Hi SUJAYS,

Refer below example.

For reading connection string refer below article.

.Net Core: Read Connection String inside Startup.cs from AppSettings.json file

Database

I have made use of table Customers with the schema as follows. CustomerId is an Auto-Increment (Identity) column.

I have already inserted few records in the table.

You can download the database table SQL by clicking the download link below.         

Download SQL file

Namespaces

using System.Data;
using System.Data.SqlClient;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Configuration;

Model

public class Customer
{
    public int Id { set; get; }
    public string Name { set; get; }
    public string Country { set; get; }
    public IEnumerable<Customer> Customers { get; set; }
}

Controller

public class HomeController : Controller
{
    private IConfiguration Configuration;
    public HomeController(IConfiguration _configuration)
    {
        Configuration = _configuration;
    }
    private string GetConnectionString()
    {
        return this.Configuration.GetConnectionString("MyConn");
    }
    public List<Customer> GetCustomers(int? id)
    {
        List<Customer> customers = new List<Customer>();
        using (SqlConnection con = new SqlConnection(GetConnectionString()))
        {
            using (SqlCommand cmd = new SqlCommand())
            {
                cmd.Connection = con;
                cmd.CommandType = CommandType.Text;
                cmd.Parameters.Clear();
                if (id != null)
                {
                    cmd.CommandText = "SELECT * FROM Customers WHERE CustomerId = @Id";
                    cmd.Parameters.AddWithValue("@Id", id);
                }
                else
                {
                    cmd.CommandText = "SELECT * FROM Customers";
                }
                con.Open();
                SqlDataReader rdr = cmd.ExecuteReader();
                while (rdr.Read())
                {
                    customers.Add(new Customer()
                    {
                        Id = Convert.ToInt32(rdr["CustomerId"]),
                        Name = rdr["Name"].ToString(),
                        Country = rdr["Country"].ToString()
                    });
                }
                con.Close();
            }
        }

        return customers;
    }
    public void AddUpdateDeleteCustomer(Customer customer, string action)
    {
        using (SqlConnection con = new SqlConnection(GetConnectionString()))
        {
            using (SqlCommand cmd = new SqlCommand())
            {
                cmd.CommandType = CommandType.Text;
                cmd.Connection = con;
                cmd.Parameters.Clear();
                if (action == "Insert")
                {
                    cmd.CommandText = "INSERT INTO Customers VALUES (@Name,@Country)";
                    cmd.Parameters.AddWithValue("@Name", customer.Name);
                    cmd.Parameters.AddWithValue("@Country", customer.Country);
                }
                else if (action == "Update")
                {
                    cmd.CommandText = "UPDATE Customers SET NAME = @Name,Country = @Country WHERE CustomerId = @Id";
                    cmd.Parameters.AddWithValue("@Id", customer.Id);
                    cmd.Parameters.AddWithValue("@Name", customer.Name);
                    cmd.Parameters.AddWithValue("@Country", customer.Country);
                }
                else if (action == "Delete")
                {
                    cmd.CommandText = "DELETE FROM Customers WHERE CustomerId = @Id";
                    cmd.Parameters.AddWithValue("@Id", customer.Id);
                }
                con.Open();
                cmd.ExecuteNonQuery();
                con.Close();
            }
        }
    }
    public IActionResult Index()
    {
        ViewBag.Name = "Add";
        Customer customer = new Customer();
        customer.Customers = GetCustomers(null);
        return View(customer);
    }
    public IActionResult Create(Customer customer)
    {
        AddUpdateDeleteCustomer(customer, "Insert");
        return RedirectToAction("Index");
    }
    public IActionResult Edit(int id)
    {
        ViewBag.Name = "Update";
        Customer customer = new Customer();
        customer.Id = id;
        customer.Name = GetCustomers(id).FirstOrDefault().Name;
        customer.Country = GetCustomers(id).FirstOrDefault().Country;
        customer.Customers = GetCustomers(null);
        return View("Index", customer);
    }
    public IActionResult Update(Customer customer)
    {
        ViewBag.Name = "Add";
        AddUpdateDeleteCustomer(customer, "Update");
        return RedirectToAction("Index");
    }
    public IActionResult Delete(int id)
    {
        ViewBag.Name = "Add";
        AddUpdateDeleteCustomer(new Customer { Id = id }, "Delete");
        return RedirectToAction("Index");
    }
}

View

Index

@model ASP.Net_Core_MVC_CRUD.Models.Customer

@{
    Layout = null;
}

<!DOCTYPE html>

<html>
<head>
    <meta name="viewport" content="width=device-width" />
    <title>Index</title>
    <link href="~/lib/bootstrap/dist/css/bootstrap.css" rel="stylesheet" />
</head>
<body>
    <div class="container">
        <div class="row">
            <div class="col-lg-12">
                <h4>Customers</h4>
                <table class="table table-responsive">
                    <thead>
                        <tr>
                            <th>@Html.DisplayNameFor(model => model.Name)</th>
                            <th>@Html.DisplayNameFor(model => model.Country)</th>
                            <th></th>
                            <th></th>
                        </tr>
                    </thead>
                    <tbody>
                        @foreach (Customer customer in Model.Customers)
                        {
                            <tr>
                                <td>@Html.DisplayFor(x => customer.Name)</td>
                                <td>@Html.DisplayFor(x => customer.Country)</td>
                                <td>@Html.ActionLink("Edit", "Edit", new { id = customer.Id }, new { @class = "btn btn-primary btn-sm" })</td>
                                <td>@Html.ActionLink("Delete", "Delete", new { id = customer.Id }, new { onclick = "return confirm('Are you sure you wish to delete this Customer?');", @class = "btn btn-danger btn-sm" })</td>
                            </tr>
                        }
                    </tbody>
                </table>
            </div>
        </div>
    </div>
    @Html.Partial("_InsertUpdatePartial", Model)
</body>
</html>

PartialView

@addTagHelper*, Microsoft.AspNetCore.Mvc.TagHelpers
@model ASP.Net_Core_MVC_CRUD.Models.Customer

<div class="container">
    <h4>Add/Update Customer</h4>
    <hr />
    <div class="row">
        <div class="col-md-4">
            <form asp-action="Create" asp-controller="Home">
                <div class="form-group">
                    <label asp-for="Id" class="control-label"></label>
                    <input asp-for="Id" class="form-control" readonly="readonly" />
                </div>
                <div class="form-group">
                    <label asp-for="Name" class="control-label"></label>
                    <input asp-for="Name" class="form-control" />
                </div>
                <div class="form-group">
                    <label asp-for="Country" class="control-label"></label>
                    <input asp-for="Country" class="form-control" />
                </div>
                <div class="form-group">
                    @if (ViewBag.Name == "Add")
                    {
                        <input type="submit" value="Add" class="btn btn-success btn-sm" />
                    }
                    else
                    {
                        <input type="submit" value="Update" asp-action="Update" class="btn btn-success btn-sm" />
                        <input type="submit" value="Cancel" asp-action="Index" class="btn btn-defaul btn-sm" />
                    }
                </div>
            </form>
        </div>
    </div>
</div>

Screenshot