Upsert with "Prefer: resolution=merge-duplicates" on specified columns (#1327) (#1432)

Allow query param 'on_conflict=key1,key2,...' to upsert with explicit columns with unique
constraint.

src/PostgREST/ApiRequest.hs

@@ -87,6 +87,7 @@ data ApiRequest = ApiRequest {
   , iFilters              :: [(Text, Text)]                   -- ^ Filters on the result ("id", "eq.10")
   , iLogic                :: [(Text, Text)]                   -- ^ &and and &or parameters used for complex boolean logic
   , iSelect               :: Maybe Text                       -- ^ &select parameter used to shape the response
+  , iOnConflict           :: Maybe Text                       -- ^ &on_conflict parameter used to upsert on specific unique keys
   , iColumns              :: Maybe Text                       -- ^ &columns parameter used to shape the payload
   , iOrder                :: [(Text, Text)]                   -- ^ &order parameters for each level
   , iCanonicalQS          :: ByteString                       -- ^ Alphabetized (canonical) request query string for response URLs
@@ -122,6 +123,7 @@ userApiRequest schema rootSpec req reqBody
       , iFilters = filters
       , iLogic = [(toS k, toS $ fromJust v) | (k,v) <- qParams, isJust v, endingIn ["and", "or"] k ]
       , iSelect = toS <$> join (lookup "select" qParams)
+      , iOnConflict = toS <$> join (lookup "on_conflict" qParams)
       , iColumns = columns
       , iOrder = [(toS k, toS $ fromJust v) | (k,v) <- qParams, isJust v, endingIn ["order"] k ]
       , iCanonicalQS = toS $ urlEncodeVars

src/PostgREST/App.hs

@@ -169,7 +169,7 @@ app dbStructure proc cols conf apiRequest =
                         else Nothing
                     , Just $ contentRangeH 1 0 $
                         if shouldCount then Just queryTotal else Nothing
-                    , if null pkCols
+                    , if null pkCols && isNothing (iOnConflict apiRequest)
                         then Nothing
                         else (\x -> ("Preference-Applied", show x)) <$> iPreferResolution apiRequest
                     ]

src/PostgREST/DbRequestBuilder.hs

@@ -324,7 +324,11 @@ addProperty f (targetNodeName:remainingPath, a) (Node rn forest) =
 mutateRequest :: Schema -> TableName -> ApiRequest -> S.Set FieldName -> [FieldName] -> ReadRequest -> Either Response MutateRequest
 mutateRequest schema tName apiRequest cols pkCols readReq = mapLeft errorResponseFor $
   case action of
-    ActionCreate -> Right $ Insert qi cols ((,) <$> iPreferResolution apiRequest <*> Just pkCols) [] returnings
+    ActionCreate -> do
+        confCols <- case iOnConflict apiRequest of
+            Nothing    -> pure pkCols
+            Just param -> pRequestOnConflict param
+        pure $ Insert qi cols ((,) <$> iPreferResolution apiRequest <*> Just confCols) [] returnings
     ActionUpdate -> Update qi cols <$> combinedLogic <*> pure returnings
     ActionSingleUpsert ->
       (\flts ->

src/PostgREST/OpenAPI.hs

@@ -133,6 +133,13 @@ makeParamDefs ti =
       & schema .~ ParamOther ((mempty :: ParamOtherSchema)
         & in_ .~ ParamQuery
         & type_ ?~ SwaggerString))
+  , ("on_conflict", (mempty :: Param)
+      & name        .~ "on_conflict"
+      & description ?~ "On Conflict"
+      & required    ?~ False
+      & schema .~ ParamOther ((mempty :: ParamOtherSchema)
+        & in_ .~ ParamQuery
+        & type_ ?~ SwaggerString))
   , ("order", (mempty :: Param)
       & name        .~ "order"
       & description ?~ "Ordering"

src/PostgREST/Parsers.hs

@@ -30,6 +30,10 @@ pRequestSelect :: Text -> Either ApiRequestError [Tree SelectItem]
 pRequestSelect selStr =
   mapError $ parse pFieldForest ("failed to parse select parameter (" <> toS selStr <> ")") (toS selStr)
 
+pRequestOnConflict :: Text -> Either ApiRequestError  [FieldName]
+pRequestOnConflict oncStr =
+  mapError $ parse pColumns ("failed to parse on_conflict parameter (" <> toS oncStr <> ")") (toS oncStr)
+
 pRequestFilter :: (Text, Text) -> Either ApiRequestError (EmbedPath, Filter)
 pRequestFilter (k, v) = mapError $ (,) <$> path <*> (Filter <$> fld <*> oper)
   where