How to Resolve the 'Attaching Entity with Duplicate Primary Key' Error in ASP.NET MVC?

Troubleshooting "Attaching Entity with Duplicate Primary Key" Errors in ASP.NET MVC

ASP.NET MVC applications using Entity Framework may throw the error: "Attaching an entity of type 'MODELNAME' failed because another entity of the same type already has the same primary key value." This usually occurs during a POST operation when attempting to update an entity. Let's explore common causes and solutions.

Problem 1: Detached Entity

The entity might be detached from the Entity Framework context, preventing it from recognizing updates. To fix this, re-attach the entity using the Attach() method before setting its state to Modified.

Problem 2: Concurrent Database Modifications

Multiple users or processes simultaneously accessing the database can lead to conflicts. Before updating, refresh the entity from the database to ensure you're working with the latest version.

Problem 3: Conflicting Validation or Access Control

Custom validation or access control logic might unintentionally modify the entity's state. If these checks load the entity before the Modified state is set, it could cause detachment. Carefully review this logic to eliminate interference.

Problem 4: Asynchronous Controller Issues

Asynchronous controller actions can create concurrency problems. Use the await keyword to ensure data modifications finish before proceeding, avoiding conflicts.

Example Scenario and Solution:

One example showed the error stemming from a custom function (canUserAccessA()) that loaded the entity before the update. The solution was to use .AsNoTracking() within the function to prevent Entity Framework from tracking the entity, thus resolving the conflict.

The above is the detailed content of How to Resolve the 'Attaching Entity with Duplicate Primary Key' Error in ASP.NET MVC?. For more information, please follow other related articles on the PHP Chinese website!