Add support for aggregate functions

The aggregate functions SUM(), MAX(), MIN(), AVG(),
and COUNT() are now supported.

src/PostgREST/ApiRequest/QueryParams.hs

@@ -31,8 +31,8 @@ import Data.Tree                     (Tree (..))
 import Text.Parsec.Error             (errorMessages,
                                       showErrorMessages)
 import Text.ParserCombinators.Parsec (GenParser, ParseError, Parser,
-                                      anyChar, between, char, digit,
-                                      eof, errorPos, letter,
+                                      anyChar, between, char, choice,
+                                      digit, eof, errorPos, letter,
                                       lookAhead, many1, noneOf,
                                       notFollowedBy, oneOf,
                                       optionMaybe, sepBy, sepBy1,
@@ -43,7 +43,8 @@ import PostgREST.RangeQuery              (NonnegRange, allRange,
                                           rangeOffset, restrictRange)
 import PostgREST.SchemaCache.Identifiers (FieldName)
 
-import PostgREST.ApiRequest.Types (EmbedParam (..), EmbedPath, Field,
+import PostgREST.ApiRequest.Types (AggregateFunction(..),
+                                   EmbedParam (..), EmbedPath, Field,
                                    Filter (..), FtsOperator (..),
                                    Hint, JoinType (..),
                                    JsonOperand (..),
@@ -58,7 +59,7 @@ import PostgREST.ApiRequest.Types (EmbedParam (..), EmbedPath, Field,
                                    SimpleOperator (..), SingleVal,
                                    TrileanVal (..))
 
-import Protolude hiding (try)
+import Protolude hiding (try, Sum)
 
 data QueryParams =
   QueryParams
@@ -452,10 +453,12 @@ pRelationSelect :: Parser SelectItem
 pRelationSelect = lexeme $ do
     alias <- optionMaybe ( try(pFieldName <* aliasSeparator) )
     name <- pFieldName
+    guard (name /= "count")
     (hint, jType) <- pEmbedParams
     try (void $ lookAhead (string "("))
     return $ SelectRelation name alias hint jType
 
+
 -- |
 -- Parse regular fields in select
 --
@@ -495,18 +498,31 @@ pFieldSelect :: Parser SelectItem
 pFieldSelect = lexeme $ try (do
     s <- pStar
     pEnd
-    return $ SelectField (s, []) Nothing Nothing)
+    return $ SelectField (s, []) Nothing Nothing Nothing)
+  <|> try (do
+    alias <- optionMaybe ( try(pFieldName <* aliasSeparator) )
+    _ <- string "count()"
+    pEnd
+    return $ SelectField ("*", []) (Just Count) Nothing alias)
   <|> do
     alias <- optionMaybe ( try(pFieldName <* aliasSeparator) )
     fld <- pField
     cast' <- optionMaybe (string "::" *> pIdentifier)
+    agg <- optionMaybe (try (char '.' *> pAggregation <* string "()"))
     pEnd
-    return $ SelectField fld (toS <$> cast') alias
+    return $ SelectField fld agg (toS <$> cast') alias
   where
     pEnd = try (void $ lookAhead (string ")")) <|>
            try (void $ lookAhead (string ",")) <|>
            try eof
     pStar = string "*" $> "*"
+    pAggregation = choice
+      [ string "sum"   $> Sum
+      , string "avg"   $> Avg
+      , string "max"   $> Max
+      , string "min"   $> Min
+      , string "count" $> Count
+      ]
 
 
 -- |

src/PostgREST/ApiRequest/Types.hs

@@ -1,6 +1,7 @@
 {-# LANGUAGE DuplicateRecordFields #-}
 module PostgREST.ApiRequest.Types
-  ( Alias
+  ( AggregateFunction(..)
+  , Alias
   , Cast
   , Depth
   , EmbedParam(..)
@@ -42,12 +43,13 @@ import PostgREST.SchemaCache.Routine      (Routine (..))
 
 import Protolude
 
--- | The value in `/tbl?select=alias:field::cast`
+-- | The value in `/tbl?select=alias:field.aggregateFunction()::cast`
 data SelectItem
   = SelectField
-    { selField :: Field
-    , selCast  :: Maybe Cast
-    , selAlias :: Maybe Alias
+    { selField              :: Field
+    , selAggregateFunction  :: Maybe AggregateFunction
+    , selCast               :: Maybe Cast
+    , selAlias              :: Maybe Alias
     }
 -- | The value in `/tbl?select=alias:another_tbl(*)`
   | SelectRelation
@@ -128,6 +130,9 @@ type Cast = Text
 type Alias = Text
 type Hint = Text
 
