feat: allow spreading one-to-many and many-to-many embedded resources

* Note: Aggregates are not implemented

src/PostgREST/Query/QueryBuilder.hs

@@ -44,9 +44,9 @@ import PostgREST.Query.SqlFragment
 import Protolude
 
 readPlanToQuery :: ReadPlanTree -> SQL.Snippet
-readPlanToQuery node@(Node ReadPlan{select,from=mainQi,fromAlias,where_=logicForest,order, range_=readRange, relToParent, relJoinConds, relSelect} forest) =
+readPlanToQuery node@(Node ReadPlan{select,from=mainQi,fromAlias,where_=logicForest,order, range_=readRange, relToParent, relJoinConds, relSelect, relSpread} forest) =
   "SELECT " <>
-  intercalateSnippet ", " ((pgFmtSelectItem qi <$> (if null select && null forest then defSelect else select)) ++ joinsSelects) <>
+  intercalateSnippet ", " (selects ++ sprExtraSelects ++ joinsSelects) <>
   fromFrag <>
   intercalateSnippet " " joins <>
   (if null logicForest && null relJoinConds
@@ -61,7 +61,11 @@ readPlanToQuery node@(Node ReadPlan{select,from=mainQi,fromAlias,where_=logicFor
     -- gets all the columns in case of an empty select, ignoring/obtaining these columns is done at the aggregation stage
     defSelect = [CoercibleSelectField (unknownField "*" []) Nothing Nothing Nothing Nothing]
     joins = getJoins node
+    selects = pgFmtSelectItem qi <$> (if null select && null forest then defSelect else select)
     joinsSelects = getJoinSelects node
+    sprExtraSelects = case relSpread of
+      Just (ToManySpread sels _) -> (\s -> pgFmtSelectItem (maybe qi (QualifiedIdentifier "") $ fst s) $ snd s) <$> sels
+      _ -> mempty
 
 getJoinSelects :: ReadPlanTree -> [SQL.Snippet]
 getJoinSelects (Node ReadPlan{relSelect} _) =
@@ -91,23 +95,28 @@ getJoins (Node ReadPlan{relSelect} forest) =
       ) relSelect
 
 getJoin :: RelSelectField -> ReadPlanTree -> SQL.Snippet
-getJoin fld node@(Node ReadPlan{relJoinType} _) =
+getJoin fld node@(Node ReadPlan{relJoinType, relSpread} _) =
   let
     correlatedSubquery sub al cond =
       " " <> (if relJoinType == Just JTInner then "INNER" else "LEFT") <> " JOIN LATERAL ( " <> sub <> " ) AS " <> al <> " ON " <> cond
     subquery = readPlanToQuery node
     aggAlias = pgFmtIdent $ rsAggAlias fld
+    selectSubqAgg = "SELECT json_agg(" <> aggAlias <> ")::jsonb AS " <> aggAlias
+    fromSubqAgg = " FROM (" <> subquery <> " ) AS " <> aggAlias
+    joinCondition = if relJoinType == Just JTInner then aggAlias <> " IS NOT NULL" else "TRUE"
   in
     case fld of
       JsonEmbed{rsEmbedMode = JsonObject} ->
         correlatedSubquery subquery aggAlias "TRUE"
-      Spread{} ->
-        correlatedSubquery subquery aggAlias "TRUE"
+      Spread{rsSpreadSel, rsAggAlias} ->
+        case relSpread of
+          Just (ToManySpread _ sprOrder) ->
+            let selSpread = selectSubqAgg <> (if null rsSpreadSel then mempty else ", ") <> intercalateSnippet ", " (pgFmtSpreadJoinSelectItem rsAggAlias sprOrder <$> rsSpreadSel)
+            in correlatedSubquery (selSpread <> fromSubqAgg) aggAlias joinCondition
+          _ ->
+            correlatedSubquery subquery aggAlias "TRUE"
       JsonEmbed{rsEmbedMode = JsonArray} ->
-        let
-          subq = "SELECT json_agg(" <> aggAlias <> ")::jsonb AS " <> aggAlias <> " FROM (" <> subquery <> " ) AS " <> aggAlias
-          condition = if relJoinType == Just JTInner then aggAlias <> " IS NOT NULL" else "TRUE"
-        in correlatedSubquery subq aggAlias condition
+        correlatedSubquery (selectSubqAgg <> fromSubqAgg) aggAlias joinCondition
 
 mutatePlanToQuery :: MutatePlan -> SQL.Snippet
 mutatePlanToQuery (Insert mainQi iCols body onConflict putConditions returnings _ applyDefaults) =

