrequency)
                    * (Math.Abs(occurrence));
                }
                else
                {
                    multi = Convert.ToInt32(invoicingFrequency) 
                    * (Math.Abs(occurrence) + 1);
                }

            }
            return next.AddMonths(multi);

        }
    }

• How to calculate a future date based on a given date ?
• Calculate next due date based on start date frequency and current date ?
• How to nearest future date from given date and frequency ?
• Best way to calculate next date from start plus frequency
• How to calculate next meeting date based on given frequency ?

After Configuring IIS on VM Server - How to access sites hosted on IIS On VM over internet

 Once we are done with Installing IIS on Azure VM, we need to open port 80 to access hosted website from internet.

Check - How to Setup IIS On Azure VM

To Enable port 80, simply login to your Azure portal, and click on VM

Then click on Networking, on click of Networking, network interface will open up, then clikc on Add Inbound port rule.

And add port 80

Once you create a rule, simply hit the Azure VM IP address from browser, it should show you default IIS page.

This is how we allow HTTP traffic to IIS hosted site on Azure VM server

How To Setup IIS on Azure VM - Configure IIS on Azure VM

 Once we have setup the Azure VM, next important thing is to Setup an IIS in the windows server and enable it to access from anywhere. So that we can host our web application on VM and access it over an Internet.

In this article, we shall achieve it.

To Enable IIS on Azure VM server

• Under Server Manager click on Manage > Add Roles and Features

Once we click on Add Roles and Features following screen will appear

Click next and go to Select Installation Type, select Role-Based or feature-based installation

On click of Next you will go to Server Selection screen, here you will see default server under server pool. Make sure Select a server from the server pool is selected

Now in Server Roles select Web Server (IIS)

Once we select Web Server (IIS) and click on Next, one pop up will appear, click on Add Features, check following image

Now select .Net framework 4.5 Features and any other required feature from list and click on next

Click on Next 

Click on Next and Select from Role Services

Now you will see confirmation screen 

Now on click of install, IIS will be installed on Azure VM. 

You can run IIS using inetmgr command

Do Win+R and type inetmger and IIS will open up.

This is how we should Setup IIS on Azure VM 

The razortaghelper task failed unexpectedly

 After updating Visual studio to New version, I suddenly started getting error 

the razortaghelper task failed unexpectedly

Well after doing some research on Internet I came across following solutions

Added the following environment variable to my user environment to make it build again:
DOTNET_HOST_PATH

%ProgramFiles%\dotnet\dotnet.exe 

Simply go to Environment Variable, check following images

 

After clicking on Environment Variables, click on New, Pop up will open up, simply add entries as per following image and click Ok

Now when you build The razortaghelper task failed unexpectedly error will go away.

How to compile Less, sass/scss, JSX, ES6, CoffeeScript in visual studio

 It is very easy to compile LESS and SCSS files in visual studio. To do this we have to use Web Compiler extension. Web compiler extension generates css file from LESS and SCSS files on run time.

Lets Install the Extension

We can download the extension from https://marketplace.visualstudio.com/items?itemName=MadsKristensen.WebCompiler

Simply download and install the extension. WebCompiler extension allows us to compile LESS, Sass, JSX, ES6 and CoffeeScript files.

Followings are the features of this extension

• Compilation of LESS, Scss, Stylus, JSX, ES6 and CoffeeScript files
• Saving a source file which triggers re-compilation automatically
• Specify compiler options for each individual file
• Error list is integrated
• MSBuild support for CI scenarios
• Minify the compiled output
• Customizable minification options for each language
• Displays a watermark when opening generated file
• Shortcut to compile all specified files in solution
• Task runner explorer is integrated
• Command line interface

Lets assume we have Visual studio solution and it Contains SCSS files, it can contain files with any of these extensions .less, .scss, .styl, .jsx, .es6 or .coffee




Any of above extensions can be compiled, for this article lets consider only scss extension, 

We have many scss files like the following image

We have style.scss file which combines all the scss files, it looks like as follows

@import 'variabls';
@import 'mixin';
@import 'common';
@import 'element/button';
@import 'section/header';
@import 'section/slider';
@import 'section/banner';
@import 'section/product';
@import 'section/blog';
@import 'section/newsletter';
@import 'section/shipping';
@import 'section/testimonial';
@import 'section/brand';
@import 'section/footer';
@import 'section/shop';
@import 'section/product-details';
@import 'section/cart-page';
@import 'section/checkout';
@import 'section/wishlist';
@import 'section/contact';
@import 'section/login';
@import 'section/faq';
@import 'section/my-account';
@import 'section/about';
@import 'section/services';
@import 'section/blog-page';
@import 'section/blog-details';
@import 'section/quick-view';
@import 'section/newsletter-popup';
@import 'section/404';
@import 'section/privacy-policy';

Now simply right click on the style.scss file and click on Web Compiler > Compile file.

A file named compilerconfig.json is created in the root of the project. This file looks like.

