Understanding the `RejectChanges()` Method in ADO.NET with C#

When working with data in C# using ADO.NET, the RejectChanges() method is a powerful feature of the DataTable class. It allows you to discard any changes made to the rows within a DataTable and restore them to their original values. This is particularly useful when you want to cancel modifications without affecting the corresponding data in the database.

In this article, we’ll explore what the RejectChanges() method does, why it’s useful, and how to use it effectively in your C# applications with clear examples and best practices.

What is the `RejectChanges()` Method?

The RejectChanges() method is used to undo changes made to a DataTable and its rows. When you call this method, it:

• Reverts all modified rows to their original state.
• Removes any newly added rows.
• Restores deleted rows.

This method is especially helpful when you want to discard changes temporarily or provide an "undo" feature in your application.

Why Use `RejectChanges()`?

Here are some scenarios where RejectChanges() can be useful:

1. Data Validation: If changes fail validation, you can discard them using RejectChanges().
2. Undo Functionality: Provide users with the ability to undo changes before saving.
3. Temporary Modifications: Make temporary changes to data and revert them if needed.

How Does `RejectChanges()` Work?

The RejectChanges() method works by:

1. Tracking Changes: The DataTable keeps track of changes made to its rows (added, modified, or deleted).
2. Reverting Changes: When RejectChanges() is called, it restores the rows to their original state based on the last time AcceptChanges() was called or when the data was first loaded.

Example: Using `RejectChanges()` in C#

Let’s walk through a practical example to understand how RejectChanges() works.

Step 1: Create a `DataTable`

We’ll create a DataTable named Employee with columns for EmployeeID, FirstName, and LastName.

using System;
using System.Data;

class Program
{
static void Main()
{
// Create a DataTable with columns
DataTable dataTable = new DataTable("Employee");
dataTable.Columns.Add("EmployeeID", typeof(int));
dataTable.Columns.Add("FirstName", typeof(string));
dataTable.Columns.Add("LastName", typeof(string));

Step 2: Add Data to the `DataTable`

We’ll add a new row to the DataTable with initial values.

        // Add a new row to the DataTable
DataRow newRow = dataTable.NewRow();
newRow["EmployeeID"] = 1;
newRow["FirstName"] = "John";
newRow["LastName"] = "Doe";
dataTable.Rows.Add(newRow);

Step 3: Modify the Data

Next, we’ll modify the FirstName and LastName values of the row.

        // Modify the data in the DataRow
newRow["FirstName"] = "Jane";
newRow["LastName"] = "Smith";

Step 4: Display the Original and Modified Data

We’ll display the data before and after calling RejectChanges().

        // Display the original data
Console.WriteLine("Original Data:");
PrintDataTable(dataTable);

// Reject the changes and restore the original values
dataTable.RejectChanges();

// Display the data after rejecting changes
Console.WriteLine("\nAfter Rejecting Changes:");
PrintDataTable(dataTable);
}

// Helper method to display data from the DataTable
static void PrintDataTable(DataTable dt)
{
foreach (DataRow row in dt.Rows)
{
	Console.WriteLine($"{row["EmployeeID"]}, {row["FirstName"]}, {row["LastName"]}");
}
}
}

Output of the Program

When you run the program, the output will look like this:

Original Data:
1, Jane, Smith

After Rejecting Changes:
1, John, Doe

Explanation of the Code

1. DataTable Creation:
   • We create a DataTable named Employee with three columns: EmployeeID, FirstName, and LastName.
2. Adding Data:
   • A new row is added to the DataTable with initial values (EmployeeID = 1, FirstName = "John", LastName = "Doe").
3. Modifying Data:
   • The FirstName and LastName values are updated to "Jane" and "Smith", respectively.
4. Rejecting Changes:
   • The RejectChanges() method is called to discard the modifications and restore the original values.
5. Displaying Data:
   • The PrintDataTable() method is used to display the data before and after rejecting changes.

Key Points to Remember

1. Undo Changes:
   • RejectChanges() reverts all changes made to the DataTable since the last call to AcceptChanges() or when the data was first loaded.
2. Row States:
   • The DataTable tracks the state of each row (Added, Modified, Deleted, Unchanged). RejectChanges() resets these states.
3. No Database Impact:
   • RejectChanges() only affects the in-memory DataTable. It does not modify the database.

Best Practices for Using `RejectChanges()`

1. Use with Caution:
   • Ensure you really want to discard changes before calling RejectChanges(), as it cannot be undone.
2. Combine with Validation:
   • Use RejectChanges() to undo changes if data validation fails.
3. Provide User Feedback:
   • Inform users when changes are discarded to avoid confusion.
4. Use Transactions:
   • When working with databases, use transactions to ensure data consistency when rejecting changes.

Real-World Use Cases

1. Data Entry Forms:
   • Allow users to discard changes if they make mistakes while entering data.
2. Batch Processing:
   • Reject changes if a batch of updates fails validation.
3. Undo Functionality:
   • Provide an "undo" feature in applications where users can revert changes.

Conclusion

The RejectChanges() method in ADO.NET is a valuable tool for managing changes to a DataTable. It allows you to discard modifications and restore data to its original state, making it ideal for scenarios where you need to provide undo functionality or handle temporary changes.

By following the examples and best practices in this article, you can use the RejectChanges() method effectively in your C# applications. Whether you’re building a data entry form, a batch processing system, or any application that requires flexible data management, RejectChanges() is a feature you’ll find incredibly useful.

Happy coding!