feat: WIP allow spread operators in to-many relationships

src/PostgREST/ApiRequest/Types.hs

@@ -86,7 +86,6 @@ data ApiRequestError
   | PutLimitNotAllowedError
   | QueryParamError QPError
   | RelatedOrderNotToOne Text Text
-  | SpreadNotToOne Text Text
   | UnacceptableFilter Text
   | UnacceptableSchema [Text]
   | UnsupportedMethod ByteString
@@ -145,7 +144,7 @@ type Cast = Text
 type Alias = Text
 type Hint = Text
 
-data AggregateFunction = Sum | Avg | Max | Min | Count
+data AggregateFunction = Sum | Avg | Max | Min | Count | JsonAgg
   deriving (Show, Eq)
 
 data EmbedParam

src/PostgREST/Error.hs

@@ -80,7 +80,6 @@ instance PgrstError ApiRequestError where
   status PutLimitNotAllowedError     = HTTP.status400
   status QueryParamError{}           = HTTP.status400
   status RelatedOrderNotToOne{}      = HTTP.status400
-  status SpreadNotToOne{}            = HTTP.status400
   status UnacceptableFilter{}        = HTTP.status400
   status UnacceptableSchema{}        = HTTP.status406
   status UnsupportedMethod{}         = HTTP.status405
@@ -176,12 +175,6 @@ instance JSON.ToJSON ApiRequestError where
     (Just $ JSON.String $ "'" <> origin <> "' and '" <> target <> "' do not form a many-to-one or one-to-one relationship")
     Nothing
 
-  toJSON (SpreadNotToOne origin target) = toJsonPgrstError
-    ApiRequestErrorCode19
-    ("A spread operation on '" <> target <> "' is not possible")
-    (Just $ JSON.String $ "'" <> origin <> "' and '" <> target <> "' do not form a many-to-one or one-to-one relationship")
-    Nothing
-
   toJSON (UnacceptableFilter target) = toJsonPgrstError
     ApiRequestErrorCode20
     ("Bad operator on the '" <> target <> "' embedded resource")
@@ -629,7 +622,7 @@ data ErrorCode
   | ApiRequestErrorCode16
   | ApiRequestErrorCode17
   | ApiRequestErrorCode18
-  | ApiRequestErrorCode19
+  -- | ApiRequestErrorCode19 -- no longer used (used to be mapped to SpreadNotToOne)
   | ApiRequestErrorCode20
   | ApiRequestErrorCode21
   | ApiRequestErrorCode22
@@ -678,7 +671,6 @@ buildErrorCode code = case code of
   ApiRequestErrorCode16  -> "PGRST116"
   ApiRequestErrorCode17  -> "PGRST117"
   ApiRequestErrorCode18  -> "PGRST118"
-  ApiRequestErrorCode19  -> "PGRST119"
   ApiRequestErrorCode20  -> "PGRST120"
   ApiRequestErrorCode21  -> "PGRST121"
   ApiRequestErrorCode22  -> "PGRST122"

src/PostgREST/Plan.hs

@@ -334,12 +334,12 @@ readPlan qi@QualifiedIdentifier{..} AppConfig{configDbMaxRows, configDbAggregate
     treeRestrictRange configDbMaxRows (iAction apiRequest) =<<
     hoistSpreadAggFunctions =<<
     validateAggFunctions configDbAggregates =<<
-    addRelSelects =<<
+    addRelSelects False =<<
     addNullEmbedFilters =<<
-    validateSpreadEmbeds =<<
     addRelatedOrders =<<
     addAliases =<<
     expandStars ctx =<<
+    addJsonAggToManySpread False =<<
     addRels qiSchema (iAction apiRequest) dbRelationships Nothing =<<
     addLogicTrees ctx apiRequest =<<
     addRanges apiRequest =<<
@@ -616,32 +616,52 @@ findRel schema allRels origin target hint =
             )
       ) $ fromMaybe mempty $ HM.lookup (QualifiedIdentifier schema origin, schema) allRels
 
-
-addRelSelects :: ReadPlanTree -> Either ApiRequestError ReadPlanTree
-addRelSelects node@(Node rp forest)
+-- Add JsonAgg aggregates to selected fields that do not have other aggregates and:
+-- * Are selected inside a to-many spread relationship
+-- * Are selected inside a to-one spread relationship but are nested inside a to-many spread relationship at any level
+addJsonAggToManySpread :: Bool -> ReadPlanTree -> Either ApiRequestError ReadPlanTree
+addJsonAggToManySpread isNested (Node rp@ReadPlan{select} forest) =
+    let newForest = addJsonAggToManySpread shouldAddJsonAgg `traverse` forest
+        newSelects
+          | shouldAddJsonAgg = fieldToJsonAgg <$> select
+          | otherwise = select
+    in Node rp { select = newSelects } <$> newForest
+    where
+      shouldAddJsonAgg = spreadRelIsInToMany isNested rp
+      fieldToJsonAgg field
+        | isJust $ csAggFunction field = field
+        | otherwise = field { csAggFunction = Just JsonAgg, csAlias = newAlias (csAlias field) (cfName $ csField field) }
+      newAlias :: Maybe Alias -> FieldName -> Maybe Alias
+      newAlias _ "*" = Nothing
+      newAlias alias fieldName = maybe (Just fieldName) pure alias
+
+addRelSelects :: Bool -> ReadPlanTree -> Either ApiRequestError ReadPlanTree
+addRelSelects isNestedInToManySpread node@(Node rp forest)
   | null forest = Right node
   | otherwise   =
-    let newForest     = rights $ addRelSelects <$> forest
-        newRelSelects = mapMaybe generateRelSelectField newForest
+    let spreadInToMany = spreadRelIsInToMany isNestedInToManySpread rp
+        newForest      = rights $ addRelSelects spreadInToMany <$> forest
+        newRelSelects  = mapMaybe (generateRelSelectField spreadInToMany) newForest
     in Right $ Node rp { relSelect = newRelSelects } newForest
 
