feat: allow aggregates inside spread one-to-many and many-to-many embedded resources

src/PostgREST/ApiRequest/QueryParams.hs

@@ -310,7 +310,8 @@ pTreePath = do
 pFieldForest :: Parser [Tree SelectItem]
 pFieldForest = pFieldTree `sepBy` lexeme (char ',')
   where
-    pFieldTree =  Node <$> try pSpreadRelationSelect <*> between (char '(') (char ')') pFieldForest <|>
+    pFieldTree =  Node <$> try pHoistedRelationSelect <*> between (char '(') (char ')') pFieldForest <|>
+                  Node <$> try pSpreadRelationSelect <*> between (char '(') (char ')') pFieldForest <|>
                   Node <$> try pRelationSelect       <*> between (char '(') (char ')') pFieldForest <|>
                   Node <$> pFieldSelect <*> pure []
 
@@ -582,6 +583,13 @@ pSpreadRelationSelect = lexeme $ do
     try (void $ lookAhead (string "("))
     return $ SpreadRelation name hint jType
 
+pHoistedRelationSelect :: Parser SelectItem
+pHoistedRelationSelect = lexeme $ do
+    name <- string "^" >> pFieldName
+    (hint, jType) <- pEmbedParams
+    try (void $ lookAhead (string "("))
+    return $ HoistedRelation name hint jType
+
 pEmbedParams :: Parser (Maybe Hint, Maybe JoinType)
 pEmbedParams = do
   prm1 <- optionMaybe pEmbedParam

src/PostgREST/ApiRequest/Types.hs

@@ -58,6 +58,12 @@ data SelectItem
     , selHint     :: Maybe Hint
     , selJoinType :: Maybe JoinType
     }
+-- | The value in `/tbl?select=^another_tbl(*)`
+  | HoistedRelation
+    { selRelation :: FieldName
+    , selHint     :: Maybe Hint
+    , selJoinType :: Maybe JoinType
+    }
   deriving (Eq, Show)
 
 type NodeName = Text

src/PostgREST/Plan/ReadPlan.hs

@@ -43,6 +43,7 @@
   , relAlias     :: Maybe Alias
   , relAggAlias  :: Alias
   , relHint      :: Maybe Hint
+  , relIsHoisted :: Bool
   , relJoinType  :: Maybe JoinType
   , relSpread    :: Maybe SpreadType
   , relSelect    :: [RelSelectField]

src/PostgREST/Plan/Types.hs

@@ -10,6 +10,7 @@
   , RelSelectField(..)
   , RelJsonEmbedMode(..)
   , SpreadSelectField(..)
+  , HoistedSelectField(..)
   , SpreadType(..)
   ) where
 
@@ -102,6 +103,10 @@
       { rsSpreadSel :: [SpreadSelectField]
       , rsAggAlias  :: Alias
       }
+  | Hoisted
+      { rsHoistedSel :: [HoistedSelectField]
+      , rsAggAlias   :: Alias
+      }
   deriving (Eq, Show)
 
 data SpreadSelectField =
@@ -113,6 +118,16 @@
   }
   deriving (Eq, Show)
 
+-- TODO(draft): DRY
+data HoistedSelectField =
+  HoistedSelectField
+  { hsSelName        :: FieldName
+  , hsSelAggFunction :: Maybe AggregateFunction
+  , hsSelAggCast     :: Maybe Cast
+  , hsSelAlias       :: Maybe Alias
+  }
+  deriving (Eq, Show)
+
 data SpreadType
   = ToOneSpread
   | ToManySpread

src/PostgREST/Query/QueryBuilder.hs

@@ -82,6 +82,8 @@ getJoinSelects (Node ReadPlan{relSelect} _) =
             Just $ "row_to_json(" <> aggAlias <> ".*)::jsonb AS " <> pgFmtIdent rsSelName
           JsonEmbed{rsSelName, rsEmbedMode = JsonArray} ->
             Just $ "COALESCE( " <> aggAlias <> "." <> aggAlias <> ", '[]') AS " <> pgFmtIdent rsSelName
+          Hoisted{rsHoistedSel, rsAggAlias} ->
+            Just $ intercalateSnippet ", " (pgFmtHoistedSelectItem rsAggAlias <$> rsHoistedSel)
           Spread{rsSpreadSel, rsAggAlias} ->
             Just $ intercalateSnippet ", " (pgFmtSpreadSelectItem rsAggAlias <$> rsSpreadSel)
 
