MONGOID-5642 Queryable::Selector#merge! does not properly handle :$in…

…/:$nin keys (#5655)

* Change Mongoid::Criteria::Queryable::Selector#merge! to correctly merge $in and $nin when provided as a symbol as well as a string

* Mongoid::Criteria::Queryable::Selector#merge! convert to strings before matching

* cleanup whitespace

lib/mongoid/criteria/queryable/selector.rb

@@ -20,7 +20,7 @@ def merge!(other)
           other.each_pair do |key, value|
             if value.is_a?(Hash) && self[key.to_s].is_a?(Hash)
               value = self[key.to_s].merge(value) do |_key, old_val, new_val|
-                case _key
+                case _key.to_s
                 when '$in'
                   new_val & old_val
                 when '$nin'

spec/mongoid/criteria/queryable/selector_spec.rb

@@ -44,7 +44,7 @@
       end
     end
 
-    context "when selector contains a $nin" do
+    context "when selector contains a $nin string" do
 
       let(:initial) do
         { "$nin" => ["foo"] }
@@ -72,7 +72,35 @@
       end
     end
 
-    context "when selector contains a $in" do
+    context "when selector contains a $nin symbol" do
+
+      let(:initial) do
+        { :$nin => ["foo"] }
+      end
+
+      before do
+        selector["field"] = initial
+      end
+
+      context "when merging in a new $nin" do
+
+        let(:other) do
+          { "field" => { :$nin => ["bar"] } }
+        end
+
+        before do
+          selector.merge!(other)
+        end
+
+        it "combines the two $nin queries into one" do
+          expect(selector).to eq({
+            "field" => { :$nin => ["foo", "bar"] }
+          })
+        end
+      end
+    end
+
+    context "when selector contains a $in string" do
 
       let(:initial) do
         { "$in" => [1, 2] }
@@ -117,6 +145,51 @@
       end
     end
 
+    context "when selector contains a $in symbol" do
+
+      let(:initial) do
+        { :$in => [1, 2] }
+      end
+
+      before do
+        selector["field"] = initial
+      end
+
+      context "when merging in a new $in with an intersecting value" do
+
+        let(:other) do
+          { "field" => { :$in => [1] } }
+        end
+
+        before do
+          selector.merge!(other)
+        end
+
+        it "intersects the $in values" do
+          expect(selector).to eq({
+                                     "field" => { :$in => [1] }
+                                 })
+        end
+      end
+
+      context "when merging in a new $in with no intersecting values" do
+
+        let(:other) do
+          { "field" => { :$in => [3] } }
+        end
+
+        before do
+          selector.merge!(other)
+        end
+
+        it "intersects the $in values" do
+          expect(selector).to eq({
+                                     "field" => { :$in => [] }
+                                 })
+        end
+      end
+    end
+
     context "when selector is not nested" do
 
       before do