field.Enum("status").
			Values("draft", "published", "archived").
			Immutable().
			Optional() // to skip Ent's validation on create

		hook.On(
			// Forbid setting status, since it is generated
			func(next ent.Mutator) ent.Mutator {
				return hook.MyEntFunc(func(ctx context.Context, m *gen.MyEntMutation) (ent.Value, error) {
					_, exists := m.Status()
					if exists {
						return nil, fmt.Errorf("status is generated, cannot be updated manually")
					}
					return next.Mutate(ctx, m)
				})
			},
			ent.OpCreate|ent.OpUpdate|ent.OpUpdateOne,
		),

    ...
    schema.WithDiffHook(statusDiffHook),
    ...

func statusDiffHook(next schema.Differ) schema.Differ {
	return schema.DiffFunc(func(current, desired *atlasSchema.Schema) ([]atlasSchema.Change, error) {
		for _, table := range desired.Tables {
			if table.Name == "my_ent" {
				for _, column := range table.Columns {
					if column.Name == "status" {
						column.SetNull(false)
						column.SetGeneratedExpr(&atlasSchema.GeneratedExpr{
							Expr: `CASE WHEN "archived_at" IS NOT NULL THEN 'archived' WHEN "published_at" IS NOT NULL THEN 'published' ELSE 'draft' END`,
						})
					}
				}
			}
		}

		changes, err := next.Diff(current, desired)
		if err != nil {
			return nil, err
		}

		return changes, nil
	})
}