[
  {
    "outputFile": "wwwroot/assets/css/style.css",
    "inputFile": "wwwroot/assets/scss/style.scss"
  }
]

We can always change the outputFile path to our css folder, I have changed it in this example to css file. Similary there is one more file named compilerconfig.json.defaults which get generated and can be used to configure minification of js/css, check following file and you can modify it as per your requirements

{
  "compilers": {
    "less": {
      "autoPrefix": "",
      "cssComb": "none",
      "ieCompat": true,
      "strictMath": false,
      "strictUnits": false,
      "relativeUrls": true,
      "rootPath": "",
      "sourceMapRoot": "",
      "sourceMapBasePath": "",
      "sourceMap": false
    },
    "sass": {
      "autoPrefix": "",
      "includePath": "",
      "indentType": "space",
      "indentWidth": 2,
      "outputStyle": "nested",
      "Precision": 5,
      "relativeUrls": true,
      "sourceMapRoot": "",
      "lineFeed": "",
      "sourceMap": false
    },
    "stylus": {
      "sourceMap": false
    },
    "babel": {
      "sourceMap": false
    },
    "coffeescript": {
      "bare": false,
      "runtimeMode": "node",
      "sourceMap": false
    },
    "handlebars": {
      "root": "",
      "noBOM": false,
      "name": "",
      "namespace": "",
      "knownHelpersOnly": false,
      "forcePartial": false,
      "knownHelpers": [],
      "commonjs": "",
      "amd": false,
      "sourceMap": false
    }
  },
  "minifiers": {
    "css": {
      "enabled": true,
      "termSemicolons": true,
      "gzip": false
    },
    "javascript": {
      "enabled": true,
      "termSemicolons": true,
      "gzip": false
    }
  }
}

This is how we can compile Less, sass/scss, jsx, CoffeeScript in visual studio, we can also use this web pack to minify JS files.

How DBCC CHECKIDENT Works - How to Reset identity seed after deleting records in SQL Server

Scenario I faced

I have inserted records into a SQL Server database table. 

The table had a primary key defined and the auto increment identity seed is set to “Yes”.  So now whenever I do an insert in DB my primary key ID starts with number 1,2,3 and so on.

Now say I have total 100 records and I delete all the records, in this case when I insert new records its primary key ID starts with 101, where as I want it to reset to 1. 

So after deleting all records from SQL Server data table, I wanted to reset identity seed to 0, so my next insert should have primary key as 1,2,3 and so on.

Use following Command to Reset SEED

DBCC CHECKIDENT (table_name [, { NORESEED | { RESEED [, new_reseed_value ]}}]) [ WITH NO_INFOMSGS ]

Example : 

  DBCC CHECKIDENT ('[TableName]', RESEED, 0); GO

Above example will Reset Identity value to initial value i.e. new entry will start from 1

In case we want to Force Identity value to set to Some specific number we use it as follows DBCC 







CHECKIDENT ('[TableName]', RESEED, 10);

So what is the Seed value and when we cannot reset it

The seed value is the value inserted into an identity column for the first row loaded into the table. All subsequent rows contain the current identity value plus the increment value where current identity value is the last identity value generated for the table or view.

You can't use DBCC CHECKIDENT for the following tasks:

• We cannot Change the original seed value specified for an identity column when the table or view was created.

• Cannot be used to Reseed existing rows in a table or view.

To change the original seed value and reseed any existing rows, we need to drop the identity column and recreate it specifying the new seed value. When the table contains data, the identity numbers are added to the existing rows with the specified seed and increment values. The order in which the rows are updated isn't guaranteed.

The entity type 'IdentityUserLogin' requires a primary key to be defined.

While developing Web application in Asp.net Core Razor page, I have come across following error

InvalidOperationException: The entity type 'IdentityUserLogin<string>' requires a primary key to be defined.

I was doing following thing in my application

• I wanted to set Unique Key constraint on Email for my two models i.e. Vendor and Member model so I had added code below in my ApplicationDbContext file. (You may have different name for your DbContext file.)

 public class ApplicationDbContext : IdentityDbContext<ApplicationUser>
    {
     public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options)
          : base(options)
        {

        }

        protected override void OnModelCreating(ModelBuilder builder)
        {
            builder.Entity<Member>().HasIndex(m => m.Email).IsUnique();
            builder.Entity<Vendor>().HasIndex(v => v.Email).IsUnique();
        }

        public DbSet<Vendor> Vendors { get; set; }

        public DbSet<Member> Members { get; set; }
        
    }    

Here if we see closely, I am missing base model Creating function. When I build and run code I get error saying 

 InvalidOperationException: The entity type 'IdentityUserLogin' requires a primary key to be defined.

 

To Resolve this error, I have added   base.OnModelCreating(builder);  in ApplicationDbContext 

check following code 

public class ApplicationDbContext : IdentityDbContext<ApplicationUser>
    {
     public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options)
          : base(options)
        {

        }

        protected override void OnModelCreating(ModelBuilder builder)
        {
            builder.Entity<Member>().HasIndex(m => m.Email).IsUnique();
            builder.Entity<Vendor>().HasIndex(v => v.Email).IsUnique();
            
              base.OnModelCreating(builder);
        }

        public DbSet<Vendor> Vendors { get; set; }

        public DbSet<Member> Members { get; set; }
        
    }     

This blog answers query - How to resolve The entity type 'IdentityUserLogin<string>' requires a primary key to be defined.