From 0abb8e58545709fc4b63fcb41eb528e43fbbe1f8 Mon Sep 17 00:00:00 2001
From: exAspArk <exaspark@gmail.com>
Date: Thu, 17 Jan 2019 15:40:58 -0500
Subject: [PATCH] Fix finding the correct value for limit and offset with where
 arrays

---
 lib/mongo_ecto/normalized_query.ex | 37 +++++++++++++++++++++++++-----
 1 file changed, 31 insertions(+), 6 deletions(-)

diff --git a/lib/mongo_ecto/normalized_query.ex b/lib/mongo_ecto/normalized_query.ex
index 6d20576..e23e919 100644
--- a/lib/mongo_ecto/normalized_query.ex
+++ b/lib/mongo_ecto/normalized_query.ex
@@ -345,8 +345,19 @@ 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
+    if {:^, l, [idx]} = expr do
+      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)
+    else
+      value(expr, params, pk, query, where)
+    end
+  end
 
   defp primary_key(nil), do: nil
 
@@ -466,9 +477,10 @@ 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 +495,10 @@ 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 +558,16 @@ 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