Make it easier to flow custom annotations through to Migrations

[Rgl88]

Custom annotations on properties are not included in generated Up/Down migration, but they are correctly included in the BuildTargetModel method
I want reorder columns in up method via my custom 'DisplayOrder' annotation.

Consider the following example:
Custom Annotations added to

[DbContext(typeof(TestDbContext))]
[Migration("13960818210148_TestDb_Migration_v1.0")]
partial class TestDb_Migration_v10
{
        protected override void BuildTargetModel(ModelBuilder modelBuilder)
        {
               modelBuilder.Entity("St.Domain.Financial.Bank", b =>
                {
				    ...
						
                    b.Property<int>("Id")
                        .ValueGeneratedOnAdd();

                    b.Property<string>("Description")
                        .HasMaxLength(512)
                        .HasAnnotation("ColumnOrder", 4);

                    b.Property<string>("Name")
                        .IsRequired()
                        .HasMaxLength(128)
                        .HasAnnotation("ColumnOrder", 2);
                    b.ToTable("Bank");
					
					...
                });
        }
}

but not exist in:

public partial class TestDb_Migration_v10 : Migration
{
        protected override void Up(MigrationBuilder migrationBuilder)
        {
            migrationBuilder.CreateTable(
                name: "Bank",
                columns: table => new
                {
				    ...
                    Id = table.Column<int>(type: "int", nullable: false)
                        .Annotation("SqlServer:ValueGenerationStrategy", SqlServerValueGenerationStrategy.IdentityColumn),
                    Description = table.Column<string>(type: "nvarchar(512)", maxLength: 512, nullable: true),
                    Name = table.Column<string>(type: "nvarchar(128)", maxLength: 128, nullable: false)
					...
                });
        }
}

C:\Users\User1>dotnet --info
.NET Command Line Tools (2.0.0)

Product Information:
Version: 2.0.0
Commit SHA-1 hash: cdcd1928c9

Runtime Environment:
OS Name: Windows
OS Version: 10.0.14393
OS Platform: Windows
RID: win10-x64
Base Path: C:\Program Files\dotnet\sdk\2.0.0\

Microsoft .NET Core Shared Framework Host
Version : 2.0.0
Build : e8b8861ac7faf042c87a5c2f9f2d04c98b69f28d

[ajcvickers]

@Rgl88 Annotations are only propagated to Migrations if they have been configured to do so. The reason for this is so that Migrations doesn't generate diffs and scaffold a new migration when any annotation changes, since many annotations only affect runtime behavior, not the database schema.

Currently this requires overriding and replacing the annotation provider for whichever database you are using. For example, for SQL Server:

public class CustomAnnotationProvider : SqlServerMigrationsAnnotationProvider
{
    public CustomAnnotationProvider(MigrationsAnnotationProviderDependencies dependencies) 
        : base(dependencies)
    {
    }

    public override IEnumerable<IAnnotation> For(IProperty property)
    {
        var baseAnnotations = base.For(property);

        var annotation = property.FindAnnotation("ColumnOrder");

        return annotation == null
            ? baseAnnotations
            : baseAnnotations.Concat(new[] { annotation });
    }
}

This must then be registered in OnConfiguring or AddDbContext:

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        => optionsBuilder
            .ReplaceService<IMigrationsAnnotationProvider, CustomAnnotationProvider>()
            .UseSqlServer(@"Server=(localdb)\mssqllocaldb;Database=TestDatabase;ConnectRetryCount=0");

I'm re-purposing this bug to consider implementing an easier way of doing this.

[weitzhandler]

@ajcvickers thanks for your helpful example!
Would be nice if the interaction between OnModelCreating and the migration process can be soften up a bit.
I opened a new issue.

[AndriySvyryd]

Related: #17740