In ADO.NET, disconnected data access means fetching data from a database, working with it in-memory (using DataSet, DataTable, or DataView), and not maintaining an active connection to the database.

DataView operates on a DataTable, which is disconnected from the database once data is retrieved. Below is a demonstration proving that DataView works without a continuous database connection.

Fetch Data from Database (Open Connection Only Once)

using System;
using System.Data;
using System.Data.SqlClient;

class Program
{
    static void Main()
    {
        // Connection string (Modify based on your database)
        string connectionString = "Server=your_server;Database=your_db;Integrated Security=True;";

        // Disconnected data access: Fetch data once, then close connection
        DataTable dt = new DataTable();

        using (SqlConnection conn = new SqlConnection(connectionString))
        {
            conn.Open();
            string query = "SELECT ID, Name, Age FROM Employees";  // Fetch data from DB
            SqlDataAdapter adapter = new SqlDataAdapter(query, conn);
            adapter.Fill(dt);  // Data loaded into DataTable (Disconnected)
            conn.Close();  // Connection is now closed
        }

        // 💡 Proof: Data is stored in-memory. We no longer need the database connection.
        Console.WriteLine("Database Connection is Closed!");
        Console.WriteLine($"Total Rows Retrieved: {dt.Rows.Count}");

        // Creating DataView from DataTable
        DataView dv = new DataView(dt);

        // Apply Sorting
        dv.Sort = "Age ASC";

        // Apply Filtering (Only employees older than 25)
        dv.RowFilter = "Age > 25";

        // Display Data (Working without DB connection)
        Console.WriteLine("\nFiltered Employees (Age > 25):");
        foreach (DataRowView row in dv)
        {
            Console.WriteLine($"ID: {row["ID"]}, Name: {row["Name"]}, Age: {row["Age"]}");
        }

        // Proving disconnection: Modify DataView without any DB connection
        DataRowView newRow = dv.AddNew();
        newRow["ID"] = 999;
        newRow["Name"] = "John Doe";
        newRow["Age"] = 35;
        newRow.EndEdit();

        Console.WriteLine("\nNew Row Added (Without DB Connection):");
        foreach (DataRowView row in dv)
        {
            Console.WriteLine($"ID: {row["ID"]}, Name: {row["Name"]}, Age: {row["Age"]}");
        }
    }
}

Proof of Disconnected Access

1. Database connection is opened only once to fetch data.
2. Data is stored in DataTable (in-memory storage).
3. DataView operates independently without requiring a live database connection.
4. Sorting, filtering, and adding new rows happen without re-querying the database.