-generateRelSelectField :: ReadPlanTree -> Maybe RelSelectField
-generateRelSelectField (Node rp@ReadPlan{relToParent=Just _, relAggAlias, relIsSpread = True} _) =
-  Just $ Spread { rsSpreadSel = generateSpreadSelectFields rp, rsAggAlias = relAggAlias }
-generateRelSelectField (Node ReadPlan{relToParent=Just rel, select, relName, relAlias, relAggAlias, relIsSpread = False} forest) =
+generateRelSelectField :: Bool -> ReadPlanTree -> Maybe RelSelectField
+generateRelSelectField isNestedInToManySpread (Node rp@ReadPlan{relToParent=Just _, relAggAlias, relIsSpread = True} _) =
+  Just $ Spread { rsSpreadSel = generateSpreadSelectFields isNestedInToManySpread rp, rsAggAlias = relAggAlias }
+generateRelSelectField isNestedInToManySpread (Node ReadPlan{relToParent=Just rel, select, relName, relAlias, relAggAlias, relIsSpread = False} forest) =
   Just $ JsonEmbed { rsEmbedMode, rsSelName, rsAggAlias = relAggAlias, rsEmptyEmbed }
   where
     rsSelName = fromMaybe relName relAlias
-    rsEmbedMode = if relIsToOne rel then JsonObject else JsonArray
+    -- If the JsonEmbed is nested in a to-many spread relationship, it will be aggregated at the top. That's why we treat it as `JsonObject`.
+    rsEmbedMode = if relIsToOne rel || isNestedInToManySpread then JsonObject else JsonArray
     rsEmptyEmbed = hasOnlyNullEmbed (null select) forest
     hasOnlyNullEmbed = foldr checkIfNullEmbed
     checkIfNullEmbed :: ReadPlanTree -> Bool -> Bool
     checkIfNullEmbed (Node ReadPlan{select=s} f) isNullEmbed =
       isNullEmbed && hasOnlyNullEmbed (null s) f
-generateRelSelectField _ = Nothing
+generateRelSelectField _ _ = Nothing
 
-generateSpreadSelectFields :: ReadPlan -> [SpreadSelectField]
-generateSpreadSelectFields ReadPlan{select, relSelect} =
+generateSpreadSelectFields :: Bool -> ReadPlan -> [SpreadSelectField]
+generateSpreadSelectFields isNestedInToManySpread rp@ReadPlan{select, relSelect} =
   -- We combine the select and relSelect fields into a single list of SpreadSelectField.
   selectSpread ++ relSelectSpread
   where
@@ -653,10 +673,18 @@ generateSpreadSelectFields ReadPlan{select, relSelect} =
     relSelectSpread = concatMap relSelectToSpread relSelect
     relSelectToSpread :: RelSelectField -> [SpreadSelectField]
     relSelectToSpread (JsonEmbed{rsSelName}) =
-      [SpreadSelectField { ssSelName = rsSelName, ssSelAggFunction = Nothing, ssSelAggCast = Nothing, ssSelAlias = Nothing }]
+      -- The regular embeds that are nested inside spread to-many relationships are also aggregated usin `json_agg()`
+      let shouldAddJsonAgg = spreadRelIsInToMany isNestedInToManySpread rp
+          (aggFun, alias) = if shouldAddJsonAgg then (Just JsonAgg, Just rsSelName) else (Nothing, Nothing) in
+      [SpreadSelectField { ssSelName = rsSelName, ssSelAggFunction = aggFun, ssSelAggCast = Nothing, ssSelAlias = alias }]
     relSelectToSpread (Spread{rsSpreadSel}) =
       rsSpreadSel
 
+-- TODO: perhaps this can be done in addRels instead? ReadPlan could have a "nestedInToManySpread" attribute
+spreadRelIsInToMany :: Bool -> ReadPlan -> Bool
+spreadRelIsInToMany isNested ReadPlan{relIsSpread, relToParent} =
+  relIsSpread && (isNested || Just False == (relIsToOne <$> relToParent))
+
 -- When aggregates are present in a ReadPlan that will be spread, we "hoist"
 -- to the highest level possible so that their semantics make sense. For instance,
 -- imagine the user performs the following request:
@@ -906,15 +934,6 @@ resolveLogicTree ctx (Expr b op lts) = CoercibleExpr b op (map (resolveLogicTree
 resolveFilter :: ResolverContext -> Filter -> CoercibleFilter
 resolveFilter ctx (Filter fld opExpr) = CoercibleFilter{field=resolveQueryInputField ctx fld, opExpr=opExpr}
 
