Merge pull request #23523 from kamipo/avoid_truncation_in_uniqueness_validation

Avoid a string value truncation in uniqueness validation

3 files changed, 49 insertions, 13 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 9a710263d7..16ce131cf4 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,20 @@
+*   SQLite: Fix uniqueness validation when values exceed the column limit.
+
+    SQLite doesn't impose length restrictions on strings, BLOBs, or numeric
+    values. It treats them as helpful metadata. When we truncate strings
+    before checking uniqueness, we'd miss values that exceed the column limit.
+
+    Other databases enforce length limits. A large value will pass uniqueness
+    validation since the column limit guarantees no value that long exists.
+    When we insert the row, it'll raise `ActiveRecord::ValueTooLong` as we
+    expect.
+
+    This fixes edge-case incorrect validation failures for values that exceed
+    the column limit but are identical to an existing value *when truncated*.
+    Now these will pass validation and raise an exception.
+
+    *Ryuta Kamizono*
+
 *   Raise `ActiveRecord::ValueTooLong` when column limits are exceeded.
     Supported by MySQL and PostgreSQL adapters.
 
diff --git a/activerecord/lib/active_record/validations/uniqueness.rb b/activerecord/lib/active_record/validations/uniqueness.rb
index 4a80cda0b8..1f59276137 100644
--- a/activerecord/lib/active_record/validations/uniqueness.rb
+++ b/activerecord/lib/active_record/validations/uniqueness.rb
@@ -67,9 +67,6 @@ module ActiveRecord
         cast_type = klass.type_for_attribute(attribute_name)
         value = cast_type.serialize(value)
         value = klass.connection.type_cast(value)
-        if value.is_a?(String) && column.limit
-          value = value.to_s[0, column.limit]
-        end
 
         comparison = if !options[:case_sensitive] && !value.nil?
           # will use SQL LOWER function before comparison, unless it detects a case insensitive collation
diff --git a/activerecord/test/cases/validations/uniqueness_validation_test.rb b/activerecord/test/cases/validations/uniqueness_validation_test.rb
index 4c14d93c66..4b0a590adb 100644
--- a/activerecord/test/cases/validations/uniqueness_validation_test.rb
+++ b/activerecord/test/cases/validations/uniqueness_validation_test.rb
@@ -349,19 +349,41 @@ class UniquenessValidationTest < ActiveRecord::TestCase
   end
 
   def test_validate_uniqueness_with_limit
-    # Event.title is limited to 5 characters
-    e1 = Event.create(:title => "abcde")
-    assert e1.valid?, "Could not create an event with a unique, 5 character title"
-    e2 = Event.create(:title => "abcdefgh")
-    assert !e2.valid?, "Created an event whose title, with limit taken into account, is not unique"
+    if current_adapter?(:SQLite3Adapter)
+      # Event.title has limit 5, but SQLite doesn't truncate.
+      e1 = Event.create(title: "abcdefgh")
+      assert e1.valid?, "Could not create an event with a unique 8 characters title"
+
+      e2 = Event.create(title: "abcdefgh")
+      assert_not e2.valid?, "Created an event whose title is not unique"
+    elsif current_adapter?(:Mysql2Adapter, :PostgreSQLAdapter, :SQLServerAdapter)
+      assert_raise(ActiveRecord::ValueTooLong) do
+        Event.create(title: "abcdefgh")
+      end
+    else
+      assert_raise(ActiveRecord::StatementInvalid) do
+        Event.create(title: "abcdefgh")
+      end
+    end
   end
 
   def test_validate_uniqueness_with_limit_and_utf8
-    # Event.title is limited to 5 characters
-    e1 = Event.create(:title => "一二三四五")
-    assert e1.valid?, "Could not create an event with a unique, 5 character title"
-    e2 = Event.create(:title => "一二三四五六七八")
-    assert !e2.valid?, "Created an event whose title, with limit taken into account, is not unique"
+    if current_adapter?(:SQLite3Adapter)
+      # Event.title has limit 5, but does SQLite doesn't truncate.
+      e1 = Event.create(title: "一二三四五六七八")
+      assert e1.valid?, "Could not create an event with a unique 8 characters title"
+
+      e2 = Event.create(title: "一二三四五六七八")
+      assert_not e2.valid?, "Created an event whose title is not unique"
+    elsif current_adapter?(:Mysql2Adapter, :PostgreSQLAdapter, :SQLServerAdapter)
+      assert_raise(ActiveRecord::ValueTooLong) do
+        Event.create(title: "一二三四五六七八")
+      end
+    else
+      assert_raise(ActiveRecord::StatementInvalid) do
+        Event.create(title: "一二三四五六七八")
+      end
+    end
   end
 
   def test_validate_straight_inheritance_uniqueness