From 390aab9592fd0d369d5ea13e6ee55d6bd165bab6 Mon Sep 17 00:00:00 2001
From: exAspArk <exaspark@gmail.com>
Date: Thu, 17 Jan 2019 12:05:47 -0500
Subject: [PATCH] Fix finding values for limit and offset with where arrays,
 close #170

---
 lib/mongo_ecto/normalized_query.ex | 39 +++++++++++++++++++++++++-----
 test/mongo_ecto_test.exs           | 11 +++++++++
 2 files changed, 44 insertions(+), 6 deletions(-)

diff --git a/lib/mongo_ecto/normalized_query.ex b/lib/mongo_ecto/normalized_query.ex
index 6d20576..8c13aad 100644
--- a/lib/mongo_ecto/normalized_query.ex
+++ b/lib/mongo_ecto/normalized_query.ex
@@ -345,8 +345,21 @@ defmodule Mongo.Ecto.NormalizedQuery do
 
   defp offset_limit(nil, _params, _pk, _query, _where), do: nil
 
-  defp offset_limit(%Query.QueryExpr{expr: expr}, params, pk, query, where),
-    do: value(expr, params, pk, query, where)
+  defp offset_limit(%Query.QueryExpr{expr: expr}, params, pk, %Query{wheres: wheres} = query, where) do
+    case expr do
+      {:^, l, [idx]} ->
+        param_offset =
+          Enum.reduce(wheres, 0, fn %Query.BooleanExpr{expr: expr}, acc ->
+            _from..to = pair_param_range(expr)
+            acc + to
+          end)
+
+        value({:^, l, [idx + param_offset]}, params, pk, query, where)
+
+      _ ->
+        value(expr, params, pk, query, where)
+    end
+  end
 
   defp primary_key(nil), do: nil
 
@@ -466,9 +479,10 @@ defmodule Mongo.Ecto.NormalizedQuery do
     {field(left, pk, query, place), ["$in": []]}
   end
 
-  defp pair({:in, _, [left, {:^, _, [ix, len]}]}, params, pk, query, place) do
+  defp pair({:in, _, [left, _]} = expr, params, pk, query, place) do
     args =
-      ix..(ix + len - 1)
+      expr
+      |> pair_param_range()
       |> Enum.map(&elem(params, &1))
       |> Enum.map(&value(&1, params, pk, query, place))
 
@@ -483,9 +497,10 @@ defmodule Mongo.Ecto.NormalizedQuery do
     {field(left, pk, query, place), [{binary_op(op), value(right, params, pk, query, place)}]}
   end
 
-  defp pair({:not, _, [{:in, _, [left, {:^, _, [ix, len]}]}]}, params, pk, query, place) do
+  defp pair({:not, _, [{:in, _, [left, _]}]} = expr, params, pk, query, place) do
     args =
-      ix..(ix + len - 1)
+      expr
+      |> pair_param_range()
       |> Enum.map(&elem(params, &1))
       |> Enum.map(&value(&1, params, pk, query, place))
 
@@ -545,4 +560,16 @@ defmodule Mongo.Ecto.NormalizedQuery do
   defp error(place) do
     raise ArgumentError, "Invalid expression for MongoDB adapter in #{place}"
   end
+
+  defp pair_param_range({:in, _, [_, {:^, _, [ix, len]}]}) do
+    ix..(ix + len - 1)
+  end
+
+  defp pair_param_range({:not, _, [{:in, _, [_, {:^, _, [ix, len]}]}]}) do
+    ix..(ix + len - 1)
+  end
+
+  defp pair_param_range(expr) do
+    0..0
+  end
 end
diff --git a/test/mongo_ecto_test.exs b/test/mongo_ecto_test.exs
index 28cf4bf..c94b868 100644
--- a/test/mongo_ecto_test.exs
+++ b/test/mongo_ecto_test.exs
@@ -91,6 +91,17 @@ defmodule Mongo.EctoTest do
     assert 10 == TestRepo.one(query)
   end
 
+  test "where in ids + dynamic limit + dynamic offset" do
+    post1 = TestRepo.insert!(%Post{})
+    post2 = TestRepo.insert!(%Post{})
+    ids = [post1.id, post2.id]
+    limit = 1
+    offset = 1
+
+    query = from p in Post, where: p.id in ^ids, limit: ^limit, offset: ^offset
+    assert TestRepo.all(query) == [post2]
+  end
+
   # test "partial update in map" do
   #   post = TestRepo.insert!(%Post{meta: %{author: %{name: "michal"}, other: "value"}})
   #   TestRepo.update_all(Post, set: [meta: change_map("author.name", "michal")])