use decimals for encoding and decoding decimals in cassandra

Author: aphillipo

Diff for: lib/xandra/protocol.ex

@@ -302,14 +302,20 @@ defmodule Xandra.Protocol do
     if boolean, do: [1], else: [0]
   end
 
-  defp encode_value(:date, date) when date in 0..0xFFFFFFFF do
-    <<date::32>>
+  defp encode_value(:decimal, float) when is_float(float) do
+    encode_value(:decimal, Decimal.new(float))
+  end
+  defp encode_value(:decimal, %Decimal{sign: sign, coef: coef, exp: exp}) do
+    [encode_value(:int, exp), encode_value(:varint, sign * coef)]
   end
-
   defp encode_value(:decimal, {value, scale}) do
     [encode_value(:int, scale), encode_value(:varint, value)]
   end
 
+  defp encode_value(:date, date) when date in 0..0xFFFFFFFF do
+    <<date::32>>
+  end
+
   defp encode_value(:double, double) when is_float(double) do
     <<double::64-float>>
   end
@@ -598,12 +604,15 @@ defmodule Xandra.Protocol do
 
   defp decode_value(<<value::8>>, :boolean), do: Kernel.!=(value, 0)
 
-  defp decode_value(<<value::32>>, :date), do: value
-
   defp decode_value(<<scale::32-signed, rest::bits>>, :decimal) do
-    {decode_value(rest, :varint), scale}
+    coef = decode_value(rest, :varint)
+    sign = if coef < 0, do: -1, else: 1
+    coef = coef * sign
+    %Decimal{sign: sign, coef: coef, exp: scale}
   end
 
+  defp decode_value(<<value::32>>, :date), do: value
+
   defp decode_value(<<value::64-float>>, :double), do: value
 
   defp decode_value(<<value::32-float>>, :float), do: value

Diff for: mix.exs

@@ -38,6 +38,7 @@ defmodule Xandra.Mixfile do
 
   defp deps() do
     [{:db_connection, "~> 1.0"},
+     {:decimal, "~> 1.0"},
      {:snappy, github: "skunkwerks/snappy-erlang-nif", only: [:dev, :test]},
      {:ex_doc, "~> 0.14", only: :dev}]
   end

Diff for: mix.lock

@@ -1,5 +1,6 @@
-%{"connection": {:hex, :connection, "1.0.4", "a1cae72211f0eef17705aaededacac3eb30e6625b04a6117c1b2db6ace7d5976", [:mix], []},
-  "db_connection": {:hex, :db_connection, "1.1.1", "f9d246e8f65b9490945cf7360875eee18fcec9a0115207603215eb1fd94c39ef", [:mix], [{:connection, "~> 1.0.2", [hex: :connection, optional: false]}, {:poolboy, "~> 1.5", [hex: :poolboy, optional: true]}, {:sbroker, "~> 1.0", [hex: :sbroker, optional: true]}]},
-  "earmark": {:hex, :earmark, "1.0.3", "89bdbaf2aca8bbb5c97d8b3b55c5dd0cff517ecc78d417e87f1d0982e514557b", [:mix], []},
-  "ex_doc": {:hex, :ex_doc, "0.14.5", "c0433c8117e948404d93ca69411dd575ec6be39b47802e81ca8d91017a0cf83c", [:mix], [{:earmark, "~> 1.0", [hex: :earmark, optional: false]}]},
+%{"connection": {:hex, :connection, "1.0.4", "a1cae72211f0eef17705aaededacac3eb30e6625b04a6117c1b2db6ace7d5976", [:mix], [], "hexpm"},
+  "db_connection": {:hex, :db_connection, "1.1.1", "f9d246e8f65b9490945cf7360875eee18fcec9a0115207603215eb1fd94c39ef", [:mix], [{:connection, "~> 1.0.2", [hex: :connection, repo: "hexpm", optional: false]}, {:poolboy, "~> 1.5", [hex: :poolboy, repo: "hexpm", optional: true]}, {:sbroker, "~> 1.0", [hex: :sbroker, repo: "hexpm", optional: true]}], "hexpm"},
+  "decimal": {:hex, :decimal, "1.4.0", "fac965ce71a46aab53d3a6ce45662806bdd708a4a95a65cde8a12eb0124a1333", [:mix], [], "hexpm"},
+  "earmark": {:hex, :earmark, "1.0.3", "89bdbaf2aca8bbb5c97d8b3b55c5dd0cff517ecc78d417e87f1d0982e514557b", [:mix], [], "hexpm"},
+  "ex_doc": {:hex, :ex_doc, "0.14.5", "c0433c8117e948404d93ca69411dd575ec6be39b47802e81ca8d91017a0cf83c", [:mix], [{:earmark, "~> 1.0", [hex: :earmark, repo: "hexpm", optional: false]}], "hexpm"},
   "snappy": {:git, "https://github.com/skunkwerks/snappy-erlang-nif.git", "0951a1bf8e58141b3c439bebe1f2992688298631", []}}

Diff for: test/integration/datatypes_test.exs

@@ -129,7 +129,7 @@ defmodule DataTypesTest do
     assert Map.fetch!(row, "blob") == <<0, 0xFF>>
     assert Map.fetch!(row, "boolean") == true
     assert Map.fetch!(row, "date") == 1358013521
-    assert Map.fetch!(row, "decimal") == {1323, -2}
+    assert Decimal.equal? Map.fetch!(row, "decimal"), %Decimal{sign: 1, coef: 1323, exp: -2}
     assert Map.fetch!(row, "double") == 3.1415
     assert Map.fetch!(row, "float") == -1.25
     assert Map.fetch!(row, "inet") == {192, 168, 0, 1}
@@ -217,6 +217,41 @@ defmodule DataTypesTest do
     assert Map.fetch!(row, "set_of_tinyint") == nil
   end
 
+  test "passing Decimal types and floats to :decimal columns", %{conn: conn}  do
+    statement = """
+    CREATE TABLE decimals
+    (id int PRIMARY KEY,
+     decimal_from_float decimal,
+     decimal_from_decimal decimal,
+     decimal_from_fraction decimal)
+    """
+    Xandra.execute!(conn, statement, [])
+
+    statement = """
+    INSERT INTO decimals
+    (id,
+     decimal_from_float,
+     decimal_from_decimal,
+     decimal_from_fraction)
+    VALUES
+    (#{"?" |> List.duplicate(4) |> Enum.join(", ")})
+    """
+    values = [
+      {"int", 1},
+      {"decimal", 0.123456789},
+      {"decimal", Decimal.new(12.4)},
+      {"decimal", Decimal.div(Decimal.new(100), Decimal.new(3))}
+    ]
+    Xandra.execute!(conn, statement, values)
+
+    page = Xandra.execute!(conn, "SELECT * FROM decimals WHERE id = 1", [])
+    assert [row] = Enum.to_list(page)
+    assert Map.fetch!(row, "id") == 1
+    assert Decimal.equal? Map.fetch!(row, "decimal_from_float"), %Decimal{sign: 1, coef: 123456789, exp: -9}
+    assert Decimal.equal? Map.fetch!(row, "decimal_from_decimal"), %Decimal{sign: 1, coef: 124, exp: -1}
+    assert Decimal.equal? Map.fetch!(row, "decimal_from_fraction"), %Decimal{sign: 1, coef: 3333333333333333333333333333, exp: -26}
+  end
+
   test "user-defined types", %{conn: conn} do
     statement = """
     CREATE TYPE full_name