more GSI fixes

dynamodb/key_codec.odin

@@ -130,32 +130,43 @@ build_partition_prefix :: proc(table_name: string, pk_value: []byte) -> []byte {
 	return bytes.buffer_to_bytes(&buf)
 }
 
-// Build GSI key: [gsi][table_name][index_name][gsi_pk][gsi_sk?]
-build_gsi_key :: proc(table_name: string, index_name: string, gsi_pk: []byte, gsi_sk: Maybe([]byte)) -> []byte {
+// Build GSI key: [gsi][table_name][index_name][gsi_pk][gsi_sk?][base_pk][base_sk?]
+build_gsi_key :: proc(
+	table_name: string,
+	index_name: string,
+	gsi_pk: []byte,
+	gsi_sk: Maybe([]byte),
+	base_pk: []byte,
+	base_sk: Maybe([]byte),
+) -> []byte {
 	buf: bytes.Buffer
 	bytes.buffer_init_allocator(&buf, 0, 512, context.allocator)
 
-	// Write entity type
 	bytes.buffer_write_byte(&buf, u8(Entity_Type.GSI))
 
-	// Write table name
 	encode_varint(&buf, len(table_name))
 	bytes.buffer_write_string(&buf, table_name)
 
-	// Write index name
 	encode_varint(&buf, len(index_name))
 	bytes.buffer_write_string(&buf, index_name)
 
-	// Write GSI partition key
 	encode_varint(&buf, len(gsi_pk))
 	bytes.buffer_write(&buf, gsi_pk)
 
-	// Write GSI sort key if present
 	if sk, ok := gsi_sk.?; ok {
 		encode_varint(&buf, len(sk))
 		bytes.buffer_write(&buf, sk)
 	}
 
+	// tie-breaker: base table primary key
+	encode_varint(&buf, len(base_pk))
+	bytes.buffer_write(&buf, base_pk)
+
+	if sk, ok := base_sk.?; ok {
+		encode_varint(&buf, len(sk))
+		bytes.buffer_write(&buf, sk)
+	}
+
 	return bytes.buffer_to_bytes(&buf)
 }