DataTable Class

The DataTable class represents an in-memory collection of data that is organized into tables. It is a core component of ADO.NET and is used to store and manipulate data from various sources, such as databases, XML files, or business objects.

Overview

A DataTable is analogous to a single table in a relational database. It contains:

A collection of DataColumn objects, which define the schema of the table (column names, data types, constraints).
A collection of DataRow objects, which represent the individual records within the table.
A collection of Constraint objects (like unique constraints and foreign key constraints) that enforce data integrity.

DataTable is a versatile class that can be used independently or as part of a DataSet, which is a collection of related DataTable objects.

Key Properties and Methods

Properties

Property	Description
`Columns`	Gets a collection of `DataColumn` objects that define the schema of the table.
`Rows`	Gets a collection of `DataRow` objects that represent the data in the table.
`TableName`	Gets or sets the name of the table.
`DataSet`	Gets the `DataSet` that contains this table.
`HasErrors`	Gets a value indicating whether any row in the table has an error.

Methods

Method	Description
`NewRow()`	Creates a new `DataRow` with the same schema as the table.
`Rows.Add(DataRow row)`	Adds a specified `DataRow` to the table.
`AcceptChanges()`	Accepts all changes made to the table since the last time `AcceptChanges` was called.
`RejectChanges()`	Reverts all changes made to the table since the last time `AcceptChanges` was called.
`Select(string filterExpression)`	Returns an array of `DataRow` objects that match the specified filter expression.

Creating and Populating a DataTable

You can create a DataTable programmatically and populate it with data.

C#

                    
using System.Data;

// Create a new DataTable
DataTable productsTable = new DataTable("Products");

// Define the columns
productsTable.Columns.Add("ProductID", typeof(int));
productsTable.Columns.Add("ProductName", typeof(string));
productsTable.Columns.Add("Price", typeof(decimal));

// Set primary key
productsTable.PrimaryKey = new DataColumn[] { productsTable.Columns["ProductID"] };

// Create a new DataRow
DataRow newRow = productsTable.NewRow();
newRow["ProductID"] = 1;
newRow["ProductName"] = "Laptop";
newRow["Price"] = 1200.50m;

// Add the row to the table
productsTable.Rows.Add(newRow);

// Add another row
productsTable.Rows.Add(2, "Keyboard", 75.00m);

// Add a third row using a more explicit method
DataRow row3 = productsTable.NewRow();
row3[0] = 3; // Access by column index
row3[1] = "Mouse";
row3["Price"] = 25.99m;
productsTable.Rows.Add(row3);

// Iterate through rows
Console.WriteLine("Products:");
foreach (DataRow row in productsTable.Rows)
{
    Console.WriteLine($"ID: {row["ProductID"]}, Name: {row["ProductName"]}, Price: {row["Price"]}");
}
                    
                

Filtering and Sorting

The Select method allows you to filter rows based on an expression. You can also use DataView for more advanced sorting and filtering.

C#

                    
// Assuming productsTable is already populated as above

// Filter for products with price greater than 100
DataRow[] expensiveProducts = productsTable.Select("Price > 100");
Console.WriteLine("\nExpensive Products:");
foreach (DataRow row in expensiveProducts)
{
    Console.WriteLine($"ID: {row["ProductID"]}, Name: {row["ProductName"]}, Price: {row["Price"]}");
}

// Sort the table by ProductName
DataRow[] sortedProducts = productsTable.Select("", "ProductName ASC");
Console.WriteLine("\nProducts Sorted by Name:");
foreach (DataRow row in sortedProducts)
{
    Console.WriteLine($"ID: {row["ProductID"]}, Name: {row["ProductName"]}, Price: {row["Price"]}");
}
                    
                

Note:

The filter and sort expressions use a syntax similar to SQL WHERE and ORDER BY clauses, but are specific to DataTable.

DataRow States

Each DataRow has a state that indicates its current status:

Added: The row is new and has not been sent to the data source.
Modified: The row's data has been changed since it was loaded or last accepted.
Deleted: The row has been deleted.
Unchanged: The row has not been changed since it was loaded or last accepted.

You can access the original version of a row using the `Original` version property when checking for changes.

Conclusion

The DataTable class is a fundamental building block for data manipulation in ADO.NET. Its ability to store, filter, and sort data in memory makes it highly efficient for working with data disconnected from its source.