MSDN Documentation

Error Handling in ADO.NET

When working with data access in .NET applications using ADO.NET, effective error handling is crucial for building robust and reliable software. ADO.NET provides mechanisms to detect, report, and manage errors that occur during data operations.

Understanding ADO.NET Errors

Errors in ADO.NET can originate from various sources, including:

• Database connection issues (e.g., invalid credentials, network problems).
• SQL command execution errors (e.g., syntax errors, constraint violations).
• Data type mismatches or conversion errors.
• Concurrency conflicts.
• Issues with the ADO.NET providers themselves.

The Exception Class Hierarchy

Like most .NET operations, ADO.NET errors are communicated through exceptions. The primary exception class for ADO.NET is System.Data.DataException, which serves as a base class for many ADO.NET-specific exceptions. Common exceptions you might encounter include:

• System.Data.SqlClient.SqlException: Specific to SQL Server operations.
• System.Data.OleDb.OleDbException: For OLE DB providers.
• System.Data.Odbc.OdbcException: For ODBC providers.
• System.Data.InvalidExpressionException: When an expression is invalid.
• System.Data.ConstraintException: When a constraint is violated.

Handling Exceptions with try-catch Blocks

The standard .NET exception handling mechanism, the try-catch block, is the primary way to handle ADO.NET errors. You wrap your data access code within a try block and catch specific exceptions in catch blocks.

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

public class DataAccessManager
{
    private string connectionString = "Your_Connection_String_Here";

    public DataTable GetData(string query)
    {
        DataTable dataTable = new DataTable();
        try
        {
            using (SqlConnection connection = new SqlConnection(connectionString))
            {
                connection.Open();
                using (SqlCommand command = new SqlCommand(query, connection))
                {
                    using (SqlDataAdapter adapter = new SqlDataAdapter(command))
                    {
                        adapter.Fill(dataTable);
                    }
                }
            }
        }
        catch (SqlException sqlEx)
        {
            Console.WriteLine($"SQL Error: {sqlEx.Message}");
            // Log the error or re-throw a custom exception
            throw new DataAccessException("Error executing SQL query.", sqlEx);
        }
        catch (Exception ex)
        {
            Console.WriteLine($"An unexpected error occurred: {ex.Message}");
            // Log the error or re-throw a custom exception
            throw new DataAccessException("An unexpected data access error occurred.", ex);
        }
        return dataTable;
    }
}

// Custom exception class for data access errors
public class DataAccessException : Exception
{
    public DataAccessException(string message) : base(message) { }
    public DataAccessException(string message, Exception innerException) : base(message, innerException) { }
}
                

Error Information in SqlException

SqlException objects provide rich information about SQL Server errors through their Errors property, which is a collection of SqlError objects. Each SqlError object contains details like error number, severity, state, and line number.

catch (SqlException sqlEx)
{
    foreach (SqlError error in sqlEx.Errors)
    {
        Console.WriteLine($"SQL Error Number: {error.Number}");
        Console.WriteLine($"Message: {error.Message}");
        Console.WriteLine($"Severity: {error.Class}"); // Note: Class property is used for severity
        Console.WriteLine($"State: {error.State}");
        Console.WriteLine($"Line Number: {error.LineNumber}");
    }
    throw; // Re-throw to allow higher-level handling
}
                

The RowError Property

The DataRow object has a RowError property. This property can be set to a string that describes an error associated with a specific row. This is particularly useful when performing bulk operations or when data validation fails at the row level.

When using DataTable.LoadError, any errors encountered during the loading of a row are collected in the RowError property of that specific row.

Error Handling Strategies

• Specific Catch Blocks: Always catch specific exceptions before a general Exception. This allows you to handle different error types appropriately.
• Logging: Implement a robust logging mechanism to record errors with all available details. This is vital for debugging and auditing.
• User Feedback: Provide clear and user-friendly error messages to the end-user without exposing sensitive technical details.
• Custom Exceptions: Create custom exception classes to abstract data access errors from your business logic.
• Resource Management: Ensure that database connections and other resources are properly disposed of, even if errors occur, using using statements.
• Transaction Management: For operations involving multiple data modifications, use ADO.NET transactions to ensure atomicity. If any part of the transaction fails, the entire transaction can be rolled back.

Handling Concurrency Conflicts

When multiple users or processes try to modify the same data, concurrency conflicts can arise. ADO.NET's DataAdapter provides mechanisms to detect and handle these conflicts, often by throwing a DBConcurrencyException.

You can override the RowUpdating and RowDeleting events of the DataAdapter to implement custom conflict resolution logic.