Add support for nested Maybe records (#405)

Required ToMaybe, ToAlias, ToAliasReference instances for SqlMaybes
Also, required implementation changes to the sqlSelectProcessRow for
SqlMaybes

changelog.md

@@ -1,3 +1,10 @@
+3.5.12.0
+========
+- @csamak
+    - [#405](https://github.com/bitemyapp/esqueleto/pull/405)
+        - `ToMaybe` instances are now derived for Maybe records.
+          See [Issue #401](https://github.com/bitemyapp/esqueleto/issues/401).
+
 3.5.11.2
 ========
 - @arguri

esqueleto.cabal

@@ -2,7 +2,7 @@ cabal-version: 1.12
 
 name:           esqueleto
 
-version:        3.5.11.2
+version:        3.5.12.0
 synopsis:       Type-safe EDSL for SQL queries on persistent backends.
 description:    @esqueleto@ is a bare bones, type-safe EDSL for SQL queries that works with unmodified @persistent@ SQL backends.  Its language closely resembles SQL, so you don't have to learn new concepts, just new syntax, and it's fairly easy to predict the generated SQL and optimize it for your backend. Most kinds of errors committed when writing SQL are caught as compile-time errors---although it is possible to write type-checked @esqueleto@ queries that fail at runtime.
                 .

src/Database/Esqueleto/Record.hs

@@ -34,7 +34,7 @@ import Data.Text (Text)
 import Control.Monad (forM)
 import Data.Foldable (foldl')
 import GHC.Exts (IsString(fromString))
-import Data.Maybe (mapMaybe, fromMaybe, listToMaybe)
+import Data.Maybe (mapMaybe, fromMaybe, listToMaybe, isJust)
 
 -- | Takes the name of a Haskell record type and creates a variant of that
 -- record prefixed with @Sql@ which can be used in esqueleto expressions. This
@@ -187,17 +187,23 @@ deriveEsqueletoRecordWith settings originalName = do
   sqlSelectInstanceDec <- makeSqlSelectInstance info
   sqlMaybeRecordDec <- makeSqlMaybeRecord info
   toMaybeInstanceDec <- makeToMaybeInstance info
+  sqlMaybeToMaybeInstanceDec <- makeSqlMaybeToMaybeInstance info
   sqlMaybeRecordSelectInstanceDec <- makeSqlMaybeRecordSelectInstance info
   toAliasInstanceDec <- makeToAliasInstance info
+  sqlMaybeToAliasInstanceDec <- makeSqlMaybeToAliasInstance info
   toAliasReferenceInstanceDec <- makeToAliasReferenceInstance info
+  sqlMaybeToAliasReferenceInstanceDec <- makeSqlMaybeToAliasReferenceInstance info
   pure
     [ recordDec
     , sqlSelectInstanceDec
     , sqlMaybeRecordDec
     , toMaybeInstanceDec
+    , sqlMaybeToMaybeInstanceDec
     , sqlMaybeRecordSelectInstanceDec
     , toAliasInstanceDec
+    , sqlMaybeToAliasInstanceDec
     , toAliasReferenceInstanceDec
+    , sqlMaybeToAliasReferenceInstanceDec
     ]
 
 -- | Information about a record we need to generate the declarations.
@@ -646,19 +652,23 @@ nonRecordConstructorMessage con =
         (RecGadtC names _fields _ret) -> head names
 
 makeToAliasInstance :: RecordInfo -> Q Dec
-makeToAliasInstance info@RecordInfo {..} = do
-  toAliasDec' <- toAliasDec info
+makeToAliasInstance RecordInfo {..} = makeToAliasInstanceFor sqlName sqlFields
+
+makeSqlMaybeToAliasInstance :: RecordInfo -> Q Dec
+makeSqlMaybeToAliasInstance RecordInfo {..} = makeToAliasInstanceFor sqlMaybeName sqlMaybeFields
+
+makeToAliasInstanceFor :: Name -> [(Name, Type)] -> Q Dec
+makeToAliasInstanceFor name fields = do
+  toAliasDec' <- toAliasDec name fields
   let overlap = Nothing
       instanceConstraints = []
-      instanceType =
-        (ConT ''ToAlias)
-          `AppT` (ConT sqlName)
+      instanceType = (ConT ''ToAlias) `AppT` (ConT name)
   pure $ InstanceD overlap instanceConstraints instanceType [toAliasDec']
 
