fix: HTTP status responses for upserts

* PUT returns 201 instead of 200 when rows are inserted
* POST with "Prefer: resolution=merge-duplicates" returns 200 instead of 201 when no rows are inserted

src/PostgREST/Query/QueryBuilder.hs

@@ -87,7 +87,8 @@ mutatePlanToQuery (Insert mainQi iCols body onConflct putConditions returnings _
   "INSERT INTO " <> fromQi mainQi <> (if null iCols then " " else "(" <> cols <> ") ") <>
   fromJsonBodyF body iCols True False applyDefaults <>
   -- Only used for PUT
-  (if null putConditions then mempty else "WHERE " <> intercalateSnippet " AND " (pgFmtLogicTree (QualifiedIdentifier mempty "pgrst_body") <$> putConditions)) <>
+  (if null putConditions then mempty else "WHERE " <> addConfigPgrstInserted True <> " AND " <> intercalateSnippet " AND " (pgFmtLogicTree (QualifiedIdentifier mempty "pgrst_body") <$> putConditions)) <>
+  (if null putConditions && mergeDups then "WHERE " <> addConfigPgrstInserted True else mempty) <>
   maybe mempty (\(oncDo, oncCols) ->
     if null oncCols then
       mempty
@@ -98,11 +99,12 @@ mutatePlanToQuery (Insert mainQi iCols body onConflct putConditions returnings _
       MergeDuplicates  ->
         if null iCols
            then "DO NOTHING"
-           else "DO UPDATE SET " <> intercalateSnippet ", " ((pgFmtIdent . cfName) <> const " = EXCLUDED." <> (pgFmtIdent . cfName) <$> iCols)
+           else "DO UPDATE SET " <> intercalateSnippet ", " ((pgFmtIdent . cfName) <> const " = EXCLUDED." <> (pgFmtIdent . cfName) <$> iCols) <> (if null putConditions && not mergeDups then mempty else "WHERE " <> addConfigPgrstInserted False)
     ) onConflct <> " " <>
-  returningF mainQi returnings
+    returningF mainQi returnings
   where
     cols = intercalateSnippet ", " $ pgFmtIdent . cfName <$> iCols
+    mergeDups = case onConflct of {Just (MergeDuplicates,_) -> True; _ -> False;}
 
 -- An update without a limit is always filtered with a WHERE
 mutatePlanToQuery (Update mainQi uCols body logicForest range ordts returnings applyDefaults)

src/PostgREST/Query/SqlFragment.hs

@@ -24,6 +24,8 @@ module PostgREST.Query.SqlFragment
   , fromJsonBodyF
   , responseHeadersF
   , responseStatusF
+  , addConfigPgrstInserted
+  , currentSettingF
   , returningF
   , singleParameter
   , sourceCTE
@@ -433,6 +435,11 @@ responseHeadersF = currentSettingF "response.headers"
 responseStatusF :: SQL.Snippet
 responseStatusF = currentSettingF "response.status"
 
+addConfigPgrstInserted :: Bool -> SQL.Snippet
+addConfigPgrstInserted add =
+  let (symbol, num) =  if add then ("+", "0") else ("-", "-1") in
+  "set_config('pgrst.inserted', (coalesce(" <> currentSettingF "pgrst.inserted" <> "::int, 0) " <> symbol <> " 1)::text, true) <> '" <> num <> "'"
+
 currentSettingF :: SQL.Snippet -> SQL.Snippet
 currentSettingF setting =
   -- nullif is used because of https://gist.github.com/steve-chavez/8d7033ea5655096903f3b52f8ed09a15

src/PostgREST/Query/Statements.hs

@@ -50,15 +50,19 @@ data ResultSet
   -- ^ the HTTP headers to be added to the response
   , rsGucStatus  :: Maybe Text
   -- ^ the HTTP status to be added to the response
+  , rsInserted   :: Maybe Int64
+  -- ^ the number of rows inserted (Only used for upserts)
   }
   | RSPlan BS.ByteString -- ^ the plan of the query
 
