From bb2e416d5fd732db6d4f2d51feade65abd6d728e Mon Sep 17 00:00:00 2001
From: Nik <nik@edgedb.com>
Date: Fri, 16 Jun 2023 22:30:58 -0400
Subject: [PATCH] fix empty set as a single object property decoding (#147)

---
 CHANGELOG.md                                |  1 +
 lib/edgedb/protocol/codecs/object.ex        | 13 ++++++++-
 test/edgedb/protocol/codecs/object_test.exs | 32 ++++++++++++++-------
 3 files changed, 34 insertions(+), 12 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 64248b60..6d2eb9ed 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -26,6 +26,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 
 - crash after updating `db_connection` to `2.5`.
+- decoding a single propery for `EdgeDB.Object` that equals to an empty set.
 - not catching an `EdgeDB.Error` exception during parameters encoding,
     which caused throwing an exception for non-`!` functions.
 
diff --git a/lib/edgedb/protocol/codecs/object.ex b/lib/edgedb/protocol/codecs/object.ex
index a14b985d..ae52c7ec 100644
--- a/lib/edgedb/protocol/codecs/object.ex
+++ b/lib/edgedb/protocol/codecs/object.ex
@@ -295,9 +295,20 @@ defimpl EdgeDB.Protocol.Codec, for: EdgeDB.Protocol.Codecs.Object do
         element.name
       end
 
+    single_property? =
+      element.cardinality in [:at_most_one, :one] and
+        (link_property?(element) or not link?(element))
+
+    value =
+      if single_property? do
+        nil
+      else
+        @empty_set
+      end
+
     field = %EdgeDB.Object.Field{
       name: name,
-      value: @empty_set,
+      value: value,
       is_link: link?(element),
       is_link_property: link_property?(element),
       is_implicit: implicit?(element)
diff --git a/test/edgedb/protocol/codecs/object_test.exs b/test/edgedb/protocol/codecs/object_test.exs
index 1d6c193b..1396dc13 100644
--- a/test/edgedb/protocol/codecs/object_test.exs
+++ b/test/edgedb/protocol/codecs/object_test.exs
@@ -232,17 +232,27 @@ defmodule Tests.EdgeDB.Protocol.Codecs.ObjectTest do
     end)
   end
 
-  test "decoding object with property equals to empty set", %{client: client} do
-    rollback(client, fn client ->
-      object =
-        EdgeDB.query_required_single!(client, """
-        select {
-          a := <str>{}
-        }
-        limit 1
-        """)
+  test "decoding object with a single property equals to empty set", %{client: client} do
+    object =
+      EdgeDB.query_required_single!(client, """
+      select {
+        a := <str>{}
+      }
+      limit 1
+      """)
 
-      assert Enum.empty?(object[:a])
-    end)
+    assert is_nil(object[:a])
+  end
+
+  test "decoding object with a multi property equals to empty set", %{client: client} do
+    object =
+      EdgeDB.query_required_single!(client, """
+      select {
+        multi a := <str>{}
+      }
+      limit 1
+      """)
+
+    assert Enum.empty?(object[:a])
   end
 end