Add support for aggregate functions

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

postgrest.cabal

@@ -201,6 +201,7 @@ test-suite spec
                       Feature.OpenApi.RootSpec
                       Feature.OpenApi.SecurityOpenApiSpec
                       Feature.OptionsSpec
+                      Feature.Query.AggregateFunctionsSpec
                       Feature.Query.AndOrParamsSpec
                       Feature.Query.ComputedRelsSpec
                       Feature.Query.CustomMediaSpec

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 (Sum, try)
 
 data QueryParams =
   QueryParams
@@ -99,7 +100,7 @@ data QueryParams =
 -- 'select' is a reserved parameter that selects the fields to be returned:
 --
 -- >>> qsSelect <$> parse False "select=name,location"
--- Right [Node {rootLabel = SelectField {selField = ("name",[]), selCast = Nothing, selAlias = Nothing}, subForest = []},Node {rootLabel = SelectField {selField = ("location",[]), selCast = Nothing, selAlias = Nothing}, subForest = []}]
+-- Right [Node {rootLabel = SelectField {selField = ("name",[]), selAggregateFunction = Nothing, selAggregateCast = Nothing, selCast = Nothing, selAlias = Nothing}, subForest = []},Node {rootLabel = SelectField {selField = ("location",[]), selAggregateFunction = Nothing, selAggregateCast = Nothing, selCast = Nothing, selAlias = Nothing}, subForest = []}]
 --
 -- Filters are parameters whose value contains an operator, separated by a '.' from its value:
 --
@@ -282,24 +283,24 @@ pTreePath = do
 -- Parse select= into a Forest of SelectItems
 --
 -- >>> P.parse pFieldForest "" "id"
--- Right [Node {rootLabel = SelectField {selField = ("id",[]), selCast = Nothing, selAlias = Nothing}, subForest = []}]
+-- Right [Node {rootLabel = SelectField {selField = ("id",[]), selAggregateFunction = Nothing, selAggregateCast = Nothing, selCast = Nothing, selAlias = Nothing}, subForest = []}]
 --
 -- >>> P.parse pFieldForest "" "client(id)"
--- Right [Node {rootLabel = SelectRelation {selRelation = "client", selAlias = Nothing, selHint = Nothing, selJoinType = Nothing}, subForest = [Node {rootLabel = SelectField {selField = ("id",[]), selCast = Nothing, selAlias = Nothing}, subForest = []}]}]
+-- Right [Node {rootLabel = SelectRelation {selRelation = "client", selAlias = Nothing, selHint = Nothing, selJoinType = Nothing}, subForest = [Node {rootLabel = SelectField {selField = ("id",[]), selAggregateFunction = Nothing, selAggregateCast = Nothing, selCast = Nothing, selAlias = Nothing}, subForest = []}]}]
 --
 -- >>> P.parse pFieldForest "" "*,client(*,nested(*))"
--- Right [Node {rootLabel = SelectField {selField = ("*",[]), selCast = Nothing, selAlias = Nothing}, subForest = []},Node {rootLabel = SelectRelation {selRelation = "client", selAlias = Nothing, selHint = Nothing, selJoinType = Nothing}, subForest = [Node {rootLabel = SelectField {selField = ("*",[]), selCast = Nothing, selAlias = Nothing}, subForest = []},Node {rootLabel = SelectRelation {selRelation = "nested", selAlias = Nothing, selHint = Nothing, selJoinType = Nothing}, subForest = [Node {rootLabel = SelectField {selField = ("*",[]), selCast = Nothing, selAlias = Nothing}, subForest = []}]}]}]
