EntityFrameworkCore.DbUpdateConcurrencyException – Database operation expected to affect n rows

The error EntityFrameworkCore.DbUpdateConcurrencyException – Database operation expected to affect n rows occurs in Entity Framework Core (EF Core) when a concurrency conflict is detected during a database update operation. This typically happens when the data being updated has been modified by another user or process since it was last read, and EF Core’s concurrency check fails.

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What is a Concurrency Conflict?

A concurrency conflict occurs when multiple users or processes attempt to modify the same data simultaneously. EF Core uses concurrency tokens (e.g., RowVersion or timestamp columns) to detect such conflicts and ensure data consistency.

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Common Causes

1. Concurrency Token Mismatch:

• The concurrency token (e.g., RowVersion) in the database does not match the value in the entity being updated.

1. Data Modified by Another Process:

• Another user or process has modified the data since it was last read by the current operation.

1. Missing or Incorrect Concurrency Token:

• The entity does not have a concurrency token configured, or the token is not properly mapped in EF Core.

1. Manual SQL Updates:

• The database was updated directly using raw SQL, bypassing EF Core’s concurrency checks.

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Solutions

1. Handle Concurrency Conflicts Gracefully

• Catch the DbUpdateConcurrencyException and resolve the conflict by reloading the entity or merging changes.
• Example: try { // Attempt to update the entity context.SaveChanges(); } catch (DbUpdateConcurrencyException ex) { // Handle the concurrency conflict foreach (var entry in ex.Entries) { var databaseValues = entry.GetDatabaseValues(); if (databaseValues == null) { Console.WriteLine("The record was deleted by another user."); } else { var currentValues = entry.CurrentValues; var originalValues = entry.OriginalValues; // Resolve the conflict (e.g., merge changes or reload the entity) entry.OriginalValues.SetValues(databaseValues); } } }

2. Use Concurrency Tokens

• Configure a concurrency token (e.g., RowVersion) in your entity and database.
• Example: public class Product { public int Id { get; set; } public string Name { get; set; } public byte[] RowVersion { get; set; } // Concurrency token } In OnModelCreating: modelBuilder.Entity<Product>() .Property(p => p.RowVersion) .IsRowVersion(); // Marks the property as a concurrency token

3. Reload the Entity

• Reload the entity from the database to get the latest values before retrying the update.
• Example:
  csharp catch (DbUpdateConcurrencyException ex) { foreach (var entry in ex.Entries) { await entry.ReloadAsync(); // Reload the entity } // Retry the update await context.SaveChangesAsync(); }

4. Merge Changes

• Merge the changes made by the current user with the changes made by another user or process.
• Example: catch (DbUpdateConcurrencyException ex) { foreach (var entry in ex.Entries) { var databaseValues = entry.GetDatabaseValues(); var currentValues = entry.CurrentValues; var originalValues = entry.OriginalValues; // Merge changes (e.g., prioritize current user's changes) foreach (var property in currentValues.Properties) { var databaseValue = databaseValues[property]; var currentValue = currentValues[property]; var originalValue = originalValues[property]; if (currentValue != originalValue) { // Keep the current user's changes } else { // Use the database value currentValues[property] = databaseValue; } } entry.OriginalValues.SetValues(databaseValues); } // Retry the update await context.SaveChangesAsync(); }

5. Avoid Manual SQL Updates

• Avoid updating the database directly using raw SQL when concurrency tokens are in use. If necessary, ensure the concurrency token is updated correctly.

6. Disable Concurrency Checks (Not Recommended)

• If concurrency conflicts are not a concern, you can disable concurrency checks by removing the concurrency token. However, this is not recommended for most scenarios.

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Debugging Steps

1. Identify the Entity Causing the Conflict:

• Use the Entries property of the DbUpdateConcurrencyException to identify the conflicting entities.

1. Check the Concurrency Token:

• Verify that the concurrency token (e.g., RowVersion) is correctly configured in the entity and database.

1. Compare Current and Database Values:

• Use GetDatabaseValues, CurrentValues, and OriginalValues to compare the values and resolve the conflict.

1. Test with Simulated Conflicts:

• Simulate concurrency conflicts by modifying the data in the database while the application is running.

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Example Scenarios and Fixes

Scenario 1: Concurrency Token Mismatch

• The RowVersion in the database does not match the value in the entity.
• Fix:
  • Reload the entity or merge changes as shown in the examples above.

Scenario 2: Missing Concurrency Token

• The entity does not have a concurrency token configured.
• Fix:
  • Add a concurrency token to the entity and database.
    csharp public byte[] RowVersion { get; set; }

Scenario 3: Manual SQL Update

• The database was updated directly using raw SQL, bypassing EF Core’s concurrency checks.
• Fix:
  • Ensure the concurrency token is updated correctly when using raw SQL.
    sql UPDATE Products SET Name = 'NewName', RowVersion = NEWID() WHERE Id = 1;

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Best Practices

1. Always Use Concurrency Tokens:

• Use concurrency tokens to detect and resolve conflicts in multi-user environments.

1. Handle Conflicts Gracefully:

• Implement logic to handle concurrency conflicts and provide a good user experience.

1. Test for Concurrency:

• Test your application with simulated concurrency conflicts to ensure it behaves as expected.

1. Avoid Manual SQL Updates:

• Use EF Core for all database updates to ensure concurrency checks are applied.

1. Log Conflicts:

• Log concurrency conflicts for debugging and auditing purposes.

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By following these steps and best practices, you can resolve the DbUpdateConcurrencyException and ensure data consistency in your application.