Implement single route selection

src/PostgREST/App.hs

@@ -19,7 +19,7 @@ import qualified Data.HashMap.Strict       as HM
 import           Data.List                 (find, sortBy, delete, transpose)
 import           Data.Maybe                (fromMaybe, fromJust, isJust, isNothing, mapMaybe)
 import           Data.Ord                  (comparing)
-import           Data.Ranged.Ranges        (emptyRange)
+import           Data.Ranged.Ranges        (emptyRange, singletonRange)
 import           Data.String.Conversions   (cs)
 import           Data.Text                 (Text, replace, strip)
 import           Data.Tree
@@ -88,10 +88,15 @@ app dbStructure conf reqBody req =
           if range == Just emptyRange
           then return $ responseLBS status416 [] "HTTP Range error"
           else do
-            let q = createReadStatement selectQuery range (not $ hasPrefer "count=none") isCsv
+            let q = createReadStatement selectQuery (if singular then Nothing else range) singular (not $ hasPrefer "count=none") isCsv
             row <- H.maybeEx q
             let (tableTotal, queryTotal, _ , body) = extractQueryResult row
-                frm = fromMaybe 0 $ rangeOffset <$> range
+            if singular
+            then return $ if queryTotal <= 0
+              then responseLBS status404 [] ""
+              else responseLBS status200 [contentTypeH] (fromMaybe "{}" body)
+            else do
+              let frm = fromMaybe 0 $ rangeOffset <$> range
                   to = frm+queryTotal-1
                   contentRange = contentRangeH frm to tableTotal
                   status = rangeStatus frm to tableTotal
@@ -183,6 +188,7 @@ app dbStructure conf reqBody req =
     isCsv         = contentType == csvMT
     contentTypeH  = (hContentType, contentType)
     echoRequested = hasPrefer "return=representation"
+    singular      = hasPrefer "plurality=singular"
     request = parseRequest schema (dbRelations dbStructure) (head path) req reqBody --TODO! is head safe?
 
 rangeStatus :: Int -> Int -> Maybe Int -> Status
@@ -404,15 +410,17 @@ parseRequest schema allRels rootTableName httpRequest reqBody =
               then M.fromList <$> (zip <$> flds <*> (head <$> vals))
               else Left "Expecting a sigle CSV line with header or a JSON object"
 
-createReadStatement :: SqlQuery -> Maybe NonnegRange -> Bool -> Bool -> B.Stmt P.Postgres
+createReadStatement :: SqlQuery -> Maybe NonnegRange -> Bool -> Bool -> Bool -> B.Stmt P.Postgres
-createReadStatement selectQuery range countTable asCsv =
+createReadStatement selectQuery range isSingle countTable asCsv =
   B.Stmt (
     wrapQuery selectQuery [
       if countTable then countAllF else countNoneF,
       countF,
       "null", -- location header can not be calucalted
-      if asCsv then asCsvF else asJsonF
+      if asCsv
-    ] selectStarF range
+        then asCsvF
+        else if isSingle then asJsonSingleF else asJsonF
+    ] selectStarF (if isNothing range && isSingle then Just $ singletonRange 0 else range)
   ) V.empty True
 
 createWriteStatement :: SqlQuery -> SqlQuery -> Bool -> Bool -> [Text] -> Bool -> B.Stmt P.Postgres

test/Feature/QuerySpec.hs

@@ -214,6 +214,24 @@ spec =
       get "/users_tasks?user_id=eq.2&task_id=eq.6&select=*, comments(content)" `shouldRespondWith`
         "[{\"user_id\":2,\"task_id\":6,\"comments\":[{\"content\":\"Needs to be delivered ASAP\"}]}]"
 
+  describe "Plurality singular" $ do
+    it "will select an existing object" $
+      request methodGet "/items?id=eq.5" [("Prefer","plurality=singular")] ""
+        `shouldRespondWith` ResponseMatcher {
+          matchBody    = Just [json| {"id":5} |]
+        , matchStatus  = 200
+        , matchHeaders = []
+        }
+
+    it "will respond with 404 when not found" $
+      request methodGet "/items?id=eq.9999" [("Prefer","plurality=singular")] ""
+        `shouldRespondWith` 404
+
+    it "can shape plurality singular object routes" $
+      request methodGet "/projects_view?id=eq.1&select=id,name,clients(*),tasks(id,name)" [("Prefer","plurality=singular")] ""
+        `shouldRespondWith`
+          "{\"id\":1,\"name\":\"Windows 7\",\"clients\":{\"id\":1,\"name\":\"Microsoft\"},\"tasks\":[{\"id\":1,\"name\":\"Design w7\"},{\"id\":2,\"name\":\"Code w7\"}]}"
+
 
   describe "ordering response" $ do
     it "by a column asc" $