feat: null filters on embedded resources

src/PostgREST/ApiRequest/Types.hs

@@ -80,6 +80,7 @@ data ApiRequestError
   | QueryParamError QPError
   | RelatedOrderNotToOne Text Text
   | SpreadNotToOne Text Text
+  | UnacceptableFilter Text
   | UnacceptableSchema [Text]
   | UnsupportedMethod ByteString
 
@@ -172,10 +173,12 @@ data LogicOperator
   | Or
   deriving Eq
 
-data Filter = Filter
+data Filter
+  = Filter
   { field  :: Field
   , opExpr :: OpExpr
   }
+  | FilterNullEmbed Bool FieldName
   deriving (Eq)
 
 data OpExpr =

src/PostgREST/Error.hs

@@ -74,6 +74,7 @@ instance PgrstError ApiRequestError where
   status QueryParamError{}       = HTTP.status400
   status RelatedOrderNotToOne{}  = HTTP.status400
   status SpreadNotToOne{}        = HTTP.status400
+  status UnacceptableFilter{}    = HTTP.status400
   status UnacceptableSchema{}    = HTTP.status406
   status UnsupportedMethod{}     = HTTP.status405
   status LimitNoOrderError       = HTTP.status400
@@ -167,6 +168,12 @@ instance JSON.ToJSON ApiRequestError where
     "details" .= ("'" <> origin <> "' and '" <> target <> "' do not form a many-to-one or one-to-one relationship" :: Text),
     "hint"    .= JSON.Null]
 
+  toJSON (UnacceptableFilter target) = JSON.object [
+    "code"    .= ApiRequestErrorCode20,
+    "message" .= ("Bad operator on the '" <> target <> "' embedded resource":: Text),
+    "details" .= ("Only is null or not is null filters are allowed on embedded resources":: Text),
+    "hint"    .= JSON.Null]
+
   toJSON (NoRelBetween parent child schema) = JSON.object [
     "code"    .= SchemaCacheErrorCode00,
     "message" .= ("Could not find a relationship between '" <> parent <> "' and '" <> child <> "' in the schema cache" :: Text),
@@ -540,6 +547,7 @@ data ErrorCode
   | ApiRequestErrorCode17
   | ApiRequestErrorCode18
   | ApiRequestErrorCode19
+  | ApiRequestErrorCode20
   -- Schema Cache errors
   | SchemaCacheErrorCode00
   | SchemaCacheErrorCode01
@@ -583,6 +591,7 @@ buildErrorCode code = "PGRST" <> case code of
   ApiRequestErrorCode17  -> "117"
   ApiRequestErrorCode18  -> "118"
   ApiRequestErrorCode19  -> "119"
+  ApiRequestErrorCode20  -> "120"
 
   SchemaCacheErrorCode00 -> "200"
   SchemaCacheErrorCode01 -> "201"

src/PostgREST/Plan.hs

@@ -97,6 +97,7 @@ readPlan :: QualifiedIdentifier -> AppConfig -> SchemaCache -> ApiRequest -> Eit
 readPlan qi@QualifiedIdentifier{..} AppConfig{configDbMaxRows} SchemaCache{dbRelationships} apiRequest  =
   mapLeft ApiRequestError $
   treeRestrictRange configDbMaxRows (iAction apiRequest) =<<
+  addNullEmbedFilters =<<
   validateSpreadEmbeds =<<
   addRelatedOrders =<<
   addRels qiSchema (iAction apiRequest) dbRelationships Nothing =<<
@@ -332,6 +333,25 @@ addRelatedOrders (Node rp@ReadPlan{order,from} forest) = do
         Nothing ->
           Left $ NotEmbedded otRelation
 
+-- Searches for null filters on embeds, e.g. `clients` on /projects?select=*,clients()&clients=not.is.null.
+-- If these are found, it changes the filter to use the internal aggregate name(`projects_clients_1`) so the filter can succeed.
+-- It fails if operators other than is.null or not.is.null are used.
+addNullEmbedFilters :: ReadPlanTree -> Either ApiRequestError ReadPlanTree
+addNullEmbedFilters (Node rp@ReadPlan{where_=oldLogic} forest) = do
+  let readPlans = rootLabel <$> forest
+  newLogic <- getFilters readPlans `traverse` oldLogic
+  Node rp{ReadPlan.where_= newLogic} <$> (addNullEmbedFilters `traverse` forest)
+  where
+    getFilters :: [ReadPlan] -> LogicTree -> Either ApiRequestError LogicTree
+    getFilters rPlans (Expr b lOp trees) = Expr b lOp <$> (getFilters rPlans `traverse` trees)
+    getFilters rPlans flt@(Stmnt (Filter (fld, []) opExpr)) =
+      let foundRP = find (\ReadPlan{relName, relAlias} -> Just fld `elem` [Just relName, relAlias]) rPlans in
+      case (foundRP, opExpr) of
+        (Just ReadPlan{relAggAlias}, OpExpr b (Is TriNull)) -> Right $ Stmnt $ FilterNullEmbed b relAggAlias
+        (Just ReadPlan{relName}, _)                         -> Left $ UnacceptableFilter relName
+        _                                                   -> Right flt
+    getFilters _ flt@(Stmnt _)        = Right flt
+
 addRanges :: ApiRequest -> ReadPlanTree -> Either ApiRequestError ReadPlanTree
 addRanges ApiRequest{..} rReq =
   case iAction of

src/PostgREST/Query/SqlFragment.hs

@@ -261,6 +261,7 @@ pgFmtOrderTerm qi ot =
 
 
 pgFmtFilter :: QualifiedIdentifier -> Filter -> SQL.Snippet
+pgFmtFilter _ (FilterNullEmbed hasNot fld) = SQL.sql (pgFmtIdent fld) <> " IS " <> (if hasNot then "NOT" else mempty) <> " NULL"
 pgFmtFilter table (Filter fld (OpExpr hasNot oper)) = notOp <> " " <> case oper of
    Op op val  -> pgFmtFieldOp op <> " " <> case op of
      OpLike  -> unknownLiteral (T.map star val)