+data AggregateFunction = Sum | Avg | Max | Min | Count
+  deriving (Show, Eq)
+
 data EmbedParam
   -- | Disambiguates an embedding operation when there's multiple relationships
   -- between two tables. Can be the name of a foreign key constraint, column

src/PostgREST/Plan.hs

@@ -317,15 +317,15 @@ initReadRequest ctx@ResolverContext{qi=QualifiedIdentifier{..}} =
             (Node defReadPlan{from=QualifiedIdentifier qiSchema selRelation, relName=selRelation, relHint=selHint, relJoinType=selJoinType, depth=nxtDepth, relIsSpread=True} [])
             fldForest:rForest
         SelectField{..} ->
-          Node q{select=(resolveOutputField ctx{qi=from q} selField, selCast, selAlias):select q} rForest
+          Node q{select=(resolveOutputField ctx{qi=from q} selField, selAggregateFunction, selCast, selAlias):select q} rForest
 
 -- | Preserve the original field name if data representation is used to coerce the value.
 addDataRepresentationAliases :: ReadPlanTree -> Either ApiRequestError ReadPlanTree
 addDataRepresentationAliases rPlanTree = Right $ fmap (\rPlan@ReadPlan{select=sel} -> rPlan{select=map aliasSelectItem sel}) rPlanTree
   where
-    aliasSelectItem :: (CoercibleField, Maybe Cast, Maybe Alias) -> (CoercibleField, Maybe Cast, Maybe Alias)
+    aliasSelectItem :: (CoercibleField, Maybe AggregateFunction, Maybe Cast, Maybe Alias) -> (CoercibleField, Maybe AggregateFunction, Maybe Cast, Maybe Alias)
     -- If there already is an alias, don't overwrite it.
-    aliasSelectItem (fld@(CoercibleField{cfName=fieldName, cfTransform=(Just _)}), Nothing, Nothing) = (fld, Nothing, Just fieldName)
+    aliasSelectItem (fld@(CoercibleField{cfName=fieldName, cfTransform=(Just _)}), Nothing, Nothing, Nothing) = (fld, Nothing, Nothing, Just fieldName)
     aliasSelectItem fld = fld
 
 knownColumnsInContext :: ResolverContext -> [Column]
@@ -348,7 +348,7 @@ expandStarsForDataRepresentations ctx@ResolverContext{qi} rPlanTree = Right $ fm
 expandStarsForTable :: ResolverContext -> ReadPlan -> ReadPlan
 expandStarsForTable ctx@ResolverContext{representations, outputType} rplan@ReadPlan{select=selectItems} =
   -- If we have a '*' select AND the target table has at least one data representation, expand.
-  if ("*" `elem` map (\(field, _, _) -> cfName field) selectItems) && any hasOutputRep knownColumns
+  if ("*" `elem` map (\(field, _, _, _) -> cfName field) selectItems) && any hasOutputRep knownColumns
     then rplan{select=concatMap (expandStarSelectItem knownColumns) selectItems}
     else rplan
   where
@@ -357,8 +357,8 @@ expandStarsForTable ctx@ResolverContext{representations, outputType} rplan@ReadP
     hasOutputRep :: Column -> Bool
     hasOutputRep col = HM.member (colNominalType col, outputType) representations
 
-    expandStarSelectItem :: [Column] -> (CoercibleField, Maybe Cast, Maybe Alias) -> [(CoercibleField, Maybe Cast, Maybe Alias)]
-    expandStarSelectItem columns (CoercibleField{cfName="*", cfJsonPath=[]}, b, c) = map (\col -> (withOutputFormat ctx $ resolveColumnField col, b, c)) columns
+    expandStarSelectItem :: [Column] -> (CoercibleField, Maybe AggregateFunction, Maybe Cast, Maybe Alias) -> [(CoercibleField, Maybe AggregateFunction,Maybe Cast, Maybe Alias)]
+    expandStarSelectItem columns (CoercibleField{cfName="*", cfJsonPath=[]}, b, c, d) = map (\col -> (withOutputFormat ctx $ resolveColumnField col, b, c, d)) columns
     expandStarSelectItem _ selectItem = [selectItem]
 