 
-prepareWrite :: QualifiedIdentifier -> SQL.Snippet -> SQL.Snippet -> Bool -> MediaType -> MediaHandler ->
-                Maybe PreferRepresentation -> [Text] -> Bool -> SQL.Statement () ResultSet
-prepareWrite qi selectQuery mutateQuery isInsert mt handler rep pKeys =
+prepareWrite :: QualifiedIdentifier -> SQL.Snippet -> SQL.Snippet -> Bool -> Bool -> MediaType -> MediaHandler ->
+                Maybe PreferRepresentation -> Maybe PreferResolution -> [Text] -> Bool -> SQL.Statement () ResultSet
+prepareWrite qi selectQuery mutateQuery isInsert isPut mt handler rep resolution pKeys =
   SQL.dynamicallyParameterized (mtSnippet mt snippet) decodeIt
  where
+  checkUpsert snip = if isInsert && (isPut || resolution == Just MergeDuplicates) then snip else "''"
+  pgrstInsertedF = checkUpsert "nullif(current_setting('pgrst.inserted', true),'')::int"
   snippet =
     "WITH " <> sourceCTE <> " AS (" <> mutateQuery <> ") " <>
     "SELECT " <>
@@ -67,7 +71,8 @@ prepareWrite qi selectQuery mutateQuery isInsert mt handler rep pKeys =
       locF <> " AS header, " <>
       handlerF Nothing qi handler <> " AS body, " <>
       responseHeadersF <> " AS response_headers, " <>
-      responseStatusF  <> " AS response_status " <>
+      responseStatusF  <> " AS response_status, " <>
+      pgrstInsertedF <> " AS response_inserted " <>
     "FROM (" <> selectF <> ") _postgrest_t"
 
   locF =
@@ -87,7 +92,7 @@ prepareWrite qi selectQuery mutateQuery isInsert mt handler rep pKeys =
   decodeIt :: HD.Result ResultSet
   decodeIt = case mt of
     MTVndPlan{} -> planRow
-    _        -> fromMaybe (RSStandard Nothing 0 mempty mempty Nothing Nothing) <$> HD.rowMaybe (standardRow False)
+    _           -> fromMaybe (RSStandard Nothing 0 mempty mempty Nothing Nothing Nothing) <$> HD.rowMaybe (standardRow False)
 
 prepareRead :: QualifiedIdentifier -> SQL.Snippet -> SQL.Snippet -> Bool -> MediaType -> MediaHandler -> Bool -> SQL.Statement () ResultSet
 prepareRead qi selectQuery countQuery countTotal mt handler =
@@ -101,7 +106,8 @@ prepareRead qi selectQuery countQuery countTotal mt handler =
       "pg_catalog.count(_postgrest_t) AS page_total, " <>
       handlerF Nothing qi handler <> " AS body, " <>
       responseHeadersF <> " AS response_headers, " <>
-      responseStatusF <> " AS response_status " <>
+      responseStatusF <> " AS response_status, " <>
+      "''" <> " AS response_inserted " <>
     "FROM ( SELECT * FROM " <> sourceCTE <> " ) _postgrest_t"
 
   (countCTEF, countResultF) = countF countQuery countTotal
@@ -127,7 +133,8 @@ prepareCall qi rout callProcQuery selectQuery countQuery countTotal mt handler =
           else "pg_catalog.count(_postgrest_t)") <> " AS page_total, " <>
         handlerF (Just rout) qi handler <> " AS body, " <>
         responseHeadersF <> " AS response_headers, " <>
-        responseStatusF <> " AS response_status " <>
+        responseStatusF <> " AS response_status, " <>
+        "''" <> " AS response_inserted " <>
       "FROM (" <> selectQuery <> ") _postgrest_t"
 
     (countCTEF, countResultF) = countF countQuery countTotal
@@ -135,7 +142,7 @@ prepareCall qi rout callProcQuery selectQuery countQuery countTotal mt handler =
     decodeIt :: HD.Result ResultSet
     decodeIt = case mt of
       MTVndPlan{} -> planRow
-      _        -> fromMaybe (RSStandard (Just 0) 0 mempty mempty Nothing Nothing) <$> HD.rowMaybe (standardRow True)
+      _           -> fromMaybe (RSStandard (Just 0) 0 mempty mempty Nothing Nothing Nothing) <$> HD.rowMaybe (standardRow True)
 
 preparePlanRows :: SQL.Snippet -> Bool -> SQL.Statement () (Maybe Int64)
 preparePlanRows countQuery =
@@ -153,6 +160,7 @@ standardRow noLocation =
              <*> (if noLocation then pure mempty else fmap splitKeyValue <$> arrayColumn HD.bytea) <*> column HD.bytea
              <*> nullableColumn HD.bytea
              <*> nullableColumn HD.text
+             <*> nullableColumn HD.int8
   where
     splitKeyValue :: ByteString -> (ByteString, ByteString)
     splitKeyValue kv =