+-- Right [Node {rootLabel = SelectField {selField = ("*",[]), selAggregateFunction = Nothing, selAggregateCast = Nothing, selCast = Nothing, selAlias = Nothing}, subForest = []},Node {rootLabel = SelectRelation {selRelation = "client", selAlias = Nothing, selHint = Nothing, selJoinType = Nothing}, subForest = [Node {rootLabel = SelectField {selField = ("*",[]), selAggregateFunction = Nothing, selAggregateCast = Nothing, selCast = Nothing, selAlias = Nothing}, subForest = []},Node {rootLabel = SelectRelation {selRelation = "nested", selAlias = Nothing, selHint = Nothing, selJoinType = Nothing}, subForest = [Node {rootLabel = SelectField {selField = ("*",[]), selAggregateFunction = Nothing, selAggregateCast = Nothing, selCast = Nothing, selAlias = Nothing}, subForest = []}]}]}]
 --
 -- >>> P.parse pFieldForest "" "*,...client(*),other(*)"
--- Right [Node {rootLabel = SelectField {selField = ("*",[]), selCast = Nothing, selAlias = Nothing}, subForest = []},Node {rootLabel = SpreadRelation {selRelation = "client", selHint = Nothing, selJoinType = Nothing}, subForest = [Node {rootLabel = SelectField {selField = ("*",[]), selCast = Nothing, selAlias = Nothing}, subForest = []}]},Node {rootLabel = SelectRelation {selRelation = "other", selAlias = Nothing, selHint = Nothing, selJoinType = Nothing}, subForest = [Node {rootLabel = SelectField {selField = ("*",[]), selCast = Nothing, selAlias = Nothing}, subForest = []}]}]
+-- Right [Node {rootLabel = SelectField {selField = ("*",[]), selAggregateFunction = Nothing, selAggregateCast = Nothing, selCast = Nothing, selAlias = Nothing}, subForest = []},Node {rootLabel = SpreadRelation {selRelation = "client", selHint = Nothing, selJoinType = Nothing}, subForest = [Node {rootLabel = SelectField {selField = ("*",[]), selAggregateFunction = Nothing, selAggregateCast = Nothing, selCast = Nothing, selAlias = Nothing}, subForest = []}]},Node {rootLabel = SelectRelation {selRelation = "other", selAlias = Nothing, selHint = Nothing, selJoinType = Nothing}, subForest = [Node {rootLabel = SelectField {selField = ("*",[]), selAggregateFunction = Nothing, selAggregateCast = Nothing, selCast = Nothing, selAlias = Nothing}, subForest = []}]}]
 --
 -- >>> P.parse pFieldForest "" ""
 -- Right []
 --
 -- >>> P.parse pFieldForest "" "id,clients(name[])"
 -- Left (line 1, column 16):
 -- unexpected '['
--- expecting letter, digit, "-", "->>", "->", "::", ")", "," or end of input
+-- expecting letter, digit, "-", "->>", "->", "::", ".", ")", "," or end of input
 --
 -- >>> P.parse pFieldForest "" "data->>-78xy"
 -- Left (line 1, column 11):
@@ -452,35 +453,37 @@ 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
 --
 -- >>> P.parse pFieldSelect "" "name"
--- Right (SelectField {selField = ("name",[]), selCast = Nothing, selAlias = Nothing})
+-- Right (SelectField {selField = ("name",[]), selAggregateFunction = Nothing, selAggregateCast = Nothing, selCast = Nothing, selAlias = Nothing})
 --
 -- >>> P.parse pFieldSelect "" "name->jsonpath"
--- Right (SelectField {selField = ("name",[JArrow {jOp = JKey {jVal = "jsonpath"}}]), selCast = Nothing, selAlias = Nothing})
