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

Learn how to resolve the `Identity column` insertion error in Entity Framework Core for SQL Server, helping you to insert data without encountering exceptions.
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Troubleshooting the Cannot insert explicit value for identity column Error with Entity Framework Core

When working with Entity Framework Core and SQL Server, developers often encounter various exceptions that can halt their progress. One particularly frustrating error is the Cannot insert explicit value for identity column error that appears when attempting to insert data into a table, particularly when the identity column settings are not configured correctly. This issue can cause problems when working with tables that have identity columns set up. In this guide, we’ll delve into the details of this error, provide context about identity columns, and walk through a solution to ensure seamless data insertion.

Understanding the Problem

In this scenario, the problem arises when trying to insert data into the ZebraSubPrinters table, which has an identity column for the ID. The identity column is a special property where the database automatically generates a unique value for each row, negating the need for us to specify one manually during an insert operation.

Example of the Error

The error message generated by SQL Server typically looks like this:

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

Why Does This Happen?

Entity Framework Core, by default, assumes that an INT data type ID is generated by the database. However, in cases where the ID column is defined with a data type such as decimal, EF Core does not automatically recognize it as an identity column. Therefore, an attempt to insert a record results in the above error since EF tries to provide a value for the identity column.

The Solution: Configuring the Identity Column in EF Core

To resolve this problem, you need to inform Entity Framework Core that the ID field in the ZebraSubPrinters table is indeed an identity column. You can achieve this by configuring the model in the OnModelCreating method of your DbContext class. Here’s a breakdown of how to implement this solution:

Step-by-Step Configuration

Open your DbContext Class: Locate your DbContext that handles the ZebraSubPrinters entity.

Override OnModelCreating: Add configuration for the ZebraSubPrinters entity to recognize the ID as an identity column.

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

Key Code Explanation

HasPrecision(18, 0): This line ensures that the precision of the decimal ID is set correctly to match the database schema.

ValueGeneratedOnAdd(): This function tells EF Core that the value for this property should be generated by the database upon insert.

Conclusion

By configuring the identity column correctly through the OnModelCreating method, Entity Framework Core will now correctly manage the ID assignments for inserts into the ZebraSubPrinters table. This solution not only resolves the error but also streamlines your data insertion process, allowing you to focus on more advanced features of your application.

If you ever encounter similar issues, remember this guideline to effectively troubleshoot identity column settings in your application. Happy coding!