SQL Server Migrations: Rebuild columns after altering HasComputedColumnSql

[maksir]

Steps to reproduce

I have a class

public class User : IdentityUser<int>
{
    public string Name { get; set; }
    public string DisplayName { get; set; }
}

and DbContext

AppDbContext : IdentityDbContext<User, Role, int>
{
    protected override void OnModelCreating(ModelBuilder builder)
    {
        base.OnModelCreating(builder);
        builder.Entity<User>().Property(p => p.DisplayName).HasComputedColumnSql("[Name]");
    }
}

execute

dotnet ef migrations add User_DisplayName
dotnet ef database update
All done.

Modify OnModelCreating() like this:

builder.Entity<User>().Property(p => p.DisplayName)
    .HasComputedColumnSql("[Name] + ' (' + [Email] + ')'");

execute again

dotnet ef migrations add User_DisplayName_fix
dotnet ef database update

The issue

Error Number:156,State:1,Class:15
Incorrect syntax near the keyword 'AS'.'

Further technical details

"Microsoft.EntityFrameworkCore.SqlServer": "1.0.0-rc2-final",
"Microsoft.EntityFrameworkCore.Tools": "1.0.0-preview1-final",
Operating system: Win 10
Visual Studio version: 2015
MS SQL 2012

Cause of the error

In this file src/Microsoft.EntityFrameworkCore.SqlServer/Migrations/SqlServerMigrationsSqlGenerator.cs
lines number 60 and 400 generating script:

alter table User alter column DisplayName as [Name] + ' (' + [Email] + ')'

This is wrong.
T-SQL does not support argument 'AS' for command 'Alter column'.

For computed column, need 2 commands.

1. drop computed column
2. create new computed column with same name

[rowanmiller]

If you are changing a column from non-computed to computed you are also dropping all the existing data from the column. Perhaps our model differ should reason about this and generate a DropColumnOperation and AddColumnOperation rather than the alter in this case.

[bricelam]

If you are changing a column from non-computed to computed...

This is not what the code above is doing. It just changes the computed expression--the column was previously computed too.

As far as I can tell, Oracle supports altering computed columns just like any other column. I think we should treat this issue as specific to SQL Server and rebuild the column in its Migrations SQL generator.