-toAliasDec :: RecordInfo -> Q Dec
-toAliasDec RecordInfo {..} = do
+toAliasDec :: Name -> [(Name, Type)] -> Q Dec
+toAliasDec name fields = do
   (statements, fieldPatterns, fieldExps) <-
-    unzip3 <$> forM sqlFields (\(fieldName', _) -> do
+    unzip3 <$> forM fields (\(fieldName', _) -> do
       fieldPatternName <- newName (nameBase fieldName')
       boundValueName <- newName (nameBase fieldName')
       pure
@@ -673,35 +683,40 @@ toAliasDec RecordInfo {..} = do
     FunD
       'toAlias
       [ Clause
-          [ RecP sqlName fieldPatterns
+          [ RecP name fieldPatterns
           ]
           ( NormalB $
               DoE
 #if MIN_VERSION_template_haskell(2,17,0)
                 Nothing
 #endif
-                (statements ++ [NoBindS $ AppE (VarE 'pure) (RecConE sqlName fieldExps)])
+                (statements ++ [NoBindS $ AppE (VarE 'pure) (RecConE name fieldExps)])
           )
           -- `where` clause.
           []
       ]
 
 makeToAliasReferenceInstance :: RecordInfo -> Q Dec
-makeToAliasReferenceInstance info@RecordInfo {..} = do
-  toAliasReferenceDec' <- toAliasReferenceDec info
+makeToAliasReferenceInstance RecordInfo {..} = makeToAliasReferenceInstanceFor sqlName sqlFields
+
+makeSqlMaybeToAliasReferenceInstance :: RecordInfo -> Q Dec
+makeSqlMaybeToAliasReferenceInstance RecordInfo {..} =
+  makeToAliasReferenceInstanceFor sqlMaybeName sqlMaybeFields
+
+makeToAliasReferenceInstanceFor :: Name -> [(Name, Type)] -> Q Dec
+makeToAliasReferenceInstanceFor name fields = do
+  toAliasReferenceDec' <- toAliasReferenceDec name fields
   let overlap = Nothing
       instanceConstraints = []
-      instanceType =
-        (ConT ''ToAliasReference)
-          `AppT` (ConT sqlName)
+      instanceType = (ConT ''ToAliasReference) `AppT` (ConT name)
   pure $ InstanceD overlap instanceConstraints instanceType [toAliasReferenceDec']
 
-toAliasReferenceDec :: RecordInfo -> Q Dec
-toAliasReferenceDec RecordInfo {..} = do
+toAliasReferenceDec :: Name -> [(Name, Type)] -> Q Dec
+toAliasReferenceDec name fields = do
   identInfo <- newName "identInfo"
 
   (statements, fieldPatterns, fieldExps) <-
-    unzip3 <$> forM sqlFields (\(fieldName', _) -> do
+    unzip3 <$> forM fields (\(fieldName', _) -> do
       fieldPatternName <- newName (nameBase fieldName')
       boundValueName <- newName (nameBase fieldName')
       pure
@@ -717,14 +732,14 @@ toAliasReferenceDec RecordInfo {..} = do
       'toAliasReference
       [ Clause
           [ VarP identInfo
-          , RecP sqlName fieldPatterns
+          , RecP name fieldPatterns
           ]
           ( NormalB $
               DoE
 #if MIN_VERSION_template_haskell(2,17,0)
                 Nothing
 #endif
-                (statements ++ [NoBindS $ AppE (VarE 'pure) (RecConE sqlName fieldExps)])
+                (statements ++ [NoBindS $ AppE (VarE 'pure) (RecConE name fieldExps)])
           )
           -- `where` clause.
           []
@@ -745,18 +760,28 @@ makeSqlMaybeRecord  RecordInfo {..} = do
 -- | Generates a `ToMaybe` instance for the given record.
 makeToMaybeInstance :: RecordInfo -> Q Dec
 makeToMaybeInstance info@RecordInfo {..} = do
-  toMaybeTDec' <- toMaybeTDec info
+  toMaybeTDec' <- toMaybeTDec sqlName sqlMaybeName 
   toMaybeDec' <- toMaybeDec info
   let overlap = Nothing
       instanceConstraints = []
       instanceType = (ConT ''ToMaybe) `AppT` (ConT sqlName)
 
   pure $ InstanceD overlap instanceConstraints instanceType [toMaybeTDec', toMaybeDec']
 
--- | Generates a `type ToMaybeT ... = ...` declaration for the given record.
-toMaybeTDec :: RecordInfo -> Q Dec
-toMaybeTDec RecordInfo {..} = do
-  pure $ mkTySynInstD ''ToMaybeT (ConT sqlName) (ConT sqlMaybeName)
+-- | Generates a `ToMaybe` instance for the SqlMaybe of the given record.
+makeSqlMaybeToMaybeInstance :: RecordInfo -> Q Dec
+makeSqlMaybeToMaybeInstance RecordInfo {..} = do
+  sqlMaybeToMaybeTDec' <- toMaybeTDec sqlMaybeName sqlMaybeName
+  let toMaybeIdDec = FunD 'toMaybe [ Clause [] (NormalB (VarE 'id)) []]
+      overlap = Nothing
+      instanceConstraints = []
+      instanceType = (ConT ''ToMaybe) `AppT` (ConT sqlMaybeName)
+  pure $ InstanceD overlap instanceConstraints instanceType [sqlMaybeToMaybeTDec', toMaybeIdDec]
+
+-- | Generates a `type ToMaybeT ... = ...` declaration for the given names.
+toMaybeTDec :: Name -> Name -> Q Dec
+toMaybeTDec nameLeft nameRight = do
+  pure $ mkTySynInstD ''ToMaybeT (ConT nameLeft) (ConT nameRight)
   where
     mkTySynInstD className lhsArg rhs =
 #if MIN_VERSION_template_haskell(2,15,0)
@@ -851,66 +876,69 @@ sqlMaybeSelectColsDec RecordInfo {..} = do
       ]
 
