Add support for Prefer: count=planned/estimated on GET /table (#1386)

test/Feature/QueryLimitedSpec.hs

@@ -13,7 +13,7 @@ import SpecHelper
 
 spec :: SpecWith Application
 spec =
-  describe "Requesting many items with server limits enabled" $ do
+  describe "Requesting many items with server limits(max-rows) enabled" $ do
     it "restricts results" $
       get "/items"
         `shouldRespondWith` [json| [{"id":1},{"id":2}] |]
@@ -29,16 +29,38 @@ spec =
           matchHeader "Content-Range" "0-0/*"
         simpleStatus r `shouldBe` ok200
 
-    it "limit works on all levels" $
+    it "works on all levels" $
       get "/users?select=id,tasks(id)&order=id.asc&tasks.order=id.asc"
         `shouldRespondWith` [json|[{"id":1,"tasks":[{"id":1},{"id":2}]},{"id":2,"tasks":[{"id":5},{"id":6}]}]|]
         { matchStatus  = 200
         , matchHeaders = ["Content-Range" <:> "0-1/*"]
         }
 
-    it "limit is not applied to parent embeds" $
+    it "is not applied to parent embeds" $
       get "/tasks?select=id,project(id)&id=gt.5"
         `shouldRespondWith` [json|[{"id":6,"project":{"id":3}},{"id":7,"project":{"id":4}}]|]
         { matchStatus  = 200
         , matchHeaders = ["Content-Range" <:> "0-1/*"]
         }
+
+    context "count=estimated" $ do
+      it "uses the query planner guess when query rows > maxRows" $
+        request methodHead "/getallprojects_view" [("Prefer", "count=estimated")] ""
+          `shouldRespondWith` ""
+          { matchStatus  = 206
+          , matchHeaders = ["Content-Range" <:> "0-1/2019"]
+          }
+
+      it "gives exact count when query rows <= maxRows" $
+        request methodHead "/getallprojects_view?id=lt.3" [("Prefer", "count=estimated")] ""
+          `shouldRespondWith` ""
+          { matchStatus  = 200
+          , matchHeaders = ["Content-Range" <:> "0-1/2"]
+          }
+
+      it "only uses the query planner guess if it's indeed greater than the exact count" $
+        request methodHead "/get_projects_above_view" [("Prefer", "count=estimated")] ""
+          `shouldRespondWith` ""
+          { matchStatus  = 206
+          , matchHeaders = ["Content-Range" <:> "0-1/3"]
+          }