What is a DataView?

A DataView is not a new data store. Instead, it is a powerful object that allows you to dynamically sort and filter the rows of a DataTable without modifying the original table itself. Each DataView object is associated with a single DataTable.

You can create multiple DataView objects for the same DataTable, each with its own unique sorting and filtering criteria. This makes it very efficient to present the same data in different ways to the end-user.

Key Features of DataView

• Sorting: Define a sort order for the rows based on one or more columns.
• Filtering: Apply filter expressions to display only a subset of rows that meet specific criteria.
• Row Navigation: Move forwards and backwards through the rows of the view.
• Dynamic Updates: Changes made to the underlying DataTable are reflected in the DataView automatically (and vice-versa, with some restrictions).
• Data Binding: Easily bind to UI controls like DataGrid (Windows Forms) or GridView (ASP.NET).

Creating and Using a DataView

To use a DataView, you first need a DataTable. You can then create a DataView instance and associate it with the table.

Example: Basic Usage

using System;
using System.Data;

public class DataViewExample
{
    public static void Main(string[] args)
    {
        // 1. Create a DataTable
        DataTable customersTable = new DataTable("Customers");
        customersTable.Columns.Add("CustomerID", typeof(int));
        customersTable.Columns.Add("CompanyName", typeof(string));
        customersTable.Columns.Add("City", typeof(string));

        customersTable.Rows.Add(1, "Alfreds Futterkiste", "Berlin");
        customersTable.Rows.Add(2, "Ana Trujillo Emparedados y helados", "México D.F.");
        customersTable.Rows.Add(3, "Around the Horn", "London");
        customersTable.Rows.Add(4, "Berglunds snabbköp", "Luleå");
        customersTable.Rows.Add(5, "Blauer See Delikatessen", "Mannheim");

        // 2. Create a DataView from the DataTable
        DataView customerView = new DataView(customersTable);

        // 3. Apply sorting
        customerView.Sort = "CompanyName ASC";

        Console.WriteLine("Customers sorted by Company Name:");
        foreach (DataRowView rowView in customerView)
        {
            Console.WriteLine($" - {rowView["CompanyName"]} ({rowView["City"]})");
        }

        Console.WriteLine("\n---------------------------\n");

        // 4. Apply filtering
        customerView.RowFilter = "City = 'London'";
        customerView.Sort = "CustomerID DESC"; // Sorting can be changed

        Console.WriteLine("Customers from London (sorted by CustomerID DESC):");
        foreach (DataRowView rowView in customerView)
        {
            Console.WriteLine($" - {rowView["CompanyName"]} ({rowView["City"]})");
        }
    }
}
                    

Sorting

The Sort property of a DataView accepts a string that specifies the column(s) to sort by and the order (ASC for ascending, DESC for descending). Multiple columns can be specified, separated by commas.

Example: customerView.Sort = "City DESC, CompanyName ASC";

Filtering

The RowFilter property accepts a string expression that specifies the criteria for filtering rows. The syntax is similar to the WHERE clause in SQL.

Common operators: =, <, >, <=, >=, <>, LIKE, IN.

String values should be enclosed in single quotes ('). Numeric values do not need quotes.

Example: customerView.RowFilter = "CustomerID > 100 AND City LIKE 'A%'";

DataRowView

When you iterate through a DataView, you get DataRowView objects. These objects provide access to the data in a particular row of the view. You can access columns by name or by index.

DataRowView currentRow = (DataRowView)customerView[0]; // Get the first row in the view
string companyName = currentRow["CompanyName"].ToString();
                    

Common Scenarios

• Displaying data in a grid with sortable columns.
• Creating master-detail relationships where a selection in one grid filters another.
• Implementing search functionalities that filter data based on user input.