Resolving the Error: Cannot insert explicit value for identity column in Entity Framework

Learn how to fix "Cannot insert explicit value for identity column" error in Entity Framework while inserting records with nested custom objects.
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Tackling the Cannot insert explicit value for identity column Error in Entity Framework

As developers, we inevitably encounter bugs and issues that can leave us scratching our heads. A particularly common error in ASP.NET applications using Entity Framework is the notorious message: "Cannot insert explicit value for identity column in table 'UserPermission' when IDENTITY_INSERT is set to OFF." This error usually occurs when we try to insert records that have relationships with other entities. In this post, we will break down the cause of the issue and provide you with a comprehensive solution.

Understanding the Problem

The error you are facing indicates that you're attempting to insert a record with an identity column into the database without properly informing Entity Framework (EF) of what is happening. In the context of your code snippet:

[[See Video to Reveal this Text or Code Snippet]]

You have a User entity that includes a UserPermission object, and you're trying to insert it into the database. However, the UserPermission entity has an ID that is meant to be auto-generated by the database. When EF sees an explicit value for this ID while IDENTITY_INSERT is off, it throws an error.

The Likely Cause

The root of this problem typically lies in how EF processes related entities. Given that UserPermission is an existing record in the database (with an identity Primary Key (PK)), EF expects it to represent a new entity unless explicitly told otherwise. If EF doesn't recognize that UserPermission is already in the database, it tries to create a duplicate, leading to the identity conflict.

The Solution: Informing EF of Existing Entities

To resolve this issue, you need to help EF recognize that the UserPermission associated with someUser is already a tracked entity in the database. This is how you can do it:

Step-by-step Solution

Check for Existing Permissions:
Before adding someUser, check if the UserPermission is already tracked by your _context.

Attach or Substitute:
If the UserPermission with the specified ID exists, substitute the existing one. If it doesn’t exist in the local context, you need to attach it.

Here's a code snippet that illustrates this solution effectively:

[[See Video to Reveal this Text or Code Snippet]]

A Few Important Notes

Existence Check: The solution assumes that the UserPermission entity exists in the database. If it doesn’t (e.g., if it was deleted), you'll end up with an exception upon calling SaveChanges(). It's vital to ensure data integrity.

Handling Detached Entities: Passing around detached references for multiple entities can complicate things. Be sure to check for existing instances for each relationship. Calling _context.Attach() indiscriminately could work until it doesn't, leading to hard-to-trace errors.

Testing is Key: Test your code thoroughly to ensure that it handles various scenarios (existing, non-existing, corrupted data) without failing.

Final Thoughts

While this error can be frustrating, understanding how EF tracks entities and how relationships work can greatly simplify the insertion of nested custom objects. By adopting this solution, you'll be able to sidestep the "Cannot insert explicit value for identity column" error and develop smoother applications with Entity Framework.

Whether you're just starting with ASP.NET and Entity Framework or consider yourself an expert, embracing these patterns will lead to a more robust application and a more enjoyable development experience.