fix a bug

Author: dtpowl

persistent/Database/Persist/Quasi/Internal/ModelParser.hs

@@ -565,8 +565,12 @@ fieldStrictness = label "strictness sigil" $ do
 fieldName :: Parser FieldName
 fieldName = label "field name" $ do
     fl <- lowerChar
-    rl <- many alphaNumChar
+    rl <- many fieldNameChar
     pure . FieldName . Text.pack $ fl : rl
+  where
+    fieldNameChar = choice [ alphaNumChar
+                           , char '_'
+                           ]
 
 ptext :: Parser Attribute
 ptext = label "plain attribute" $ do