 -- | Enforces the `max-rows` config on the result
@@ -770,7 +770,7 @@ inferColsEmbedNeeds (Node ReadPlan{select} forest) pkCols
   | "*" `elem` fldNames = ["*"]
   | otherwise           = returnings
   where
-    fldNames = cfName . (\(f, _, _) -> f) <$> select
+    fldNames = cfName . (\(f, _, _, _) -> f) <$> select
     -- Without fkCols, when a mutatePlan to
     -- /projects?select=name,clients(name) occurs, the RETURNING SQL part would
     -- be `RETURNING name`(see QueryBuilder).  This would make the embedding
@@ -839,8 +839,8 @@ binaryField AppConfig{configRawMediaTypes} acceptMediaType proc rpTree
       _                        -> False
 
     fstFieldName :: ReadPlanTree -> Maybe FieldName
-    fstFieldName (Node ReadPlan{select=(CoercibleField{cfName="*", cfJsonPath=[]}, _, _):_} [])  = Nothing
-    fstFieldName (Node ReadPlan{select=[(CoercibleField{cfName=fld, cfJsonPath=[]}, _, _)]} [])  = Just fld
+    fstFieldName (Node ReadPlan{select=(CoercibleField{cfName="*", cfJsonPath=[]}, _, _, _):_} [])  = Nothing
+    fstFieldName (Node ReadPlan{select=[(CoercibleField{cfName=fld, cfJsonPath=[]}, _, _, _)]} [])  = Just fld
     fstFieldName _                                               = Nothing
 
 

src/PostgREST/Plan/ReadPlan.hs

@@ -6,8 +6,8 @@ module PostgREST.Plan.ReadPlan
 
 import Data.Tree (Tree (..))
 
-import PostgREST.ApiRequest.Types         (Alias, Cast, Depth, Hint,
-                                           JoinType, NodeName)
+import PostgREST.ApiRequest.Types         (AggregateFunction, Alias, Cast, Depth,
+                                           Hint, JoinType, NodeName)
 import PostgREST.Plan.Types               (CoercibleField (..),
                                            CoercibleLogicTree,
                                            CoercibleOrderTerm)
@@ -28,7 +28,7 @@ data JoinCondition =
   deriving (Eq, Show)
 
 data ReadPlan = ReadPlan
-  { select       :: [(CoercibleField, Maybe Cast, Maybe Alias)]
+  { select       :: [(CoercibleField, Maybe AggregateFunction, Maybe Cast, Maybe Alias)]
   , from         :: QualifiedIdentifier
   , fromAlias    :: Maybe Alias
   , where_       :: [CoercibleLogicTree]

src/PostgREST/Query/QueryBuilder.hs

@@ -50,12 +50,13 @@ readPlanToQuery (Node ReadPlan{select,from=mainQi,fromAlias,where_=logicForest,o
   (if null logicForest && null relJoinConds
     then mempty
     else "WHERE " <> intercalateSnippet " AND " (map (pgFmtLogicTree qi) logicForest ++ map pgFmtJoinCondition relJoinConds)) <> " " <>
+  groupF qi select <> " " <>
   orderF qi order <> " " <>
   limitOffsetF readRange
   where
     fromFrag = fromF relToParent mainQi fromAlias
     qi = getQualifiedIdentifier relToParent mainQi fromAlias
-    defSelect = [(unknownField "*" [], Nothing, Nothing)] -- gets all the columns in case of an empty select, ignoring/obtaining these columns is done at the aggregation stage
+    defSelect = [(unknownField "*" [], Nothing, Nothing, Nothing)] -- gets all the columns in case of an empty select, ignoring/obtaining these columns is done at the aggregation stage
     (selects, joins) = foldr getSelectsJoins ([],[]) forest
 
 getSelectsJoins :: ReadPlanTree -> ([SQL.Snippet], [SQL.Snippet]) -> ([SQL.Snippet], [SQL.Snippet])

src/PostgREST/Query/SqlFragment.hs

@@ -9,6 +9,7 @@ module PostgREST.Query.SqlFragment
   ( noLocationF
   , aggF
   , countF
+  , groupF
   , fromQi
   , limitOffsetF
   , locationF
@@ -50,7 +51,8 @@ import Control.Arrow ((***))
 import Data.Foldable                 (foldr1)
 import Text.InterpolatedString.Perl6 (qc)
 
-import PostgREST.ApiRequest.Types        (Alias, Cast,
+import PostgREST.ApiRequest.Types        (AggregateFunction (..),
+                                          Alias, Cast,
                                           FtsOperator (..),
                                           JsonOperand (..),
                                           JsonOperation (..),
@@ -82,7 +84,7 @@ import PostgREST.SchemaCache.Routine     (ResultAggregate (..),
                                           funcReturnsSetOfScalar,
                                           funcReturnsSingleComposite)
 
