How can specify ROWGUIDCOL property to Guid type column in code first or with ColumnBuilder?

After some research and asking around, I don't think it's possible. The way I got around it in my code is to get a new GUID when I new up an object:

    public class MyPOCO {
           public MyPOCO() { 
                RowGuid = Guid.NewGuid();
           }
      //.....
   }

In this way, I'm always generating a new GUID when I insert a new row into the table. I miss using ROWGUIDCOL but EF does make my life simple.

It does not appear that the ROWGUIDCOL property can be set directly via Entity Framework, but it might be possible to inject the property into the generate SQL by making "creative" ;-) use of the storeType parameter (assuming storeType truly allows you to override the default datatype). Starting with the code from the original question, try something like the following:

 CreateTable(
            "dbo.Document",
            c => new
                {
                    RowGuid = c.Guid(nullable: false, identity: true,  
                                     defaultValueSql: "newid()",
                                     storeType: "UNIQUEIDENTIFIER ROWGUIDCOL"),
                    Person_Id = c.Int()
                })
            .Index(t => t.RowGuid, true);

Unfortunately, I do not have a way to test this, but given that the following SQL works, I think it is worth a shot:

CREATE TABLE dbo.Test1
(
    Col1 INT NOT NULL,
    Col2 UNIQUEIDENTIFIER ROWGUIDCOL NOT NULL UNIQUE DEFAULT NEWID()
)

The "UNIQUE" requirement is accomplished via a Unique Index created by the second parameter being "true" in the Index() method.

Please note that there might be some issue using "identity: true" in the Guid() method if the table already has a column marked with IDENTITY. I found this related question which addresses that situation: Entity Framework Code First Using Guid as Identity with another Identity Column

I imagine you want this for a table with a FILESTREAM column. Hinting EF with an EntityTypeConfiguration makes it generate correct scripts and doesn't need you to manually edit it (EF Core 2.2).

Taking this sample entity:

public class FileEntity
{
    public Guid FileGuid { get; private set; }
    public byte[] Document { get; private set; }
}

And this configuration:

public class FileEntityConfiguration : IEntityTypeConfiguration<FileEntity>
{
    public void Configure(EntityTypeBuilder<FileEntity> builder)
    {
        builder
            .Property(m => m.Document)
            .HasColumnType("VARBINARY(MAX) FILESTREAM");

        builder
            .Property(m => m.FileGuid)
            .HasColumnType("UNIQUEIDENTIFIER ROWGUIDCOL")
            .IsRequired();

        builder
            .HasAlternateKey(m => m.FileGuid);
    }
}

EF generates a correct migration script:

FileGuid = table.Column<Guid>(type: "UNIQUEIDENTIFIER ROWGUIDCOL", nullable: false),
Document = table.Column<byte[]>(type: "VARBINARY(MAX) FILESTREAM", nullable: true)