Entity Framework Core: SqlNullValueException 'Data is Null'—How Can I Debug This?

Entity Framework Core: SqlNullValueException: Data is Null. How to troubleshoot?

You're using Entity Framework Core and encountering a SqlNullValueException with the message "Data is Null." followed by "System.Data.SqlClient.SqlBuffer.get_String()." It indicates that a property marked as "required" is returning a null value from the database. This issue is likely caused by a mismatch between your entity model and database schema.

Here's how to troubleshoot and resolve this issue:

1. Check your entity model: Ensure that properties marked as "[Required]" in the model have a corresponding "not null" constraint in the related database table. In your case, the following properties are required in the model:

   • CompanyStreetAddress
   • CompanyCity
   • CompanyZipCode
   • CompanyVatNumber
   • ContactFirstName
   • ContactLastName

   Compare these properties in your code with the table definitions in the database and ensure there are no discrepancies.

2. Verify database constraints: Open your database, make sure the "not null" constraint is set for the columns representing the above-mentioned properties, and there's data in the corresponding columns.
3. Examine the query: You mentioned that tracing the query didn't help identify the specific column causing the exception. However, To help identify the offending column or columns, I recommend using a logging framework like Serilog or NLog to log the complete SQL query being executed by Entity Framework. This should provide more context to the exact statement causing the exception and the specific column or property involved.
4. Update Entity Framework: You have found that your code operates correctly with previous versions of Entity Framework Core. However, it's important to note that EF Core still actively undergoes changes and bug fixes. It's possible that an issue, mentioned above, was resolved in a later version. Try updating to the latest stable version of Entity Framework Core and see if the issue persists.

Remember, the "SqlNullValueException" signifies that a required property has returned a null value. By checking the model, database constraints, query logs, and ensuring that you're using the latest version of EF Core, you should be able to troubleshoot and resolve this issue effectively.

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