upload first, then store the key as virtual fk

entc/gen/template/dialect/sql/meta.tmpl

@@ -53,6 +53,9 @@ in the LICENSE file in the root directory of this source tree.
 				{{ $f.Constant }},
 			{{- end }}
 		{{- end }}
+		{{- range $bk := $.BlobKeys }}
+			"{{ $bk.Field.Name }}",
+		{{- end }}
 	}
 	{{/* If any of the edges owns a foreign-key */}}
 	{{ with $.UnexportedForeignKeys }}
@@ -65,6 +68,23 @@ in the LICENSE file in the root directory of this source tree.
 		}
 	{{ end }}
 
+	{{ with $.BlobKeys }}
+		// BlobKeys holds the SQL columns for blob storage keys.
+		var BlobKeys = []string{
+			{{- range $bk := . }}
+				"{{ $bk.Field.Name }}",
+			{{- end }}
+		}
+	{{ end }}
+
+	{{- range $f := $.BlobFields }}
+		{{- if $f.HasBlobKey }}
+			// {{ $f.BlobKeyName }} generates the blob storage key for the {{ $f.Name }} field.
+			// It is set by the runtime/init package from the schema descriptor.
+			var {{ $f.BlobKeyName }} func(context.Context) (string, error)
+		{{- end }}
+	{{- end }}
+
 	{{ with $.NumM2M }}
 		var (
 			{{- range $e := $.Edges }}
@@ -94,6 +114,13 @@ func ValidColumn(column string) bool {
 			}
 		}
 	{{- end }}
+	{{- with $.BlobKeys }}
+		for i := range BlobKeys {
+			if column == BlobKeys[i] {
+				return true
+			}
+		}
+	{{- end }}
 	{{- with $.DeprecatedFields }}
 		for _, f := range [...]string{ {{- range . }}{{ .Constant }},{{ end }} } {
 			if column == f {