--- Validates that spread embeds are only done on to-one relationships
-validateSpreadEmbeds :: ReadPlanTree -> Either ApiRequestError ReadPlanTree
-validateSpreadEmbeds (Node rp@ReadPlan{relToParent=Nothing} forest) = Node rp <$> validateSpreadEmbeds `traverse` forest
-validateSpreadEmbeds (Node rp@ReadPlan{relIsSpread,relToParent=Just rel,relName} forest) = do
-  validRP <- if relIsSpread && not (relIsToOne rel)
-    then Left $ SpreadNotToOne (qiName $ relTable rel) relName -- TODO using relTable is not entirely right because ReadPlan might have an alias, need to store the parent alias on ReadPlan
-    else Right rp
-  Node validRP <$> validateSpreadEmbeds `traverse` forest
-
 -- Find a Node of the Tree and apply a function to it
 updateNode :: (a -> ReadPlanTree -> ReadPlanTree) -> (EmbedPath, a) -> Either ApiRequestError ReadPlanTree -> Either ApiRequestError ReadPlanTree
 updateNode f ([], a) rr = f a <$> rr

src/PostgREST/Query/QueryBuilder.hs

@@ -75,6 +75,7 @@ getJoinSelects (Node ReadPlan{relSelect} _) =
         case fld of
           JsonEmbed{rsEmptyEmbed = True} ->
             Nothing
+          -- Maybe there needs to be a flag here or treat as a Spread?
           JsonEmbed{rsSelName, rsEmbedMode = JsonObject} ->
             Just $ "row_to_json(" <> aggAlias <> ".*)::jsonb AS " <> pgFmtIdent rsSelName
           JsonEmbed{rsSelName, rsEmbedMode = JsonArray} ->

src/PostgREST/Query/SqlFragment.hs

@@ -284,10 +284,11 @@ pgFmtApplyAggregate Nothing _ snippet = snippet
 pgFmtApplyAggregate (Just agg) aggCast snippet =
   pgFmtApplyCast aggCast aggregatedSnippet
   where
-    convertAggFunction :: AggregateFunction -> SQL.Snippet
+    aggregatedSnippet = aggFunction <> "(" <> aggArgument <> ")" <> aggFilter
     -- Convert from e.g. Sum (the data type) to SUM
-    convertAggFunction = SQL.sql . BS.map toUpper . BS.pack . show
-    aggregatedSnippet = convertAggFunction agg <> "(" <> snippet <> ")"
+    (aggFunction, aggArgument, aggFilter) = case agg of
+      JsonAgg -> (SQL.sql "json_agg", snippet, mempty)
+      a       -> (SQL.sql . BS.map toUpper . BS.pack $ show a, snippet, mempty)
 
 pgFmtApplyCast :: Maybe Cast -> SQL.Snippet -> SQL.Snippet
 pgFmtApplyCast Nothing snippet = snippet

test/spec/Feature/Query/AggregateFunctionsSpec.hs

@@ -214,14 +214,16 @@ allowed =
             {"name": "Mary", "process_supervisor": [{"name": "Batch", "sum": 220.00}]},
             {"name": "John", "process_supervisor": [{"name": "Batch", "sum": 70.00}, {"name": "Mass", "sum": 200.00}]},
             {"name": "Peter", "process_supervisor": [{"name": "Batch", "sum": 180.00}, {"name": "Mass", "sum": 120.00}]},
-            {"name": "Sarah", "process_supervisor": [{"name": "Batch", "sum": 180.00}]}]|]
+            {"name": "Sarah", "process_supervisor": [{"name": "Batch", "sum": 180.00}]},
+            {"name": "Jane", "process_supervisor": []}]|]
           { matchHeaders = [matchContentTypeJson] }
         get "/supervisors?select=name,process_supervisor(...processes(...process_costs(cost_sum:cost.sum()),...process_categories(category:name)))" `shouldRespondWith`
           [json|[
             {"name": "Mary", "process_supervisor": [{"category": "Batch", "cost_sum": 220.00}]},
             {"name": "John", "process_supervisor": [{"category": "Batch", "cost_sum": 70.00}, {"category": "Mass", "cost_sum": 200.00}]},
             {"name": "Peter", "process_supervisor": [{"category": "Batch", "cost_sum": 180.00}, {"category": "Mass", "cost_sum": 120.00}]},
-            {"name": "Sarah", "process_supervisor": [{"category": "Batch", "cost_sum": 180.00}]}]|]
+            {"name": "Sarah", "process_supervisor": [{"category": "Batch", "cost_sum": 180.00}]},
+            {"name": "Jane", "process_supervisor": []}]|]
           { matchHeaders = [matchContentTypeJson] }
 
       context "supports count() aggregate without specifying a field" $ do