EF Core 6 adds a default value in SQL when nullable reference types are on and a column is changed from string? to string

Question

Nullable Reference Types are turned on for my project and I have an entity in my EF Core model which had a string? property that I changed to string.

old:

public string? Name { get; set; };

new:

public string Name { get; set; } = default!;

I then generated a migration and EF added a default value to the column

migrationBuilder.AlterColumn<string>(
    name: "Name",
    table: "MyTable",
    type: "varchar(25)",
    unicode: false,
    maxLength: 25,
    nullable: false,
    defaultValue: "", // <-- here
    oldClrType: typeof(string),
    oldType: "varchar(25)",
    oldUnicode: false,
    oldMaxLength: 25,
    oldNullable: true);

In SQL

DECLARE @var0 sysname;
SELECT @var0 = [d].[name]
FROM [sys].[default_constraints] [d]
INNER JOIN [sys].[columns] [c] ON [d].[parent_column_id] = [c].[column_id] AND [d].[parent_object_id] = [c].[object_id]
WHERE ([d].[parent_object_id] = OBJECT_ID(N'[MyTable]') AND [c].[name] = N'Name');
IF @var0 IS NOT NULL EXEC(N'ALTER TABLE [MyTable] DROP CONSTRAINT [' + @var0 + '];');
ALTER TABLE [MyTable] ALTER COLUMN [Name] varchar(25) NOT NULL;
ALTER TABLE [MyTable] ADD DEFAULT '' FOR [Name];
GO

But instead of having the database generate a default value if null is sent, I want an exception to be thrown, so the user must input a value.

I already tried adding

[DatabaseGenerated(DatabaseGeneratedOption.None)]

or

HasDefaultValueSql(null)

or

HasDefaultValue(null)

but that does not change anything.

How can I tell EF Core to not generate a default for that column?

Answer 1

I'm not sure if Entity Framework has some tricks up it's sleeve, but with normal SQL, you would need two changes. One change of the NOT NULL status, that requires a default value, because what else should that field be set to if a null-value is encountered. And then a second change, that removes the default value from an already NOT NULL field.

So I would not be surprised if Entity Framework needed those two seperate steps, too. Just create two migrations, that should work.