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The reason Entity Framework Core (EF Core) scaffolds your model with null for string properties, even though the database columns are NOT NULL, is because in C#, strings are reference types, and EF Core doesn’t assume a default value unless explicitly told to. This means even if your database enforces NOT NULL, EF Core won't automatically assign an empty string (string.Empty); it just ensures the column can't be null when stored in the database.

This happens because

C# Default Behavior: Since strings are reference types, they default to null unless initialized explicitly.
EF Core Doesn't Assume Defaults: It only respects the database constraint but doesn’t enforce a default value in your C# model.
Flexibility for Developers: Some prefer handling default values in their application logic instead of having EF enforce it.

How to Fix This?

If you don’t want null values in your C# objects, here are a few ways to handle it:

Use Default Initialization in the Model

Modify your model to initialize string properties with string.Empty:

public class StudyInvitation { public int Id { get; set; } public string Name { get; set; } = string.Empty; public string Subject { get; set; } = string.Empty; public string Body { get; set; } = string.Empty; }

This ensures the properties are never null in your C# objects.
Use a Constructor

Another approach is to initialize them inside a constructor:

public class StudyInvitation
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string Subject { get; set; }
    public string Body { get; set; }

    public StudyInvitation()
    {
        Name = string.Empty;
        Subject = string.Empty;
        Body = string.Empty;
    }
}

Configure EF Core to Use Default Values

You can also configure EF Core using Fluent API inside your DbContext class:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<StudyInvitation>()
        .Property(e => e.Name)
        .IsRequired()
        .HasDefaultValue(string.Empty);

    modelBuilder.Entity<StudyInvitation>()
        .Property(e => e.Subject)
        .IsRequired()
        .HasDefaultValue(string.Empty);

    modelBuilder.Entity<StudyInvitation>()
        .Property(e => e.Body)
        .IsRequired()
        .HasDefaultValue(string.Empty);
}

This ensures that even if you forget to initialize these properties, the database will automatically use an empty string.

Which One Should You Use?

If you want to prevent null in your C# code, go with Option 1 (Default Initialization) or Option 2 (Constructor).

If you want to enforce it at the database level too, use Option 3 (Fluent API).

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