Add suggestions with fuzzy text search when no relationship is found (#2583)

src/PostgREST/ApiRequest/Types.hs

@@ -35,7 +35,8 @@ import PostgREST.MediaType                (MediaType (..))
 import PostgREST.SchemaCache.Identifiers  (FieldName,
                                            QualifiedIdentifier)
 import PostgREST.SchemaCache.Proc         (ProcDescription (..))
-import PostgREST.SchemaCache.Relationship (Relationship)
+import PostgREST.SchemaCache.Relationship (Relationship,
+                                           RelationshipsMap)
 
 import Protolude
 
@@ -72,7 +73,7 @@ data ApiRequestError
   | InvalidRpcMethod ByteString
   | LimitNoOrderError
   | NotFound
-  | NoRelBetween Text Text Text
+  | NoRelBetween Text Text (Maybe Text) Text RelationshipsMap
   | NoRpc Text Text [Text] Bool MediaType Bool [QualifiedIdentifier] [ProcDescription]
   | NotEmbedded Text
   | ParseRequestError Text Text

src/PostgREST/Error.hs

@@ -18,6 +18,7 @@ module PostgREST.Error
 import qualified Data.Aeson                as JSON
 import qualified Data.ByteString.Char8     as BS
 import qualified Data.FuzzySet             as Fuzzy
+import qualified Data.HashMap.Strict       as HM
 import qualified Data.Text                 as T
 import qualified Data.Text.Encoding        as T
 import qualified Data.Text.Encoding.Error  as T
@@ -36,12 +37,14 @@ import           PostgREST.ApiRequest.Types (ApiRequestError (..),
 import           PostgREST.MediaType        (MediaType (..))
 import qualified PostgREST.MediaType        as MediaType
 
-import PostgREST.SchemaCache.Identifiers  (QualifiedIdentifier (..))
+import PostgREST.SchemaCache.Identifiers  (QualifiedIdentifier (..),
+                                           Schema)
 import PostgREST.SchemaCache.Proc         (ProcDescription (..),
                                            ProcParam (..))
 import PostgREST.SchemaCache.Relationship (Cardinality (..),
                                            Junction (..),
-                                           Relationship (..))
+                                           Relationship (..),
+                                           RelationshipsMap)
 import Protolude
 
 
@@ -174,11 +177,11 @@ instance JSON.ToJSON ApiRequestError where
     "details" .= ("Only is null or not is null filters are allowed on embedded resources":: Text),
     "hint"    .= JSON.Null]
 
-  toJSON (NoRelBetween parent child schema) = JSON.object [
+  toJSON (NoRelBetween parent child embedHint schema allRels) = JSON.object [
     "code"    .= SchemaCacheErrorCode00,
     "message" .= ("Could not find a relationship between '" <> parent <> "' and '" <> child <> "' in the schema cache" :: Text),
-    "details" .= JSON.Null,
-    "hint"    .= ("Verify that '" <> parent <> "' and '" <> child <> "' exist in the schema '" <> schema <> "' and that there is a foreign key relationship between them. If a new relationship was created, try reloading the schema cache." :: Text)]
+    "details" .= ("Searched for a foreign key relationship between '" <> parent <> "' and '" <> child <> maybe mempty ("' using the hint '" <>) embedHint <> "' in the schema '" <> schema <> "', but no matches were found."),
+    "hint"    .= noRelBetweenHint parent child schema allRels]
 
   toJSON (AmbiguousRelBetween parent child rels) = JSON.object [
     "code"    .= SchemaCacheErrorCode01,
@@ -214,6 +217,52 @@ instance JSON.ToJSON ApiRequestError where
     "details" .= JSON.Null,
     "hint"    .= ("Try renaming the parameters or the function itself in the database so function overloading can be resolved" :: Text)]
 
+-- |
+-- If no relationship is found then:
+--
+-- Looks for parent suggestions if parent not found
+-- Looks for child suggestions if parent is found but child is not
+-- Gives no suggestions if both are found (it means that there is a problem with the embed hint)
+--
+-- >>> :set -Wno-missing-fields
+-- >>> let qi t = QualifiedIdentifier "api" t
+-- >>> let rel ft = Relationship{relForeignTable = qi ft}
+-- >>> let rels = HM.fromList [((qi "films", "api"), [rel "directors", rel "roles", rel "actors"])]
+--
+-- >>> noRelBetweenHint "film" "directors" "api" rels
+-- Just "Perhaps you meant 'films' instead of 'film'."
+--
+-- >>> noRelBetweenHint "films" "role" "api" rels
+-- Just "Perhaps you meant 'roles' instead of 'role'."
+--
+-- >>> noRelBetweenHint "films" "role" "api" rels
+-- Just "Perhaps you meant 'roles' instead of 'role'."
+--
+-- >>> noRelBetweenHint "films" "actors" "api" rels
+-- Nothing
+--
+-- >>> noRelBetweenHint "noclosealternative" "roles" "api" rels
+-- Nothing
+--
+-- >>> noRelBetweenHint "films" "noclosealternative" "api" rels
+-- Nothing
+--
+-- >>> noRelBetweenHint "films" "noclosealternative" "noclosealternative" rels
+-- Nothing
+--
+noRelBetweenHint :: Text -> Text -> Schema -> RelationshipsMap -> Maybe Text
+noRelBetweenHint parent child schema allRels = ("Perhaps you meant '" <>) <$>
+  if isJust findParent
+    then (<> "' instead of '" <> child <> "'.") <$> suggestChild
+    else (<> "' instead of '" <> parent <> "'.") <$> suggestParent
+  where
+    findParent = HM.lookup (QualifiedIdentifier schema parent, schema) allRels
+    fuzzySetOfParents  = Fuzzy.fromList [qiName (fst p) | p <- HM.keys allRels, snd p == schema]
+    fuzzySetOfChildren = Fuzzy.fromList [qiName (relForeignTable c) | c <- fromMaybe [] findParent]
+    suggestParent = Fuzzy.getOne fuzzySetOfParents parent
+    -- Do not give suggestion if the child is found in the relations (weight = 1.0)
+    suggestChild  = headMay [snd k | k <- Fuzzy.get fuzzySetOfChildren child, fst k < 1.0]
+
 -- |
 -- If no function is found with the given name, it does a fuzzy search to all the functions
 -- in the same schema and shows the best match as hint.

src/PostgREST/Plan.hs

@@ -208,7 +208,7 @@ getJoinConditions tblAlias parentAlias Relationship{relTable=qi,relForeignTable=
 findRel :: Schema -> RelationshipsMap -> NodeName -> NodeName -> Maybe Hint -> Either ApiRequestError Relationship
 findRel schema allRels origin target hint =
   case rels of
-    []  -> Left $ NoRelBetween origin target schema
+    []  -> Left $ NoRelBetween origin target hint schema allRels
     [r] -> Right r
     rs  -> Left $ AmbiguousRelBetween origin target rs
   where