-import Protolude hiding (cast)
+import Protolude hiding (cast, Sum)
 
 sourceCTEName :: Text
 sourceCTEName = "pgrst_source"
@@ -260,12 +262,21 @@ pgFmtCoerceNamed :: CoercibleField -> SQL.Snippet
 pgFmtCoerceNamed CoercibleField{cfName=fn, cfTransform=(Just formatterProc)} = pgFmtCallUnary formatterProc (pgFmtIdent fn) <> " AS " <> pgFmtIdent fn
 pgFmtCoerceNamed CoercibleField{cfName=fn} = pgFmtIdent fn
 
-pgFmtSelectItem :: QualifiedIdentifier -> (CoercibleField, Maybe Cast, Maybe Alias) -> SQL.Snippet
-pgFmtSelectItem table (fld, Nothing, alias) = pgFmtTableCoerce table fld <> pgFmtAs (cfName fld) (cfJsonPath fld) alias
+pgFmtSelectItem :: QualifiedIdentifier -> (CoercibleField, Maybe AggregateFunction, Maybe Cast, Maybe Alias) -> SQL.Snippet
+pgFmtSelectItem table (fld, agg, Nothing, alias) = pgFmtApplyAggregate agg (pgFmtTableCoerce table fld) <> pgFmtAs (cfName fld) (cfJsonPath fld) alias
 -- Ideally we'd quote the cast with "pgFmtIdent cast". However, that would invalidate common casts such as "int", "bigint", etc.
 -- Try doing: `select 1::"bigint"` - it'll err, using "int8" will work though. There's some parser magic that pg does that's invalidated when quoting.
 -- Not quoting should be fine, we validate the input on Parsers.
-pgFmtSelectItem table (fld, Just cast, alias) = "CAST (" <> pgFmtTableCoerce table fld <> " AS " <> SQL.sql (encodeUtf8 cast) <> " )" <> pgFmtAs (cfName fld) (cfJsonPath fld) alias
+pgFmtSelectItem table (fld, agg, Just cast, alias) = pgFmtApplyAggregate agg ("CAST (" <> pgFmtTableCoerce table fld <> " AS " <> SQL.sql (encodeUtf8 cast) <> " )") <> pgFmtAs (cfName fld) (cfJsonPath fld) alias
+
+pgFmtApplyAggregate :: Maybe AggregateFunction -> SQL.Snippet -> SQL.Snippet
+pgFmtApplyAggregate Nothing snippet = snippet
+pgFmtApplyAggregate (Just agg) snippet = case agg of
+  Sum   -> "SUM( "   <> snippet <> " )"
+  Max   -> "MAX( "   <> snippet <> " )"
+  Min   -> "MIN( "   <> snippet <> " )"
+  Avg   -> "AVG( "   <> snippet <> " )"
+  Count -> "COUNT( " <> snippet <> " )"
 
 -- 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
@@ -409,6 +420,19 @@ pgFmtAs fName jp Nothing = case jOp <$> lastMay jp of
   Nothing -> mempty
 pgFmtAs _ _ (Just alias) = " AS " <> pgFmtIdent alias
 
+groupF :: QualifiedIdentifier -> [(CoercibleField, Maybe AggregateFunction, Maybe Cast, Maybe Alias)] -> SQL.Snippet
+groupF _ [] = mempty
+groupF qi fields =
+  if all (\(_, agg, _, _) -> isNothing agg) fields || all (\(_, agg, _, _) -> isJust agg) fields
+    then
+      mempty
+    else
+    " GROUP BY " <> intercalateSnippet ", " (pgFmtGroup qi <$> (filter (\(_, agg, _, _) -> isNothing agg) fields))
+
+pgFmtGroup :: QualifiedIdentifier -> (CoercibleField, Maybe AggregateFunction, Maybe Cast, Maybe Alias) -> SQL.Snippet
+pgFmtGroup _ (_, Just _, _, _) = mempty
+pgFmtGroup qi (fld, _, _, _) = pgFmtField qi fld
+
 countF :: SQL.Snippet -> Bool -> (SQL.Snippet, SQL.Snippet)
 countF countQuery shouldCount =
   if shouldCount
@@ -496,6 +520,7 @@ setConfigLocalJson prefix keyVals = [setConfigLocal mempty (prefix, gucJsonVal k
     arrayByteStringToText :: [(ByteString, ByteString)] -> [(Text,Text)]
     arrayByteStringToText keyVal = (T.decodeUtf8 *** T.decodeUtf8) <$> keyVal
 
+-- Investigate this
 aggF :: Maybe Routine -> ResultAggregate -> SQL.Snippet
 aggF rout = \case
   BuiltinAggJson             -> asJsonF rout False