EF Core 无法加载具有可为空字符串值的实体

Question

I am having an issue retrieving any records which have a null string value from the database. I am using SQL Server 2012, .NET 5.0.

My model class:

public class Project
{
    public int ProjectId { get; set; }

    [StringLength(50)]
    public string ProjectSaleTypeId { get; set; }

    [JsonIgnore]
    public ProjectSaleType ProjectSaleType { get; set; }
}

public class ProjectSaleType
{

    [StringLength(50)]
    public string ProjectSaleTypeId { get; set; }

    [JsonIgnore]
    public ICollection<Project> Projects { get; set; }
}

Then when I make a request to get the entity with id 365 :

_context.Projects.FirstOrDefault(x => x.ProjectId == 365);

the following error occurs:

System.InvalidOperationException: 'An error occurred while reading a database value for property 'Project.ProjectSaleTypeId'. The expected type was 'System.String' but the actual value was null.'

It should be noted that entities which have a ProjectSaleTypeId are working properly.

I understand that C# 8.0 introduced nullable reference types. But I have not enabled these in my project; https://docs.microsoft.com/en-us/ef/core/miscellaneous/nullable-reference-types

Why do I get this error when retrieving a entity with the ProjectSaleTypeId equal to null?

Answer 1

This error means that the ProjectSaleTypeId is a non-nullable string property but your database table is allowing NULL values for that column.

If EF is handling your database it should not happen, but it might occur that you accidentally changed the DB column type and didn't migrate properly.