C-Sharp Linq

Updating Disconnected Entities in LINQ: A Comprehensive Guide

When working with LINQ in C#, developers often encounter scenarios where they need to update entities that are disconnected from the database. This is particularly common in applications that utilize patterns like disconnected architectures or service-oriented architecture (SOA). However, this can lead to frustrating errors, such as the infamous InvalidOperationException. In this blog post, we’ll delve into the problem and explore effective solutions to ensure smooth updates of disconnected entities.

Understanding the Problem

Consider the following code snippet, which attempts to update a LINQ entity after disconnecting it from the database:

public void Foo()
{
    DataContext context = new DataContext();
    LinqEntity item = new LinqEntity() { Id = 1, Name = "John", Surname = "Doe" };
    context.LinqEntities.Attach(item, true);
}

This code results in an InvalidOperationException because, by default, LINQ checks all fields of an entity for concurrency when making updates. If any of the values deviate from what’s stored in the database, the update fails. The question arises: How can we successfully update an entity that is no longer connected to the database?

Solutions for Updating Disconnected Entities

There are primarily two approaches for managing the update of disconnected entities in LINQ:

1. Setting Update Check to Never

To address the InvalidOperationException, you can modify the Update Check property for each field of the entity to Never. This allows you to bypass the row version check when updating the entity. Here’s how to implement this:

  • You’ll need to ensure you define this property for every field in the entity model.
  • After attaching the entity to the context with the correct settings, invoke context.SubmitChanges() to finalize the update.

2. Using Original Values for Update

If you prefer to manage the concurrency check manually, another approach is to first attach the entity to the context with the original values and perform the necessary updates. Here’s how you can do this:

LinqEntity item = new LinqEntity() { Id = 1, Name = "OldName", Surname = "OldSurname" };
context.LinqEntities.Attach(item);
item.Name = "John";
item.Surname = "Doe";
context.SubmitChanges();

Steps to Follow:

  1. Create a New Entity with Original Values: Ensure to pass in existing values from the database during attachment.
  2. Attach the Entity: Use the Attach method to connect this entity back to the context.
  3. Modify Desired Properties: Update the properties of the entity with new values.
  4. Submit Changes: Finally, call context.SubmitChanges() to commit your changes to the database.

Conclusion

Updating disconnected entities in LINQ can initially seem challenging, but with the right approach, it becomes manageable. By understanding the underlying concurrency checks and leveraging the two mentioned strategies—setting update checks to never or using original values—you can perform updates effectively, avoiding common exceptions.

Whether you’re building a web service or a desktop application, these techniques will enhance your data handling capabilities in LINQ and ensure a smoother development process without running into pesky errors.

Feel free to share your thoughts or ask any questions in the comments section below!