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 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 ?

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.

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.