@@ -108,6 +110,8 @@ getJoin fld node@(Node ReadPlan{relJoinType, relSpread} _) =
     case fld of
       JsonEmbed{rsEmbedMode = JsonObject} ->
         correlatedSubquery subquery aggAlias "TRUE"
+      Hoisted{} ->
+        correlatedSubquery subquery aggAlias "TRUE"
       Spread{rsSpreadSel, rsAggAlias} ->
         case relSpread of
           Just (ToManySpread _ sprOrder) ->

src/PostgREST/Query/SqlFragment.hs

@@ -16,6 +16,7 @@ module PostgREST.Query.SqlFragment
   , orderF
   , pgFmtColumn
   , pgFmtFilter
+  , pgFmtHoistedSelectItem
   , pgFmtIdent
   , pgFmtJoinCondition
   , pgFmtLogicTree
@@ -79,6 +80,7 @@ import PostgREST.Plan.Types              (CoercibleField (..),
                                           CoercibleLogicTree (..),
                                           CoercibleOrderTerm (..),
                                           CoercibleSelectField (..),
+                                          HoistedSelectField (..),
                                           RelSelectField (..),
                                           SpreadSelectField (..),
                                           ToTsVector (..),
@@ -281,8 +283,13 @@ pgFmtSpreadSelectItem :: Alias -> SpreadSelectField -> SQL.Snippet
 pgFmtSpreadSelectItem aggAlias SpreadSelectField{ssSelName, ssSelAggFunction, ssSelAggCast, ssSelAlias} =
   pgFmtApplyAggregate ssSelAggFunction ssSelAggCast (pgFmtFullSelName aggAlias ssSelName) <> pgFmtAs ssSelAlias
 
+-- TODO(draft): DRY
+pgFmtHoistedSelectItem :: Alias -> HoistedSelectField -> SQL.Snippet
+pgFmtHoistedSelectItem aggAlias HoistedSelectField{hsSelName, hsSelAggFunction, hsSelAggCast, hsSelAlias} =
+  pgFmtApplyAggregate hsSelAggFunction hsSelAggCast (pgFmtFullSelName aggAlias hsSelName) <> pgFmtAs hsSelAlias
+
 pgFmtApplyAggregate :: Maybe AggregateFunction -> Maybe Cast -> SQL.Snippet -> SQL.Snippet
-pgFmtApplyAggregate Nothing _ snippet = snippet
+pgFmtApplyAggregate Nothing _ snippet =snippet
 pgFmtApplyAggregate (Just agg) aggCast snippet =
   pgFmtApplyCast aggCast aggregatedSnippet
   where
@@ -458,7 +465,7 @@ groupF qi select relSelect
   | otherwise = " GROUP BY " <> intercalateSnippet ", " groupTerms
   where
     noSelectsAreAggregated = null $ [s | s@(CoercibleSelectField { csAggFunction = Just _ }) <- select]
-    noRelSelectsAreAggregated = all (\case Spread sels _ -> all (isNothing . ssSelAggFunction) sels; _ -> True) relSelect
+    noRelSelectsAreAggregated = all (\case Hoisted sels _ -> all (isNothing . hsSelAggFunction) sels; _ -> True) relSelect
     groupTermsFromSelect = mapMaybe (pgFmtGroup qi) select
     groupTermsFromRelSelect = mapMaybe groupTermFromRelSelectField relSelect
     groupTerms = groupTermsFromSelect ++ groupTermsFromRelSelect
@@ -477,6 +484,19 @@ groupTermFromRelSelectField (Spread { rsSpreadSel, rsAggAlias }) =
     processField SpreadSelectField{ssSelName, ssSelAlias} =
       Just $ pgFmtIdent rsAggAlias <> "." <> pgFmtIdent (fromMaybe ssSelName ssSelAlias)
     groupTerms = mapMaybe processField rsSpreadSel
+-- TODO(draft): DRY
+groupTermFromRelSelectField (Hoisted { rsHoistedSel, rsAggAlias }) =
+  if null groupTerms
+  then Nothing
+  else
+    Just $ intercalateSnippet ", " groupTerms
+  where
+    processField :: HoistedSelectField -> Maybe SQL.Snippet
+    processField HoistedSelectField{hsSelAggFunction = Just _} = Nothing
+    processField HoistedSelectField{hsSelName, hsSelAlias} =
+      Just $ pgFmtIdent rsAggAlias <> "." <> pgFmtIdent (fromMaybe hsSelName hsSelAlias)
+    groupTerms = mapMaybe processField rsHoistedSel
+
 
 pgFmtGroup :: QualifiedIdentifier -> CoercibleSelectField -> Maybe SQL.Snippet
 pgFmtGroup _  CoercibleSelectField{csAggFunction=Just _} = Nothing