src/PostgREST/Query/SqlFragment.hs

@@ -22,6 +22,7 @@ module PostgREST.Query.SqlFragment
   , pgFmtOrderTerm
   , pgFmtSelectItem
   , pgFmtSpreadSelectItem
+  , pgFmtSpreadJoinSelectItem
   , fromJsonBodyF
   , responseHeadersF
   , responseStatusF
@@ -257,7 +258,7 @@ pgFmtField table cf = case cfToTsVector cf of
   _                      -> fmtFld
   where
     fmtFld = case cf of
-      CoercibleField{cfFullRow=True}                                          -> fromQi table
+      CoercibleField{cfFullRow=True}                                          -> pgFmtIdent (qiName table)
       CoercibleField{cfName=fn, cfJsonPath=[]}                                -> pgFmtColumn table fn
       CoercibleField{cfName=fn, cfToJson=doToJson, cfJsonPath=jp} | doToJson  -> "to_jsonb(" <> pgFmtColumn table fn <> ")" <> pgFmtJsonPath jp
                                                                   | otherwise -> pgFmtColumn table fn <> pgFmtJsonPath jp
@@ -278,11 +279,7 @@ pgFmtSelectItem table CoercibleSelectField{csField=fld, csAggFunction=agg, csAgg
 
 pgFmtSpreadSelectItem :: Alias -> SpreadSelectField -> SQL.Snippet
 pgFmtSpreadSelectItem aggAlias SpreadSelectField{ssSelName, ssSelAggFunction, ssSelAggCast, ssSelAlias} =
-  pgFmtApplyAggregate ssSelAggFunction ssSelAggCast fullSelName <> pgFmtAs ssSelAlias
-  where
-    fullSelName = case ssSelName of
-      "*" -> pgFmtIdent aggAlias <> ".*"
-      _   -> pgFmtIdent aggAlias <> "." <> pgFmtIdent ssSelName
+  pgFmtApplyAggregate ssSelAggFunction ssSelAggCast (pgFmtFullSelName aggAlias ssSelName) <> pgFmtAs ssSelAlias
 
 pgFmtApplyAggregate :: Maybe AggregateFunction -> Maybe Cast -> SQL.Snippet -> SQL.Snippet
 pgFmtApplyAggregate Nothing _ snippet = snippet
@@ -294,6 +291,14 @@ pgFmtApplyAggregate (Just agg) aggCast snippet =
     convertAggFunction = SQL.sql . BS.map toUpper . BS.pack . show
     aggregatedSnippet = convertAggFunction agg <> "(" <> snippet <> ")"
 
+pgFmtSpreadJoinSelectItem :: Alias -> [CoercibleOrderTerm] -> SpreadSelectField -> SQL.Snippet
+pgFmtSpreadJoinSelectItem aggAlias order SpreadSelectField{ssSelName, ssSelAlias} =
+  "COALESCE(json_agg(" <> fmtField <> " " <> fmtOrder <> "),'[]')::jsonb" <> " AS " <> fmtAlias
+  where
+    fmtField = pgFmtFullSelName aggAlias ssSelName
+    fmtOrder = orderF (QualifiedIdentifier "" aggAlias) order
+    fmtAlias = pgFmtIdent (fromMaybe ssSelName ssSelAlias)
+
 pgFmtApplyCast :: Maybe Cast -> SQL.Snippet -> SQL.Snippet
 pgFmtApplyCast Nothing snippet = snippet
 -- Ideally we'd quote the cast with "pgFmtIdent cast". However, that would invalidate common casts such as "int", "bigint", etc.
@@ -301,6 +306,11 @@ pgFmtApplyCast Nothing snippet = snippet
 -- Not quoting should be fine, we validate the input on Parsers.
 pgFmtApplyCast (Just cast) snippet = "CAST( " <> snippet <> " AS " <> SQL.sql (encodeUtf8 cast) <> " )"
 
+pgFmtFullSelName :: Alias -> FieldName -> SQL.Snippet
+pgFmtFullSelName aggAlias fieldName = case fieldName of
+  "*" -> pgFmtIdent aggAlias <> ".*"
+  _   -> pgFmtIdent aggAlias <> "." <> pgFmtIdent fieldName
+
 -- TODO: At this stage there shouldn't be a Maybe since ApiRequest should ensure that an INSERT/UPDATE has a body
 fromJsonBodyF :: Maybe LBS.ByteString -> [CoercibleField] -> Bool -> Bool -> Bool -> SQL.Snippet
 fromJsonBodyF body fields includeSelect includeLimitOne includeDefaults =