Singular response for PATCH request (#634)

* Allow a singular entity to be returned from an update

Since a `PATCH` will be an update that could affect many rows, there might be
more than one object returned. By allowing asking for a singular response,
the/an object will be returned instead of a list. This is useful in cases when
the `PATCH` is against single entity (i.e. `/items?pkey=eq.99`).

* Add tests for plurality=singular for `PATCH` requests

* Disallow updating more than one row if `plurality=singular`

As discussed in #634, we don't want to allow updating several rows with
a `PATCH` request when the `Prefer` header specifies
`return=representation;plurality=singular` as this would almost
certainly be a client error.

* Add test for patching multiple objects with singular response

Patching > 1 object with `return=representation;plurality=singular`
should return `400 Bad Request`.

* Only add singleton range for read API requests

* Disallow inserting more than one row if `plurality=singular`

Disallow inserting several rows with a `POST` request when the `Prefer`
header specifies `return=representation;plurality=singular` as this
would almost certainly be a client error.

* Only import `q` from `Text.InterpolatedString.Perl6`

* Update OpenAPI response for PATCH/POST to mention `plurality=singular`

The OpenAPI response for PATCH/POST requests now includes the `Prefer` value
`return=representation;plurality=singular`.

* Add entry in changelog

test/Feature/InsertSpec.hs

@@ -398,6 +398,35 @@ spec = do
           [json| { id: 99 } |]
           `shouldRespondWith` [json| [{id:99}] |]
 
+    context "in a table" $ do
+      it "can provide a singular representation when updating one entity" $ do
+        _ <- post "/addresses" [json| { id: 97, address: "A Street" } |]
+        p <- request methodPatch
+          "/addresses?id=eq.97"
+          [("Prefer", "return=representation;plurality=singular")]
+          [json| { address: "B Street" } |]
+        liftIO $ simpleBody p `shouldBe` [str|{"id":97,"address":"B Street"}|]
+      it "raises an error when attempting to update multiple entities with plurality=singular" $ do
+        _ <- post "/addresses" [json| { id: 98, address: "xxx" } |]
+        _ <- post "/addresses" [json| { id: 99, address: "yyy" } |]
+        p <- request methodPatch
+          "/addresses?id=gt.0"
+          [("Prefer", "return=representation;plurality=singular")]
+          [json| { address: "zzz" } |]
+        liftIO $ simpleStatus p `shouldBe` status400
+      it "can provide a singular representation when creating one entity" $ do
+        p <- request methodPost
+          "/addresses"
+          [("Prefer", "return=representation;plurality=singular")]
+          [json| [ { id: 100, address: "xxx" } ] |]
+        liftIO $ simpleBody p `shouldBe` [str|{"id":100,"address":"xxx"}|]
+      it "raises an error when attempting to create multiple entities with plurality=singular" $ do
+        p <- request methodPost
+          "/addresses"
+          [("Prefer", "return=representation;plurality=singular")]
+          [json| [ { id: 100, address: "xxx" }, { id: 101, address: "xxx" } ] |]
+        liftIO $ simpleStatus p `shouldBe` status400
+
       it "can set a json column to escaped value" $ do
         _ <- post "/json" [json| { data: {"escaped":"bar"} } |]
         request methodPatch "/json?data->>escaped=eq.bar"