+-- Right (SelectField {selField = ("name",[JArrow {jOp = JKey {jVal = "jsonpath"}}]), selAggregateFunction = Nothing, selAggregateCast = Nothing, selCast = Nothing, selAlias = Nothing})
 --
 -- >>> P.parse pFieldSelect "" "name::cast"
--- Right (SelectField {selField = ("name",[]), selCast = Just "cast", selAlias = Nothing})
+-- Right (SelectField {selField = ("name",[]), selAggregateFunction = Nothing, selAggregateCast = Nothing, selCast = Just "cast", selAlias = Nothing})
 --
 -- >>> P.parse pFieldSelect "" "alias:name"
--- Right (SelectField {selField = ("name",[]), selCast = Nothing, selAlias = Just "alias"})
+-- Right (SelectField {selField = ("name",[]), selAggregateFunction = Nothing, selAggregateCast = Nothing, selCast = Nothing, selAlias = Just "alias"})
 --
 -- >>> P.parse pFieldSelect "" "alias:name->jsonpath::cast"
--- Right (SelectField {selField = ("name",[JArrow {jOp = JKey {jVal = "jsonpath"}}]), selCast = Just "cast", selAlias = Just "alias"})
+-- Right (SelectField {selField = ("name",[JArrow {jOp = JKey {jVal = "jsonpath"}}]), selAggregateFunction = Nothing, selAggregateCast = Nothing, selCast = Just "cast", selAlias = Just "alias"})
 --
 -- >>> P.parse pFieldSelect "" "*"
--- Right (SelectField {selField = ("*",[]), selCast = Nothing, selAlias = Nothing})
+-- Right (SelectField {selField = ("*",[]), selAggregateFunction = Nothing, selAggregateCast = Nothing, selCast = Nothing, selAlias = Nothing})
 --
 -- >>> P.parse pFieldSelect "" "name!hint"
 -- Left (line 1, column 5):
 -- unexpected '!'
--- expecting letter, digit, "-", "->>", "->", "::", ")", "," or end of input
+-- expecting letter, digit, "-", "->>", "->", "::", ".", ")", "," or end of input
 --
 -- >>> P.parse pFieldSelect "" "*!hint"
 -- Left (line 1, column 2):
@@ -495,18 +498,36 @@ pFieldSelect :: Parser SelectItem
 pFieldSelect = lexeme $ try (do
     s <- pStar
     pEnd
-    return $ SelectField (s, []) Nothing Nothing)
+    return $ SelectField (s, []) Nothing Nothing Nothing Nothing)
+  <|> try (do
+    alias    <- optionMaybe ( try(pFieldName <* aliasSeparator) )
+    _        <- string "count()"
+    aggCast' <- optionMaybe (string "::" *> pIdentifier)
+    pEnd
+    return $ SelectField ("*", []) (Just Count) (toS <$> aggCast') Nothing alias)
   <|> do
-    alias <- optionMaybe ( try(pFieldName <* aliasSeparator) )
-    fld <- pField
-    cast' <- optionMaybe (string "::" *> pIdentifier)
+    alias    <- optionMaybe ( try(pFieldName <* aliasSeparator) )
+    fld      <- pField
+    cast'    <- optionMaybe (string "::" *> pIdentifier)
+    agg      <- optionMaybe (try (char '.' *> pAggregation <* string "()"))
+    aggCast' <- optionMaybe (string "::" *> pIdentifier)
     pEnd
-    return $ SelectField fld (toS <$> cast') alias
+    return $ SelectField fld agg (toS <$> aggCast') (toS <$> 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 "count" $> Count
+      -- Using 'try' for "min" and "max" to allow backtracking.
+      -- This is necessary because both start with the same character 'm',
+      -- and without 'try', a partial match on "max" would prevent "min" from being tried.
+      , try (string "max") $> Max
+      , try (string "min") $> Min
+      ]
 
