Add support for getting json by array index

* Also support json negative array index

src/PostgREST/Parsers.hs

@@ -80,11 +80,16 @@ pFieldName = do
     dash :: Parser Char
     dash = isDash *> pure '-'
 
-pJsonPathStep :: Parser Text
-pJsonPathStep = toS <$> try (string "->" *> pFieldName)
-
-pJsonPath :: Parser [Text]
-pJsonPath = (<>) <$> many pJsonPathStep <*> ( (:[]) <$> (string "->>" *> pFieldName) )
+pJsonPath :: Parser JsonPath
+pJsonPath = (<>) <$> many pJsonPathOp <*> ( (:[]) <$> (string "->>" *> (try pJIdx <|> pJKey)) )
+  where
+    pJsonPathOp :: Parser JsonPathOp
+    pJsonPathOp = try (string "->" *> pJIdx) <|> try (string "->" *> pJKey)
+    pJKey = JKey . toS <$> pFieldName
+    pJIdx = JIdx . toS <$> ((:) <$> option '+' (char '-') <*> many1 digit) <* pEnd
+    pEnd = try (void $ lookAhead (string "->")) <|>
+           try (void $ lookAhead (string "::")) <|>
+           try eof
 
 pField :: Parser Field
 pField = lexeme $ (,) <$> pFieldName <*> option [] pJsonPath

src/PostgREST/QueryBuilder.hs

@@ -1,7 +1,8 @@
-{-# LANGUAGE FlexibleInstances    #-}
-{-# LANGUAGE FlexibleContexts    #-}
-{-# LANGUAGE DuplicateRecordFields    #-}
-{-# OPTIONS_GHC -fno-warn-orphans #-}
+{-# LANGUAGE FlexibleInstances     #-}
+{-# LANGUAGE FlexibleContexts      #-}
+{-# LANGUAGE DuplicateRecordFields #-}
+{-# LANGUAGE LambdaCase            #-}
+{-# OPTIONS_GHC -fno-warn-orphans  #-}
 {-|
 Module      : PostgREST.QueryBuilder
 Description : PostgREST SQL generating functions.
@@ -394,8 +395,8 @@ pgFmtField :: QualifiedIdentifier -> Field -> SqlFragment
 pgFmtField table (c, jp) = pgFmtColumn table c <> pgFmtJsonPath jp
 
 pgFmtSelectItem :: QualifiedIdentifier -> SelectItem -> SqlFragment
-pgFmtSelectItem table (f@(_, jp), Nothing, alias, _) = pgFmtField table f <> pgFmtAs jp alias
-pgFmtSelectItem table (f@(_, jp), Just cast, alias, _) = "CAST (" <> pgFmtField table f <> " AS " <> cast <> " )" <> pgFmtAs jp alias
+pgFmtSelectItem table (f@(fName, jp), Nothing, alias, _) = pgFmtField table f <> pgFmtAs fName jp alias
+pgFmtSelectItem table (f@(fName, jp), Just cast, alias, _) = "CAST (" <> pgFmtField table f <> " AS " <> cast <> " )" <> pgFmtAs fName jp alias
 
 pgFmtOrderTerm :: QualifiedIdentifier -> OrderTerm -> SqlFragment
 pgFmtOrderTerm qi ot = unwords [
@@ -448,16 +449,25 @@ pgFmtLogicTree qi (Expr hasNot op forest) = notOp <> " (" <> intercalate (" " <>
 pgFmtLogicTree qi (Stmnt flt) = pgFmtFilter qi flt
 
 pgFmtJsonPath :: JsonPath -> SqlFragment
-pgFmtJsonPath [] = ""
-pgFmtJsonPath [x] = "->>" <> pgFmtLit x
-pgFmtJsonPath (x:xs) = "->" <> pgFmtLit x <> pgFmtJsonPath xs
+pgFmtJsonPath = \case
+  []     -> ""
+  [x]    -> "->>" <> pgFmtJsonPathOp x
+  (x:xs) -> "->" <> pgFmtJsonPathOp x <> pgFmtJsonPath xs
+  where
+    pgFmtJsonPathOp (JKey k) = pgFmtLit k
+    pgFmtJsonPathOp (JIdx i) = pgFmtLit i <> "::int"
 
-pgFmtAs :: JsonPath -> Maybe Alias -> SqlFragment
-pgFmtAs [] Nothing = ""
-pgFmtAs jp Nothing = case lastMay jp of
-  Just alias -> " AS " <> pgFmtIdent alias
+pgFmtAs :: FieldName -> JsonPath -> Maybe Alias -> SqlFragment
+pgFmtAs _ [] Nothing = ""
+pgFmtAs fName jp Nothing = case lastMay jp of
+  Just (JKey key) -> " AS " <> pgFmtIdent key
+  Just (JIdx _)   -> " AS " <> pgFmtIdent (fromMaybe fName lastKey)
+    -- We get the lastKey because on:
+    -- `select=data->1->mycol->>2`, we need to show the result as [ {"mycol": ..}, {"mycol": ..} ]
+    -- `select=data->3`, we need to show the result as [ {"data": ..}, {"data": ..} ]
+    where lastKey = jpOp <$> find (\case JKey{} -> True; _ -> False) (reverse jp)
   Nothing -> ""
-pgFmtAs _ (Just alias) = " AS " <> pgFmtIdent alias
+pgFmtAs _ _ (Just alias) = " AS " <> pgFmtIdent alias
 
 pgFmtEnvVar :: Text -> (Text, Text) -> SqlFragment
 pgFmtEnvVar prefix (k, v) =

src/PostgREST/Types.hs

@@ -238,7 +238,12 @@ instance Show LogicOperator where
 data LogicTree = Expr Bool LogicOperator [LogicTree] | Stmnt Filter deriving (Show, Eq)
 
 type FieldName = Text
-type JsonPath = [Text]
+type JsonPath = [JsonPathOp]
+{-|
+  Json path operands as specified in https://www.postgresql.org/docs/9.5/static/functions-json.html
+  the array index is Text because we reuse our escaping functons and let pg do the casting with '1'::int
+-}
+data JsonPathOp = JKey{jpOp :: Text} | JIdx{jpOp :: Text} deriving (Show, Eq)
 type Field = (FieldName, JsonPath)
 type Alias = Text
 type Cast = Text