From bff566fc93ffa2aa027cdd9aeccefdf25908e4b6 Mon Sep 17 00:00:00 2001
From: Yifan Chen <30335308+emecii@users.noreply.github.com>
Date: Wed, 9 Sep 2026 21:36:37 -0700
Subject: [PATCH 1/2] GH-51271: [Ruby] Fix Date values in
 ArrowFormat::Date32Array

---
 ruby/red-arrow-format/lib/arrow-format/array.rb  |  3 ++-
 ruby/red-arrow-format/test/test-array-builder.rb |  5 +++--
 ruby/red-arrow-format/test/test-date32-array.rb  | 12 ++++++++++++
 3 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/ruby/red-arrow-format/lib/arrow-format/array.rb b/ruby/red-arrow-format/lib/arrow-format/array.rb
index 20929493e906..8bf7393fd960 100644
--- a/ruby/red-arrow-format/lib/arrow-format/array.rb
+++ b/ruby/red-arrow-format/lib/arrow-format/array.rb
@@ -489,11 +489,12 @@ def type
     end
 
     private
+    UNIX_EPOCH = 2440588
     def pack_value(value, template, type)
       if value.nil?
         [0].pack(template)
       elsif value.is_a?(Date)
-        [value.day].pack(template)
+        [value.jd - UNIX_EPOCH].pack(template)
       else
         [value].pack(template)
       end
diff --git a/ruby/red-arrow-format/test/test-array-builder.rb b/ruby/red-arrow-format/test/test-array-builder.rb
index bae8e88c029b..f2e6a70fc55c 100644
--- a/ruby/red-arrow-format/test/test-array-builder.rb
+++ b/ruby/red-arrow-format/test/test-array-builder.rb
@@ -144,7 +144,8 @@ def test_time
 
   def test_date
     values = [Date.new(2026, 7, 17)]
-    assert_equal(ArrowFormat::Date32Array.new(values),
-                 ArrowFormat::Array.build(values))
+    array = ArrowFormat::Array.build(values)
+    assert_equal(ArrowFormat::Date32Array, array.class)
+    assert_equal([20651], array.to_a)
   end
 end
diff --git a/ruby/red-arrow-format/test/test-date32-array.rb b/ruby/red-arrow-format/test/test-date32-array.rb
index 331daabd833a..2d9a22c4c9b3 100644
--- a/ruby/red-arrow-format/test/test-date32-array.rb
+++ b/ruby/red-arrow-format/test/test-date32-array.rb
@@ -35,6 +35,18 @@ def test_mixed
       assert_equal(values,
                    ArrowFormat::Date32Array.new(values).to_a)
     end
+
+    def test_date
+      values = [
+        Date.new(1969, 12, 31),
+        Date.new(1970, 1, 1),
+        nil,
+        Date.new(2025, 12, 9),
+      ]
+      expected = [-1, 0, nil, @date_2025_12_09]
+      assert_equal(expected,
+                   ArrowFormat::Date32Array.new(values).to_a)
+    end
   end
 
   sub_test_case("#==") do

From b848efba5128c457619f0abad4bb9eddf7488060 Mon Sep 17 00:00:00 2001
From: Yifan Chen <30335308+emecii@users.noreply.github.com>
Date: Thu, 10 Sep 2026 08:55:04 -0700
Subject: [PATCH 2/2] GH-51271: Address Date32 review feedback

---
 ruby/red-arrow-format/lib/arrow-format/array.rb  | 3 ++-
 ruby/red-arrow-format/test/test-array-builder.rb | 5 ++---
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/ruby/red-arrow-format/lib/arrow-format/array.rb b/ruby/red-arrow-format/lib/arrow-format/array.rb
index 8bf7393fd960..90a3be41ce9d 100644
--- a/ruby/red-arrow-format/lib/arrow-format/array.rb
+++ b/ruby/red-arrow-format/lib/arrow-format/array.rb
@@ -16,6 +16,7 @@
 # under the License.
 
 require "bigdecimal"
+require "date"
 
 require_relative "array-builder"
 require_relative "bitmap"
@@ -489,7 +490,7 @@ def type
     end
 
     private
-    UNIX_EPOCH = 2440588
+    UNIX_EPOCH = Date.new(1970, 1, 1).jd
     def pack_value(value, template, type)
       if value.nil?
         [0].pack(template)
diff --git a/ruby/red-arrow-format/test/test-array-builder.rb b/ruby/red-arrow-format/test/test-array-builder.rb
index f2e6a70fc55c..bae8e88c029b 100644
--- a/ruby/red-arrow-format/test/test-array-builder.rb
+++ b/ruby/red-arrow-format/test/test-array-builder.rb
@@ -144,8 +144,7 @@ def test_time
 
   def test_date
     values = [Date.new(2026, 7, 17)]
-    array = ArrowFormat::Array.build(values)
-    assert_equal(ArrowFormat::Date32Array, array.class)
-    assert_equal([20651], array.to_a)
+    assert_equal(ArrowFormat::Date32Array.new(values),
+                 ArrowFormat::Array.build(values))
   end
 end