 -- | Generates the `sqlSelectProcessRow` declaration for an `SqlSelect`
--- instance.
+-- instance for a SqlMaybe.
 sqlMaybeSelectProcessRowDec :: RecordInfo -> Q Dec
 sqlMaybeSelectProcessRowDec RecordInfo {..} = do
-  let
-    sqlOp x = case x of
-            -- AppT (ConT ((==) ''Entity -> True)) _innerType -> id
-            -- (ConT ((==) ''Maybe -> True)) `AppT` ((ConT ((==) ''Entity -> True)) `AppT` _innerType) -> (AppE (VarE 'pure))
-            -- inner@((ConT ((==) ''Maybe -> True)) `AppT` _inner) -> (AppE (VarE 'unValue))
-            (AppT (ConT ((==) ''SqlExpr -> True)) (AppT (ConT ((==) ''Value -> True)) _)) -> (AppE (VarE 'unValue))
-            (AppT (ConT ((==) ''SqlExpr -> True)) (AppT (ConT ((==) ''Entity -> True)) _)) -> id
-            (AppT (ConT ((==) ''SqlExpr -> True)) (AppT (ConT ((==) ''Maybe -> True)) _)) -> (AppE (VarE 'pure))
-            (ConT _) -> id
-            _ -> error $ show x
-
-  fieldNames <- forM sqlFields (\(name', typ) -> do
-    var <- newName $ nameBase name'
-    pure (name', var, sqlOp typ (VarE var)))
-
-  let
-    joinedFields =
-        case (\(_,x,_) -> x) `map` fieldNames of
-          [] -> TupP []
-          [f1] -> VarP f1
-          f1 : rest ->
-            let helper lhs field =
-                  InfixP
-                    lhs
-                    '(:&)
-                    (VarP field)
-             in foldl' helper (VarP f1) rest
-
+  -- See sqlSelectProcessRowDec, which is similar but does not have special handling for Maybe
+  (statements, fieldExps) <-
+    unzip <$> forM (zip fields sqlMaybeFields) (\((fieldName', fieldType), (_, sqlType')) -> do
+      valueName <- newName (nameBase fieldName')
+      pattern <- sqlSelectProcessRowPat fieldType valueName
+      pure
+        ( BindS
+            pattern
+            (AppTypeE (VarE 'takeColumns) sqlType')
+        , (valueName, wrapJust fieldType $ VarE valueName)
+        ))
 
   colsName <- newName "columns"
+  processName <- newName "process"
 
-  let
-#if MIN_VERSION_template_haskell(2,17,0)
-    bodyExp = DoE Nothing
-#else
-    bodyExp = DoE
-#endif
-        [ BindS joinedFields (AppE (VarE 'sqlSelectProcessRow) (VarE colsName))
-        , NoBindS
-            $ AppE (VarE 'pure) (
-                case fieldNames of
-                    [] -> ConE constructorName
-                    (_,_,e):xs -> foldl'
-                        (\acc (_,_,e2) -> AppE (AppE (VarE '(<*>)) acc) e2)
-                        (AppE (AppE (VarE 'fmap) (ConE constructorName)) e)
-                        xs
-            )
-        ]
+  bodyExp <- [e|
+    first (fromString ("Failed to parse " ++ $(lift $ nameBase sqlMaybeName) ++ ": ") <>)
+          (evalStateT $(varE processName) $(varE colsName))
+    |]
 
   pure $
     FunD
       'sqlSelectProcessRow
       [ Clause
           [VarP colsName]
           (NormalB bodyExp)
-          []
+          -- `where`
+          [ ValD
+              (VarP processName)
+              (NormalB $
+                  DoE
+#if MIN_VERSION_template_haskell(2,17,0)
+                    Nothing
+#endif
+                    (statements ++ [
+                      NoBindS $ AppE (VarE 'pure) (
+                        CondE
+                          (AppE
+                            (VarE 'or)
+                            (ListE $ fmap (\(n, _) -> AppE (VarE 'isJust) (VarE n)) fieldExps))
+                          (case snd <$> fieldExps of
+                              [] -> ConE constructorName
+                              x:xs ->  foldl'
+                                (\a b -> InfixE (Just a) (VarE '(<*>)) (Just b))
+                                (InfixE (Just $ ConE constructorName) (VarE '(<$>)) (Just x))
+                                xs)
+                          (ConE 'Nothing)
+                        )
+                      ]
+                    )
+              )
+              []
+          ]
       ]
+  where
+    wrapJust x = case x of
+      AppT (ConT ((==) ''Entity -> True)) _innerType -> id
+      ((ConT ((==) ''Maybe -> True)) `AppT` _inner) -> AppE (ConE 'Just)
+      (ConT _) -> id
+      _ -> error $ show x
 
 -- | Generates the `sqlSelectColCount` declaration for an `SqlSelect` instance.
 sqlMaybeSelectColCountDec :: RecordInfo -> Q Dec