Refator nil map joins (#4602)

Author: greg-rychlewski

Diff for: integration_test/cases/repo.exs

@@ -1432,6 +1432,26 @@ defmodule Ecto.Integration.RepoTest do
       assert p3 == %{id: pid3}
     end
 
+    test "take with join nil maps" do
+      TestRepo.insert!(%Post{})
+
+      assert {%{title: nil}, %{title: nil}} ==
+               from(p1 in Post)
+               |> join(:left, [p1], p2 in Post, on: p1.id == p2.id)
+               |> select([p1, p2], {map(p1, [:title]), map(p2, [:title])})
+               |> TestRepo.one()
+    end
+
+    test "take with join nil source" do
+      TestRepo.insert!(%Post{})
+
+      assert {%{title: nil}, nil} ==
+               from(p1 in Post)
+               |> join(:left, [p1], p2 in Post, on: p2.id == -1)
+               |> select([p1, p2], {map(p1, [:title]), p2})
+               |> TestRepo.one()
+    end
+
     test "take with preload assocs" do
       %{id: pid} = TestRepo.insert!(%Post{title: "post"})
       TestRepo.insert!(%Comment{post_id: pid, text: "comment"})

Diff for: lib/ecto/repo/queryable.ex

@@ -203,11 +203,11 @@ defmodule Ecto.Repo.Queryable do
     struct_load!(types, values, [{field, value} | acc], all_nil?, struct, adapter)
   end
 
-  def struct_load!([], values, _acc, true, _struct, _adapter) do
+  def struct_load!([], values, _acc, true, struct, _adapter) when struct != %{} do
     {nil, values}
   end
 
-  def struct_load!([], values, acc, false, struct, _adapter) do
+  def struct_load!([], values, acc, _all_nil?, struct, _adapter) do
     {Map.merge(struct, Map.new(acc)), values}
   end
 
@@ -310,7 +310,7 @@ defmodule Ecto.Repo.Queryable do
 
   defp process(row, {:merge, left, right}, from, adapter) do
     {left, row} = process(row, left, from, adapter)
-    {right, row} = process_merge(row, right, from, adapter)
+    {right, row} = process(row, right, from, adapter)
 
     data =
       case {left, right} do
@@ -427,15 +427,6 @@ defmodule Ecto.Repo.Queryable do
     end)
   end
 
-  defp process_merge(row, {:source, {source, schema}, prefix, types}, _from, adapter) do
-    struct = Ecto.Schema.Loader.load_struct(schema, prefix, source)
-    struct_load!(types, row, [], false, struct, adapter)
-  end
-
-  defp process_merge(row, process, from, adapter) do
-    process(row, process, from, adapter)
-  end
-
   @compile {:inline, load!: 5}
   defp load!(type, value, field, struct, adapter) do
     case Ecto.Type.adapter_load(adapter, type, value) do