refactored the TopologyDescription.select_servers function.

Author: zookzook

lib/mongo/topology.ex

@@ -329,18 +329,18 @@ defmodule Mongo.Topology do
     nil
   end
 
-  defp get_connection([], _state), do: nil
-  defp get_connection([address], %{connection_pools: pools}), do: Map.fetch(pools, address)
+  defp get_connection(nil, _state), do: nil
+  defp get_connection(address, %{connection_pools: pools}), do: Map.fetch(pools, address)
 
-  defp get_limits([], _topology), do: nil
-  defp get_limits([address], %{servers: servers}) do
+  defp get_limits(nil, _topology), do: nil
+  defp get_limits(address, %{servers: servers}) do
     with {:ok, desc} <- Map.fetch(servers, address) do
       {:ok, Map.take(desc, @limits)}
     end
   end
 
-  defp wire_version([], _topology), do: nil
-  defp wire_version([address], topology) do
+  defp wire_version(nil, _topology), do: nil
+  defp wire_version(address, topology) do
     with {:ok, server} <- Map.fetch(topology.servers, address) do
       server.max_wire_version
     else

lib/mongo/topology_description.ex

@@ -82,8 +82,8 @@ defmodule Mongo.TopologyDescription do
            |> Enum.take_random(1)
 
     case addr do
-      [] -> :empty
-      _  -> {:ok, {addr, opts}}
+      []        -> :empty
+      [result]  -> {:ok, {result, opts}}
     end
   end
   def select_servers(topology, :read, opts) do
@@ -110,8 +110,8 @@ defmodule Mongo.TopologyDescription do
 
     # check now three possible cases
     case addr do
-      [] -> :empty
-      _  -> {:ok, {addr, opts}}
+      []        -> :empty
+      [result]  -> {:ok, {result, opts}}
     end
   end
 

test/mongo/topology_description_test.exs

@@ -4,7 +4,7 @@ defmodule Mongo.TopologyDescriptionTest do
   import Mongo.TopologyTestData
 
   test "single server selection" do
-    single_server = ["localhost:27017"]
+    single_server = "localhost:27017"
 
     opts = [
       read_preference: ReadPreference.primary(%{mode: :secondary})
@@ -27,60 +27,60 @@ defmodule Mongo.TopologyDescriptionTest do
     opts = [
       read_preference: ReadPreference.primary(%{mode: :secondary})
     ]
-    {:ok, {[server], _}} = TopologyDescription.select_servers(repl_set_with_master(), :read, opts)
+    {:ok, {server, _}} = TopologyDescription.select_servers(repl_set_with_master(), :read, opts)
 
     assert Enum.any?(seconardaries, fn sec -> sec == server end)
 
     opts = [
       read_preference: ReadPreference.primary(%{mode: :primary})
     ]
-    assert {:ok, {[master], _}} = TopologyDescription.select_servers(repl_set_with_master(), :read, opts)
+    assert {:ok, {master, _}} = TopologyDescription.select_servers(repl_set_with_master(), :read, opts)
 
     opts = [
       read_preference: ReadPreference.primary(%{mode: :primary_preferred})
     ]
-    assert {:ok, {[master], _}} = TopologyDescription.select_servers(repl_set_with_master(), :read, opts)
+    assert {:ok, {master, _}} = TopologyDescription.select_servers(repl_set_with_master(), :read, opts)
 
     opts = [
       read_preference: ReadPreference.primary(%{mode: :primary_preferred})
     ]
-    {:ok, {[server], _}} = TopologyDescription.select_servers(repl_set_no_master(), :read, opts)
+    {:ok, {server, _}} = TopologyDescription.select_servers(repl_set_no_master(), :read, opts)
     assert Enum.any?(seconardaries, fn sec -> sec == server end)
 
 
     opts = [
       read_preference: ReadPreference.primary(%{mode: :nearest})
     ]
-    {:ok, {[server], _}} = TopologyDescription.select_servers(repl_set_with_master(), :read, opts)
+    {:ok, {server, _}} = TopologyDescription.select_servers(repl_set_with_master(), :read, opts)
     assert Enum.any?(all_hosts, fn sec -> sec == server end)
 
     opts = [
       read_preference: ReadPreference.primary(%{mode: :secondary})
     ]
-    {:ok, {[server], _}} = TopologyDescription.select_servers(repl_set_no_master(), :read, opts)
+    {:ok, {server, _}} = TopologyDescription.select_servers(repl_set_no_master(), :read, opts)
     assert Enum.any?(seconardaries, fn sec -> sec == server end)
 
     opts = [
       read_preference: ReadPreference.primary(%{mode: :secondary_preferred})
     ]
-    {:ok, {[server], _}} = TopologyDescription.select_servers(repl_set_with_master(), :read, opts)
+    {:ok, {server, _}} = TopologyDescription.select_servers(repl_set_with_master(), :read, opts)
     assert Enum.any?(seconardaries, fn sec -> sec == server end)
 
-    assert {:ok, {[^master], _}} = TopologyDescription.select_servers(repl_set_only_master(), :read, opts)
+    assert {:ok, {^master, _}} = TopologyDescription.select_servers(repl_set_only_master(), :read, opts)
 
-    {:ok, {[server], _}} = TopologyDescription.select_servers(repl_set_no_master(), :read, opts)
+    {:ok, {server, _}} = TopologyDescription.select_servers(repl_set_no_master(), :read, opts)
     assert Enum.any?(seconardaries, fn sec -> sec == server end)
 
     opts = [
       read_preference: ReadPreference.primary(%{mode: :nearest})
     ]
-    {:ok, {[server], _}} = TopologyDescription.select_servers(repl_set_no_master(), :read, opts)
+    {:ok, {server, _}} = TopologyDescription.select_servers(repl_set_no_master(), :read, opts)
     assert Enum.any?(all_hosts, fn sec -> sec == server end)
 
   end
 
   test "Simplified server selection" do
-    single_server = ["localhost:27017"]
+    single_server = "localhost:27017"
 
     opts = [
       read_preference: %{mode: :secondary}