 
 -- |

src/PostgREST/ApiRequest/Types.hs

@@ -1,6 +1,7 @@
 {-# LANGUAGE DuplicateRecordFields #-}
 module PostgREST.ApiRequest.Types
-  ( Alias
+  ( AggregateFunction(..)
+  , Alias
   , Cast
   , Depth
   , EmbedParam(..)
@@ -42,12 +43,14 @@ 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
+    , selAggregateCast     :: Maybe Cast
+    , selCast              :: Maybe Cast
+    , selAlias             :: Maybe Alias
     }
 -- | The value in `/tbl?select=alias:another_tbl(*)`
   | SelectRelation
@@ -65,7 +68,8 @@ data SelectItem
   deriving (Eq, Show)
 
 data ApiRequestError
-  = AmbiguousRelBetween Text Text [Relationship]
+  = AggregatesNotAllowed
+  | AmbiguousRelBetween Text Text [Relationship]
   | AmbiguousRpc [Routine]
   | BinaryFieldError MediaType
   | MediaTypeError [ByteString]
@@ -135,6 +139,9 @@ 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/Config.hs

@@ -69,6 +69,7 @@ import Protolude hiding (Proxy, toList)
 
 data AppConfig = AppConfig
   { configAppSettings              :: [(Text, Text)]
+  , configDbAggregates             :: Bool
   , configDbAnonRole               :: Maybe BS.ByteString
   , configDbChannel                :: Text
   , configDbChannelEnabled         :: Bool
@@ -137,7 +138,8 @@ toText conf =
   where
     -- apply conf to all pgrst settings
     pgrstSettings = (\(k, v) -> (k, v conf)) <$>
-      [("db-anon-role",              q . T.decodeUtf8 . fromMaybe "" . configDbAnonRole)
+      [("db-aggregates",                 T.toLower . show . configDbAggregates)
+      ,("db-anon-role",              q . T.decodeUtf8 . fromMaybe "" . configDbAnonRole)
       ,("db-channel",                q . configDbChannel)
       ,("db-channel-enabled",            T.toLower . show . configDbChannelEnabled)
       ,("db-extra-search-path",      q . T.intercalate "," . configDbExtraSearchPath)
@@ -230,6 +232,7 @@ parser :: Maybe FilePath -> Environment -> [(Text, Text)] -> RoleSettings -> Rol
 parser optPath env dbSettings roleSettings roleIsolationLvl =
   AppConfig
     <$> parseAppSettings "app.settings"
+    <*> (fromMaybe False <$> optBool "db-aggregates")
     <*> (fmap encodeUtf8 <$> optString "db-anon-role")
     <*> (fromMaybe "pgrst" <$> optString "db-channel")
     <*> (fromMaybe True <$> optBool "db-channel-enabled")

src/PostgREST/Error.hs

@@ -61,6 +61,7 @@ class (JSON.ToJSON a) => PgrstError a where
     responseLBS (status err) (baseHeader : headers err) $ errorPayload err
 
 instance PgrstError ApiRequestError where
+  status AggregatesNotAllowed{}  = HTTP.status400
   status AmbiguousRelBetween{}   = HTTP.status300
   status AmbiguousRpc{}          = HTTP.status300
   status BinaryFieldError{}      = HTTP.status406
@@ -198,6 +199,9 @@ instance JSON.ToJSON ApiRequestError where
     (Just $ JSON.String $ T.decodeUtf8 ("Invalid preferences: " <> BS.intercalate ", " prefs))
     Nothing
 
+  toJSON AggregatesNotAllowed = toJsonPgrstError
+    ApiRequestErrorCode23 "Use of aggregate functions is not allowed" Nothing Nothing
+
   toJSON (NoRelBetween parent child embedHint schema allRels) = toJsonPgrstError
     SchemaCacheErrorCode00
     ("Could not find a relationship between '" <> parent <> "' and '" <> child <> "' in the schema cache")
@@ -604,6 +608,7 @@ data ErrorCode
   | ApiRequestErrorCode20
   | ApiRequestErrorCode21
   | ApiRequestErrorCode22
+  | ApiRequestErrorCode23
   -- Schema Cache errors
   | SchemaCacheErrorCode00
   | SchemaCacheErrorCode01
@@ -652,6 +657,7 @@ buildErrorCode code = "PGRST" <> case code of
   ApiRequestErrorCode20  -> "120"
   ApiRequestErrorCode21  -> "121"
   ApiRequestErrorCode22  -> "122"
+  ApiRequestErrorCode23  -> "123"
 
   SchemaCacheErrorCode00 -> "200"
   SchemaCacheErrorCode01 -> "201"