fix: Decimal precision problem when converting BigDecimal to Arrow::D…

…ecimalXXX

Gemfile.lock

@@ -1,21 +1,21 @@
 PATH
   remote: .
   specs:
-    parqueteur (1.3.0)
+    parqueteur (1.3.1)
       red-parquet (~> 5.0)
 
 GEM
   remote: https://rubygems.org/
   specs:
-    bigdecimal (3.0.0)
-    extpp (0.0.9)
-    gio2 (3.4.6)
-      gobject-introspection (= 3.4.6)
-    glib2 (3.4.6)
+    bigdecimal (3.0.2)
+    extpp (0.1.0)
+    gio2 (3.4.9)
+      gobject-introspection (= 3.4.9)
+    glib2 (3.4.9)
       native-package-installer (>= 1.0.3)
       pkg-config (>= 1.3.5)
-    gobject-introspection (3.4.6)
-      glib2 (= 3.4.6)
+    gobject-introspection (3.4.9)
+      glib2 (= 3.4.9)
     native-package-installer (1.1.1)
     pkg-config (1.4.6)
     rake (13.0.6)

examples/hello-world.rb

@@ -22,7 +22,7 @@ class FooParquetConverter < Parqueteur::Converter
     'id' => i,
     'my_string_array' => %w[a b c],
     'my_date' => Date.today,
-    'my_decimal' => BigDecimal('789000.5678'),
+    'my_decimal' => BigDecimal('0.03'),
     'my_int' => rand(1..10),
     'my_map' => { 'a' => 'b' },
     'my_string' => 'Hello World',
@@ -52,5 +52,6 @@ class FooParquetConverter < Parqueteur::Converter
 # Arrow Table
 table = converter.to_arrow_table
 table.each_record do |record|
+  # pp record['my_decimal'].to_f
   pp record.to_h
 end

lib/parqueteur/types/decimal128_type.rb

@@ -3,14 +3,25 @@
 module Parqueteur
   module Types
     class Decimal128Type < Parqueteur::Type
+      def initialize(options = {}, &block)
+        @scale = options.fetch(:scale)
+        @precision = options.fetch(:precision)
+        @format_str = "%.#{@scale}f"
+        super(options, &block)
+      end
+
       def build_value_array(values)
-        Arrow::Decimal128ArrayBuilder.build(@arrow_type, values)
+        Arrow::Decimal128ArrayBuilder.build(
+          @arrow_type,
+          values.map do |value|
+            Arrow::Decimal128.new(format(@format_str, BigDecimal(value)))
+          end
+        )
       end
 
       def arrow_type_builder
         Arrow::Decimal128DataType.new(
-          precision: @options.fetch(:precision),
-          scale: @options.fetch(:scale)
+          @precision, @scale
         )
       end
     end

lib/parqueteur/types/decimal256_type.rb

@@ -3,14 +3,25 @@
 module Parqueteur
   module Types
     class Decimal256Type < Parqueteur::Type
+      def initialize(options = {}, &block)
+        @scale = options.fetch(:scale)
+        @precision = options.fetch(:precision)
+        @format_str = "%.#{@scale}f"
+        super(options, &block)
+      end
+
       def build_value_array(values)
-        Arrow::Decimal256ArrayBuilder.build(@arrow_type, values)
+        Arrow::Decimal256ArrayBuilder.build(
+          @arrow_type,
+          values.map do |value|
+            Arrow::Decimal256.new(format(@format_str, BigDecimal(value)))
+          end
+        )
       end
 
       def arrow_type_builder
         Arrow::Decimal256DataType.new(
-          precision: @options.fetch(:precision),
-          scale: @options.fetch(:scale)
+          @precision, @scale
         )
       end
     end

lib/parqueteur/version.rb

@@ -1,5 +1,5 @@
 # frozen_string_literal: true
 
 module Parqueteur
-  VERSION = '1.3.0'
+  VERSION = '1.3.1'
 end